Synthesis and Actions of Juvenile Hormones In Insect Development (MS Word)

M. Phil (Zoology), 2M. Phil (Zoology), 2ndnd
SemesterSemester
Roll: BUR MP ZOORoll: BUR MP ZOO No.: 2008 / 9No.: 2008 / 9
Registration No.: 2546 of 2008 – 2009Registration No.: 2546 of 2008 – 2009
The University of BurdwanThe University of Burdwan
Burdwan – 713 104Burdwan – 713 104
West Bengal, IndiaWest Bengal, India
TERM PAPER – ITERM PAPER – I
Submitted in Partial Fulfillment of the Requirement for theSubmitted in Partial Fulfillment of the Requirement for the
Degree of Master of Philosophy (Science).Degree of Master of Philosophy (Science).
April, 2009April, 2009

AcknowledgementAcknowledgement
I express my deep sense of gratitude to Dr. Abhijit Mazumdar, Reader, Department ofI express my deep sense of gratitude to Dr. Abhijit Mazumdar, Reader, Department of
Zoology, The University of Burdwan, for his invaluable, consistent and able guidanceZoology, The University of Burdwan, for his invaluable, consistent and able guidance
and all sorts of assistance in preparing this Review Work successful.and all sorts of assistance in preparing this Review Work successful.
I pay my humble respect to Prof. Prasanta Kumar Chaudhuri, for rendering usefulI pay my humble respect to Prof. Prasanta Kumar Chaudhuri, for rendering useful
suggestions and assistance, valuable suggestions and also for his counsel in order tosuggestions and assistance, valuable suggestions and also for his counsel in order to
compile as well as make it in fruition.compile as well as make it in fruition.
I am equally grateful to Dr. Niladri Hazra, Reader and Head, Department ofI am equally grateful to Dr. Niladri Hazra, Reader and Head, Department of
Zoology, The University of Burdwan for giving me constant encouragements andZoology, The University of Burdwan for giving me constant encouragements and
necessary informations as well as suggestions whenever it is necessary.necessary informations as well as suggestions whenever it is necessary.
I am especially thankful to Prof. Tara Charan Banerjee, Prof. Anadi Prasad Nandi,I am especially thankful to Prof. Tara Charan Banerjee, Prof. Anadi Prasad Nandi,
Dr. Padmanabha Chakrabarti, Dr. Goutam Chandra, Dr. Goutam Aditya, Dr. AnupamDr. Padmanabha Chakrabarti, Dr. Goutam Chandra, Dr. Goutam Aditya, Dr. Anupam
Basu, Dr. Anandamay Barik, Dr. Soumendra Nath Chatterjee, Dr. Koushik Ghosh andBasu, Dr. Anandamay Barik, Dr. Soumendra Nath Chatterjee, Dr. Koushik Ghosh and
Dr. Sumedha Roy for sparing me some of their invaluable time and giving me someDr. Sumedha Roy for sparing me some of their invaluable time and giving me some
important suggestions during preparing this Review Work.important suggestions during preparing this Review Work.
Name of Mr. Amitava Nandi, Librarian of the Department of Zoology, TheName of Mr. Amitava Nandi, Librarian of the Department of Zoology, The
University of Burdwan demands special mention for providing me required books andUniversity of Burdwan demands special mention for providing me required books and
review papers for preparing this Review Work Report.review papers for preparing this Review Work Report.
Mr. Asif Hossain, Miss Mou Nandi, JRF Scholars and Mrs. Sangita Mitra, SRFMr. Asif Hossain, Miss Mou Nandi, JRF Scholars and Mrs. Sangita Mitra, SRF
Scholar of the Entomology Research Unit, The University of Burdwan for their timelyScholar of the Entomology Research Unit, The University of Burdwan for their timely
assistances in manifold ways in completing the works for which my appreciationassistances in manifold ways in completing the works for which my appreciation
known no bound.known no bound.
Other Scholars of Zoology Department, The University of Burdwan to whom I amOther Scholars of Zoology Department, The University of Burdwan to whom I am
indebted for various courtesies.indebted for various courtesies.
Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development 22

The liberal assistance of the non – teaching staffs and technical assistance of theThe liberal assistance of the non – teaching staffs and technical assistance of the
Technical Assistant of our Department is also acknowledged.Technical Assistant of our Department is also acknowledged.
I would also like to thank Dr. Manas Mahapatra, Scientist and Director, SimultalaI would also like to thank Dr. Manas Mahapatra, Scientist and Director, Simultala
Conservationist, an NGO working with Wildlife Institute of India, Dehradun, IndiaConservationist, an NGO working with Wildlife Institute of India, Dehradun, India
for giving me constant encouragements and necessary suggestions in preparing thisfor giving me constant encouragements and necessary suggestions in preparing this
Review Work Report extremely successful.Review Work Report extremely successful.
I also take this opportunity to acknowledge the assistance, encouragements,I also take this opportunity to acknowledge the assistance, encouragements,
appreciations and co – operations received from my entire classmates.appreciations and co – operations received from my entire classmates.
I would also like to mention the name of my husband, Mr. Chandra Kanta De, butI would also like to mention the name of my husband, Mr. Chandra Kanta De, but
for whose unrelenting indulgences and patience with me, this Review Work Reportfor whose unrelenting indulgences and patience with me, this Review Work Report
would never have made its journey to this printed form.would never have made its journey to this printed form.
Lastly, but not the least, I would like to express my gratitude to my parents, parentLastly, but not the least, I would like to express my gratitude to my parents, parent
– in laws and my sister for their constant encouragements and blessings on me.– in laws and my sister for their constant encouragements and blessings on me.
----------------------------------------------------------------------------------------------------------------------------------------------
SARAMITA DE (CHAKRAVASARAMITA DE (CHAKRAVARTI)RTI)
M. Phil (Zoology),M. Phil (Zoology), 22ndnd
SemesterSemester
Roll:Roll: BUR MP ZOOBUR MP ZOO No.:No.: 2008 / 92008 / 9
Registration No.:Registration No.: 2546 of 2008 – 20092546 of 2008 – 2009

C O N T E N T SC O N T E N T S
Page No.(s)Page No.(s)
●● Literature ReviewLiterature Review 66
●● PrefacePreface 77
●● Isolation of Juvenile HormonesIsolation of Juvenile Hormones 7 – 87 – 8
●● Chemical Characteristics of Juvenile HormonesChemical Characteristics of Juvenile Hormones 8 – 128 – 12
●● Juvenoids or JH Analogues (JHa)Juvenoids or JH Analogues (JHa) 12 – 1512 – 15
›› History›› History 12 – 1312 – 13
›› Chemical Nature›› Chemical Nature 13 – 1513 – 15
●● The Mevalonate Pathway and Synthesis of theThe Mevalonate Pathway and Synthesis of the
Juvenile Hormones in InsectsJuvenile Hormones in Insects
16 – 2016 – 20
›› The Formation of Juvenile Hormones›› The Formation of Juvenile Hormones 16 – 1716 – 17
›› Juvenile Hormones’ Synthesis in the Corpora Allata›› Juvenile Hormones’ Synthesis in the Corpora Allata 17 – 1817 – 18
›› Regulation›› Regulation 19 – 2019 – 20
›› Cellular Receptors for JH›› Cellular Receptors for JH 2020
●● Degradation of JHDegradation of JH 20 – 2120 – 21

●● Mechanism of ActionsMechanism of Actions 22 – 2722 – 27
›› Actions of Juvenile Hormones on Endocrine Systems›› Actions of Juvenile Hormones on Endocrine Systems 25 – 2625 – 26
›› Roles of Juvenile Hormones in embryonic development›› Roles of Juvenile Hormones in embryonic development 26 – 2726 – 27
›› Diapause›› Diapause 2727
●● Molecular Actions of Juvenile HormonesMolecular Actions of Juvenile Hormones 28 – 3328 – 33
›› Regulation of the Ecdysone – Induced Transcription›› Regulation of the Ecdysone – Induced Transcription
Factor Cascade (ETFC)Factor Cascade (ETFC)
29 – 3029 – 30
›› Regulation of Cuticular Melanization›› Regulation of Cuticular Melanization 30 – 3130 – 31
›› Larval Pupal Commitment›› Larval Pupal Commitment 31 – 3331 – 33
●● Applications of JHs and JHa(s)Applications of JHs and JHa(s) 33 – 3533 – 35
●● SummarySummary 3636
●● ReferencesReferences 37 – 5037 – 50
Literature ReviewLiterature Review

The first group of insect hormones was discovered in association with metamorphosis.The first group of insect hormones was discovered in association with metamorphosis.
The preventing activity of corpus allatum in metamorphosis was first shown byThe preventing activity of corpus allatum in metamorphosis was first shown by
Wigglesworth (1935) in his classic parabiosis experiments withWigglesworth (1935) in his classic parabiosis experiments with Rhodnius prolixus.Rhodnius prolixus.
Later in 1936, he demonstrated how 6Later in 1936, he demonstrated how 6thth
instar giant nymphs got changed eventuallyinstar giant nymphs got changed eventually
followed by another moult into the giant imago. The author showed not only thefollowed by another moult into the giant imago. The author showed not only the
source of these inhibitory effects, but also provided the first definite evidence of itssource of these inhibitory effects, but also provided the first definite evidence of its
hormonal character. Wigglesworth (1940) started use of juvenile hormone in lieu ofhormonal character. Wigglesworth (1940) started use of juvenile hormone in lieu of
the original term ‘inhibitory hormone’ after its active role in producing larvalthe original term ‘inhibitory hormone’ after its active role in producing larval
characters in adults. Later a number of other authors for various other insect speciescharacters in adults. Later a number of other authors for various other insect species
confirmed this discovery, likewise – Bounhiol et al. (1965) forconfirmed this discovery, likewise – Bounhiol et al. (1965) for Bombyx moriBombyx mori;;
Pflugfelder (1937) forPflugfelder (1937) for Carausius morosusCarausius morosus; Piepho (1938) for; Piepho (1938) for Galleria mellonellaGalleria mellonella. At. At
the same time, Wigglesworth (1936) also discovered the effect of the corpora allatathe same time, Wigglesworth (1936) also discovered the effect of the corpora allata
hormone on ovarian development. They confirmed those for a number of otherhormone on ovarian development. They confirmed those for a number of other
species whilst in others, such asspecies whilst in others, such as Bombyx moriBombyx mori, no ovarian control by a corresponding, no ovarian control by a corresponding
humoral factor was found. Such apparent contradiction between the inhibitory,humoral factor was found. Such apparent contradiction between the inhibitory,
metamorphosis – suppressing effect of the corpora allata hormone and its totalmetamorphosis – suppressing effect of the corpora allata hormone and its total
metabolism – increasing influence, suggested to a number of authors that there weremetabolism – increasing influence, suggested to a number of authors that there were
two or more corpora allata hormones having different effects. All the available datatwo or more corpora allata hormones having different effects. All the available data
were then explained by the operation of a single substance, JH (Juvenile Hormone),were then explained by the operation of a single substance, JH (Juvenile Hormone),
possessing the character of a growth hormone (Novák, 1951 and 1956). Thepossessing the character of a growth hormone (Novák, 1951 and 1956). The
interordinal non – specificity of Juvenile Hormone (JH) was shown by theinterordinal non – specificity of Juvenile Hormone (JH) was shown by the
transplantation of corpora allata between Blattoptera and Hemiptera (Novák, 1949transplantation of corpora allata between Blattoptera and Hemiptera (Novák, 1949
and 1951) and Phasmida and Lepidoptera (Piepho, 1950). Williams (1956),and 1951) and Phasmida and Lepidoptera (Piepho, 1950). Williams (1956),
Schneiderman and Gilbert (1958) made the first attempts at elucidating the chemicalSchneiderman and Gilbert (1958) made the first attempts at elucidating the chemical
nature of Juvenile Hormone, using ether extracts of male abdomens of the Saturniidnature of Juvenile Hormone, using ether extracts of male abdomens of the Saturniid
P. cecropiaP. cecropia. Röller and his co – workers (1965) determined its chemical structure for. Röller and his co – workers (1965) determined its chemical structure for
the first time.the first time.
PrefacePreface

Insect development is under the control of two hormones, Ecdysone and JuvenileInsect development is under the control of two hormones, Ecdysone and Juvenile
Hormone. JH is a sesquiterpenoid molecule that modulates Ecdysone action andHormone. JH is a sesquiterpenoid molecule that modulates Ecdysone action and
functions in prevention of adult differentiation, retention of larval structures andfunctions in prevention of adult differentiation, retention of larval structures and
regulation of the ovarian maturation. JH is a regulator of insect development which isregulation of the ovarian maturation. JH is a regulator of insect development which is
synthesized and released by the glandular corpora allata. α – Ecdysone (E) and itssynthesized and released by the glandular corpora allata. α – Ecdysone (E) and its
precursors are synthesized by the prothoracic glands following stimulation byprecursors are synthesized by the prothoracic glands following stimulation by
Prothoracicotropic Hormone (PTTH), which is produced by neurosecretory cells inProthoracicotropic Hormone (PTTH), which is produced by neurosecretory cells in
the brain and is realesed from their terminals either in the corpora cardiaca or in thethe brain and is realesed from their terminals either in the corpora cardiaca or in the
corpora allata in the Lepidoptera. In Lepidoptera, the role of JH in insect developmentcorpora allata in the Lepidoptera. In Lepidoptera, the role of JH in insect development
is well studied. The activity of the corpora allata is regulated by humoral factors suchis well studied. The activity of the corpora allata is regulated by humoral factors such
as allatotropin and allatostatin as well as by nervous connections. In addition toas allatotropin and allatostatin as well as by nervous connections. In addition to
having multiple functions in blocking adult differentiation, retaining larval structures,having multiple functions in blocking adult differentiation, retaining larval structures,
and regulating ovarian maturation, JH is a key player for phase polymorphism inand regulating ovarian maturation, JH is a key player for phase polymorphism in
armyworms, aphids and locusts and for caste differentiation in termites and ants.armyworms, aphids and locusts and for caste differentiation in termites and ants.
Moulting is caused by 20 – hydroxyecdysone (E). The action of JH on development isMoulting is caused by 20 – hydroxyecdysone (E). The action of JH on development is
always associated with Ecdysone action. JH does not prevent Ecdysone action inalways associated with Ecdysone action. JH does not prevent Ecdysone action in
inducing the moult, but modulates its action. In the haemolymph, JH usually binds toinducing the moult, but modulates its action. In the haemolymph, JH usually binds to
the haemolymph JH – binding protein, so that it is protected from metabolism by thethe haemolymph JH – binding protein, so that it is protected from metabolism by the
general esterases.general esterases.
Isolation of Juvenile HormonesIsolation of Juvenile Hormones
JH is present in the haemolymph throughout the larval (nymphal) life, through theJH is present in the haemolymph throughout the larval (nymphal) life, through the
penultimate instar, and its presence causes a larval (nymphal) moult when the 20Epenultimate instar, and its presence causes a larval (nymphal) moult when the 20E
titer increases. In the insect subclass Hemimetabola, JH is about during adulttiter increases. In the insect subclass Hemimetabola, JH is about during adult
development in the last instar nymph. Its role in the regulation of pupation indevelopment in the last instar nymph. Its role in the regulation of pupation in
Holometabola is much more complicated. Williams (1956) found that a lipid extractHolometabola is much more complicated. Williams (1956) found that a lipid extract
from the abdomen offrom the abdomen of CecropiaCecropia males produced JH effects in Coleoptera (males produced JH effects in Coleoptera (TenebrioTenebrio
molitormolitor, Schmialek and Wigglesworth, 1958 and 1961) and in Bugs and Cockroaches,, Schmialek and Wigglesworth, 1958 and 1961) and in Bugs and Cockroaches,
etc. as well as inetc. as well as in H.H. ccecropiaecropia and other moths. Gilbert and Schneiderman (1957 andand other moths. Gilbert and Schneiderman (1957 and

1960) and Schneiderman (1961) studied in details the occurrence of the active1960) and Schneiderman (1961) studied in details the occurrence of the active
principle in the body of theprinciple in the body of the Hyalophora cecropiaHyalophora cecropia silkworm during ontogeny. Röllersilkworm during ontogeny. Röller
and Bjerke (1965), Röller et al. (1965), and Röller et al. (1967) isolated the substancesand Bjerke (1965), Röller et al. (1965), and Röller et al. (1967) isolated the substances
similar to the active component of the abdominal extract from adultsimilar to the active component of the abdominal extract from adult HyalophoraHyalophora
cecropiacecropia males; afterwards Dahm et al. (1967), Röller et al. (1967) and several othersmales; afterwards Dahm et al. (1967), Röller et al. (1967) and several others
like Meyer and Ax (1965), Meyer et al. (1968 and 1970), Meyer (1971) identified inlike Meyer and Ax (1965), Meyer et al. (1968 and 1970), Meyer (1971) identified in
same laboratory and subsequently Loew et al. (1970) together with a key intermediatesame laboratory and subsequently Loew et al. (1970) together with a key intermediate
to its synthesis (Mori, 1972) successfully synthesized in their laboratories.to its synthesis (Mori, 1972) successfully synthesized in their laboratories.
Chemical Characteristics of Juvenile HormonesChemical Characteristics of Juvenile Hormones
JH is a sesquiterpenoid compound produced in the cells of the corpora allata (CA),JH is a sesquiterpenoid compound produced in the cells of the corpora allata (CA),
which are bilaterally paired structures in Lepidoptera, but are often fused into onewhich are bilaterally paired structures in Lepidoptera, but are often fused into one
mass of tissue in other groups of insects. In 1956, the experiment by Williams on themass of tissue in other groups of insects. In 1956, the experiment by Williams on the
H. cH. cecropiaecropia males facilitated the chemical identification of the active principle.males facilitated the chemical identification of the active principle. Of theOf the
many workers who investigated the nature of thismany workers who investigated the nature of this ‘H. c‘H. cecropiaecropia oiloil’’, the most, the most
successful were who succeeded in isolating the active principle by means of gassuccessful were who succeeded in isolating the active principle by means of gas
chromatography. They proposed the chemical formula of malechromatography. They proposed the chemical formula of male H. cH. cecropiaecropia extract asextract as
Methyl – 10 – epoxy – 7 – ethyl – 3, 11 – dimethyl – 2, 6 – tridecadienoate or MethylMethyl – 10 – epoxy – 7 – ethyl – 3, 11 – dimethyl – 2, 6 – tridecadienoate or Methyl
– 12, 14 – dihomo juvenate (Meyer, 1970)– 12, 14 – dihomo juvenate (Meyer, 1970) Fig. (1)Fig. (1)..
CHCH33
CHCH33 CHCH22 CH3CH3 OO
HH33CC CC CHCH22 CC CHCH22 CC C OCH3C OCH3
CHCH22 O CHO CH CHCH22 CHCH CHCH22 CHCH
Fig. (1): - Chemical formula of MaleFig. (1): - Chemical formula of Male H. cH. cecropiaecropia extractextract
As seen from the followingAs seen from the following Table – (A)Table – (A),, thethe H. cH. cecropiaecropia JH content is fairly highJH content is fairly high
in unfertilized eggs, during the embryonic period and in the freshly hatched larvae. Itin unfertilized eggs, during the embryonic period and in the freshly hatched larvae. It

decreases at the end of larval development and in the pupa, practically disappearsdecreases at the end of larval development and in the pupa, practically disappears
when development recommences after the pupal diapause and does not reappear untilwhen development recommences after the pupal diapause and does not reappear until
just before adult emergence, when it increases slowly in the female, but rapidly in thejust before adult emergence, when it increases slowly in the female, but rapidly in the
male.male.
Table – (A): - Juvenile Hormone content ofTable – (A): - Juvenile Hormone content of H. cH. cecropiaecropia during developmentduring development
(After Schneiderman, 1961)(After Schneiderman, 1961)
Stages of DevelopmentStages of Development JH content / gm freshJH content / gm fresh
weight compared with adultweight compared with adult
male (in %)male (in %)
1. Unfertilized Eggs1. Unfertilized Eggs 4.304.30
2. 7 – days old Embryos with yolk2. 7 – days old Embryos with yolk 3.703.70
3. 13. 1stst
instar larvae (freshly hatched)instar larvae (freshly hatched) 6.406.40
4. 54. 5thth
instar larvae (mixed ages)instar larvae (mixed ages) 0.500.50
5. Freshly moulted pupae5. Freshly moulted pupae 0.750.75
6. Diapausing Pupae (1 month old)6. Diapausing Pupae (1 month old) 0.550.55
7. Chilled Pupae (6 months old)7. Chilled Pupae (6 months old) 0.000.00
8. Pupae 2 days of adult development8. Pupae 2 days of adult development 0.000.00
12. Pupae 22 days of adult development (males)12. Pupae 22 days of adult development (males) 50.0050.00
13. Adult males, 2 days old13. Adult males, 2 days old 100.00100.00
14. Adult females, 2 days old14. Adult females, 2 days old 3.203.20
Five JH variants (six, if one includes methylfarneosate, which is the immediateFive JH variants (six, if one includes methylfarneosate, which is the immediate
precursor of the JH molecules and which is secreted by some insects and has JHprecursor of the JH molecules and which is secreted by some insects and has JH
activity on its own) are known. The structures of JH I, JH II, JH III, JH 0 and the isoactivity on its own) are known. The structures of JH I, JH II, JH III, JH 0 and the iso
JH 0 (also called 4 – methyl JH I) are shown inJH 0 (also called 4 – methyl JH I) are shown in Fig. (2)Fig. (2). Although JH III has most. Although JH III has most
often been found as the principal or only JH molecule in many insects, more detailedoften been found as the principal or only JH molecule in many insects, more detailed
analyses with GC – Ms (Bergot et al., 1981) have shown multiple JHs in some insects,analyses with GC – Ms (Bergot et al., 1981) have shown multiple JHs in some insects,
particularly Lepidoptera. JH III is only detectable as a trace, but JH I and JH II areparticularly Lepidoptera. JH III is only detectable as a trace, but JH I and JH II are
often the principal JHs. In addition, JH II acid and JH I acid are also released from theoften the principal JHs. In addition, JH II acid and JH I acid are also released from the
CA. Although JH is the principal JH of early instars ofCA. Although JH is the principal JH of early instars of Manduca sextaManduca sexta (Schooley et(Schooley et

al., 1984), production of the JH acids seems to be the normal process in the last instaral., 1984), production of the JH acids seems to be the normal process in the last instar
ofof M. sextaM. sexta, which loses the enzymatic ability to methylate the final step in synthesis, which loses the enzymatic ability to methylate the final step in synthesis
of the various JHs (Bhaskaran et al., 1986).of the various JHs (Bhaskaran et al., 1986).
(Cntd. to next page)(Cntd. to next page)
Synthesis and Actions of Juvenile Hormones In Insect DevelopmentSynthesis and Actions of Juvenile Hormones In Insect Development
C
O
OCH3
O
CH3
iso JH 0
4 – methyl JH I
C
O
OCH3
O
CH3
JH 0
C
O
OCH3
O
CH3
JH I
C
O
OCH3
O
CH3
JH II
1010

Methyl – 10, 11 – epoxy -, 7, 11 – trimethyl – 2 – trans –Methyl – 10, 11 – epoxy -, 7, 11 – trimethyl – 2 – trans –
6 – trans - dodecadienoate6 – trans - dodecadienoate
JH bisepoxideJH bisepoxide
Fig. (2): - Molecules with juvenile hormone (JH) activityFig. (2): - Molecules with juvenile hormone (JH) activity
[JH III may be the most common JH of insects; JH I, JH II, JH III, JH 0 and iso JH 0 have[JH III may be the most common JH of insects; JH I, JH II, JH III, JH 0 and iso JH 0 have
been found in some Lepidoptera. JH bisepoxide is synthesized by the ring gland of Diptera.]been found in some Lepidoptera. JH bisepoxide is synthesized by the ring gland of Diptera.]
JH acid production continues into the pupal and adult stages. The JH acids haveJH acid production continues into the pupal and adult stages. The JH acids have
little biological activity, but they can be methylated slowly in imaginal disc tissueslittle biological activity, but they can be methylated slowly in imaginal disc tissues
(Sparagana et al., 1985) and the slow methylation may be important to overall(Sparagana et al., 1985) and the slow methylation may be important to overall
function of JH and metamorphosis infunction of JH and metamorphosis in M. sextaM. sexta and possibly other Lepidoptera (Gilbertand possibly other Lepidoptera (Gilbert
et al., 1996). JH bisepoxide (JHB3) is the principal JH ofet al., 1996). JH bisepoxide (JHB3) is the principal JH of Drosophila melanogasterDrosophila melanogaster
(Richard et al., 1989) and in some other insects. JH molecules have chiral centers, and(Richard et al., 1989) and in some other insects. JH molecules have chiral centers, and
their natural enantiomers may be more active and less rapidly degraded than unnaturaltheir natural enantiomers may be more active and less rapidly degraded than unnatural
enantiomers. (Tobe and King, 1993). JH II has a chiral center at Cenantiomers. (Tobe and King, 1993). JH II has a chiral center at C1010 and the other JHand the other JH
molecules have chiral centers at Cmolecules have chiral centers at C1010 and Cand C1111. JHB3 has three chiral centers at C. JHB3 has three chiral centers at C66, C, C77
and Cand C1010..
C
O
OCH3
O
CH3
JH III
C
O
OCH3
CH3 OO
1111

Juvenoids or JH Analogues (JHa)Juvenoids or JH Analogues (JHa)
Since the metamorphosis hormones and their effects were discovered, a number ofSince the metamorphosis hormones and their effects were discovered, a number of
substances possessing physiological activity more or less identical with that of somesubstances possessing physiological activity more or less identical with that of some
of the insect hormones have been found in extracts of other animal tissues and variousof the insect hormones have been found in extracts of other animal tissues and various
plants. The first of these was the isoprenoid alcohol, farnesol, whose juvenilizingplants. The first of these was the isoprenoid alcohol, farnesol, whose juvenilizing
effects were found in the brain extracts (Schmialek and Wigglesworth, 1959 andeffects were found in the brain extracts (Schmialek and Wigglesworth, 1959 and
1961). As soon as practical implications of substances with this type of effect became1961). As soon as practical implications of substances with this type of effect became
evident, chemists immediately turned their attention to this problem, with the resultevident, chemists immediately turned their attention to this problem, with the result
that, to date, over 1000 synthetic Juvenoids or JHa have been produced. The greatthat, to date, over 1000 synthetic Juvenoids or JHa have been produced. The great
theoretical importance of JHa is that they can be used to analyze all problems oftheoretical importance of JHa is that they can be used to analyze all problems of
insect growth and morphogenesis far more easily and thoroughly than by the corporainsect growth and morphogenesis far more easily and thoroughly than by the corpora
allata transplantation method, which was employed before their discovery. From theallata transplantation method, which was employed before their discovery. From the
practical aspect, their main promise and immense importance is that they offerpractical aspect, their main promise and immense importance is that they offer
prospects of biological control of new types.prospects of biological control of new types.
HistoryHistory
The history of the discovery of substances of this type dates back only a few yearsThe history of the discovery of substances of this type dates back only a few years
and its rapid development keeps pace with the development of insect endocrinologyand its rapid development keeps pace with the development of insect endocrinology
or ahead of it. The prelude to this was the discovery that the abdomens of the matureor ahead of it. The prelude to this was the discovery that the abdomens of the mature
Hyalophora cecropiaHyalophora cecropia male contained a large amount of a substance whose effectsmale contained a large amount of a substance whose effects
correspond with those of JH and which could be isolated by simple extraction withcorrespond with those of JH and which could be isolated by simple extraction with
ethyl ether or methanol (Williams, 1956). Extracts from related species, or even fromethyl ether or methanol (Williams, 1956). Extracts from related species, or even from
the female of the same species displayed little or no JH activity at all. Soon afterthe female of the same species displayed little or no JH activity at all. Soon after
Williams’ workout and finding, discovery of ether extracts of the most diverse tissuesWilliams’ workout and finding, discovery of ether extracts of the most diverse tissues
showed similar JH effects. In addition to the tissues of insects and other invertebrates,showed similar JH effects. In addition to the tissues of insects and other invertebrates,
these included cow’s milk and later on, tissue extracts from many plants and micro –these included cow’s milk and later on, tissue extracts from many plants and micro –
organisms (Schneiderman, 1960 and Gilbert, 1964). Schmialek (1961) working inorganisms (Schneiderman, 1960 and Gilbert, 1964). Schmialek (1961) working in
collaboration with Karlson (1965) and with Wigglesworth (1961), showed that acollaboration with Karlson (1965) and with Wigglesworth (1961), showed that a

relatively simple alcohol of plant origin, i.e., farnesol and a number of its derivatives,relatively simple alcohol of plant origin, i.e., farnesol and a number of its derivatives,
were also highly effective when administered in the same manner. Shortly afterwards,were also highly effective when administered in the same manner. Shortly afterwards,
Sláma (1963) disclosed that various saturated and unsaturated fatty acids, certain fattySláma (1963) disclosed that various saturated and unsaturated fatty acids, certain fatty
alcohols and other natural and synthetic compounds produced juvenilizing effects ofalcohols and other natural and synthetic compounds produced juvenilizing effects of
varying intensity.varying intensity.
Chemical NatureChemical Nature
The substances so far known, whether synthesized or isolated from various materialsThe substances so far known, whether synthesized or isolated from various materials
of vegetables and other origin, can be divided into the following eight groupsof vegetables and other origin, can be divided into the following eight groups
according to their chemical structure (Sláma, 1971). Substances similar to the activeaccording to their chemical structure (Sláma, 1971). Substances similar to the active
component of the abdominal extract of malecomponent of the abdominal extract of male H. cH. cecropiaecropia (adult), isolated by Röller et(adult), isolated by Röller et
al. (1965) and others shown to be Methyl – 10 – epoxy – 7 – ethyl – 3, 11 – dimethylal. (1965) and others shown to be Methyl – 10 – epoxy – 7 – ethyl – 3, 11 – dimethyl
– 2, 6 – tridecadienoate (JH I)or Methyl – 12, 14 – dihomo juvenate (JH II) (Meyer,– 2, 6 – tridecadienoate (JH I)or Methyl – 12, 14 – dihomo juvenate (JH II) (Meyer,
1970). One 6 – 7 days old male1970). One 6 – 7 days old male Hyalophora cecropiaHyalophora cecropia abdomen contained 0.2 – 0.5 µgabdomen contained 0.2 – 0.5 µg
JH I and 0.02 – 0.12 µg JH II. The stereochemistry of JH I and the biological activityJH I and 0.02 – 0.12 µg JH II. The stereochemistry of JH I and the biological activity
(ranging from 1 to 5000 Tu / µg) of some of its isomers and related compounds have(ranging from 1 to 5000 Tu / µg) of some of its isomers and related compounds have
been determined (Dahm et al., 1968)been determined (Dahm et al., 1968) Table – (B)Table – (B). The nearest to the preceding group. The nearest to the preceding group
are acrylic terpenoids, which are similar to farnesenic acid derivatives, but lack theare acrylic terpenoids, which are similar to farnesenic acid derivatives, but lack the
epoxy group and have a methyl instead of ethyl radical at Cepoxy group and have a methyl instead of ethyl radical at C1717 and Cand C1111. This group. This group
comprises the most well studied JHa, such as Dichloro – dimethyl – farnesoate.comprises the most well studied JHa, such as Dichloro – dimethyl – farnesoate.
Aromatic ethers, thio – ethers and amines form he largest JHa group. They are mostlyAromatic ethers, thio – ethers and amines form he largest JHa group. They are mostly
phenol or aniline derivatives in the ortho position, with a differently modified orphenol or aniline derivatives in the ortho position, with a differently modified or
substituted acrylic, mono or sesquiterpenic chain. Monocyclic sesquiterpenoids, tosubstituted acrylic, mono or sesquiterpenic chain. Monocyclic sesquiterpenoids, to
which the paper factor, or Juvabione, and its derivatives belong. They are active onlywhich the paper factor, or Juvabione, and its derivatives belong. They are active only
in bugs of Pyrrhocoridae family. Certain fatty acids and alcohols (both saturated andin bugs of Pyrrhocoridae family. Certain fatty acids and alcohols (both saturated and
unsaturated fatty acids) and some of their derivatives, demonstrated for the first timeunsaturated fatty acids) and some of their derivatives, demonstrated for the first time
by Sláma (1962 and 1963). The most recently discovered group of compounds with aby Sláma (1962 and 1963). The most recently discovered group of compounds with a
peptide structure (Zaoral and Sláma, 1970) whose derivatives are all composed of 2 –peptide structure (Zaoral and Sláma, 1970) whose derivatives are all composed of 2 –
3 amino acids and a branched aliphatic residues. The most active is the L – isoleucyl –3 amino acids and a branched aliphatic residues. The most active is the L – isoleucyl –

L – alanyl – aminobenzoic acid ethyl ester, which in Pyrrhocoris is twice as active asL – alanyl – aminobenzoic acid ethyl ester, which in Pyrrhocoris is twice as active as
Juvabione. Its Chemical Structure is asJuvabione. Its Chemical Structure is as Fig. (3)Fig. (3)..
OO
NN
HH COOCCOOC22HH55
NN
HH
NHNH22 OO
Fig. (3): - Chemical Structure of the most activeFig. (3): - Chemical Structure of the most active
JH AnalogueJH Analogue
Table – (B): - Biological activity and RTable – (B): - Biological activity and RFF values of the authenticvalues of the authentic
juvenile hormone and the synthesized compounds*juvenile hormone and the synthesized compounds*
(After Dahm et al., 1968)(After Dahm et al., 1968)

Name of the CompoundName of the Compound Specific ActivitySpecific Activity
(Tu / µg)(Tu / µg) ****
RRFF******
1. t, t – C1. t, t – C1212 – ethyl – ester (VI)– ethyl – ester (VI) Inactive (at 10µg / animal)Inactive (at 10µg / animal) 0.670.67
2. c, t – C2. c, t – C1212 – ethyl – ester– ethyl – ester Inactive (at 10µg / animal)Inactive (at 10µg / animal) 0.710.71
3. t, t – C3. t, t – C1515 – ketone (VIII)– ketone (VIII) 55 0.480.48
4. t, t, t – C4. t, t, t – C1717 – methyl – ester (IX)– methyl – ester (IX) 200200 0.670.67
5. t, c, t – C5. t, c, t – C1717 – methyl – ester– methyl – ester 3030 0.670.67
6. c, t, t – C6. c, t, t – C1717 – methyl – ester– methyl – ester 11 0.730.73
7. c, c, t – C7. c, c, t – C1717 – methyl – ester– methyl – ester 11 0.730.73
8. dl – t, t, t – 10 – epoxy – C8. dl – t, t, t – 10 – epoxy – C1717 – methyl – ester (X)– methyl – ester (X) 20002000 0.400.40
9. dl – t, c, t – 10 – epoxy – C9. dl – t, c, t – 10 – epoxy – C1717 – methyl – ester (XIII)– methyl – ester (XIII) 150150 0.400.40
10. dl – t, c, t – 10 – epoxy – C10. dl – t, c, t – 10 – epoxy – C1717 – methyl – ester (XIV)– methyl – ester (XIV) 1010 0.410.41
11. dl – c, c, t – 10 – epoxy – C11. dl – c, c, t – 10 – epoxy – C1717 – methyl – ester (XV)– methyl – ester (XV) 1010 0.410.41
12. dl – t, t, t – 6 – epoxy – C12. dl – t, t, t – 6 – epoxy – C1717 – methyl – ester (XI)– methyl – ester (XI) 200200 0.440.44
13. Juvenile Hormone (from13. Juvenile Hormone (from H. cH. cecropiaecropia oil)oil) 200200 0.400.40
** = All compounds were obtained by gas chromatography in pure state= All compounds were obtained by gas chromatography in pure state
**** = Tu / µg means Tenebrio Units per Microgram= Tu / µg means Tenebrio Units per Microgram
****** = Thin Layer Chromatography on Silica Gel G (E. Merck) activated 2 hrs. at= Thin Layer Chromatography on Silica Gel G (E. Merck) activated 2 hrs. at
120ºC, Benzene:Ethyl acetate = 15:1120ºC, Benzene:Ethyl acetate = 15:1
The Mevalonate Pathway and Synthesis of the JuvenileThe Mevalonate Pathway and Synthesis of the Juvenile
Hormones in InsectsHormones in Insects
The mevalonate pathway in insects has two important peculiarities, the absence of theThe mevalonate pathway in insects has two important peculiarities, the absence of the
sterol branch and the synthesis of juvenile hormone (JH) that may have influenced thesterol branch and the synthesis of juvenile hormone (JH) that may have influenced the
mechanisms of regulation. JH modulates transcript levels of a number of genes of themechanisms of regulation. JH modulates transcript levels of a number of genes of the
mevalonate pathway or can influence the translatability and / or stability of themevalonate pathway or can influence the translatability and / or stability of the
transcripts themselves. The mevalonate pathway is a ramified metabolic route basedtranscripts themselves. The mevalonate pathway is a ramified metabolic route based
on reductive polymerization of acetyl – CoA, which leads to a great diversity ofon reductive polymerization of acetyl – CoA, which leads to a great diversity of
isopenoid compounds. Final products of the pathway also include hormonalisopenoid compounds. Final products of the pathway also include hormonal

messengers, such as cytokinins and phytoalexins in plants, steroid hormones inmessengers, such as cytokinins and phytoalexins in plants, steroid hormones in
mammals and defensive secretions, pheromones and JH in insects.mammals and defensive secretions, pheromones and JH in insects.
The Formation of Juvenile HormonesThe Formation of Juvenile Hormones
The conversion of farnesol to farnesal was believed to be catalyzed by a nicotinamideThe conversion of farnesol to farnesal was believed to be catalyzed by a nicotinamide
– dependent dehydrogenase, but recent studies in the lepidopteran– dependent dehydrogenase, but recent studies in the lepidopteran Manduca sextaManduca sexta
suggest that it is a metal – or – flavin – dependent oxidase. In orthopteroid insects,suggest that it is a metal – or – flavin – dependent oxidase. In orthopteroid insects,
esterification of farnesoic acid occurs before epoxidation precedes esterification,esterification of farnesoic acid occurs before epoxidation precedes esterification,
which is under developmental control, and the corresponding JH methyl transferasewhich is under developmental control, and the corresponding JH methyl transferase
was cloned fromwas cloned from B. moriB. mori. JH methyl transferase transfers a methyl group of S –. JH methyl transferase transfers a methyl group of S –
adenosyl – L – methionine (SAM) to farnesoic acid or epoxyfarnesoic acid. Thus, it isadenosyl – L – methionine (SAM) to farnesoic acid or epoxyfarnesoic acid. Thus, it is
not strange that the amino acid sequences of the insect JH methyl transferase containnot strange that the amino acid sequences of the insect JH methyl transferase contain
conserved SAM – binding motif typical of the family of SAM – dependent methylconserved SAM – binding motif typical of the family of SAM – dependent methyl
transferases. Orthologs of insect JH methyl transferases from a number of crustaceantransferases. Orthologs of insect JH methyl transferases from a number of crustacean
species are known. More, recently, a specific JH epoxidase has been cloned andspecies are known. More, recently, a specific JH epoxidase has been cloned and
characterized from the corpora allata (CA) of the cockroachcharacterized from the corpora allata (CA) of the cockroach Diploptera punctataDiploptera punctata
Table – (C)Table – (C). It belongs to the large superfamily of cytochrome P450 proteins and. It belongs to the large superfamily of cytochrome P450 proteins and
epoxidizes methyl farnesoate with high regio- and stereo- selectivity. A clear orthologepoxidizes methyl farnesoate with high regio- and stereo- selectivity. A clear ortholog
of this JH epoxidase has been identified in the genome ofof this JH epoxidase has been identified in the genome of Anopheles gambiaeAnopheles gambiae,,
whereas structurally related sequences have been found inwhereas structurally related sequences have been found in B. moriB. mori andand D.D.
melanogastermelanogaster..
Table – (C): - Species in which genomic or cDNA sequences for enzymes ofTable – (C): - Species in which genomic or cDNA sequences for enzymes of
the mevalonate pathway and juvenile hormone synthesis are available.the mevalonate pathway and juvenile hormone synthesis are available.
EnzymesEnzymes SpeciesSpecies
Bombyx moriBombyx mori
Anopheles gambiaeAnopheles gambiae

JH methyl transferase.JH methyl transferase.
Manduca sextaManduca sexta
Drosophila melanogasterDrosophila melanogaster
Callosobruchus maculatesCallosobruchus maculates
Apis melliferaApis mellifera
JH epoxidaseJH epoxidase
Diploptera punctataDiploptera punctata
Anopheles gambiaeAnopheles gambiae
Juvenile Hormones’ Synthesis in the Corpora AllataJuvenile Hormones’ Synthesis in the Corpora Allata
Biochemical informations implicate the mevalonate pathway in the synthesis of JH,Biochemical informations implicate the mevalonate pathway in the synthesis of JH,
including data from studies on the production of JH by the CA, which showed that theincluding data from studies on the production of JH by the CA, which showed that the
addition of precursors such as mevalonate, farnesol, or farnesoic acid increased JHaddition of precursors such as mevalonate, farnesol, or farnesoic acid increased JH
production, whereas the use of HMG – R inhibitors such as compactin or meviloninproduction, whereas the use of HMG – R inhibitors such as compactin or mevilonin
decrease it, thus indicating that isopenoid flux modulates the rates of JH synthesisdecrease it, thus indicating that isopenoid flux modulates the rates of JH synthesis
(Bellés et al., 2004)(Bellés et al., 2004) Fig. (4)Fig. (4)..
Acetyl – CoAAcetyl – CoA
Acetoacetyl – CoA thiolaseAcetoacetyl – CoA thiolase
Acetoacetyl – CoAAcetoacetyl – CoA
3 – Hydroxy – 3 – methylglutaryl – CoA synthase3 – Hydroxy – 3 – methylglutaryl – CoA synthase
(HMG – S)(HMG – S)
Hydroxymethylglutharyl – CoAHydroxymethylglutharyl – CoA
3 – Hydroxy – 3 – methylglutaryl – CoA reductase3 – Hydroxy – 3 – methylglutaryl – CoA reductase
(HMG – R)(HMG – R)
MevalonateMevalonate
Mevalonate kinaseMevalonate kinase
Mevalonate – 5 – PMevalonate – 5 – P
Phosphomevalonate kinasePhosphomevalonate kinase
Mevalonate – 5 – PPMevalonate – 5 – PP
Diphosphomevalonate decarboxylaseDiphosphomevalonate decarboxylase
Isopentenyl AdenineIsopentenyl Adenine Isopentenyl – PPIsopentenyl – PP Dimethyl allyl – PPDimethyl allyl – PP
(tRNA)(tRNA)
Geranyl – PPGeranyl – PP

Farnesyl diphosphate synthase (FPPS)Farnesyl diphosphate synthase (FPPS)
DolicholDolichol Farnesyl – PPFarnesyl – PP SqualeneSqualene
Heme AHeme A Farnesyl diphosphateFarnesyl diphosphate synthasesynthase
UbiquinoneUbiquinone pyrophosphatasepyrophosphatase
Prenylated ProteinsPrenylated Proteins
FarnesolFarnesol SqualeneSqualene
SqualeneSqualene
Farnesol oxidaseFarnesol oxidase monomono
oxigenaseoxigenase
FarnesalFarnesal Squalene epoxideSqualene epoxide
LanosterolLanosterol
Farnesal dehydrogenaseFarnesal dehydrogenase synthasesynthase
JUVENILEJUVENILE
Farnesoic AcidFarnesoic Acid LanosterolLanosterol
HORMONESHORMONES
JH methyl transferaseJH methyl transferase
BRANCHBRANCH
Methyl farnesoateMethyl farnesoate CHOLESTEROLCHOLESTEROL
IN INSECTSIN INSECTS JH epoxidaseJH epoxidase
Lost in InsectsLost in Insects
JUVENILE HORMONESJUVENILE HORMONES
Fig. (4): - Flux Diagram of the Mevalonate Pathway andFig. (4): - Flux Diagram of the Mevalonate Pathway and
JH Biosynthesis in Insects (Nation, 2002)JH Biosynthesis in Insects (Nation, 2002)
RegulationRegulation
Unveiling the regulatory mechanisms of the Mevalonate Pathway and the synthesis ofUnveiling the regulatory mechanisms of the Mevalonate Pathway and the synthesis of
JH in insects is a major challenge in the field of Entomology. Different studies haveJH in insects is a major challenge in the field of Entomology. Different studies have
shown that JH itself is a key regulatory element of the pathway at least in selectedshown that JH itself is a key regulatory element of the pathway at least in selected
insect models and processes. In insects, cholesterol does not regulate the Mevalonateinsect models and processes. In insects, cholesterol does not regulate the Mevalonate
pathway, rather than SREBP pathway (Sterol – dependent regulation) plays thatpathway, rather than SREBP pathway (Sterol – dependent regulation) plays that
pivotal role. Insect SREBP pathway would be homologous to the SREBP – 1c systempivotal role. Insect SREBP pathway would be homologous to the SREBP – 1c system
of mammals (Goldstein and Brown, 1990). In Scolytids, biochemical analysisof mammals (Goldstein and Brown, 1990). In Scolytids, biochemical analysis
demonstrated that JH regulates isoprenoid pheromone production de novo in thedemonstrated that JH regulates isoprenoid pheromone production de novo in the
midgut ofmidgut of I. piniI. pini males. Further, analysis revealed that JH increases mRNA levels ofmales. Further, analysis revealed that JH increases mRNA levels of
HMG – R and HMG – S inHMG – R and HMG – S in I. paraconfususI. paraconfusus,, I. piniI. pini andand D. jeffreyiD. jeffreyi although there werealthough there were
differences among these species in terms of dose dependency and timing of induction.differences among these species in terms of dose dependency and timing of induction.

JH activated HMG – R more strongly (8 folds inJH activated HMG – R more strongly (8 folds in I. piniI. pini and 30 folds inand 30 folds in D. jeffreyiD. jeffreyi))
than HMG – S (4 folds inthan HMG – S (4 folds in D. jeffreyiD. jeffreyi). Moreover, JH elicited a modest induction of). Moreover, JH elicited a modest induction of
geranyl diphosphate synthase expression in malegeranyl diphosphate synthase expression in male I. piniI. pini. A recent study on. A recent study on I. piniI. pini
using quantitative real – time PCR examined feeding – induced changes in geneusing quantitative real – time PCR examined feeding – induced changes in gene
expression of seven mevalonate pathway genes, namely acetoacetyl – CoA thiolase,expression of seven mevalonate pathway genes, namely acetoacetyl – CoA thiolase,
HMG – S, HMG – R, diphosphomevalonate decarboxylase, isopentenyl diphosphateHMG – S, HMG – R, diphosphomevalonate decarboxylase, isopentenyl diphosphate
isomerase, geranyl diphosphate synthase and FPPs. After feeding, expression in allisomerase, geranyl diphosphate synthase and FPPs. After feeding, expression in all
seven genes increased in males, but only first five genes increased in females. Thisseven genes increased in males, but only first five genes increased in females. This
suggests that feeding stimulates JH biosynthesis in the corpora allata, which, inturnsuggests that feeding stimulates JH biosynthesis in the corpora allata, which, inturn
stimulates the enzymes involved in the anterior midgut of males. Investigations on thestimulates the enzymes involved in the anterior midgut of males. Investigations on the
role of JH in the regulation of the mevalonate pathway in cockroach (role of JH in the regulation of the mevalonate pathway in cockroach (B. germanicaB. germanica))
suggests that JH may regulate the translatability and (or the stability of the enzymesuggests that JH may regulate the translatability and (or the stability of the enzyme
transcripts).transcripts).
Research focused on JH, working on two different models: - the production of theResearch focused on JH, working on two different models: - the production of the
pheromones in male Scolytids and the synthesis of JH and other processes related topheromones in male Scolytids and the synthesis of JH and other processes related to
cockroach female reproduction. Results suggested that JH can exert a pleiotropic rolecockroach female reproduction. Results suggested that JH can exert a pleiotropic role
upon regulation of the mevalonate pathway, acting in some tissues stages, andupon regulation of the mevalonate pathway, acting in some tissues stages, and
associated physiological processes as a transcriptional activator (pheromoneassociated physiological processes as a transcriptional activator (pheromone
biosynthesis in Scolytids; and also modulating the translatability and / or stability ofbiosynthesis in Scolytids; and also modulating the translatability and / or stability of
the transcripts themselves / processes related to reproduction in cockroaches). Often,the transcripts themselves / processes related to reproduction in cockroaches). Often,
data have shown that JH can act in parallel with a number of enzymes in the pathway,data have shown that JH can act in parallel with a number of enzymes in the pathway,
which suggest that the mevalonate pathway in insects can best be interpreted in termswhich suggest that the mevalonate pathway in insects can best be interpreted in terms
of co – ordinated regulation and metabolic control analysis, rather than in terms of aof co – ordinated regulation and metabolic control analysis, rather than in terms of a
key regulatory step (s).key regulatory step (s).
Cellular Receptors for JHCellular Receptors for JH
A number of studies have shown that the various JH molecules are bound toA number of studies have shown that the various JH molecules are bound to
haemolymph components and to cytoplasmic and nuclear proteins (Goodman andhaemolymph components and to cytoplasmic and nuclear proteins (Goodman and
Chang, 1985). A 29 kDa nuclear protein has been isolated from larval epidermal andChang, 1985). A 29 kDa nuclear protein has been isolated from larval epidermal and

fat body cells offat body cells of M. sextaM. sexta with high specificity for binding JH I and JH II (Riddiford,with high specificity for binding JH I and JH II (Riddiford,
1990; Riddiford and Truman, 1993). This nuclear binding protein is not present in the1990; Riddiford and Truman, 1993). This nuclear binding protein is not present in the
nuclei of epidermal cells when no high – affinity JH binding sites are present, such asnuclei of epidermal cells when no high – affinity JH binding sites are present, such as
in wandering larvae or in those larvae that are allatectomized. This protein isin wandering larvae or in those larvae that are allatectomized. This protein is
considered a putative JH receptor. Another JH receptor has been purified from fatconsidered a putative JH receptor. Another JH receptor has been purified from fat
body cells of both adult sexes of the cockroachbody cells of both adult sexes of the cockroach Leucophaea manderaeLeucophaea manderae (Engelman,(Engelman,
1995). It is a binding protein of about 64 kDa composed of two 32 kDa subunits. This1995). It is a binding protein of about 64 kDa composed of two 32 kDa subunits. This
JH receptor appears to be more related to the egg production in the adult than to theJH receptor appears to be more related to the egg production in the adult than to the
development of immature stages. At present, the receptor has only been detected I thedevelopment of immature stages. At present, the receptor has only been detected I the
last instar and adult, both stages capable of responding to exogenous JH or JH analoglast instar and adult, both stages capable of responding to exogenous JH or JH analog
by synthesizing vitellogenin (in females) for incorporation into eggs.by synthesizing vitellogenin (in females) for incorporation into eggs.
Degradation of JHDegradation of JH
The main degradative pathways for JH involve specific and non – specific. JHThe main degradative pathways for JH involve specific and non – specific. JH
esterases (JHEs) described from numerous insects and JH epoxide hydrolasesesterases (JHEs) described from numerous insects and JH epoxide hydrolases
(JHEHs) reported from some insects. The esterases attack the ester linkage, while(JHEHs) reported from some insects. The esterases attack the ester linkage, while
epoxide hydrolases open the epoxide ring and create a diolepoxide hydrolases open the epoxide ring and create a diol Fig. (5)Fig. (5).. Only one, or bothOnly one, or both
actions, occur in some insects. The metabolic changes not only eliminate all or mostactions, occur in some insects. The metabolic changes not only eliminate all or most
of the hormonal activity of the molecules, but those become more water soluble andof the hormonal activity of the molecules, but those become more water soluble and
can be excreted by the Malpighian tubules.can be excreted by the Malpighian tubules.
OO
CH3
JH I
2020
O O
O

A.A. JH I diol.JH I diol. B.B. JH I acid.JH I acid.
(Inactive)(Inactive) (Inactive)(Inactive)
C.C. acid – diol form.acid – diol form.
(Inactive)(Inactive)
Fig. (5): - Metabolic pathways for the degradation of JHFig. (5): - Metabolic pathways for the degradation of JH
[The epoxide ring can be opened with hydrolysis and production of two hydroxyl groups , as[The epoxide ring can be opened with hydrolysis and production of two hydroxyl groups , as
in (in (AA), or the ester group can be hydrolyzed to the free acid as in (), or the ester group can be hydrolyzed to the free acid as in (BB), Both (), Both (AA) and () and (BB) are) are
inactive, and either or both can occur in most insects (White, 1972)]inactive, and either or both can occur in most insects (White, 1972)]
Mechanism of ActionsMechanism of Actions
Various theories can explain the mode of action of JH, some obviously contradictory.Various theories can explain the mode of action of JH, some obviously contradictory.
According to Wigglesworth’s original idea (1936), JH affects morphogenesis on theAccording to Wigglesworth’s original idea (1936), JH affects morphogenesis on the
principle of Goldschmidt’s hypothesis of different reaction velocities. Novák (1951principle of Goldschmidt’s hypothesis of different reaction velocities. Novák (1951
and 1956) suggested a theory or hypothesis on the mode of action of JH on the basisand 1956) suggested a theory or hypothesis on the mode of action of JH on the basis
of the gradient – factor as a factor conditioning the JH – independent growth of theof the gradient – factor as a factor conditioning the JH – independent growth of the
imaginal parts of the body. According to this theory, JH produces its effect by takingimaginal parts of the body. According to this theory, JH produces its effect by taking
the place of the GF (Gradient factor) in those parts of the body which lose it in thethe place of the GF (Gradient factor) in those parts of the body which lose it in the
course of development. Such parts are the larval parts of the body during larvalcourse of development. Such parts are the larval parts of the body during larval
O
O O
O
O
2121
OH
OH
HO
OH
OH
HO
O

development, the ovarian follicle in adult females, and a number of other tissues atdevelopment, the ovarian follicle in adult females, and a number of other tissues at
particular times during development. According to Novák (1954) and Sláma andparticular times during development. According to Novák (1954) and Sláma and
Wenig (1961), the effect of JH seems to depend on the conditioning of proteinWenig (1961), the effect of JH seems to depend on the conditioning of protein
synthesis and other functions in the larval parts of the bodysynthesis and other functions in the larval parts of the body Fig. (6)Fig. (6)..
The series of successive moulting processes subdivides the post – embryonicThe series of successive moulting processes subdivides the post – embryonic
development in insects into several intermoult periods, or instars, during which (butdevelopment in insects into several intermoult periods, or instars, during which (but
not at any other time) growth and morphogenesis are possible. This cyclical eventnot at any other time) growth and morphogenesis are possible. This cyclical event
repeated in each of the instars, which are strictly inter – related, are induced andrepeated in each of the instars, which are strictly inter – related, are induced and
controlled by the three metamorphosis hormones; JH is one of them. Thus, insect’scontrolled by the three metamorphosis hormones; JH is one of them. Thus, insect’s
development which includes both growth and morphogenesis is complicateddevelopment which includes both growth and morphogenesis is complicated Fig. (7)Fig. (7)..
Long.Long. Cap.Cap. Cap.Cap. c.g.c.g. f.g.f.g.

RelativeRelative
IncreaseIncrease 11stst
22ndnd
33rdrd
44thth
55thth
OO Larval InstarsLarval Instars
Fig. (6): - Growth of the corpora allata compared with other
parts of the body during the 5th
larval instar of Bombyx mori
[[Abscissa –Abscissa – Laval instars,Laval instars, Ordinate –Ordinate – Relative increase.Relative increase.
f.g. = Frontal Ganglion,f.g. = Frontal Ganglion, c.g. = Cerebral Ganglion,c.g. = Cerebral Ganglion, Cap = Breadth of the Head,Cap = Breadth of the Head,
Cap = Height of the Head,Cap = Height of the Head, Long = length of the BodyLong = length of the Body (Novák, 1954)(Novák, 1954)]]

Fig. (7): -Fig. (7): - Schematic representation of juvenile hormone (JH) and ecdysteroid titers duringSchematic representation of juvenile hormone (JH) and ecdysteroid titers during
development in Hemimetabola (development in Hemimetabola (Nauphoeta cineraNauphoeta cinera) and Holometabola () and Holometabola (Manduca sextaManduca sexta), and various), and various
events that are caused by each hormone. All of the events in Holometabola are results from studies ofevents that are caused by each hormone. All of the events in Holometabola are results from studies of
bothboth Mamestra brassicaeMamestra brassicae andand M. sextaM. sexta. The horizontal black bars indicate the critical periods of JH. The horizontal black bars indicate the critical periods of JH
for commitments.for commitments. 20E =20E = 20 – Hydroxyecdysone;20 – Hydroxyecdysone; PTGPTG = Prothoracic gland;= Prothoracic gland;
PTTHPTTH = Prothoracicotropic hormone;= Prothoracicotropic hormone; HCSHCS = Head capsule slippage= Head capsule slippage [Lanzrein et al. (1985)][Lanzrein et al. (1985)]

Actions of Juvenile Hormones on Endocrine SystemsActions of Juvenile Hormones on Endocrine Systems
JH not only modulates Ecdysone action on various tissues, but also affects theJH not only modulates Ecdysone action on various tissues, but also affects the
activities of other endocrine organs that are responsible for moulting andactivities of other endocrine organs that are responsible for moulting and
metamorphosis – in particular, the brain and the prothoracic gland.metamorphosis – in particular, the brain and the prothoracic gland.
Larval MoultLarval Moult
The prolonged high JH titer seen during the penultimate larval instar is necessary toThe prolonged high JH titer seen during the penultimate larval instar is necessary to
cause an increase in Ecdysteroid titer at a proper time in both Hemimetabolouscause an increase in Ecdysteroid titer at a proper time in both Hemimetabolous
((Rhodnius prolixusRhodnius prolixus) and Holometabolous () and Holometabolous (MamestraMamestra andand ManducaManduca) insects. When JH) insects. When JH
is removed by allatectomy, the large moulting surges of Ecdysteroid are drasticallyis removed by allatectomy, the large moulting surges of Ecdysteroid are drastically
depressed, but the application of JH restores these surges. Indepressed, but the application of JH restores these surges. In MamestraMamestra, JH apparently, JH apparently
activates the brain to synthesize and / or release PTTH, which then stimulatesactivates the brain to synthesize and / or release PTTH, which then stimulates
Ecdysteroid synthesis and release by the prothoracic glands.Ecdysteroid synthesis and release by the prothoracic glands.
Larval – Pupal CommitmentLarval – Pupal Commitment
After the last larval ecdysis, the nature of the brain and prothoracic glands changesAfter the last larval ecdysis, the nature of the brain and prothoracic glands changes
dramatically. During the feeding stage indramatically. During the feeding stage in ManducaManduca, the secretion of PTTH is strongly, the secretion of PTTH is strongly
inhibited by JH and growth continues if JH is present. Therefore, the decline of JH isinhibited by JH and growth continues if JH is present. Therefore, the decline of JH is
important for the brain to release PTTH, which is responsible for the commitmentimportant for the brain to release PTTH, which is responsible for the commitment
peak of ecdysteroid. The commitment peak does not appear until JH disappearspeak of ecdysteroid. The commitment peak does not appear until JH disappears
completely. The signal for the decline of JH depends on the weight of the larvae, butcompletely. The signal for the decline of JH depends on the weight of the larvae, but
the means of recognition of the critical weight is unknown. After exposure of thethe means of recognition of the critical weight is unknown. After exposure of the
commitment peak of ecdysteroid, the responsiveness of prothoracic glands to JHcommitment peak of ecdysteroid, the responsiveness of prothoracic glands to JH
dramatically changes indramatically changes in MamestraMamestra,, ManducaManduca andand Spodoptera littoralisSpodoptera littoralis. The. The
prothoracic glands before this exposure are inhibited by JH (larval type). Inprothoracic glands before this exposure are inhibited by JH (larval type). In
MamestraMamestra, this transformation is caused by PTTH, which is responsible for the, this transformation is caused by PTTH, which is responsible for the
commitment peak and / or α – ecdysone from the prothoracic glands in the absence ofcommitment peak and / or α – ecdysone from the prothoracic glands in the absence of
JH. Unlike PTTH, the stimulatory action of JH on prothoracic glands appears to beJH. Unlike PTTH, the stimulatory action of JH on prothoracic glands appears to be

indirect. Inindirect. In ManducaManduca, JH causes the fat body to produce a haemolymph protein that, JH causes the fat body to produce a haemolymph protein that
enhances the production of ecdysteroids by the prothoracic glands.enhances the production of ecdysteroids by the prothoracic glands.
Pupal MoultPupal Moult
During the pupal moult, JH plays an important role not only for normal pupation butDuring the pupal moult, JH plays an important role not only for normal pupation but
also for the timing of pupation. The removal of this JH by allatectomy delays pupalalso for the timing of pupation. The removal of this JH by allatectomy delays pupal
ecdysis by a day or so in bothecdysis by a day or so in both MamestraMamestra andand ManducaManduca. Because the moulting peak. Because the moulting peak
ecdysteroid is also delayed under these conditions, the reappearance of JH at this timeecdysteroid is also delayed under these conditions, the reappearance of JH at this time
is likely important in conjunction with environmental signals that stimulate PTTHis likely important in conjunction with environmental signals that stimulate PTTH
release.release.
Roles of Juvenile Hormones in embryonic developmentRoles of Juvenile Hormones in embryonic development
Both ecdysteroids and JH are found in freshly laid eggs in the locust,Both ecdysteroids and JH are found in freshly laid eggs in the locust, LocustaLocusta
migratoriamigratoria. The ecdysteroids are inactive conjugates; at times corresponding to the. The ecdysteroids are inactive conjugates; at times corresponding to the
early embryonic moults, these inactive conjugates are converted to 20E and otherearly embryonic moults, these inactive conjugates are converted to 20E and other
metabolites. The later ecdysteroid surges are likely a result of the prothoracic glandsmetabolites. The later ecdysteroid surges are likely a result of the prothoracic glands
of the embryo. The JH is wiped out by the JH esterases that appear with the onset ofof the embryo. The JH is wiped out by the JH esterases that appear with the onset of
the embryonic development, and then JH reappears late during embryogenesis, whenthe embryonic development, and then JH reappears late during embryogenesis, when
it is secreted by the embryonic corpora allata. Init is secreted by the embryonic corpora allata. In NauphoetaNauphoeta, two surges of JH appear, two surges of JH appear
shortly after dorsal closure. JH mimetics are applied to insect eggs during earlyshortly after dorsal closure. JH mimetics are applied to insect eggs during early
embryogenesis to cause disruption of blastokinesis (the movement of the embryoembryogenesis to cause disruption of blastokinesis (the movement of the embryo
within the egg, so that its dorsal surface is towards the egg shell, known aswithin the egg, so that its dorsal surface is towards the egg shell, known as
Katatrepsis) and often cause defects in dorsal closure. In the Hemimetabola, such asKatatrepsis) and often cause defects in dorsal closure. In the Hemimetabola, such as
in the Locust, the presence of JH at the time of Katatrepsis, when JH is not normallyin the Locust, the presence of JH at the time of Katatrepsis, when JH is not normally
present, also causes premature termination of patterning, suppression of growth, andpresent, also causes premature termination of patterning, suppression of growth, and
precocious differentiation of the nymphal stage. In Holometabola, as exemplified byprecocious differentiation of the nymphal stage. In Holometabola, as exemplified by
Lepidopterans, despite the effect of JH on blastokinesis, there is little effect on growthLepidopterans, despite the effect of JH on blastokinesis, there is little effect on growth
and differentiation. This lack of effect of applied JH is thought to be due to the earlierand differentiation. This lack of effect of applied JH is thought to be due to the earlier

appearance of JH and other considerations have led Truman and Riddiford toappearance of JH and other considerations have led Truman and Riddiford to
hypothesize that during the evolution of complete metamorphosis, the embryos ofhypothesize that during the evolution of complete metamorphosis, the embryos of
holometabolous insects showed advancement in the timing of JH secretion by theholometabolous insects showed advancement in the timing of JH secretion by the
embryonic corpora allata. The resultant alteration in tissue patterning and precociousembryonic corpora allata. The resultant alteration in tissue patterning and precocious
differentiation was then important for the evolution of the novel from the larva.differentiation was then important for the evolution of the novel from the larva.
DiapauseDiapause
Many insects enter diapause (cease of normal progression of growth) at differentMany insects enter diapause (cease of normal progression of growth) at different
stages and it is triggered by environmental cues such as the temperature, day length,stages and it is triggered by environmental cues such as the temperature, day length,
and humidity. Usually, diapausing insects differ from non – diapausing individualsand humidity. Usually, diapausing insects differ from non – diapausing individuals
from the physiological and biochemical point of view. The programming of diapausefrom the physiological and biochemical point of view. The programming of diapause
is also under the control of hormones. Embryonic diapause inis also under the control of hormones. Embryonic diapause in BombyxBombyx is induced by ais induced by a
suboesophageal ganglion diapause hormone that acts on the ovarioles of femalessuboesophageal ganglion diapause hormone that acts on the ovarioles of females
during egg maturation, and the females lay diapausing eggs therefore. Pupal diapauseduring egg maturation, and the females lay diapausing eggs therefore. Pupal diapause
is caused by arrest of PTTH release, so that the prothoracic glands are not stimulated.is caused by arrest of PTTH release, so that the prothoracic glands are not stimulated.
JH is a key player in larval and adult diapause. Adult diapause is characterized by theJH is a key player in larval and adult diapause. Adult diapause is characterized by the
halt of reproduction and is basically due to the cessation of secretion of JH by thehalt of reproduction and is basically due to the cessation of secretion of JH by the
corpora allata. Diapause in last – instar Lepidopteran larvae has been well – studied.corpora allata. Diapause in last – instar Lepidopteran larvae has been well – studied.
In both the rice Stem – borer,In both the rice Stem – borer, Chilo suppressalisChilo suppressalis, and the South Western Corn – borer,, and the South Western Corn – borer,
Diatraea grandiosellaDiatraea grandiosella, the JH titer in the haemolymph is high during the diapause that, the JH titer in the haemolymph is high during the diapause that
not only induces diapause but also maintains its status. A high JH titer also inducesnot only induces diapause but also maintains its status. A high JH titer also induces
the prepupal diapause in the slug moth,the prepupal diapause in the slug moth, Monema flavescensMonema flavescens. Apart from that, there are. Apart from that, there are
so many insects in the world, where larval diapause can be artificially induced by theso many insects in the world, where larval diapause can be artificially induced by the
application of JH or even by Juvenoids also.application of JH or even by Juvenoids also.

Molecular Actions of Juvenile HormonesMolecular Actions of Juvenile Hormones
Various authors have attempted to explain the mode of JH at the molecular level. InVarious authors have attempted to explain the mode of JH at the molecular level. In
addition to the hypothesis by Wigglesworth of the existence of two alternativeaddition to the hypothesis by Wigglesworth of the existence of two alternative
enzyme systems (larval and imaginal), Williams (1961) concluded that JH ‘blocks theenzyme systems (larval and imaginal), Williams (1961) concluded that JH ‘blocks the
flow of fresh genetic information from nucleus to cytoplasm’. JH could do this byflow of fresh genetic information from nucleus to cytoplasm’. JH could do this by
affecting one or more possible feedback systems concerned with the repression ofaffecting one or more possible feedback systems concerned with the repression of
specific regulators or some other link in the chain of protein synthesis. Clarke andspecific regulators or some other link in the chain of protein synthesis. Clarke and
Baldwin (1960) considered the possibility that JH controls ATP synthesis by acting oBaldwin (1960) considered the possibility that JH controls ATP synthesis by acting o
the mitochondrial cytochrome system. On the basis of the experiments on the flightthe mitochondrial cytochrome system. On the basis of the experiments on the flight
musculature of the Colorado Beetle, Stegwee (1960) suggested that the hormonemusculature of the Colorado Beetle, Stegwee (1960) suggested that the hormone
might stimulate succinate oxidation and that the site of stimulation was that part of themight stimulate succinate oxidation and that the site of stimulation was that part of the
respiratory chain between succinate and cytochrome – c. Gilbert (1964) concludedrespiratory chain between succinate and cytochrome – c. Gilbert (1964) concluded
that the site of action of JH might be the nucleus, where it influenced chromosomalthat the site of action of JH might be the nucleus, where it influenced chromosomal
metabolism and thus affected the specificity of the protein synthesis. Ilan et. al. (1970)metabolism and thus affected the specificity of the protein synthesis. Ilan et. al. (1970)
suggested that JH might control gene expression at the translational level. Schmialeksuggested that JH might control gene expression at the translational level. Schmialek
(1972) had showed many chemical evidences in support of the explanation of JH(1972) had showed many chemical evidences in support of the explanation of JH
action, i.e., the coupling of DNA molecules with certain isoprenoid compounds,action, i.e., the coupling of DNA molecules with certain isoprenoid compounds,
which include many of the effective JH analogues (McMullen, 1961). Williams andwhich include many of the effective JH analogues (McMullen, 1961). Williams and
Kafatos (1971 and 1973) formulated a new version of the ‘repression’ theory of JHKafatos (1971 and 1973) formulated a new version of the ‘repression’ theory of JH
action. Following the ‘depression’ theory of Jacob and Monod, they consider that JHaction. Following the ‘depression’ theory of Jacob and Monod, they consider that JH
plays the role of an activator (= co – repressor) of the pupal and adult ‘master – genes’plays the role of an activator (= co – repressor) of the pupal and adult ‘master – genes’
determining pupal and imaginal differentiation. The corresponding repressors aredetermining pupal and imaginal differentiation. The corresponding repressors are
active only in presence of JH.active only in presence of JH.
JH enters the larval epidermal cell inJH enters the larval epidermal cell in ManducaManduca and one – third goes to the nucleusand one – third goes to the nucleus
photoaffinity – labeled JH I, JH II and methoprene (a JH mimic) bind to a 29KDaphotoaffinity – labeled JH I, JH II and methoprene (a JH mimic) bind to a 29KDa
protein that is found in the larval epidermis. Once it was thought that this protein is aprotein that is found in the larval epidermis. Once it was thought that this protein is a
JH receptor, but further studies have shown only a low – affinity binding protein.JH receptor, but further studies have shown only a low – affinity binding protein.
Recently, it has been reported thatRecently, it has been reported that DrosophilaDrosophila ultraspiracle protein (USP) binds JH IIIultraspiracle protein (USP) binds JH III

and JH III bisepoxide with low affinity (about 4 X 10and JH III bisepoxide with low affinity (about 4 X 10 -7-7
µ). JH III and methopreneµ). JH III and methoprene
cannot replace the bacterial phospholipid found in the ligand – binding pocket ofcannot replace the bacterial phospholipid found in the ligand – binding pocket of
recombinant USP, but JH I acid is predicted to fit into this pocket. However, norecombinant USP, but JH I acid is predicted to fit into this pocket. However, no
functional studies of the role of USP as a JH receptor have been reported. There are afunctional studies of the role of USP as a JH receptor have been reported. There are a
number of reports regarding JH – binding proteins. Among them, most interesting arenumber of reports regarding JH – binding proteins. Among them, most interesting are
the methoprene – tolerant (Met) gene inthe methoprene – tolerant (Met) gene in DrosophilaDrosophila mutants, that have an intracellularmutants, that have an intracellular
JH – binding protein with reduced JH –JH – binding protein with reduced JH – binding activity. The Met protein is found inbinding activity. The Met protein is found in
the nucleus and has a high degree of similarity to the basic helix – loop – helix Per,the nucleus and has a high degree of similarity to the basic helix – loop – helix Per,
Arnt and Sim (PAS) domain family members. How this is related to JH action is stillArnt and Sim (PAS) domain family members. How this is related to JH action is still
not known fully. Null mutants show no defect in development, but have delayed andnot known fully. Null mutants show no defect in development, but have delayed and
reduced vitellogenesis. Therefore, a JH receptor for insect development is still elusive.reduced vitellogenesis. Therefore, a JH receptor for insect development is still elusive.
Regulation of the Ecdysone – Induced TranscriptionRegulation of the Ecdysone – Induced Transcription
Factor Cascade (ETFC)Factor Cascade (ETFC)
Most of the events caused by 20E are through the control of the Ecdysone ReceptorMost of the events caused by 20E are through the control of the Ecdysone Receptor
(EcR), but EcR is an inactive receptor and it needs to partner with Ultraspiracle(EcR), but EcR is an inactive receptor and it needs to partner with Ultraspiracle
protein to be functional. 20 – Hydroxy – Ecdysone enters the cells and then theprotein to be functional. 20 – Hydroxy – Ecdysone enters the cells and then the
nucleus, where EcR and USP are bound to the DNA. Once 20E binds to EcR, thenucleus, where EcR and USP are bound to the DNA. Once 20E binds to EcR, the
20E / EcR / USP complex directly activates the early gene (e.g. E75 and BR – C), the20E / EcR / USP complex directly activates the early gene (e.g. E75 and BR – C), the
protein products of which in turn activate the late tissue specific genes (e.g. L71 in theprotein products of which in turn activate the late tissue specific genes (e.g. L71 in the
salivary gland) and inhibit the early genes. 2 – 3 isoforms of EcR and USP are knownsalivary gland) and inhibit the early genes. 2 – 3 isoforms of EcR and USP are known
from various insects, and the receptor levels fluctuate with development. The primaryfrom various insects, and the receptor levels fluctuate with development. The primary
role of JH in morphogenesis is to modulate the ecdysone action, and JH alsorole of JH in morphogenesis is to modulate the ecdysone action, and JH also
modulates the ecdysone – inducible EcR and USP expression. Expression of both EcRmodulates the ecdysone – inducible EcR and USP expression. Expression of both EcR
and USP is up – regulated by 20E in a complex fashion. In theand USP is up – regulated by 20E in a complex fashion. In the ManducaManduca epidermis,epidermis,
the expression of all of the EcR (EcR – A and EcR – B1) and USP (USP – 1 and USPthe expression of all of the EcR (EcR – A and EcR – B1) and USP (USP – 1 and USP
– 2) isoforms is induced by 20E, but JH prevents this action. The one exception is– 2) isoforms is induced by 20E, but JH prevents this action. The one exception is

USP – 2, which is unaffected by JH. JH is also known to prolong the half – life ofUSP – 2, which is unaffected by JH. JH is also known to prolong the half – life of
both EcR – A and EcR – B1 proteins.both EcR – A and EcR – B1 proteins.
Regulation of Cuticular MelanizationRegulation of Cuticular Melanization
Larval pigmentation is under the control of JH in many insects, but there are not manyLarval pigmentation is under the control of JH in many insects, but there are not many
studies at the molecular level. Normally,studies at the molecular level. Normally, ManducaManduca larvae have a transparent cuticlelarvae have a transparent cuticle
with black markings. Yet when JH is removed by allatectomy about 30 hrs. before thewith black markings. Yet when JH is removed by allatectomy about 30 hrs. before the
last larval ecdysis, cuticular melanization occurs in the newly synthesized Vlast larval ecdysis, cuticular melanization occurs in the newly synthesized Vthth
instarinstar
larval cuticle and can be prevented by application of JHlarval cuticle and can be prevented by application of JH Fig. (7)Fig. (7)..
CUTICULAR MELANIZATIONCUTICULAR MELANIZATION ------
JHJH
DDCDDC Granular POGranular PO
DopaDopa Dopamine MelaninDopamine Melanin
COMMITMENTCOMMITMENT --------
JHJH
E75AE75A
BR – CBR – C BR - CBR - C
BR – CBR – C BR - CBR - C
Fig. (8): - Models for molecular actions of juvenile hormones (JH)Fig. (8): - Models for molecular actions of juvenile hormones (JH)
[DDC = Dopa decarboxylase; PO = Phenoloxidase; BR – C = Broad Complex;[DDC = Dopa decarboxylase; PO = Phenoloxidase; BR – C = Broad Complex;
= Induction; = Inhibition]= Induction; = Inhibition]
Larva Pupa Adult

The melanin is dopamine – melanin and found in granules deposited to the cuticle.The melanin is dopamine – melanin and found in granules deposited to the cuticle.
Accordingly, Dopa decarboxylase (DDC) [converts Dopa to Dopamine] and granularAccordingly, Dopa decarboxylase (DDC) [converts Dopa to Dopamine] and granular
phenoloxidase (PO) [oxidizes Dopamine in the first step of the oxidative path tophenoloxidase (PO) [oxidizes Dopamine in the first step of the oxidative path to
melanin] are crucial enzymes for this process. In allatectomized melanizing larvae, themelanin] are crucial enzymes for this process. In allatectomized melanizing larvae, the
abdominal epidermis produces a granular pro – PO that is incorporated to the newabdominal epidermis produces a granular pro – PO that is incorporated to the new
cuticle in the premelanin granules. The pro – PO is later activated by the decline ofcuticle in the premelanin granules. The pro – PO is later activated by the decline of
ecdysteroid titer. The application of JH 25 to 30 hrs. before ecdysis completelyecdysteroid titer. The application of JH 25 to 30 hrs. before ecdysis completely
prevents the production of this enzymeprevents the production of this enzyme Fig. (8)Fig. (8). DDC is essential for not only. DDC is essential for not only
melanization but also for cuticular sclerotization, and its activity and its mRNAmelanization but also for cuticular sclerotization, and its activity and its mRNA
increases titer. In allatectomized larvae, the levels are two folds higher than those inincreases titer. In allatectomized larvae, the levels are two folds higher than those in
non – melanizing normal larvaenon – melanizing normal larvae Fig. (8)Fig. (8). The excess dopamine is incorporated to the. The excess dopamine is incorporated to the
granules deposited in the cuticle, where activated granular PO is present, so thatgranules deposited in the cuticle, where activated granular PO is present, so that
melanization occurs within the granules. The action of JH on DDC gene expression ismelanization occurs within the granules. The action of JH on DDC gene expression is
thus to modify the amount of gene expression, as is also seen in E75A, rather than thethus to modify the amount of gene expression, as is also seen in E75A, rather than the
suppression of new gene expression, as seen in granular PO. The mode of action ofsuppression of new gene expression, as seen in granular PO. The mode of action of
JH in both cases is still unknown.JH in both cases is still unknown.
Larval Pupal CommitmentLarval Pupal Commitment
In the ecdysone cascade, in addition to EcR and USP, JH affects the expression of aIn the ecdysone cascade, in addition to EcR and USP, JH affects the expression of a
few other transcription factors. Infew other transcription factors. In ManducaManduca, studies of the metamorphic role of these, studies of the metamorphic role of these
factors show that JH enhances the expression of one of the 20E – inducedfactors show that JH enhances the expression of one of the 20E – induced
transcription factors, E75A, in larval epidermis, where it prevents pupal commitmenttranscription factors, E75A, in larval epidermis, where it prevents pupal commitment
of the epidermis, suggesting that a high titer of E75A is important for maintenance ofof the epidermis, suggesting that a high titer of E75A is important for maintenance of
the larval statethe larval state Fig. (8)Fig. (8). Another 20E – induced transcription factor, BR – C, is. Another 20E – induced transcription factor, BR – C, is
expressed only from the time of pupal commitment through the time of pupation inexpressed only from the time of pupal commitment through the time of pupation in
bothboth ManducaManduca andand DrosophilaDrosophila. In. In ManducaManduca, the appearance of BR – C protein, the appearance of BR – C protein
correlates with pupal commitment of the abdominal epidermis on day 3 of the finalcorrelates with pupal commitment of the abdominal epidermis on day 3 of the final
larval instar, and the prevention of pupal commitment by JH prevents BR – Clarval instar, and the prevention of pupal commitment by JH prevents BR – C
expression bothexpression both inin vivovivo andand inin vitrovitro Fig. (8)Fig. (8). Expression of BR – C in the abdominal. Expression of BR – C in the abdominal

epidermis occurs in a strict spatial pattern that coincides with the loss of theepidermis occurs in a strict spatial pattern that coincides with the loss of the
sensitivity to JH. Furthermore, once epidermis is exposed to 20E for 6 hrs, at whichsensitivity to JH. Furthermore, once epidermis is exposed to 20E for 6 hrs, at which
time BR – C mRNA is first detectable, JH can no longer prevent BR – C expression.time BR – C mRNA is first detectable, JH can no longer prevent BR – C expression.
Similarly, JH can not prevent the pupal commitment once the cells are exposed toSimilarly, JH can not prevent the pupal commitment once the cells are exposed to
20E, in the absence of JH, for more than 6 hrs. The appearance of BR – C mRNA in20E, in the absence of JH, for more than 6 hrs. The appearance of BR – C mRNA in
wing discs also correlates with their pupal commitment. Therefore, BR – C expressionwing discs also correlates with their pupal commitment. Therefore, BR – C expression
is one of the first molecular events underlying pupal commitment of both abdominalis one of the first molecular events underlying pupal commitment of both abdominal
epidermis and wing discs. In addition,epidermis and wing discs. In addition, DrosophilaDrosophila mutants that lack BR – C entirelymutants that lack BR – C entirely
develop normally until metamorphosis, but die before pupation. These observationsdevelop normally until metamorphosis, but die before pupation. These observations
suggest that BR – C is a key factor for metamorphosis.suggest that BR – C is a key factor for metamorphosis.
A recent breakthrough on the molecular mechanism of pupal commitment hasA recent breakthrough on the molecular mechanism of pupal commitment has
been reported by Zhou and Riddiford (2002), who clearly showed inbeen reported by Zhou and Riddiford (2002), who clearly showed in ManducaManduca and inand in
DrosophilaDrosophila that BR – C is a pupal – specifying transcription factorthat BR – C is a pupal – specifying transcription factor Fig. (8)Fig. (8). Normally. Normally
BR – C is present during pupal cuticle formation but is not present during the adultBR – C is present during pupal cuticle formation but is not present during the adult
moult. When JH is given just before or after pupal ecdysis inmoult. When JH is given just before or after pupal ecdysis in ManducaManduca, BR – C, BR – C
mRNA can be also inducedmRNA can be also induced inin vitrovitro by exposing the pupal wing to 20E in the presenceby exposing the pupal wing to 20E in the presence
of JH. Inof JH. In DrosophilaDrosophila, the application of JH at pupariation causes the formation of a, the application of JH at pupariation causes the formation of a
“pharate adult” with a normal adult head and thorax, but a pupal – like abdomen. In“pharate adult” with a normal adult head and thorax, but a pupal – like abdomen. In
these JH – treated insects, BR – C mRNA is re – expressed during adult developmentthese JH – treated insects, BR – C mRNA is re – expressed during adult development
in the abdomen, but not in the thorax and the head. Moreover, pupal gene is or pupalin the abdomen, but not in the thorax and the head. Moreover, pupal gene is or pupal
cuticle genes are re – expressed and an adult cuticle gene is suppressed in the JH –cuticle genes are re – expressed and an adult cuticle gene is suppressed in the JH –
treated abdomen. These findings show that the abdominal cells are making a secondtreated abdomen. These findings show that the abdominal cells are making a second
pupal cuticle. The use of transgenicpupal cuticle. The use of transgenic DrosophilaDrosophila carrying the various BR – C isoformscarrying the various BR – C isoforms
under a heat – shock promoter allows determination of the effects of misexpression ofunder a heat – shock promoter allows determination of the effects of misexpression of
each of the four isoforms (Z1 – Z4) on pupal cuticle production. Expression of the Z1each of the four isoforms (Z1 – Z4) on pupal cuticle production. Expression of the Z1
isoform at the onset of cuticle production induces re – expression of an adult cuticleisoform at the onset of cuticle production induces re – expression of an adult cuticle
gene, causing the deposition of a second pupal cuticle. Unlike the JH – treated flies,gene, causing the deposition of a second pupal cuticle. Unlike the JH – treated flies,
this induction of a new pupal cuticle occurs in the head and thorax as well as in thethis induction of a new pupal cuticle occurs in the head and thorax as well as in the
abdomen. Interestingly, misexpression of the Z1 isoform during the second larvalabdomen. Interestingly, misexpression of the Z1 isoform during the second larval

moult causes premature expression of a pupal cuticle gene and suppresses expressionmoult causes premature expression of a pupal cuticle gene and suppresses expression
of a larval cuticle gene. The other isoforms have similar effects on some, but not all,of a larval cuticle gene. The other isoforms have similar effects on some, but not all,
cuticle genes. These findings clearly show that BR – C is indeed a pupal – specifyingcuticle genes. These findings clearly show that BR – C is indeed a pupal – specifying
transcription factor.transcription factor.
Applications of JHs and JHa(s)Applications of JHs and JHa(s)
JH and JHa perform important roles in caste determination in both termites and inJH and JHa perform important roles in caste determination in both termites and in
Hymenoptera. So, in one hand, dominant importance of JH in most mechanismsHymenoptera. So, in one hand, dominant importance of JH in most mechanisms
concerned with morphogenesis and in other hand, the broad unity of morphogeneticconcerned with morphogenesis and in other hand, the broad unity of morphogenetic
differentiation mechanisms on the other. JH provide a mechanism for interfering withdifferentiation mechanisms on the other. JH provide a mechanism for interfering with
the very principle of morphogenesis and for producing genetic environments inthe very principle of morphogenesis and for producing genetic environments in
insects resulting in what are known as Phenocopies. The most obvious example is theinsects resulting in what are known as Phenocopies. The most obvious example is the
possibility of inducing experimental neoteny (progressive metathetely) by the actionpossibility of inducing experimental neoteny (progressive metathetely) by the action
of JH at a suitable stage of development and under various temperatures or surgicalof JH at a suitable stage of development and under various temperatures or surgical
treatments. The possibility of utilizing substances with insect hormone activity, i.e.,treatments. The possibility of utilizing substances with insect hormone activity, i.e.,
with far – reaching effects on all principal functions of the insect organism, to controlwith far – reaching effects on all principal functions of the insect organism, to control
harmful insects was suggested long before it was really practicable, thanks to theharmful insects was suggested long before it was really practicable, thanks to the
discovery of the two main types of Entocones (JH and MHd).Teplakova (1947)discovery of the two main types of Entocones (JH and MHd).Teplakova (1947)
studied the effect of the metamorphosis hormones, particularly JH, on the viability ofstudied the effect of the metamorphosis hormones, particularly JH, on the viability of
the bugthe bug Eurygaster integricepsEurygaster integriceps as part of a complete investigation of this serious grainas part of a complete investigation of this serious grain
pest in Eastern Europe. Her work showed that the effect of the secretion of thepest in Eastern Europe. Her work showed that the effect of the secretion of the
corpora allata is one of the most important internal influences on viability and thecorpora allata is one of the most important internal influences on viability and the
physiological state of the insect organism. This hormone (JH) thus has a profoundphysiological state of the insect organism. This hormone (JH) thus has a profound
effect on those features of the insect organism which are of economic importance botheffect on those features of the insect organism which are of economic importance both
in the control of pests and the rearing of useful species. The effects of all the JHa soin the control of pests and the rearing of useful species. The effects of all the JHa so
far studied are in every case identical with those of the corpus allatum hormone,far studied are in every case identical with those of the corpus allatum hormone,
except for the group specificity of some (the corpora allata hormone seems to beexcept for the group specificity of some (the corpora allata hormone seems to be
entirely non – specific). Emmerich and Barth (1968) had demonstrated genuineentirely non – specific). Emmerich and Barth (1968) had demonstrated genuine
juvenilizing action by farnesol methyl ether, which had a positive effect on ovarianjuvenilizing action by farnesol methyl ether, which had a positive effect on ovarian

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