Insect Pests of Fruits

SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
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Insect Pests of Fruits
Insects are the members of the largest class (Class Insecta / Hexapoda) of the Phylum
Arthropoda, which is itself the largest of the animal phyla. Insects are distinguished from
other arthropods by their body, which is divided into three major regions:
 Head: it bears the mouthparts, eyes, and a pair of antennae.
 Thorax: it usually has three pairs of legs (hence “Hexapoda”) in adults and usually
one or two pairs of wings.
 Abdomen: it contains the digestive, excretory, and reproductive organs.
Beneficial Aspects of Insects:
Many insects, however, are beneficial from a human viewpoint:
 They pollinate plants
 They produce useful substances, i.e. formic acid in ant’s sting
 They control other pest insects
 They act as scavengers
 They serve as food for other animals (insectivorous animals)
Furthermore, insects are valuable objects of study in Biology and Ecology. Much of the
scientific knowledge of genetics has been gained from fruit fly experiments and of
population biology from flour beetle studies. Insects are often used in investigations of
hormonal action, nerve and sense organ function, and many other physiological
processes. Insects are also used as environmental quality indicators to assess water
quality and soil contamination and are the basis of many studies of biodiversity.
Insects as Pests:
Pests are any organisms deemed undesirable by humans, because they compete with
us for food, spoil our food resources (including crops and stored food), spread diseases,

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or annoy us in any way. Many insect species are common pests such as fruit flies,
aphids, cloth moths, leafhoppers, hornets, etc. These insects feed on our food
resources and as a result, cause economic losses to us. Many methods have been
devised to exterminate them, including but not limited to toxic pesticides.
Insect Pests of Fruits:
Several insect pests feed on and destroy or fruit crops and stored stock as well. Some
of the most infamous of these are discussed in detail as follows:
1. Fruit Flies
Fruit flies include a wide variety of species which are serious pests of fruits and
vegetables in Pakistan.
Figure: Oriental / Mango Fruit-fly (Bactrocera dorsalis). Left – Male, Right – Female.
They cause intensive fruit loss, almost 50 to 90%. Some affected fruits include
mangoes, guavas, citrus fruits, melons, etc. They cause a drop in the quality of fruits,
financial losses, health problems, and quarantine risk. Prominent species of fruit flies
found in Pakistan include:

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 Oriental / Mango Fruit-fly (Bactrocera dorsalis)
 Peach Fruit-fly (Bactrocera zonata)
 Melon Fly (Bactrocera cucurbitae)
 Lesser Pumpkin Fly (Dacus cilliatus)
General Life Cycle:
Due to a short life cycle, their population increases incredibly fast. Lifecycle consists of
4 stages and their duration is dependent on temperature. Mostly, they complete
development in 21-37 days. Adults are larger than house flies.
1. Females lay eggs under the surface of fruits in groups.
2. Eggs hatch within a few (1-2) days.
3. Larvae feed on fruit pulp and develop within 7-8 days.
4. Infested fruits fall on the ground.
5. Mature larvae pupate in the soil.
6. Adult flies emerge in 8-10 days from pupae, ready to infest more fruit.
Figure: Diagrammatic representation of the Fruit-fly life cycle.

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Mode of Damage:
Fruit flies damage fruits by oviposition (laying eggs via an organ called ovipositor) inside
the fruit. After oviposition, eggs hatch, and maggots (larval form) feed on the fleshy part
of fruits. Larval feeding causes most of the damage. Eventually, the fruit drops from the
tree, and decomposition is started by microorganisms. The larval tunnel offers entry for
bacteria and fungi, which lead to the rotting of the fruit. Maggots also attack seedlings,
roots, and buds of the host plant. Such damage affects both the quantity and quality of
the fruit.
"Pakistani mangoes are banned for export to Japan, Turkey, and the USA due to the fruit
fly infestation."
Symptoms of Attack:
Attacked fruits usually show signs of oviposition punctures. Fruits with high sugar content
exude a sugary liquid, which usually solidifies adjacent to the oviposition site.
Management:
Different methods can be used for fruit fly management:
 Field sanitation: Infested fruits must be removed from the field and buried deep 3
feet inside the soil so that the flies fail to reach the surface and die.
 Bait spray: Different proteins are used as bait with insecticides, after feeding on
this bait, the fruit flies will die.
 Sterile Insect Technique (SIT): In this technique, artificially sterilized males (i.e.
unable to fertilize the female) are released, which then compete with the fertile
males for access to females, as a result, the population size drops. It is only
useful against a small isolated population.
 Insecticides: Different insecticides like Deltamethrine, Diptrex, Confidor, and
Diazinon etc. are being used for fruit fly management. Sometimes different

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mixtures are also used for effective control. Although they are persistent and
highly toxic.
 Traps: Pheromone traps, Liquid trap with food bait, etc. are used to lure the pests
which are then killed.
 Biological Control: Natural predators and parasites of fruit-flies that pose no harm
to us can be used as a form of Biological control. Hens in the field feed on
surface larvae. Other predators include ants, earwigs, and nematodes, which
reduce the pest population. Parasites like wasps also control the fruit fly
population.
2. Lemon Butterfly (Papilio demoleus)
Papilio demoleus is a common and widespread butterfly, it is also known as the lime
butterfly, lemon butterfly, lime swallowtail, and chequered swallowtail. These common
names refer to their host plants, which are usually citrus species such as lime. This
butterfly is a pest and invasive species.
Figure: Lemon Butterfly (Papilio demoleus)

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Life Cycle:
These butterflies have 8 generations per year. Their life cycle stages are as follows:
1. The females lay nearly 100-150 eggs singly or in groups.
2. The egg stage lasts for 3.1 to 6.1 days and then the eggs hatch.
3. Larva stage lasts for 12.9 and 22.7 days.
4. Pupa stage lasts for 8.0 to 22.4 days.
5. The adult stage lasts for 4 to 6 days with an average of 5.1 days.
Mode of damage
The actual damage is done by the larval stage. Larvae feed on young leaves and
terminal shoots. Their habit is to eat from edges up to midrib. Larger caterpillars can
feed on mature leaves.
Figure: Leaves of lime, eaten by larvae of Lemon Butterfly.
Control:
These butterflies and their larvae can be controlled in the following ways:
 Physical Control: Hand-picking of larvae.
 Biological Control: Trichogramma spp. (wasps) are effective egg parasitoids of these
butterflies, they can be used as a measure of biological control.

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 Natural Insecticide: Spraying trees with 3% neem extract.
 Synthetic Insecticides: Spraying trees with endosulfan 35 EC or methamidophos 60
SL (200ml/100L of water).
3. Aphids
Aphids are small sap-sucking insects and members of the superfamily Aphidoidea.
They suck the sap from the leaves and branches, and cause great damage to trees; as
a result, they reduce the yield of fruiting trees. Aphid attack is severe during February
and April in Pakistan. 40% Dizenon or 20% Eldrine, 1 kg in 450 liters of water can be
used to kill them. Insecticides are highly toxic and hence should not be applied 6 weeks
before the marketing of the fruit.
Figure: Left – Aphid feeding on a tree's branch. Right – Diagrammatic representation of
aphid's proboscis, sucking sap from the phloem.
4. Red Scales (Aonidiella aurantii)
Aonidiella aurantii or red scale is an armored scale insect and a major pest of citrus fruit
trees. These are sucking types of insects and cause great damage to oranges and
lemons in Punjab. They can survive throughout the year. Scale insects of all ages feed
by sucking sap.

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They are found on all parts of the plant but are most noticeable on the fruit. Heavy
infestations may cause discoloration, shoot distortion, and leaf drop. The fruit may
become pitted and unmarketable. The tree's bark may split and the twigs and branches
may die back and this sometimes results in the death of the tree. Parathion or Malathion
(752 grams in 450 liters of water per acre) can be used for its effective control.
Figure: Left – Red spots on infested leaf due to Red Scale infestation. Right – Adult Red
Scale.
5. Mango Hopper (Idioscopus nitidulus & Idioscopus clypealis)
The mango hopper is a major insect pest of mango. The hoppers make holes and suck
the nutrients from soft tissues of panicles (cluster of flowers), leaves, flowers, fruits, and
fresh twigs. Hoppers also release sweet liquid onto the leaves, on which a black colored
fungus develops, which reduces the strength of the plant. Heavy attacks cause curling
and drying of infested parts. If young trees experience a severe attack, they are much
retarded while severely attacked older trees do not bear fruit, which results in a
complete loss of yield.
Adult hoppers are brown and are wedge or triangular. The young ones are similar in
shape to the adult but vary in size and color. Both are very active and move sideways.

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Hoppers are present all year round in the orchard. Females lay eggs from February to
March on flowers. Peaks in population are observed from February to April and July to
August.
Figure: Left – Lateral view of Idioscopus nitidulus. Right – Idioscopus clypealis.
Figure: Infestation of Mango Hoppers on a Mango Tree.
Management:
The management of this insect pest should be largely based on cultural control rather
than chemicals because it’s been found that the hoppers have become resistant to
some pesticides.
 Prune/cut the plants so that the sunlight can pass through the canopy and aeration
can be improved.
 Pruning should be done twice a year i.e. after harvesting of fruit in September and at
blossom in December/January.

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 No plant part or twig should intermingle with the adjacent plant.
 If the population is still observed then spray imidacloprid (0.3ml/liter of water) at the
early stages of panicle formation.
 Secondly, spray with thiamethoxam (2g/liter of water) or acephate (1.5g/liter of
water) should be done at fruit set.
6. Banana Weevil (Cosmopolites sordidus)
The banana weevil is the most important insect pest of banana. It is about 1-1.5 cm
long. It is present worldwide, i.e. in all banana-growing areas of the world. The larva
(grub) is most destructive; it bores irregular tunnels in the rhizome/corm and pseudo-
stems at ground level. A large proportion of the tissue is destroyed, this reduces the
amount of water and nutrients the plants can take up as well as decreasing their
anchorage. Heavy infestation may kill young plants. Older plants are easily blown over
by the wind.
Figure: Left – Adult Banana Weevil. Center & Right – Grub (Larva) feeding.
Control:
The following measures can be taken to control the banana weevil:
 Prevention: To prevent an infestation, use non-infested planting material, destroy
the shelter and feeding places of the adult weevil, and maintain a clean area
around the plant mat.

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 Physical Control: Chop up the infested rhizome/corm and pseudo-stem to hasten
decomposition, trapping, and collection of the adults.
 Biological Control: Some ants are important natural enemies of the banana weevil
and are being used for its control.
 Natural Insecticide: Neem powder and/or extract can be used to effectively control
weevils.
 Crop Management: A combination of good crop management such as the
application of cow dung and neem treatments resulted in yield increases of 50 to
75%.
 Neem Seed Solution: Dipping suckers in a 20% neem seed solution at planting
protects the young suckers from weevil attack by reducing egg-laying through its
repellent effect on adult weevils. Egg hatching rates may also be lowered in
neem-treated plants.
 Hot-water Treatment: Hot-water treatment of banana suckers helps against banana
weevils.

Insect Pests of Fruits

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