Biological control of insects

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ENT-402-Applied Entomology
Lecture 9
Biological Control

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Biological Control
 “Use of natural enemies of pests to reduce their population to a level where
economic losses are either eliminated or suppressed”
 Biological control involves the use of natural enemies of pests –predators and
parasites (also called beneficial insects) and disease causing organisms – and
encouraging their development.
 Some pests or, in some cases, non-pest species, must always be available to
provide a food supply, and there often is a time lag between the increase of a
pest population and the increase of natural enemies.
 Non-purposeful manipulation/natural control: Weather, food
 Purposeful manipulation: Biological control

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Goals of biological control
1. Establishment of self-sustained system by introduction
2. Suppress pests
3. Keep pest density below EIL
Biological Control Agents
 Invertebrates: insects, bacteria, fungi, nematodes,
 Vertebrates: Reptiles, amphibians, fish, birds
Parasite: (Endo- and ectoparasites): An organism which at one time or
other lives on the body of host which may or may not be killed after it has
completed development.

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Parasitoid: An organism which completes its life on one host only and kills
its. Parasitoids are parasitic in immature stage and free living as an adult.
Predator: (Mono-, Oligo- and polyphagous) A free living animal
which kills its host immediately.
Pathogens: Disease causing micro-organisms.
Types of Biocontrol Program
1. Introduction/Importation/Classical Biological Control: Identify
the natural enemies that regulate a pest in its original location and introduce
these into the pest’s new location with the hope that it will become
established in that location and permanently reduce the pest’s general
equilibrium position. e.g., Control of Cottony Cushion scale with Vedalia
beetle.

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Types of Biocontrol Program
2. Augmentation: Any activity designed to increase the number or effect of
existing natural enemies is called augmentation. It involves releasing additional
number of natural enemy into a system or modifying the environment in such a
way to promote the number or effectiveness. Augmentative releases are expected
to result only in temporary suppression.
Types of Augmentation
1) Inundative release
2) Inoculative release
3) Environmental manipulation

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Types of Augmentation
a) Inundative releases involve the release of large numbers of a natural enemy
such that their population completely overwhelms that of the pest.
b) Inoculative release involves the release of natural enemies with expectation
to be colonized and spread throughout an area naturally.
c) Environmental manipulation: Environmental manipulation involves the
utilization of the crop or its surroundings as “field insectaries” to increase the
number or make the existing numbers more efficient.
3. Conservation: Conservation involves identifying the factor(s) which may
limit the effectiveness of a particular natural enemy and modifying them to
increase the effectiveness of the beneficial species.
 In general, conservation of natural enemies involves either, reducing factors
which interfere with natural enemies or providing resources that natural enemies
need in their environment.

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Information needed for bio-control program:
1. Life history of pest and bio-control agent/s
2. Physical environment
3. Factors regulating the pest
4. Advantages of bio-control program
5. Persistence or long-term benefits
6. Safety to environment
7. Economical for use
Disadvantages of bio-control program
1. Long time is needed
2. Need other methods in collaboration
3. Affected equally as pest by environmental factors.
4. Multi-pest situation creates problem
5. Difficulty of mass rearing

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Enhancing Biological Control
 Unsprayed crops contain a wide range of beneficial organisms (predators,
parasites and disease-causing organisms), which feed on pests and provided a
large measure of control.
 The conservation and enhancement of these beneficial organisms is the
most cost effective and sustainable means of pest management and must be a
priority in any IPM programme.
 The beneficial organisms are present in the crop itself, and also in
neighboring fields and crops, and the vegetation between fields and along
canal banks, waste ground, and roadsides.
 However, this vegetation can also harbor pests which can spread into cultivated
crop areas, and the importance of the surrounding vegetation in harboring
beneficial insects relative to pests should be assessed as part of the IPM
programme.

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Enhancing Biological Control
 Predators (ladybirds, spiders, lacewings, birds etc.) are the most commonly
observed natural enemies, but parasites (parasitic wasps, flies etc.) often
have the greater control effect – these are often referred to as ’farmer’s
friends’.
 In many circumstances natural enemies are extremely common in fields that
have not been sprayed with a pesticide. When certain pesticides are used in a
crop, the beneficial insects are also killed. Brown Planthopper in rice is, in
many instances, only a problem as a result of the pesticides used also killing
the beneficial insects.
 Natural enemies can be encouraged by using pesticides only, when
necessary, particularly early in the crop season so as to allow populations of
natural enemies to build up. If early season pesticide applications are often
required, a seed dressing should be used instead of foliar sprays.

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Enhancing Biological Control
 Refuge habitats should be left around fields where natural enemies can
shelter and find food.
 Spot spraying, timing of sprays when the pest is active but the natural
enemies are inactive and sheltered, and accurate placement of chemical
sprays can all help to preserve natural enemies if a pesticide has to be used.
 Pests also naturally suffer from diseases caused by viruses, bacteria, fungi,
protozoa and nematodes, and which can reduce pest numbers. These diseases
may be commercially formulated for application as pesticides, such as
nucleopolyhedrosis virus and Bacillus thuringiensis (Bt).
 Pests can be biologically changed by the use of Insect Growth
Regulators, which prevent the pest from developing from one stage to
another, and by pheromone mating disruption, which prevents the adult pests
from finding one another to mate.

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Enhancing Biological Control
 Biological control can be enhanced by the mass rearing and release of
beneficial insects. Those commonly used include Trichogramma, Bracon, and
Chrysopera. In certain circumstances, the numbers of natural enemies can also be
enhanced by intercropping, border planting, and relay cropping.
 Intercropping is the planting of strips of crops or plants, which are either
habitats for natural enemies or which attract pests out of the main crop, between
the main crop or next to it. Examples are lucerne in cotton, which encourages
populations of natural enemies of aphids, although Spodoptera leafworms can
also develop in lucerne.
 Border planting is the establishment of refuge habitats of flowering plants
around the edges of fields which attract natural enemies. Suitable plants are
fennel, coriander, brassicas, crucifers, legumes and castor.

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Enhancing Biological Control
 Relay cropping is the planting of short duration crops early in the season, into
which the main crop is planted shortly before the harvesting of the relay crop. The
natural enemies which develop in these crops will then move into the main crop
when they are harvested.
 Examples are crucifers (e.g., cabbage), legumes (e.g., beans), or cucurbits (e.g.,
cucumber).
However, the relay crops need to be selected with care, as the first crop may
increase pest numbers in the following crop.
 Aphids can develop on cucurbits or tobacco,
 Thrips is often present in large numbers on onions,
 Helicoverpa bollworm on maize, sunflower, legumes and tomatoes.

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CONTACT US
http://www.uaar.edu.pk/pak_korea/index.php
PMAS-Arid Agriculture University Rawalpindi
asifaziz@uaar.edu.pk
+322 686 – 2246
Department of
Entomology
PMAS-AAUR