2. CONTENTS
2
Introduction
Types Of Parasitism
Classification of Parasitiods
Important Of Parasitoids
Examples of importation biological control
Benefits of parasitoids
Limitations of parasitoids
Evidence of parasitism
Parasitoid susceptibility to pesticides
Summary
References
3. INTRODUCTION
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Biological control or biocontrol is a method of controlling
pests, such as insects, mites, weeds, and plant diseases,
using other organisms.
It relies on predation, parasitism, herbivory, or other natural
mechanisms, but typically also involves an active human
management role.
It can be an important component of integrated pest
management programs.
A parasite is an organism that lives on or in the body of
another organism called host during some part of its life
cycle.
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Often only the immature stage of the parasite feeds on the
host.
Insect parasites can develop on the inside or outside of the
host's body.
Often only the immature stage.
Most parasitic insects are either flies (Order Diptera or
wasps (Order Hymenoptera).
It generally lay its eggs within or upon the host, the larva
feed within (Endo Parasitiods) or upon the host (Ecto
Parasitiods).
Endo Parasitiods Ecto Parasitiods
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Organism often of same size as its host, kills its host.
Requires only one host for development into a free
living adult.
Parasitic in Immature Stages but Adult Is Free living.
6 orders (86 families) Diptera, Hymenoptera,
Lepidoptera, Neuroptera, Coleoptera, and
Strepsiptera have listed as Parasitiods.
Among these Hymenoptera And Diptera are most
important.
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Types Of Parasitism
Hyper parasitism
A hyper parasitoid is a parasitoid which developed on
another parasitoid.
A parasite of a parasite. It depend on the food chain as
host primary, secondary, tertiary and so on.
Super parasitism
The condition resulting from the use of a single host
individual by more number of individual parasitiods of
the same species than it can successfully switch to
maturity because of nutritional limitation.
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Multiple Parasitism
It refers to that condition in which individuals of two
or more species of parasitiods occur on the same
single host at the same time.
E.g. Many of primary tachinid parasitoids of the
spruce budworm compete with ichneumonid
parasites.
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Classification of Parasitiods
Egg Parasitoid
e.g. Trichogramma sp. , Telenomus sp.
Egg Larval Parasitoid
e.g. Braconid, Chelonus blackburni
Larval Parasitoid
e.g. DBM Parasitiods, Isotima sp. Campoletis chloridae
Larval Pupal Parasitoid
e.g. Pleurotropis epilachnae on Epilachna spp
Pupal Parasitoid
e.g. Tetrastichus sp., Elasmus sp., Fruit Fly parasitiods
Adult Parasitoid
e.g. Blaesoziphae kellyi a parasitiods of locust.
Nymphal Adult Parasitoid
e.g. Epiricania melanoleuca parasitic on Pyrilla perpusilla.
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Important Of Parasitoids
Among all natural enemies, perhaps, no other group is
more important to maintaining pest insect populations
below damaging levels than parasitoids.
Although individual predators tend to kill many prey,
while each parasitoid kills only one at most, the sheer
number and efficiency of parasitoids is so great that the
cumulative impact often outweighs that of predators.
Their efficiency is due to several factors. Parasitoids
tend to specialize, attacking only one type host, and
this specificity makes them very effective against their
target host.
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Their life cycles are closely synchronized with that of
their prey, so that parasitoids are out hunting when their
hosts are also active in the garden.
Parasitoids are efficient at finding hosts
they are very active and adult female parasitoids often
use host related chemical cues to help them find prey
even when population densities are low.
Some parasitoids also get a head start on finding prey in
early spring when they are in scarce supply by
overwintering in their hosts' bodies.
Parasitoids may lay one to several eggs within a host and
eggs can develop into one or multiple larvae. Once inside
the parasitoid consumes the host and develop through
instars much like any other insect would.
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Examples of importation biological control
Alfalfa weevils populations are kept in check by
several different imported wasp species that together
attack all life stages of the weevil.
Pea aphids have been successfully controlled by two
wasps, Aphidius smithi and Aphidius ervi.
Tetrastichus julis was imported and has provided
significant control of cereal leaf beetle.
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Benefits of parasitoids
They are usually extremely well adapted to their natural host and
are very good at finding them even when densities of the host are
relatively low
Limitations of parasitoids
They are often host specific and often will attack only one
species of pest.
They are generally more delicate than predators and hence more
vulnerable to pesticides.
parasitoids spend most of their life cycle developing within their
prey, they are less visible than predators, and their performance
may be underestimated as a result.
Parasitoids can be parasitised by other parasitoids. This is known
as hyperparasitism - a natural and common occurrence which can
reduce the effectiveness of some beneficial species. Little can be
done to manage hyperparasitism.
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Evidence of parasitism
• Look for evidence of an exit hole in the host
• Dissect samples (may be difficult with very small
insects)
• Rear pests in an insect proof cage to see if
parasitoids emerge
• Check for deformed insects e.g. caterpillars or
mummified / bloated insects such as aphids .
• Look for wasp cocoons near caterpillars
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Parasitoid susceptibility to pesticides
• Parasitoids are often more susceptible to insecticides
than predators.
• Adult parasitoids are usually more susceptible than their
hosts.
• Immature parasitoids, especially if protected within the
egg of their host or in their own cocoon, may tolerate
pesticides better than adults, but immature parasitoids
will usually die if their host is killed.
• To improve the abundance and diversity of beneficial
insects consider native vegetation on the farm as a part
of a pest management strategy.
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Advantages of parasitiods
Survival is usually good.
Good host finding ability.
Only 1 or fewer host is required for
its complete development.
Short life cycle .
Synchronized with that pest density.
Simple and cheap mass propagation
techniques are available.
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Disadvantages of parasitiods
Host searching capacity may be
reduced by weather or other factors.
Only the female searches.
Often the best searcher lay few eggs.
Synchronization is often difficult.
Multi and Super Parasitism reduces the
effectiveness.
Timing of release is important.
17. SUMMARY
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Parasites have been used successfully against a large variety of
pests occurring in completely different cropping systems and in all
major climates.
Success seems largely to have been the result of the amount of
research directed to the solution of a pest problem.
The ratio of successes obtained with parasites compared to those
achieved with predators and pathogens is 82:7:1, respectively.
The rate of success after introduction is high for natural enemies
(±6%) when compared with that for chemicals (±0.1 0.05% of the
tested chemicals is marketable).
Data on economic aspects are also positive for biological control
programs.
The risks of using parasites for pest control are minimal,
especially when compared with chemical pesticide use.
