All about potatoes.pdf - Vegetableipmasia.org

6.
INSECT ECOLOGY
6.5 Beneficial insects
Insects that prey on insect pests, or diseases that infect insect pests, are called
"farmers’ friends" or "natural enemies". They help farmers to control the number of
insect pests and prevent damage to crops. Natural enemies can effectively control
many insect pests. Predators, parasitoids, pathogens (diseases) and nematodes are
all classified as natural enemies. The characteristics of natural enemies depend on
their class, as is described below.
Predators:
• Predators stalk and catch moving prey.
• Predators eat many preys of different species in their lifetimes.
• In some insect species, both larval and adult stages of insects can be predators.
In other species, though, only the larval or the adult stage is predatory.
• Predators commonly found on potato crops are spiders, ladybirds, earwigs, hunter
flies, hoverflies, praying mantises and dragonflies.
Parasitoids:
• Parasitoids found on potato crops are specific types of wasps and flies.
• Parasitoids attack their prey when it is vulnerable, usually in their egg or larval
stages, by laying an egg inside or on the top of their victim. The egg will hatch and
the newly emerged larva of the parasitoid slowly consumes its victim.
• Parasitoids only parasitize one insect in their lifetime.
• Parasitoids have very specific relationships with their host.
• Parasitoids are usually much smaller than their host.
Pathogens:
• Pathogens are similar to diseases in humans, such as flu, typhus, tuberculosis
etc. They are extremely small and invisible to the naked eye.
• Pathogens require humidity and certain temperatures in order to infect insects.
• Pathogens are immobile, and wait until they come into contact with their host
before they can cause disease.
• Pathogens can only infect certain species of insects during certain stages of their
development. For example, the pathogen GV on potato tuber moth larvae.
• Fungi, bacteria and viruses are included in this category.
Nematodes:
• Nematodes are tiny worms. Certain species of nematodes can be pests, while
others can act as natural enemies.
To be effective, a natural enemy must:
• Have capacity to develop many eggs and young in order to remain in balance with
the number of insect pests.
• Be highly capable of attacking their prey.
• Be host specific.
• Be adaptable to changing environments.
• Proliferate at the same times and rate as their prey.
Strategies for increasing the effectiveness of natural enemies are:
• Observing natural enemy species in the field - This is essential as the basis for
determining further measures.
• Manipulating the environment - Done when the natural enemies found in the field
are not playing an effective role (despite the presence of natural enemies, insect
pests are still prevalent and causing damage to the crop).
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ALL ABOUT POTATOES