All about potatoes.pdf - Vegetableipmasia.org

6.
INSECT ECOLOGY
• Releasing new natural enemies into the field - Done when no effective hostregulating
natural enemies are found, or when they are present only in very small
numbers.
• Making natural enemy release cages – You can do this to increase the number of
leafminer fly natural enemies. Cages measure 1 x 1 x 1m, and are closed on all
sides with gauze. The gauze must have holes large enough for the parasitoids to
escape, but small enough to keep leafminer flies trapped inside. Collect potato
and green bean leaves or weeds showing signs of leafminer fly damage. Put them
inside the cage, the place the cage in the middle of the field making sure to keep it
sheltered from the rain. Parasitoids will escape and survive, while leafminer flies
will be trapped and perish inside the cage.
Ways of manipulating the environment to increase the role of natural enemies are as
follows:
• Accept a low level of insect pests in the field - Insect pests are a food source for
natural enemies. If there are no pests, there will be no natural enemies.
• Not using insecticides - Natural enemies are more sensitive to insecticides. Tests
have shown that natural enemies are more numerous in quantity and species
diversity in unsprayed fields than they are in fields sprayed with insecticides. The
overall result is smaller pest populations in fields that have not been sprayed.
• Planting nectar-producing plants - Adult insects that act as natural enemies
(particularly parasitoids) feed on nectar. Therefore, planting flowers on the edges
of fields will provide food for these parasitoid species and induce longevity.
• Using compost - Predatory flies need compost as a habitat for its maggots.
• If you are forced to use insecticide, do spot applications to affected plants only,
and select insecticides with low toxicity.
6.6 Pest management
6.6.1 Biological control
Natural enemies have been discussed in the section above on farmer-friendly
insects. Biological control will develop better if supported with another strategy, i.e.
using natural pesticides, which originate from plants and are less likely to disturb or
kill natural enemies. Plant materials that can be used as insecticides are the
following:
Neem:
Neem (Azadirachta indica) is a tree that is toxic and repellent to numerous pests,
particularly insect larvae, aphids and thrips. All parts of this plant are toxic, but
toxicity is highest in the seeds.
How to use it: Pulverize plant parts until they are soft, and dilute them with clean
water. Spray the mixture onto plants. To help it stick to the leaves you can add
detergent. Because the toxicity does not last long in direct sunlight, it is best to spray
in the late afternoon. If the mixture is too concentrated, it will poison plants leaving
them looking as if they have been burnt.
Tuba:
The tuba plant (Derris elliptica) is commonly found in tropical forests. All parts of the
plant are toxic, but the roots have the highest toxicity. This plant can be used to
control leaf-eating insects such as caterpillars, grasshoppers, aphids, thrips, etc.
A HANDBOOK TO THE ECOLOGY AND INTEGRATED MANAGEMENT OF POTATO 33