This article is part of our Organic Pest Control Series, which includes articles on attracting beneficial insects, controlling specific garden pests, and using organic pesticides.
Trichogramma Wasps (Hymenoptera)
These extremely small, gnat-sized wasps lay their eggs inside the eggs of other insects, where the young trichogramma develop as internal parasites. Because the trichogramma’s life cycle is very short — just seven to 10 days from egg to adult — populations can grow rapidly.
What Do Wasps Eat?
Trichogramma larvae eat insect eggs, especially those of cabbage worms, codling moths, European corn borer, diamondback moths, and other moths and butterflies. Insect eggs that have been parasitized by trichogramma wasps turn black or metallic blue. Adult trichogramma wasps consume flower nectar and sugary substances produced by special glands on the leaves and stems of many garden plants.
How to Attract Trichogramma Wasps to Your Garden
Trichogramma wasps are so tiny that observing them in the open garden is often impossible. However, scientists have found that the flower nectar from buckwheat and sweet alyssum enhanced wasp health and reproduction in lab experiments.
Trichogramma wasp eggs are available commercially, and are much less costly compared with other purchased beneficial insects. Sold as parasitized eggs attached to small paper cards, they are placed outdoors at night, usually hung from branches. Organic fruit and nut growers often purchase trichogramma wasp eggs and hang the cards when codling moths, pecan nut casebearers, or other pests are in egg-laying mode. On vegetable farms, trichogramma wasps are sometimes introduced to control European corn borer in corn, peppers or potatoes. Trichogramma wasps are often used to control several important pests of cotton.
More information on trichogramma wasps is available from Washington State University, University of California, and Cornell University.