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Updated: Feb 14, 2022


If you have trees, at one time or another you’ve probably had problems with bagworms, webworms, and tent catepillars. But before you spray your yard with toxic chemicals, consider using a tiny, microscopic beneficial insect instead. Trichogramma wasps are teeny, tiny flying creatures that won’t harm people, pets, or plants. Adult trichogramma wasps feed on pollen and nectar. It’s their young that wreak havoc on harmful worms and catepillars because trichogramma wasps parasitize the eggs of moths, worms, and butterflies (Lepidoptera). In fact, they are one of the most effective beneficial insects known for controlling lepidopterous insects.

A female Trichogramma wasp injects its eggs into the egg of a lepidopterous insect such as a webworm, tent caterpillar, cabbageworm, or tomato hormworm. The tiny adult lives on nectar and is completely harmless.

One note of warning: Don’t put these voracious creatures in your butterfly garden! Trichogramma wasps can help get rid of cabbageworms, tomato hornworms, corn earworms, codling moths, cutworms, armyworms, webworms, cabbage loopers, corn borers, fruitworms, and cane borers, and around 200 other pest worm species. In the Dallas-Fort Worth area, trichogramma wasps are the preferred method for dealing with web worms and pecan case borers. Experiments have shown Trichogramma wasps to be 60% to 95% better at controlling pests such as the bollworm and tobacco budworm than in untreated fields.

Trichogrammas often consume up to 98% of a host’s eggs in nature. Females deposit their eggs inside the eggs of host insects. The parasitic young soon hatch and feed on the juices within the host egg, thus killing it. Within 8 to 10 days the young Trichogrammas have grown through the larval and pupae stages and emerge as adults, which immediately begin parasitizing more pest eggs. Early application of Trichogrammas, before pests emerge, is the ideal way to begin a pest control program.

Trichogramma wasp eggs are glued onto small sheets of paper containing about 3,300 eggs per sheet. Sheets can be hung on a tree branch or tacked to a fence.

Weekly applications throughout the growing season are recommended.

Trichogramma eggs from Marshall Grain come attached to paper cards, with approximately 3,300 eggs per card. Tack the cards in a sheltered spot on the tree, preferably near where a limb emerges from the trunk. The adult wasps will fly around in search of new host eggs to attack. Emerging wasps will have the best chance of success when the weather is moderate, so avoid releasing them when the weather is extremely hot, cold, stormy or windy. Frequent releases over a period of time will be more effective than a single release. Trichogrammas are sensitive to pesticides. Take care not to spray release areas with insecticides while they are around. Give them a chance to do their job first.


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