Trichogramma Wasps

Trichogramma wasps are small but mighty.

Trichogramma wasp laying eggs in armyworm eggs (Dr Victor Fursov) CC BY-SA 4.0

These microscopic parasitic wasps protect an astounding collection of edible plants.

It might be easier to list those they do not protect, but your almond, apple, avocado, beet, blackberry, blueberry, celery, cherry, corn, cotton, grape, orange and other citrus, legume, papaya, peach, peanut, pear, plum, pumpkin, quince, squash, strawberry, tomato, walnut, and zucchini plants and trees are better off when Trichogramma wasps are in the neighborhood. These tiny wasps protect your plants from damage by parasitizing the eggs of these garden pests:

• armyworms
• bagworms
• cabbageworms
• cane borers
• codling moth
• cotton bollworm
• cutworms
• eastern spruce budworm

• European corn borers
• leafrollers
• light brown apple moth 
• peach borers
• squash vine borers
• tomato hornworms
• treehoppers
• webworms

Parasitic wasps

Parasitic wasps lay their eggs in many common garden pests. This group of beneficial wasps includes braconids, chalcids, Goniozus wasps, ichneumon wasps, and Trichogramma wasps. 

Female Trichogramma wasps seek out the eggs of pesky moths and butterflies and sawflies to use as nurseries for her own eggs. When she finds one, the first thing she does is drum on it with her antennae and ovipositor to see if it has already been used. Drumming also helps her determine how big and useful the host egg is. This dictates how many eggs she will insert.

​After being inserted into a host egg, the wasp egg develops, pupates, and then hatches, after which it feeds on the contents of the host egg. This turns the host black. If you use a hand lens and see a healthy white host egg with a chewed hole, it means the egg was not parasitized and a healthy (destructive) caterpillar emerged instead.

Trichogramma wasp species

Unless you are a scientist with a very powerful microscope, you will never see a Trichogramma wasp. At 1/25“ to 1/50” long, you could fit 20 to 40 of them nose-to-tail across a dime. If you could see them, you might be struck by the simple beauty of a minuscule yellow wasp with red eyes. Or, you might not. There are over 200 species of Trichogramma around the world.

Before you order a shipment of Trichogramma wasps as a biocontrol, keep in mind that different species of Trichogramma parasitize different hosts. It is important that you order from a reputable seller to avoid releasing a threat to other beneficial insects into your garden. When reading product descriptions, take the time to do a little research before you buy. 

Trichogramma wasp eggs are shipped as larvae in host eggs that have been glued to cards. If you buy Trichogramma wasps for release, these tips will give them the best chance at being successful:

• keep cards in a warm, humid location
• wait until most of the wasps have emerged from the host eggs
• place cards only after moths are seen
• release wasps in the morning or evening, upwind of affected trees, out of direct sunlight
• do not release wasps on rainy, windy, hot, or cold days
• do not use pesticides when releasing these beneficial wasps

Keep in mind that Trichogramma wasps will not kill all the pests they come across. What they do is provide one piece of an integrated pest management program that uses natural processes to reduce the overall impact of pests, rather than spraying chemical poisons on your food.

Watch out for the yellow jackets and hornets, leave mud daubers and paper wasps to go about their business, and add some insectary plants to attract and provide for beneficial wasps, such as the Trichogramma.