Trichogramma wasps

Order: Hymenoptera
Family: Trichogrammatidae

Species: Trichogramma spp.

Description: To describe Trichogramma wasps with one word: tiny. These wasps are one of the smallest insects on the planet. One closely related genus, Megaphragma, is only 0.18 mm in length as a fully-grown adult. To put this in perspective, that is the size of some bacteria! Even though they are small, they still look like wasps, miniature yellow jackets. Trichogramma wasps have constricted abdomens, short antennae and raspberry colored eyes with few facets. As with all wasps, Trichogramma wasps have two pairs of wings and an ovipositor (stinger) on the females. The wings are unusual because they are short stalks with long fringes of hair, instead of the typical membranous wing. Since these critters are so small, not much is known to describe the eggs, larvae or pupae.

Life History: You might be asking now, “Well, why are these things so small and why the heck are they my friends if I can’t even see them?” Trichogramma wasps are small because they are parasitoids of other insect eggs. Yes, there is actually a wasp out there that fully develops to adulthood inside a thrips egg. Basically, here is a snapshot of the life of a Trichogramma wasp. Adult wasps search for a host egg by smell. Most cues to find the host are found by odors emitted by the actual host egg. For example, for Trichogramma that parasitize moth eggs, the adult wasps use odors from moth scales accidentally knocked off while the moth was laying the eggs. Once the female has found a host egg, she probes it with her ovipositor to determine a few things. She decides that it is an acceptable host only if the host egg is fresh, healthy, and not parasitized by another wasp. If the egg is suitable, she deposits her own egg inside that of the developing host egg. The wasp larva hatches and begins to consume the egg yolk and insect embryo. After the egg is consumed and the wasp completes its larval development, the larva pupates. Many times when the larvae of Trichogramma wasps pupate, they cause the insect egg that they are living in to change in color. In the case of Trichogramma that parasitize moth eggs, the moth egg usually changes to a dark metallic blue. Once the pupal stage is completed, the new adult chews a hole through the egg and emerges. When the adult is out, they immediately smell and inspect the egg that they came from. This is how they find out what kind of cues or odors they should be looking for to find the next host egg.

Beneficial Features: Trichogrammatids have been used in agriculture for many years to control insect pests. Once they find an area where there are host eggs, they are very good at parasitizing most of them. A tree right here in Bellingham, was infected severely with the cherry bark tortrix. I observed that once Trichogramma wasps learned that there were a lot of good eggs to eat on that tree, they parasitized 98% of the eggs by the end of the season! They are extremely prolific under laboratory conditions and fairly easy to produce in large quantities. In fact, the WSU and United States Department of Agriculture have produced and released 200,000 Trichogramma cacoeciae wasps in North Western Washington to manage the cherry bark tortrix.

Recruitment: If you have these guys working in your yard and gardens, you are blessed with one the most unique (and common) beneficial insects out there. To keep them in your yard, reduce pesticide usage if you can. Also since these wasps are so small, provide very small flowers as a nectar source. Although, I am not sure that the adult wasps even eat nectar, it can not hurt to have these small flowers in your garden during this transition to fall. Many other beneficial insects will appreciate it too. Mostly populations build in the late season (like now) but it is important to have a population ready to go in early spring for them to impact the pest populations. Get your hand lens out and scout around. Whenever you encounter insect eggs look for any discolored ones. This is a good sign that you have Trichogramma working in your yard. Feel free to bring them in and take a gander under the microscope in the master gardener room.

Just Plain Interesting: Entomologists love working with this wasp because it reproduces so readily and prolifically. Mostly females exist and males can be extremely rare so the females don’t have to waste anytime being courted and mating; they can immediately start laying eggs and killing pests. Many insects have learned how to get rid of males and successfully reproduce with out them. Recently, scientists have discovered why males are rare in this group of insects. They are infected with a bacterium, Wolbachia, which kills the males. This bacterium lives in the cytoplasm, something that insect sperm doesn’t have, and creates a situation by only living in and being passed to females and their progeny. But get this, the bacterium has developed many ways to insure that it will be passed on in an egg; the bacterium can feminize a male embryo and completely change it to a female. If you feed a colony of Trichogramma antibiotics, you can usually get that colony to produce males after a generation. Just like curing a cold, you can ‘cure’ Trichogramma of a male-free living. Pretty weird, huh? Scientists needed to learn this because a female Trichogramma species is almost impossible to identify. Most of the time, an expert entomologist needs to see the male to identify it to species. Well, when my bosses Drs. Tanigoshi and Bai and I found a Trichogramma that ate the cherry bark tortrix here in Bellingham, we sent it to Dr. Stouthamer, in the Netherlands, to get it identified by an expert. We later found that this was difficult because he could not ‘cure’ the Trichogramma but he found genes of the Wolbachia bacterium specific to the species, T. cacoeciae. So now the Dutch scientist believes that some how the Wolbachia bacterium has incorporated itself (its genes) into the genes of the Trichogramma. This is very unusual to witness in nature (or at least we don’t recognized it very often!). It makes you start to wonder where your genes came from… your ancestors or your ancestors’ parasites!

To reach Todd Murray please call (360) 676-6736 or e-mail him at: tmurray@wsu.edu