A Comprehensive Guide to
Safe Biological Pest Control
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Trichogramma wasps are tiny parasites that attack the eggs of over 200 species of moths and caterpilars. They are extremely small - 4 or 5 will fit on the head of a pin. Trichogramma lays its eggs inside the eggs of moths preventing the moth egg from hatching into a caterpillar. This prevents the damage caused by the feeding caterpillars, and also breaks the life cycle of the pest, effectively preventing the pest from reproducing. In some species of moth up to 5 parasite eggs may be laid in each moth egg. As the parasite develops within the egg, it turns black, and after about 10 days, an adult Trichogramma emerges. Adult Trichogramma can live up to 14 days after emergence.
Some of the common pests Trichogramma combat are: Cabbageworm, Tomato Hornworm, Corn Earworm, Codling Moth, Cutworm, Armyworm, Webworm, Cabbage Looper, Corn Borer, Fruitworms, and Cane Borers.
The wasp larvae kill pests before they damage plants by consuming their eggs. They are shipped while still parasitized in the host egg. You receive what looks like a small piece of sandpaper that has been inoculated with approximately 5,000 eggs. Trichogramma wasps protect plants throughout the growing season. In general, regular releases of Trichogramma ensures generations of mated females ready to attack moth eggs, and improves levels of control. Releases should be started when moths are first detected. Although the Trichogramma is minute, it can seasrch for moth eggs over considerable distances. 12,000 Trichogramma will treat up to 500 sq. ft. For orchards, field crops, etc. use 40,000 - 200,000 per acre on a weekly basis for 4 - 6 weeks during peak seasons. Release at peak egg laying, when adult moths are seen flying. Pheromone traps and visual inspection are necessary for maximum effectiveness.
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 parasitizes 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: Trichogramma 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 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 cannot 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.