Sunday, July 10, 2011

Beneficial Insects: Trichogramma Wasps

Trichogramma Wasp about to lay its eggs in pest eggs.

Trichogramma Wasps 
(pronounced TRICK-oh-gram-uh)
Latin Name: Genus Trichogramma (over 230 species )

A pair of wasps laying eggs

Why are they beneficial?
This tiny parasitic wasp lays its eggs inside the eggs of pests (moths and butterflies).  Their prey includes eggs of the alafala caterpillar, armyworms (but not beet armyworms), bagworms, bollworms, cabbage looper, cankerworm, codling moth, corn borers, corn earworm, cutworm, fruitworms, leafworms, peach borers, squash borers, tomato hornworm, wax moth, and webworms.


What is their life cycle?
An adult female with lay eggs in up to 300 pest eggs on average during her 9-11 day adult life. Sometimes a female may lay up to 50 eggs in one pest egg.  The wasp eggs will hatch and the larvae will slowly grow, feeding on the contents (embryo and yolk) of the pest egg.  Adult wasps emerge from their hosts in 7-75 days, after pupating within the egg and then chewing a hole through the shell.  This length of time depends on the species and the climatic conditions.  Almost immediately, the Trichogramma Wasps will start looking for new pest eggs in which to deposit their own eggs.  They may or may not mate.  Most Trichogramma Wasps are female and usually don't need a male to reproduce.

These are tiny little wasps!

What do they look like?
These wasps are TINY... almost microscopic at less than 1 millimeter (less than 1/50th of an inch).  They are also called "stingless" wasps since they are in the same Order (Hymenoptera) as bees and other wasps, but they are too small to harm humans.  While they do resemble miniature yellow jackets (dark yellow or yellow and black with red eyes), most of the over 230 species are so similar that only experts can tell them apart.  Their eggs and larvae are so small that little (no pun intended) is known about them.  You can try to spot them in your garden with a magnifying glass.  The eggs of parasitized pest eggs with change color, usually becoming darker than the other eggs near it (sometimes turning metallic blue).

Another great image of the tiny Trichogramma Wasp

What do they need?
They need healthy prey.  What does that mean?  Don't use pesticides.  Pesticides will kill the hosts (caterpillar and worm eggs), but will also destroy the Trichogramma Wasps - either directly or by not providing them with food.  These wasps can destroy up to 98% of the pest eggs in some areas.  If we can accept a little bit of depredation of our crops to allow food for these voracious wasps, we can almost eliminate the need for chemicals on and in our food plants.  Scientists still don't know if the Trichogramma Wasps eat anything other than pest eggs, but tiny flowers with nectar would be the likely food choice.  Since these flowers are so useful in feeding other beneficial insects, you should always have a good supply in bloom just in case.

Examples of plants that provide nectar and pollen to beneficial insects: basket of gold, buckwheat, butterfly weed,carpet bugleweed, chamomile, chervil, chives, clover, cornflower, cosmos, coreopsis, cinquefoil, coriander, dandelion, dill, fennel, four-wing saltbush, golden marguerite, marigold, mustard, parsley, queen anne's lace, scented geraniums, spike speedwell, sunflowers, tansy, vetch, wild carrot, and yarrow.

Trichogramma Wasp eggs ready for relase

Purchased
You can purchase Trichogramma Wasps from many online retailers.  They come on 1 inch square tabs of paper that contain 3,000-5,000 pest eggs "infected" with Trichogramma Wasp pupae.  Release rates vary depending on the source but range from 1 tab per 1,000-5,000 square feet or 5-10 tabs per acre.  It is often recommended to continue to put out tabs once every 2-6 weeks during the growing season depending on the pest load.  You can stick the tabs on a branch or other solid garden surface with a needle, paperclip, or heavy string.
Note: When purchasing, keep in mind that some species of Trichogramma Wasp only prey on certain species of pest eggs.  Review the pests in your area and let find out which wasp(s) will be best for your garden.

Check out these other pages on beneficial insects in your garden!
Bees
Lacewings
Ladybugs
Praying Mantis
Trichogramma Wasps

No comments:

Post a Comment