The tomato crop in my garden was less than satisfying this year. In fact, it was the worst disaster I have had in my (cough-cough) years of gardening.
One good thing has come from a failure to thrive this year. A braconid wasp (Cotesia congregatus) found a hornworm on one of my container tomatoes and laid her eggs in it. Soon, a whole new generation of wasps will be born to terrorize the hornworm population.
If you notice these white pupae (actually probably cocoons when you become aware of them) hitching a ride on a hornworm in your garden, give thanks and don’t destroy the good gals/guys with the pest. Let this hornworm live to nurture its parasites. It will soon die when they mature.
The female braconid wasp deposits her eggs just under the skin of the hornworm. The eggs hatch and the larvae feed on the insides of the hornworm until they are ready to pupate. The hornworm stops eating, saving your precious tomato plants. Then the larvae break through the skin and spin cocoons on the hornworm’s back, which look like clusters of white eggs. The braconid wasps emerge from their cocoons as adults only an eighth of an inch long. The hornworm is finished and with the birth of fresh generations of braconid wasps, new hornworms will become “infected.”
The more braconid wasps you have in your garden, the fewer problems you will have with hornworms. They are a perfect beneficial to incorporate into your garden, since contaminated hornworms stop eating. So, when you see white cases attached to a hornworm, let the bad caterpillar live so that the good wasps can thrive.
Just so you know, adult braconid wasps are not only good guys in the garden, you do not have to be afraid of them. Braconid wasps do not sting humans unless the humans abuse them. Don’t try to corner them or hold them prisoner in your hand. If you do, they might defend themselves.
All articles are copyrighted and remain the property of the author.
By Ron Harrison, Ph.D., Entomologist and Orkin Technical Services Director
Photographs courtesy of Orkin
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