Tomato hornworms (Manduca quinquemaculata) are a serious problem for tomato growers. These caterpillars have a large appetite and can quickly defoliate a tomato plant. If you find hornworms in your tomatoes, simply pick them off and drop them in soapy water. However, if you find a hornworm with white oblong obtrusions, leave it!
The white obtrusions are actually the cocoons of a parasitic wasp. A female wasp has laid her eggs under the skin of that hornworm. As the eggs hatch the larvae actually feed on the hornworm insides. The larvae eat their way out of the caterpillar and spin the cocoons you see. Eventually adult wasps will emerge from the cocoons and the weakened hornworm will die.
The hope is that the emerging wasps will find other tomato hornworms to parasitize and you will have managed that pest. There are some generalist parasitic wasps that will provide that service for you. There is a braconid wasp, Cotesia congregates, that specifically looks for tomato hornworms. This small wasp has clear wings and as an adult they are nectar feeders. To persuade the wasps to stay in your garden you will need to have flowers. The small braconid wasps are attracted to small flowers like yarrow and small asters.
Instead of reaching for an insecticide for tomato hornworms encourage the ecosystem to assist you in managing that pest!
Happy Gardening!
Becky is a Georgia Certified Beekeeper and works with community and school gardeners to increase beneficial insect habitat.She is the coordinator of the Great Georgia Pollinator Census, happening this year on August 19th and 20th, 2022.She is also part of UGA's Native Plants and Beneficial Insect Working Group.
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Hi Becky! I recently found what I believe is a tomato hornworm moth pupa in my garden bed. I put it back under the soil because I wanted to keep checking on it as it developed. Yesterday, I went to check on it and it was broken in half with small larvae inside. Do you know what kind of wasp would parasitize the pupa? Thank you so much!!
Hi Christine, Yes, there are parasitic wasps that attack tomato hornworms and I couldn’t tell you what type attacked your pupa. It sounds interesting, though. I hope you are staying well.
Thanks, I found a few of these zombie hookworms on the tomato leaves, and your explanation is very informed and helpful. Thanks!
Thank you; I’m a container gardener, and I have been concerned about the lack of bees in my area, but I have seen the wasps you describe above. Since I have an abundance of tomatoes on my plants, I think they’ve been the primary pollinators. I’ve also found several tomato hornworm caterpillars munching away, but all of them have egg cases/cocoons on their backs. I didn’t kill them, but I did move them off my tomatoes and onto my lawn abour an acre away. Hopefully, the wasps will develop into adulthood and will manage the hornworm population for my garden and my neighbor’s garden.
Why do we want the wasps?
The wasps lay their eggs in the hornworm limiting its ability to do more crop damage. Great question!
Hello… so are the wasps that emerge out of the cocoons beneficial?… or will they sting and be a nusainse???
They are very beneficial. And, small. You won’t even notice them.