Hornworms are immature moths that can be devastating pests, especially on crops in the Solanaceae family such as peppers and tomatoes. These moths are in the Sphingidae family. The tobacco and tomato hornworms are especially damaging during their caterpillar stage. Usually found underneath the leaves, these chewing insects can desecrate a crop within a few days, eating every part of the plant in its path.
Integrated Pest Management (IPM) involves a well rounded approach to managing a pest problem. That plan consists of prevention, biological, mechanical, cultural and chemical controls. Biological control is the method of using one living organism to control or suppress another. This could be in the form of parasitism. While there are a variety of chemical control options for hornworms, nature also provides a solution.
Braconid wasps, such as Cotesia congregata, are members of the Braconidae family, with over 400 species known. During oviposition, about 65 eggs are laid into the hornworm’s hemolymph. When larvae emerge (2-3 days later), they begin feeding within the hornworm, essentially eating it alive. The growing larvae will emerge through it’s host cuticles after 12-16 days. At the third and final molt, the larvae will spin their white cocoons and pupate for 3-8 days, depending on temperature. Cocoons often fall off the host into the soil, where an adult wasp will hatch.
These tiny, 2-3mm wasps are harmless to humans, and likely unnoticeable on the farm or at your home garden. Being familiar with the life cycle of pests can help us prevent accidentally controlling natural enemies. While scouting for pests, also check for predators, and use it as a learning opportunity to teach about utilizing biological control.