June 28, 2017

Worm vs. Wasp

Kristina Rubio Photo | Tomato hornworm parasitized by a braconid wasp, Cotesia congregatus

Kristina Rubio Photo | Tomato hornworm parasitized by a braconid wasp, Cotesia congregatus

Damage to tomato plants can come from a number of sources, and one voracious eater is the tomato hornworm, which can devour both leaves and fruit when fully grown.

What is fully grown? It equals about 4 inches in length. And hornworm is not exclusive to tomatoes, but to any relatives, including potatoes, peppers and eggplant.

The hornworm pictured above is the larval stage of Manduca quinquemaculata, the tomato hornworm moth, which is also called the sphinx, hawk or hummingbird moth. It lays its eggs on the underside of leaves in spring, and those mature into the hornworm larvae that can do so much damage.

One of the most easily effective ways of controlling hornworm is to simply pick off the larvae as you find them.

But you might get a hand from nature in this, for the larval stage of the hornworm is a vulnerable one. Just look at the picture with all those little white grains attached to the hornworm.

It turns out that a braconid wasp, Cotesia congregatus, uses the hornworm to lay its eggs, parasitizing the hornworm. The larvae from those eggs will feed on the hornworm until the new wasps are ready to emerge. What you see in this photo are the cocoons.

What to do? “The wasps will kill the hornworms when they emerge from the cocoons and will seek out other hornworms to parasitize,” according to the VegEdge from the University of Minnesota.

That old canon “let nature take its course” comes to mind.

Thanks to Kristina Rubio for asking what was up with this on our Facebook page.

– Janine Pineo