Beneficial Insect to Veggie Pests – Cotesia congregatus

Cotesia congregatus Parasitoid Cocoons on Hornworm *Click for detail* > UF Laura Sanagorski<

I like to stress how nature tends to find a balance without our help, such as in the case of pest and beneficial insects.  The photo on the left is an example of the beneficial Cotesia congregatus wasp’s activity on tomato hornworm.  If you or your customers grow tomatoes, eggplant, peppers, etc.,  you know this hornworm can be really destructive.

The Cotesia congregatus wasp helps to keep hornworm populations in check.  This insect is part of the Braconid family, which is made up of over 1000 species of tiny wasps that pose no threat to humans.  Insects in this family act as parasitoids, which are organisms that spend most of their life attached in some way to their hosts, which will eventually die.  Wasps in this family are excellent biological control options for a number of harmful caterpillars, aphids, and other landscape pests.

Cotesia congregatus Parasitoid Cocoons on Hornworm *Click for detail* > UF Laura Sanagorski<

The lifecycle of the Cotesia congregatus is pretty interesting.  The wasp lays its eggs just under the skin of the hormworm.  When larvae emerge, they begin feeding on the insides of the hormworm, essentially eating it alive.  When the juvenile wasps have matured, they eat through the skin of the hornworm, and spin their cocoons.  In the picture above, you can see that most of the adults have emerged through the tops of the cocoons.  Although the hornworm won’t do much damage to plants throughout the  whole process, it will finally die after the adult wasps emerge.  The wasps will then mate and seek out other hormworms to attack.

Only 0.6% of all insects in the United States are considered pests.  Most insects are beneficial, or at least harmless to us, such as in the case of this braconid wasp.  This is good reason to apply pesticides responsibly.  If you see signs of this wasp on properties you manage, take care not to disturb them.