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FIGURE 1. After larvae emerge through the body of a tobacco hornworm caterpillar, they spin silken cocoons. A total of 154 cocoons of Cotesia congregata was produced on this tobacco hornworm caterpillar.

   
 

 

FIGURE 2. Four days after emerging through the body of this tobacco hornworm caterpillar, adult wasps started to emerge from cocoons
through an opening on the tip end.

   
 

 

FIGURE 3. Adult Cotesia congregata wasps are very small (less than 1/8 inch) and pose no threat to humans, i.e., they do not sting.
 

   
 

 

FIGURE 4. A majority of cocoons with caps indicates that most wasps have made their emergence.

   

Quick Facts

Common Name:

Braconid wasp (applied to a variety of species)

Genus / Species:

Cotesia congregatus (syn. = Apanteles congregatus)

Type of Beneficial::

Insect parasitoid

Type of Metamorphosis:

Immature stages appear different from adults (i.e., complete metamorphosis)

Beneficial Stage(s):

Larval stages only

Prey:

Tobacco hornworm; tomato hornworm

Occurrence:

Widespread across the county and important parasite of tobacco and tomato hornworms  

Mounted Specimen?

Yes (mounted specimen for viewing available in insect collection at County Extension Office)

Homegrown tomatoes,
Homegrown tomatoes,
What would life be without
Homegrown tomatoes?

From a song sung by John Denver

Like John Denver, many of us are ardent fans of homegrown tomatoes: REAL tomatoes with REAL flavor and REAL texture. Just recently, this gardener has become aware of an important aid to the perilous journey from tomato seed to tomatoes on the table and would like to introduce my fellow dirt-diggers to it.

Meet the Braconidae, a wasp family that is a friend to the home gardener and commercial producer alike. (Yes, I did use “friend” and “wasp” in the same sentence!) Belonging to Hymenoptera, the same order as ants, bees and other wasps, these little jewels are a significant biological control against thousands of other insect species, including many that are considered pests.

Although highly variable in appearance, they are usually dark with four transparent wings and rarely over one-half inch long. Their size and the fact that there are over 15,000 described species make them difficult to notice, much less identify.

The quality that makes this insect family worth noticing is that most of them are parasitoids: parasites which usually kill their hosts. And, they like to feed on things we don’t like in our gardens: hornworms, caterpillars, beetles, aphids, squash bugs and stink bugs are among the many pests that members of the Braconidae family consider gourmet delicacies.

Different species attack their insect hosts during different stages of development, as eggs, larvae, pupae, or adults. They may become internal or external parasites. Braconid females can use the ovipositor, the tube through which eggs are laid, to sting. They generally don’t unless trapped or mishandled. The sting is considered medically harmless.

Individual species tend to be specialized to a particular host. A good example is the Cotesia congregatus (older name, Apanteles congregatus). Less than 1/8 inch long, black with yellowish legs and clear wings, this tiny wasp considers the tobacco hornworm (Manduca sexta) and the tomato hornworm (Manduca quinquemaculata) “meals on wheels.”

The female wasp uses her ovipositor to lay eggs just under the skin of an unlucky hornworm. As the eggs hatch, the larvae feed on the hornworm’s viscera–literally eating a hornworm alive. Larvae chew their way out through the host’s skin when they mature.

Once outside, the future wasps pupate, spinning tiny oval cocoons that look like insect eggs along the external back and sides of the worm. These fellows–and ladies–are not just innocently hitching a ride. When the adult wasps emerge from the cocoons, the already weakened hornworm will soon die, thus preventing any further defoliation on tomato plants.

So, if you see a bright green hornworm carrying what looks like a clutch of white-colored insect eggs on its back, leave it there! The hornworm is not only feeding its own destruction, it is also carrying potential destroyers of hornworm brothers, sisters and descendants. That means we get those wonderful, luscious tomatoes right off the vine, the braconids get a meal and a future, and the hornworms get…GONE!

Beneficials in the Garden & Landscape is an Earth-KindTM program coordinated through Extension Horticulture at Texas A&M University. Earth-Kind uses research-proven techniques to provide maximum gardening and landscape enjoyment while preserving and protecting our environment.

 

This web site is maintained by Master Gardener Laura Bellmore, under the direction of William M. Johnson, Ph.D., County Extension Agent-Horticulture & Master Gardener Program Coordinator.

All digital photographs are the property of  the Galveston County Master Gardener Association, Inc. (GCMGA) © 2002-2006 GCMGA - All Rights Reserved.