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Learning what pest-eaters had for lunch.

Learning What Pest-Eaters Had for Lunch

When ARS entomologist Matthew H. Greenstone set out to study the diets of some of the natural killers that eliminate crop-destroying pests, he found it no easy job. Predators of the corn earworm, including big-eyed bugs, soldier bugs, spiders, lacewings, and many others, are difficult to study. They're secretive, and they don't feed often.

"In addition, most of them liquify and suck the innards from their prey. You can't simply dissect them to determine what they've been eating," Greenstone says.

Greenstone hopes to increase knowledge of the role that predators and parasites such as spiders and wasps play in reducing insect populations that attack crops. His allies in the war against crop pests are among the newest in technologies.

Ultimately, biocontrol methods may lead to the use of smaller amounts of chemical insecticides. However, to reap this benefit we first need accurate estimates of the impact of natural enemies in reducing pest populations.

Greenstone and biological tech nician Clyde E. Morgan at the ARS Biocontrol of Insects Research Laboratory in Columbia, Missouri, focus on the corn earworm, which is also known as the cotton bollworm and tomato fruitworm. The corn earworm Helicoverpa zea, formerly Heliothis zea, and the related tobacco budworm, Heliothis virescens, are blamed for nearly $2 billion in damages annually to important agricultural crops.

Greenstone borrowed a method commonly used in biomedical research and adapted it to indirectly identify the contents of a predator's stomach. It makes use of hybridoma (monoclonal antibody) technology that can produce large amounts of identical antibodies that are specific to proteins found in the insect pests.

Greenstone and Morgan have published an enzyme-linked immunosorbent assay that uses monoclonal antibodies to detect remains of corn earworm caterpillars in predators' stomachs. The assay is specific and sensitive but has one serious disadvantage: an expensive reader is needed to evaluate the results.

To solve this problem, ARS postdoctoral research associate Melissa K. Stewart developed an immunodot test in collaboration with Greenstone. In performing the test, researchers liquefy individual predators in a mini-blender. The mixture is then used along with the monoclonal antibodies to detect certain proteins of the corn earworm.

"The antibodies we're using are very specific. They have to be specific because we want to distinguish the insect from its close relatives that may live in the same crop field," Greenstone says.

It's quick and accurate: Hundreds of immunodot tests can be done in less than 3 hours. This test requires inexpensive equipment and demands little training to perform and evaluate.

Similar tests are used by medical researchers to identify bacteria and viruses, and to determine pregnancy.

Parasitic wasps also attack the corn earworm. There are several closely related species of parasitic wasps that lay their eggs inside of corn earworm caterpillars. As their larvae develop, they consume the caterpillar.

In this case, researchers could dissect caterpillars and look for eggs and larvae of the parasite under a microscope. "But dissecting insects is tedious and requires special skills," says Greenstone.

Stewart and Greenstone have developed a monoclonal antibody that distinguishes larvae of one of the parasitic wasp species from all the others. They are developing a fast immunoassay built around this antibody.

Matthew Greenstone is at the USDA-ARS Biological Control of Insects Research Laboratory, Research Park, P.O. Box 7629, Columbia, MO 65202. Phone (314) 875-5361. Melissa K. Stewart is at the USDA-ARS Stored Products Insects Research Laboratory, Madison, WI 53706. Phone (608) 262-3795.

PHOTO : A spined soldier bug feeds on a corn earworm.
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Title Annotation:predator insects that feed on corn earworm
Author:Cooke, Linda
Publication:Agricultural Research
Date:Aug 1, 1991
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