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Releasing Beneficial Insects in Sweet Corn

Answers are sought to how long beneficial wasps will last and how far they will travel

Cornell entomologist Mike Hoffmann added some new brushstrokes to the biological control picture in sweet corn this year. Hoffmann continued an ongoing investigation into the ability of Trichogramma ostriniae, a small wasp that parasitizes eggs, to control the insect pest European corn borer (ECB). What was different about this year's work was that instead of using "inundative" releases of the wasps Hoffmann tried one, early-season "inoculative" release.

Inundative releases are those in which massive numbers of wasps (such as 120,000 per acre) are released in a field each week in the hopes that they will take the insect pests by storm. With inoculative releases, only a few wasps are released, and the release is carefully timed. The hope with this approach is that the wasps will reproduce and spread out on their own in search of the insect pests.

This year's releases took place on four farms in central New York. The farms were particularly compatible sites for biological control because of their reduced insecticide inputs. At each farm about 200,000 T. ostriniae females were put in six half-pint cartons fitted with screening for protection from predators. The cartons were attached to individual corn plants. Emergence of the wasps was verified by retrieval of the cartons several days later. This method is simpler and less expensive than the inundative method, making it more likely to be one that growers can and will adopt.

How well did it work? The T. ostriniae, known to be relatively short-lived creatures, continued to feed on ECB egg masses up to 80 days after their release, showing successful establishment and reproduction in the fields. The tiny wasps also showed their ability to "cover the territory." They were observed traveling over distances of at least 300 feet within and between corn fields, and it is believed they will travel further where conditions make it worth their while.

While additional trials are needed to fine tune best times and densities for releases, it is clear that this method of biological control shows promise as part of an IPM strategy for the ECB. As Hoffmann points out, this method has potential uses that extend "beyond New York and also into crops other than sweet corn."