Tiny wasps take on the European Corn Borer
European corn borer (ECB), the most significant insect pest of sweet corn in upstate New York, is managed in a typical year with statewide applications of some 82,000 pounds of synthetic insecticides, at an economic cost of $1,600,000. What if this persistent pest could be managed instead by a natural enemy, a tiny wasp called Trichogramma ostriniae, for approximately the same price tag?
In 1996 an IPM demonstration project brought together an IPM area extension educator, a Cornell entomologist, and two insectaries for the first commercial-scale releases in New York sweet corn of these beneficial wasps. Trichogramma ostriniae (abbreviated T. ostriniae), with a track record of successful control of the Asian corn borer in China, was the species chosen for the project.
T. ostriniae, which attacks ECB eggs, consistently parasitized more than 80 percent of the naturally occurring ECB egg masses in the fields in which the wasps had been released. Because of the excellent dispersal ability of the wasps, there were also high levels of parasitism in the plots in which no releases had been made. While the levels of control of ECB are higher with conventional insecticide sprays (usually 95-100 percent), it is entirely possible that the level of protection provided by T. ostriniaewill prove to be sufficient to produce equivalent yields of marketable corn.
"If we find that one or two releases are sufficient, it means that the wasps will be a cost-effective method for growers."
-Abby Seaman, Area IPM Extension Educator
A side benefit of substituting wasps for conventional insecticides is that other beneficial insects that cannot survive conventional insecticide treatments do survive in the release fields. Lady bird beetles, lacewings, and other predators that feed on aphids (another insect pest of sweet corn) were so numerous in the release fields that they provided aphid control comparable to that achieved with insecticides.
Successful mating of the wasps in the field - indicated by the high number of female wasps emerging from the parasitized ECB egg masses - was another positive finding. "This means," explained Area IPM Extension Educator Abby Seaman, principal investigator on this project, "that it may be possible to make one or two releases early in the season and have the Trichogramma ostriniae population sustain itself through the rest of the season. If we find that one or two releases are sufficient, it means that the wasps will be a cost-effective method for growers." The dollar outlay for the wasps is comparable to that required for an insecticide on a per-acre, per-application basis. Environmental costs of the two methods are, of course, worlds apart. There are no known ill effects associated with use of the beneficial wasps.
Not all test sites had equal success with the biological control releases in 1996. Extremely high infestation levels of the ECB at some of the sites meant that the amount of damage to the corn was unacceptably high despite successful establishment of the wasps. One explanation for this is that the wasps may have been released later than the optimal time; high densities of ECB eggs were seen in one field prior to the first release. When populations of ECB are lower than these extreme levels, however, T. ostriniaeshould keep the amount of ECB damage within the range of acceptability.
Until further research is conducted, a reasonable approach to using this biological control agent may be to combine it with scouting and - when needed - applications of Bt, a naturally occurring insecticide that is not harmful to beneficial organisms.