corn, T. nubilale is not now competitive, but with relatively modest improvements in effectiveness it would be nearly competitive with current control tactics. Use of T. nubilale in seed corn production is nearly competitive even under current conditions. Technical improvements could result in increases in net revenue of more than $60 an acre in this corn commodity. Although any technical improvement would improve the competitiveness of T. nubilale, increases in efficacy would result in fivefold to sevenfold greater increases in benefits than decreases in costs.
Two approaches have been used for improving efficacy of Trichogramma. Strains of Trichogramma can be screened to identify the most effective. Although screening methods are still being developed, current methods can identify better-performing strains for more intensive evaluation. The other approach has been to analyze the limitations of a particular strain to identify characteristics that need improvement. Artificial selection can then be used to improve the strain. Evaluation of data from several field releases reveals that limitations of T. nubilale are associated with processes relating release numbers to parasitism rates, including variability in the quality of parasitoids released, and environmental factors such as plant structure, weather, and availability of alternative food sources.
To further characterize some of the environmental components potentially limiting T. nubilale, the effects of time in the season, corn variety, and corn height were examined experimentally. Variety and time in the season had no effect on effectiveness of T. nubilale, and effectiveness was better in shorter corn than in taller corn, contrary to preliminary expectations. Other factors, such as temperature and quality of the released parasitoids, could have greater effects on effectiveness. Even at the highest observed parasitism rate, the expected reduction in European corn borer populations is low. Improvements to existing or additional strains or species is essential for making Trichogramma a competitive control tactic in the United States.
Andow, D. A. 1990. "Characterization of predation on egg masses of Ostrinia nubilalis (Hübner)" Annals of the Entomological Society of America 83:482-86.
Andow, D. A., and D. R. Prokrym. 1991. "Release density, efficiency and disappearance of Trichogramma nubilale for control of European corn borer". Entomophaga 36:105-13.
Andow, D. A., G. C. Klacan, D. Bach, and T. C. Leahy. 1995. "Limitations of Trichogramma nubilale (Hymenoptera: Trichogrammatidae) as an inundative biological control of Ostrinia nubilalis (Lepidoptera: Crambidae)". Environmental Entomology 24:1352-57.
Bartels, D. W., and W. D. Hutchison. 1996. "Corn (Sweet), European corn borer". Arthropod Management Tests 21:107-8.
Bigler, F., and R. Brunetti. 1986. "Biological control of Ostrinia nubilalis Hbn. by Trichogramma maidis Pint. et Voeg. on corn for seed production in southern Switzerland". Journal of Applied Entomology 102:303-8.
Bode, W. M., and D. Calvin. 1990. "Yield-loss relationships and economic injury levels for European corn borer (Lepidoptera: Pyralidae) populations infesting Pennsylvania field corn". Journal of Economic Entomology 83:1595-603.