FATE OF EGGS OF 1ST-GENERATION OSTRINIA-NUBILALIS (LEPIDOPTERA, PYRALIDAE) IN 3 CONSERVATION TILLAGE SYSTEMS

Percentage hatch, chewing predation, Chrysopa sp. predation, other sucking predation, and parasitism by Trichogramma sp. of egg masses of first-generation Ostrinia nubilalis (Hubner) were estimated in spring chisel plow, ridge tillage, and no-tillage maize, Zea mays L., in southeastern Minnesota during 1986 and 1987. Tillage plots were split with and without terbufos application and with and without Bacillus thuringiensis-permethrin application in all combinations. Egg masses from laboratory reared O. nubilalis were exposed to natural enemies in the field eight times during the oviposition period of first-generation O. nubilalis, and population densities of Coleomegilla maculata DeGeer were estimated. Parasitism was 0.6% and predation was low during 1986. During 1987, chewing predation was highest in the chisel-plow system and lowest in the no-tillage system; Chrysopa sp. predation was lowest in the chisel-plow system and highest in the no-tillage system. C. maculata population densities were highest in the chisel-plow system and lowest in the no-tillage system, and chewing predation was positively related to C. maculata density. Predation by other unknown chewing predators was also higher in the chisel-plow system and lowest in the no-tillage system. The inverse relation between chewing and Chrysopa sp. predation was probably related to species-specific responses to the tillage environments.