Abstracts Biological Sciences

Phenological, physiological, and ecological influences of transgenic Bt corn on European corn borer management

by Clinton Drake Pilcher

Field and laboratory studies were conducted to determine the use of altered planting dates as a means for integrating transgenic Bt corn into a pest management system for European corn borer, Ostrinia nubilalis. Transgenic Bt and non-Bt corn were planted at the same time on 3 separate planting dates (minimum of 10 day separation). Phenological corn development, O. nubilalis egg mass densities, Guthrie ratings, stalk tunneling, natural enemy populations, and yield data were recorded. No differences occurred in egg density between Bt and non-Bt corn for either the first or second generation; however, differences among planting dates did occur. Between 50 and 100% of the eggs were laid on the earliest planted corn during the first generation. In addition, between 40 and 65% of the eggs were laid on the latest planted corn for the second generation. However, egg density and larval tunneling is not highly correlated, except in southwestern Iowa;Significant differences and preferences for certain corn growth stages were observed among planting dates for most of the natural enemy species sampled including Coleomegilla maculata, Cycloneda munda, Chrysoperla carnea, Orius insidiosus, Macrocentrus grandii, and Syrphidae. Natural enemy presence during the first or second O. nubilalis generations varied among species and certain species showed higher correlations with O. nubilalis egg density and stalk injury than others. Macrocentrus grandii was affected by the presence of Bt corn. Numbers were 30 – 60% lower in Bt corn compared to non-Bt corn;Grain moisture and yields were recorded to determine the economic benefits of Bt corn planted on the different dates, based on O. nubilalis population and corn damage data collected prior to harvest. Greater benefits were realized when Bt corn was planted late during the planting sequence in southwestern and central Iowa. In addition, planting Bt corn early in northern Iowa provided more economic benefits;Drought stress may affect the activity of the Bt protein in leaf tissue during reproductive stages of growth; lower mortality of 3 rd instar O. nubilalis was observed. Decreased efficacy from drought stress will affect management of certain Bt corn events. Larvae receiving a sublethal dose of Bt will have resistance management implications.