Interactions between Spodoptera frugiperda (Lepidoptera: Noctuidae) and Bt-transgenic sweet corn.

Abstract

Field experiments were conducted to investigate the effects of Cry1Ab toxin of Bacillus thuringiensis expressed in transgenic sweet corn (Attribute™) on larval dispersal and larval density of the fall armyworm, Spodoptera frugiperda (Smith), which could affect rates of adaptation to Bt corn. Crop phenology and agronomy were also tested to determine the affects of rapid corn maturation and tillers on insect survival. Behavior and dispersal of larvae from the neonate to 10 day-old larval stage was measured in single variety plots of Bt and conventional plants. Each plot was artificially infested with one egg mass to test the hypothesis that Bt toxins affect larval behavior, increasing dispersal of early instars. Results indicated that crawling behavior of neonates was similar in both varieties but larvae settled faster on conventional plants. Larval dispersal among plants was also statistically similar in both varieties at all sampling dates. In separated plots, two larval densities and three planting dates were studied. Mortality of fall armyworm larvae in Bt sweet corn was not density-dependent. Early entry of the corn plant into reproductive stage apparently affected larval survival. There is not differential larval utilization and survival in tillers versus main whorls of Bt and non-Bt plants. Insect adaptation to Bt toxins is likely affected by larval dispersal and rapid maturation of corn plants.