AN ECOLOGICAL RISK ASSESSMENT OF BT TRANSGENIC SWEET CORN ON NON-TARGET ARTHROPOD COMMUNITIES

Abstract

An ecological risk assessment evaluating potential adverse affects to non-target arthropods is necessary when releasing a novel transgenic crop. Field studies were conducted to assess tritrophic level effects of insecticide treated and untreated Bt and non-Bt sweet corn hybrids on the abundances, species diversity and functional processes of foliage-dwelling, aerial and soil surface arthropods. The diversity and abundance of decomposers, predators and parasitoids were determined by plant inspections, sticky card, and pitfall trap sampling for two years at two Maryland locations. Functional processes including predation, parasitism, reproduction and colonization were evaluated at one location over three years. Predation rates were estimated from sentinel egg masses of a lepidopteran; levels of parasitism were measured from naturally-occurring chrysopid eggs; emergence traps determined the recruitment rates of arthropods emerging from soil-litter; and litterbags measured arthropod colonization and litter degradation rates. Beneficial arthropod communities and functional processes were not significantly affected by exposure to Bt sweet corn. Insecticides significantly reduced arthropod diversity and abundance as well as the rate of predation, parasitism, colonization and recruitment of organisms. Less disruption occurred in Bt plots treated once than compared with non-Bt plots treated five times. Since the number of insecticide applications are reduced, planting Bt sweet corn will result in benefits to non-target arthropods and ecological processes. A second aspect of the ecological risk assessment focused on laboratory and field studies to evaluate the effects of Bt pollen on honey bee survival, brood development and foraging behavior. Results also were used to examine the statistical power of study protocols. Laboratory tests showed no effects of feeding on Bt pollen on survival or hypopharyngeal gland development measured indirectly by head weight gain of newly-emerged bees. In field studies conducted for two years at three locations, colonies foraging in sweet corn plots and fed Bt pollen cakes for 28 days showed no adverse effects on bee weight, hive strength, brood development and foraging behavior. Foraging bee weight, number of foragers returning with pollen loads, pollen load weight, and brood size were the most reliable endpoints to examine for non-target effects on the general fitness of colonies.