Investigating insect behavioral responses to insecticidal proteins

R.R. Binning¹, S.A. Lefko², F. Cheng¹ and K. Liao³

¹Pioneer Hi-Bred, Johnston, IA, USA
²Pioneer Hi-Bred, Newark, DE, USA
³DuPont, Newark, DE, USA

Worldwide in 2004, 15.6 million hectares of maize were protected from insect damage by plant expression of insecticidal proteins. In some instances, plant protection may result from a combination of pest susceptibility and host discrimination behavior. Measuring the contribution of both is important to characterizing the mechanism of trait protection and considering trait longevity. This paper describes methods to measure the behavioral response of a target pest to a binary insecticidal protein in a quantitative, efficient, and statistically robust manner.

Western corn rootworms (Diabrotica virgifera virgifera) are insect pests of maize; the larvae damage maize roots and cost growers $1 billion per year in control costs and crop losses in the United States. Pioneer Hi-Bred International and Dow AgroSciences LLC are developing a plant-genetic solution for minimizing this loss; the protection mechanism is plant expression of the binary Cry34Ab1 and Cry35Ab1 insecticidal protein.

Strnad and Dunn (1990) described larval search behaviors of rootworms associated with host quality. Building on these techniques, Pioneer Hi-Bred developed an assay using EthoVision^® (Noldus Information Technology bv, The Netherlands) to observe and quantify search behavior of larvae after exposure to Cry34Ab1 and Cry35Ab1 proteins incorporated into an artificial insect diet. This experiment was designed to characterize search behavior after exposure to different concentrations of both proteins. The concentrations correspond to the range of Cry34Ab1 and Cry35Ab1 expressed in roots; the search pattern should indicate each larva’s perception of host quality. Parameters such as area searched, unique points, and non-overlapping distance were chosen to describe the search behavior. Analyses of variance were applied to these parameters to detect treatment effects.

This assay technique significantly decreases the input required to measure the behavioral response of an insect like western corn rootworm to an insecticidal protein and provides statistically robust quantitative results. These methods may be applied to other insect species with results that contribute to target-pest resistance and non-target risk assessments.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

© 2005 Noldus Information Technology bv