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
larvas 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
, 5th International Conference on Methods and Techniques
in Behavioral Research, 30 August - 2 September 2005, Wageningen, The
Netherlands.
© 2005 Noldus
Information Technology bv
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