Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2003
Publication Date: 4/1/2004
Citation: Ebert, T.A., Derksen, R.C. 2004. A Geometric Model of Mortality and Crop Protection for Insects Feeding on Discrete Taxicant Deposits. Journal of Economic Entomology. 97(2):155-162. Interpretive Summary: The success of any insecticide application depends on an understanding of not only how the chemical agent affects the target organism but also on the behavior of the insect and how pesticides are dispersed under field conditions. While it is understood that pesticide distribution affects the success of an application, the interactions between pesticide distribution and availability on a plant surface are not well understood. This work set out to develop a model that would help understand how individual insects interact with pesticide deposits on a leaf surface. Feeding behavior is important to understanding the outcome as well as the effect of sub-lethal doses on the target insect. The model showed that deposits that contain less than a lethal dose of pesticide result in increased damage to a leaf and that behavior of individual insects influences control when the insect must feed on multiple pesticide deposits to ingest a lethal dose of pesticide. In addition, this model revealed that droplet distribution on the leaf surface should be based on allowable leaf damage and the quantity of leaf an insect could eat before the actual pesticide decays and becomes ineffective. Understanding the role of pesticide distribution will help aid the development of new pest management strategies based on the pesticide chemistry or method of delivery of the pesticide which will ultimately improve food safety and increase crop quality and yield.
Technical Abstract: The relationship between spray deposits and insect feeding behaviors is not well established. An individually based spatially explicit model was developed that explains how individual insects could interact with discrete toxicant deposits on a leaf surface. The model starts off with a simple example of a single insect encountering a single deposit on a leaf surface. It builds to incorporate the effects of individual and aggregate behavior, multiple individuals, and multiple deposits. The model shows that retention is a poor estimate of the biological impact of a toxicant. This is because efficacy is mainly determined by how that toxicant is distributed in the target's environment assuming that the dose is sufficient to be lethal. The model shows that uniform distribution of toxicant is a wasteful use of toxicant when some damage is allowable. It shows that there should be an optimal deposit size based on insect behavior, and there will be an optimal distribution of lethal deposits that is also determined by feeding behavior. Applications where individual deposits are sublethal will be less effective and wasteful, while distributions with deposits containing more than a lethal dose will be wasteful. Understanding the role of distribution in determining efficacy is crucial to effective deployment of both old and new toxicants. It may also be important in a range of other endeavors such as managing resistance development and understanding plant-insect interactions.