Grantee Research Project Results
Enhancing the Sustainability of Environmentally Friendly Whitefly ControlEPA Grant Number: F5F21876
Title: Enhancing the Sustainability of Environmentally Friendly Whitefly Control
Investigators: Crowder, David W.
Institution: University of Arizona
EPA Project Officer: Lee, Sonja
Project Period: August 16, 2005 through August 15, 2008
Project Amount: $111,344
RFA: STAR Graduate Fellowships (2005) RFA Text | Recipients Lists
Research Category: Academic Fellowships
I intend to study the management of resistance to the insect growth regulator pyriproxifen in the sweet-potato whitefly, Bemisia tabaci (Gennadius). The whitefly is a key pest of cotton, melons, and vegetables in Arizona, as well as one of the world's most devastating crop pests. Pyriproxyfen is a key biorational insecticide that improves the sustainability of whitefly control in several crops. The use of pyriproxyfen also significantly reduces the dependence on broad-spectrum insecticides and contributes in preserving natural enemies. To enhance the ability to design sound strategies for managing resistance to pyriproxifen in the whitefly, I will:
- compare resistance to pyriproxyfen between males and females,
- determine the dominance of resistance in females,
- determine if fitness costs are associated with pyriproxyfen resistance,
- and develop and apply resistance management models.
Results from this project will be used to help develop novel management strategies for controlling B. tabaci in Arizona and abroad using environmentally-friendly tactics. In addition, knowledge generated from this research can be used to improve management of other similar pests.
I will be able to achieve the objectives because we have selected B. tabaci strains with substantial pyriproxyfen resistance (>1000-fold). Laboratory bioassays will be used to compare resistance to pyriproxyfen between males and females, determine the dominance of resistance in females, and determine if fitness costs are associated with pyriproxyfen resistance. These bioassays will compare the responses of susceptible and resistant male and female B. tabaci on untreated (control) plants and plants treated with various concentrations of pyriproxyfen. Results will indicate whether there are differences in male and female susceptibility to pyriproxyfen, the extent that resistance affects survival, and the affects of toxin concentration on survival. Results from these laboratory experiments will be combined with models that simulate the population dynamics and genetics of B. tabaci. The models will evaluate the potential for whitefly resistance to pyriproxyfen under various simulated conditions to better understand how resistance evolves and to develop novel management strategies for B. tabaci.
Because males are generally smaller than females and may therefore be exposed to higher concentrations of toxin, we expect survival will be lower in males than females. If this is the case, resistance could be significantly delayed in the field. We expect that dominance of resistance in females to pyriproxyfen will decrease as pyriproxifen concentration increases, meaning that resistance will evolve at a slower rate if higher toxin concentrations are used. Longer development time or smaller body size in resistant than susceptible females will indicate fitness costs in females. Longer development time, smaller body size, or higher mortality in resistant than susceptible males will indicate fitness costs in males. In the simulation models, as the degree of dominance in females decreases, the time for resistance to develop should significantly increase. We expect that higher toxin concentrations and larger areas not treated with pyriproxyfen will delay the evolution of resistance. In a sensitivity analysis, we expect that dispersal between fields and mating interactions between individuals from refuges and treated fields will significantly affect the results.