ARS | Publication request: Improved high-throughput bioassay for Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 7, 2012
Publication Date: January 1, 2013
Citation: Oppert, B.S., Morgan, T.D. 2013. Improved high-throughput bioassay for Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). Journal of Stored Products Research. 52: 68-73. http://dx.doi.org/10.1016/j.jspr.2012.11.001.

Interpretive Summary: We need a high throughput bioassay to evaluate the effects of potential test compounds for control of larvae of a major storage pest, the lesser grain borer. Traditional bioassay methods are not optimal for insects like the lesser grain borer, with immature stages that develop inside wheat kernels. We developed a diet consisting of egg yolk, brewer’s yeast, and amylopectin that supports the larval stages of lesser grain borer. The diet can be made into a slurry that is easy to pipette and can be washed away to collect immature stages for other tests. We demonstrate that X-ray analysis can be used to observe developing larvae. However, simple weighing of groups of infested diet during the second week of the bioassay proved sufficient to distinguish between diets containing materials that were harmful to developing lesser grain borer larvae. The method is applicable for screening potential biopesticides to control lesser grain borer damage to grains and stored products.

Technical Abstract: As we gain more information through functional genomic studies of Rhyzopertha dominica (F.), we need a high throughput bioassay system to screen potential biopesticides. R. dominica is an internal feeder during immature stages and presents unique challenges with traditional bioassay methods. Our primary goal was to develop a fast method to evaluate larval development on small amounts of material incorporated homogenously in an artificial diet. Herein we describe a new method that incorporates an artificial diet composed of egg yolk, brewer’s yeast, and amylopectin for evaluating the effect of potential biopesticides on the development of R. dominica larvae. Evaluation is accomplished through visual inspection of digital X-ray images, or weighing containers of infested larvae on diet treatments. We demonstrate the method with aprotinin and Bacillus thuringiensis Cry3Aa protoxin, test materials that retard the development of R. dominica larvae. Different bioassay containers were evaluated, including a single-larva assay with pipette tips or 8-strip tubes, or a group bioassay in black 16-well trays. In addition to improvements in time and manual manipulations, larvae can now be obtained for biochemical studies by gently washing away the diet. Discrimination of the effect of test materials by weighing the infested containers was the most simplified approach to rapidly screen test compounds.