Density-mediated Responses of Two Stored-product Insects to Host Food and Pheromonal Stimuli

Abstract

Stored product insects result in losses of 10-30% after harvest. Tribolium castaneum, (the red flour beetle), and Rhyzopertha dominica (the lesser grain borer), are recognized as cosmopolitan, destructive post-harvest pests. Although research has investigated how volatile emissions from various densities of T. castaneum affect attraction to the aggregation pheromone by conspecifics, research into the ways in which T. castaneum and R. dominica respond to various food cues when they are in crowded conditions has been lacking. Our goal was to observe the density-mediated effects of crowding on the behavioral response of both species to common food-based and pheromonal stimuli, and how the volatile emission patterns from grain differed under increasing densities. To accomplish this, the density of colonies for both species was altered (10–500 adults) on a fixed quantity of food (10 g of flour or whole wheat), then the behavioral response to food and pheromonal cues was evaluated in a wind tunnel and release-recapture experiment, and the volatiles from the colonies were examined through gas chromatography coupled with mass spectrometry (GCMS). Importantly, our results suggest that, at least for T. castaneum, crowded conditions attenuates attraction to food-based stimuli, but not pheromonal stimuli. Crowding seemed to have no effect on R. dominica at the densities tested. The abundance and identity of headspace volatiles emitted varied significantly with different densities of beetles and was also species-specific. Overall, our results have implications for behaviorally-based management tactics such as push-pull that may be able to improve the sustainability of postharvest agriculture.