Cold acclimation and crowding effects on kairomone-mediated behaviors of khapra beetle larvae

Insect quiescence and diapause are characterized by suspension of development, often accompanied by obvious signs of inactivity such as loss of mobility and reduced respiration. However, in some stored product insects such as the khapra beetle (Trogoderma granarium Everts, Coleoptera: Dermestidae), larvae may fail to develop with few obvious behavioral indicators. A series of experiments were performed to test whether temperature acclimation or crowding that delays development can also affect subsequent adult reproduction, larval orientation toward food-associated kairomones in a wind tunnel, and outcomes of trapping assays. Results indicate that both mechanisms for delaying reproduction led to greater offspring production compared to normal colonies. It was also found that normal larvae were more likely to approach or enter baited traps than cold-acclimated or crowded larvae. Normal larvae were more likely to recognize and walk upwind to wheat odors when they were present, unlike the cold-acclimated or crowded larvae, whose behavior was not affected by the food odor. However, the 2 types of developmental delay treatments differed in that cold-acclimated larvae were more likely to make no movements at all in the wind tunnel compared to the crowded larvae. The results indicate that both triggers for developmental delay may affect the ability of larvae to orient toward kairomone-baited traps, potentially reducing overall population estimates.