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

Authors: DOMINGUE, MICHAEL - Animal And Plant Health Inspection Service (APHIS); Gerken, Alison; Scully, Erin; MYERS, SCOTT - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2025
Publication Date: 11/21/2025
Citation: Domingue, M.J., Gerken, A.R., Scully, E.D., Myers, S.W. 2025. Cold acclimation and crowing effects on kairomone-mediated behaviors of khapra beetle larvae. Environmental Entomology. https://doi.org/10.1093/jee/toaf298.
DOI: https://doi.org/10.1093/jee/toaf298

Interpretive Summary: Insects often enter prolonged periods of inactivity when exposed to stressful conditions, such as overpopulation, cold temperatures, and lack of food availability. This creates challenges for trap-based monitoring of insect populations and other pest management tactics because the insects may be less likely to respond to lures used for traps. In this study, we assessed behavioral responses of the khapra beetle, a stored product insect with quarantine status in the US, to food and pheromone-baited traps after exposure to either cold treatments or crowded conditions. Insects that were exposed to crowded conditions or cold treatments were less likely than insects reared order normal environmental conditions to enter traps and exhibit attraction to food odors and pheromones. Moreover, movement and activity levels were significantly reduced in insects that had been exposed to cold treatments compared to those exposed to crowded or normal environmental conditions, further reducing trap catches. Interestingly, insects that were exposed to crowded conditions and cold treatments produced significantly more offspring than insects than insects that were exposed to normal environmental conditions. These results indicate that khapra beetle populations may be underestimated under unfavorable environmental conditions and that population levels may greatly expand after a return to better conditions. For this reason, it may be beneficial to undertake additional surveillance tactics at ports of entry where these insects might be intercepted and introduced.

Technical Abstract: 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 Trogoderma granarium, 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 semiochemicals 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 semiochemically 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 two 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 semiochemically baited traps, potentially reducing overall population estimates.