Impacts of food, temperature, and humidity on recovery in <i>Tribolium castaneum</i> (Coleoptera: Tenebrionidae) after exposure to a contact pyrethroid insecticide

Insects that infest postharvest commodities cause significant damage or destruction, costing billions of dollars in lost products yearly. Insecticide treatments applied as contact insecticides are effective in managing insect populations. However, recovery of the insects after exposure to these insecticides is increased if food is present, reducing the efficacy of surface treatments and leading to continued infestations. In addition, variation in temperature and humidity could play a significant role in recovery. Here, we assess the role of food, temperature, and humidity on the recovery of Tribolium castaneum Herbst, red flour beetle, after exposure to a contact insecticide. We found food is an important factor in recovery under different temperature and humidity conditions. While recovery was higher at warmer temperatures and higher humidities, recovery increased further when food was present versus absent. Moreover, we found that any amount of flour, even a dusting, resulted in over 90% of beetles recovering after insecticide exposure, but when sand was substituted for flour, recovery was 25% lower compared to a no food treatment. These results highlight the importance of how environmental factors and the availability of food influence efficacy of insecticide treatments. Sanitation in food facilities is critically important as even the smallest amount of food present can cause substantial recovery, allowing beetles to escape treated areas and move throughout facilities. Further work pinpointing variation in underlying recovery between different populations and among different insect species is needed to understand local adaptation potential.