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

Authors: Gerken, Alison; Scott, Rose; Khosla, Sonika; Markley, Alexus; Mueller, Codi; Scheff, Deanna

Submitted to: Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2025
Publication Date: 3/14/2025
Citation: Gerken, A.R., Scott, R.L., Khosla, S.N., Markley, A.L., Mueller, C.E., Scheff, D.S. 2025. Impacts of food, temperature, and humidity on recovery in Tribolium castaneum (Coleoptera: Tenebrionidae) after exposure to a contact pyrethroid insecticide. Insect Science. 25(2):4;ieaf021. https://doi.org/10.1093/jisesa/ieaf021.
DOI: https://doi.org/10.1093/jisesa/ieaf021

Interpretive Summary: Insects can infest stored grain and grain-based products and cause considerable damage in the postharvest supply chain, amounting to over $500 million per year of product losses in the U.S. alone. Contact insecticides are often applied to surfaces within food facilities to control insects; however, some insects recover after exposure, which reduces effectiveness of the insecticide and can lead to the development of insecticide resistance. Although the presence of food has been shown to increase recovery following insecticide treatments, the underlying cause of recovery is not known. Here we determined whether temperature, humidity, and amount of food available influence recovery in the red flour beetle, Tribolium castaneum, a common pest of processed grain products. We exposed insects to a common contact insecticide on concrete surfaces and found that over 90% of insects with food recovered at warm and humid conditions compared to around 30% at cooler and dryer conditions after seven days. Interestingly, even a small dusting of food resulted in over 90% of insects recovering after exposure to contact insecticides. However, replacing food with an abrasive material (sand) eliminated recovery in the presence of food. We hypothesize that the sand damaged surface of the insect cuticle, allowing insecticide to be more efficiently absorbed. This research demonstrates that sanitation combined with lower temperatures and humidity increase the efficacy of contact insecticides in food facilities.

Technical Abstract: Insects that infest postharvest commodities can cause significant damage or destruction, costing billions of dollars in lost products yearly. Insecticide treatments applied to surfaces as contact insecticides are effective in managing insect populations. However, recovery after exposure to these insecticides is significantly increased if there is food present, which can reduce the efficacy of surface treatments and lead to continued infestations. In addition, variation in temperature and humidity could also 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 that food played an important factor in recovery under different temperature and humidity conditions. While recovery was higher overall at warmer temperatures and higher humidities, recovery was increased further under these conditions 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 exposure to insecticide, but when sand was substituted for flour, recovery was diminished and was 25% lower compared to a no food treatment. We hypothesize that the sand caused friction and damage to the cuticle, increasing the efficacy of the insecticide. These results highlight the importance of understanding how environmental factors and the availability of food influence efficacy of insecticide treatments. Sanitation in these 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 population adaptation potential.