The contribution of gut bacteria to pesticide resistance of Tribolium castaneum (Herbst)

The stored product pest, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), has developed resistance against many classes of pesticides applied in grain storage. Knowledge about mechanisms behind pesticide resistance is essential to developing novel pest management strategies. Although more and more studies reveal that pesticide resistance of insects is associated with their symbionts, the link between gut symbionts and host resistance to contact pesticides has not been reported in T. castaneum. This study aims to reveal the relationship between gut bacteria and resistance of T. castaneum against contact pesticides and to determine its underlying mechanism. Ten culturable bacteria were isolated from the guts of pesticide-resistant T. castaneum adults, among which two isolates, Bacillus cereus and Achromobacter xylosoxidans, exhibited the ability to decompose and utilize malathion, pirimiphos-methyl, and deltamethrin for their growth. Reintroduction of a detoxifying bacterial isolate to sterile beetles significantly increased survival rates and activities of metabolic detoxification enzymes of adult T. castaneum when exposed to pesticides. Furthermore, in the absence of pesticides, two detoxifying bacteria had positive effects on the development of the F1 generation of T. castaneum. Positive effects of these two gut bacteria on host pesticide detoxification metabolism and fitness facilitate the formation of symbiont-mediated pesticide resistance in T. castaneum. These results provide further insight into the function and evolution of microbe-insect symbioses and enable novel pest management strategies by depleting these bacteria with antibiotics to increase host sensitivity to pesticides.