Differential susceptibilities of two closely-related stored product pests, the red flour beetle (Tribolium castaneum) and the confused flour beetle (Tribolium confusum), to five selected insecticides

Authors: YAO, JIANXIU - KANSAS STATE UNIVERSITY; CHEN, CHENGYU - CHINA AGRICULTURAL UNIVERSITY; WU, HUA - NORTHWEST AGRICULTURAL & FORESTRY UNIVERSITY; CHANG, JING - KANSAS STATE UNIVERSITY; SILVER, KRISTOPHER - KANSAS STATE UNIVERSITY; Campbell, James - Jim; ARTHUR, FRANKLIN; ZHU, KUN YAN - KANSAS STATE UNIVERSITY

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2019
Publication Date: 10/15/2019
Citation: Yao, J., Chen, C., Wu, H., Chang, J., Silver, K., Campbell, J.F., Arthur, F.H., Zhu, K. 2019. Differential susceptibilities of two closely-related stored product pests, the red flour beetle (Tribolium castaneum) and the confused flour beetle (Tribolium confusum), to five selected insecticides. Journal of Stored Products Research. 84:101524. https://doi.org/10.1016/j.jspr.2019.101524.
DOI: https://doi.org/10.1016/j.jspr.2019.101524

Interpretive Summary: The red flour beetle and the confused flour beetle are two closely-related insect species that infest flour mills and rice mills in the United States. However, the adults often show different levels of susceptibility to insecticides, and their ranking can vary among insecticides. There are less data available on the susceptibility of larvae of these species, even though these are often the most abundant developmental stage. In an evaluation of five different insecticides applied to late-stage larvae of both species, red flour beetle were less susceptible to the organophosphate dichlorvos and the pyrethroid esfenvalerate compared to the confused flour beetle, but the reverse was true for natural pyrethrins. In addition, the confused flour beetle was much more tolerant to the insect growth regulators pyriproxyfen and methoprene compared to the red flour beetle. Combining insecticides with different synergists and then evaluating changes in susceptibility can provide insight into the methods used in detoxification of the insecticides that may contribute to the observed differential susceptibility. Results of this evaluation suggest the involvement of esterases in the detoxification of dichlorvos and pyrethrins, and cytochrome P450 monooxygenases in the detoxification of esfenvalerate in both species. Interestingly, the two species responded differently to pre-treatment with synergists. Our results show that although red flour beetle and confused flour beetles are two closely related species, they display very different susceptibilities to different insecticides, and different metabolic detoxification mechanisms may contribute to their differential insecticide susceptibilities. Mill managers and pest management professionals can use this information to more accurately use insecticides in control programs that target one or both of these insect species, and results also provide a foundation to develop ways to improve the effectiveness of these insecticides.

Technical Abstract: The red flour beetle (Tribolium castaneum Herbst) and the confused flour beetle (Tribolium confusum Jacquelin du Val) are among the most commonly encountered insects infesting stored food, but their susceptibilities to different insecticides often differ significantly, which complicates efforts to manage populations in milling and processing facilities. In this study, the susceptibilities of T. castaneum and T. confusum late-stage larvae to five selected insecticides, esfenvalerate, pyrethrins, dichlorvos, methoprene and pyriproxyfen, were assessed with and without synergists using topical applications. In four-day bioassays (without flour) with dichlorvos, esfenvalerate and pyrethrins, T. castaneum larvae were less susceptible (low larval mortality) to dichlorvos and esfenvalerate than T. confusum, whereas the reverse was true for treatment with pyrethrins. Pre-treatment with one of three synergists, piperonyl butoxide (PBO, cytochrome P450 monooxygenase inhibitor), S,S,S-tributyl phosphorotrithioate (DEF, esterase inhibitor), or diethyl maleate (DEM, glutathione S-transferase inhibitor), suggested involvement of esterases in the detoxification of dichlorvos and pyrethrins, and cytochrome P450 monooxygenases in the detoxification of esfenvalerate in both species. Interestingly, pre-treatment with some synergists increased the toxicity of insecticides in only one species: DEM and DEF increased the toxicity of dichlorvos to T. castaneum, whereas only DEF increased dichlorvos toxicity to T. confusum. In 28-day bioassays with larvae treated with each of two insect growth regulators (IGRs), methoprene and pyriproxifen, T. confusum was the more tolerant species. All T. castaneum died in either the larval or pupal stages with either IGR. In contrast, only pyriproxyfen caused complete mortality in T. confusum larvae, and even the highest dose of methoprene allowed nearly 70% of T. confusum larvae to pupate, and 4.5% of adults to emerge. Our results show that although T. castaneum and T. confusum are two closely related species, they display very different susceptibilities to different insecticides, and different metabolic detoxification mechanisms may contribute to their differential insecticide susceptibilities.