Rating knockdown of flour beetles after exposure to two insecticides as an indicator of mortality

Authors: ATHANASSIOU, CHRISTOS - University Of Thessaly; KAVALLIERATOS, NICKOLAS - University Of Athens; Arthur, Franklin; NAKAS, CHRISTOS - University Of Bern

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2020
Publication Date: 1/13/2021
Citation: Athanassiou, C.G., Kavallieratos, N.G., Arthur, F.H., Nakas, C.T. 2021. Rating knockdown of flour beetles after exposure to two insecticides as an indicator of mortality. Scientific Reports. 11:1145. https://doi.org/10.1038/s41598-020-78982-z.
DOI: https://doi.org/10.1038/s41598-020-78982-z

Interpretive Summary: When adult stored product beetle pests are exposed on a surface treated with insecticides, they are often incapacitated by the insecticide, and will either be on their backs, unable to move, or capable of moving only a short distance before falling over. This stage is termed "knockdown", and the exposed insects can either recover from knockdown, remain in this state for some time, or transition to a death stage. However, knockdown is very subjective, so we developed an index that went from 1, mortality, to 5, no difference in behavioral movement compared to insects exposed on an untreated surface. Knockdown as assessed at 1, 3, and 7 days after the adults were placed on arenas treated with either cyfluthrin (Tempo®) or chlorfenapyr (Phantom®). Cyfluthrin gave immediate knockdown to red flour beetle and confused flour beetle exposed for 1 day, but after 7 days many of the exposed adults had not died and were still in the knockdown state. In contrast, there was little immediate knockdown of adults 1 day after they were exposed to chlorfenapyr but after 7 days most exposed adults were dead. Efficacy of cyfluthrin slightly decreased over a 5-week residual testing period, while efficacy of chlorfenapyr remained stable. Light:dark conditions had no effect on residual efficacy. Results show that knockdown of stored product beetles after exposure to insecticides can be quantified, but direct relationships between knockdown and mortality may depend on the specific insecticide. Managers can use the results of this study to more effectively plan control programs for stored product insects when using these insecticides or similar products.

Technical Abstract: Knockdown and mortality of adults of the red flour beetle, Tribolium castaneum (Herbst) and the confused flour beetle, Tribolium confusum Jacquelin du Val, were assessed after exposure to two contact insecticides, chlorfenapyr and cyfluthrin, on a concrete surface. Laboratory bioassays were based on scaling knockdown of exposed adults according to their mobility from 1, which were immobilized adults to 5, which normally moving (similar to the controls). Adults were assessed and scaled 1, 3 and 7 days post-exposure. After the final assessment, adults were discarded, and the same procedure was repeated for 5 weeks with new adults exposed on the same treated surfaces. Only cyfluthrin gave immediate knockdown, but many individuals did not eventually die after exposure. In contrast, adults exposed to chllorfenapyr were not initially knocked down after exposure, but most died after 7 days. These trends were similar during the entire 5-week residual testing period. The storage of the treated dishes in illuminated or non-illuminated conditions did not affect the insecticidal effect of either insecticide. The results of the study can be expanded towards the design of a “lethality index” for stored product insects that can serve as a quick indicator of knockdown and mortality after exposure to insecticides.