Residual efficacy of deltamethrin as assessed by rapidity of knockdown of Tribolium castaneum on a treated surface: Temperature and seasonal effects in field and laboratory settings

Authors: Arthur, Franklin

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2018
Publication Date: 3/1/2018
Citation: Arthur, F.H. 2018. Residual efficacy of deltamethrin as assessed by rapidity of knockdown of Tribolium castaneum on a treated surface: Temperature and seasonal effects in field and laboratory settings. Journal of Stored Products Research. 76:151-160. https://doi.org/10.1016/j.jspr.2018.02.001.
DOI: https://doi.org/10.1016/j.jspr.2018.02.001

Interpretive Summary: The insecticide deltamethrin can be used as a pre-binning treatment to the flooring area of grain bins and elevator silos, and also as a residual treatment to floors inside milling and production facilities. Concrete exposure arenas treated with deltamethrin at a range of label rates and held inside a building, a grain bin, or an environmental chamber, for two autumn trials and two summer trials were used to evaluate residual efficacy of this insecticide. Knockdown of adult red flour beetles was slower and reduced on the arenas held inside the grain bin compared to the building or the chamber, and declined during the residual testing period of 10 weeks. There were more hours of temperature above 90°F during the summer in the grain bin compared to the other two sites, which led to increased degradation of the residues, which in turn affected rapidity of knockdown on the treated surface. Results show that if deltamethrin is used as a pre-binning treatment during the summer before grain is stored, a more precise timing may be necessary by doing these treatments shortly before the grain is loaded into the bin rather than doing these treatments weeks in advance. In addition, there was little difference between the label rates used in the test, thus selecting a middle range rate may be optimal and could also reduce costs of treatments by using less insecticide. Facility managers can utilize these results to optimize the use of deltamethrin to control stored product insects.

Technical Abstract: Concrete arenas were treated with the pyrethroid deltamethrin at rates of 8, 16, and 24 mg active ingredient [AI]/m2, and held either in a chamber set at 27 °C, inside a non-climate controlled interior building, or inside an empty metal grain bin on the flooring area. Bioassays of the arenas were conducted at 1 day (week 0), or 2, 4, 6, 8, and 10 weeks post-treatment, by exposing mixed-sex adult Tribolium castaneum Herbst and assessing knockdown every 30 minutes for 3 hours. Four separate trials were conducted, two during Autumn of 2015 and 2016 and two during Summer of 2016 and 2017. Knockdown did not increase with increasing application rate. Equations were fit to the combined rate data at each residual bioassay week for each location, and mean data were also compared to determine differences between arenas held in the different locations. During both summer trials, knockdown was generally slower after two weeks on arenas held inside the grain bin compared to arenas held inside the building or inside the chamber. The arenas inside the bin experienced more hours of temperature above 32.2 °C during the summer compared to the arenas inside the building or chamber, which presumably contributed to increased degradation of the residues and affected rapidity of knockdown. During autumn rapidity of knockdown was generally similar on arenas held in all three locations. In all trials, the total hours of temperature accumulation were far greater in the chamber compared to the building or the grain bin, but this had little effect on efficacy. The extreme temperatures, not the average temperature or the temperature accumulations, were the most important factor in assessing efficacy through rapidity of knockdown on the treated surface. Managers can use this information to more precisely apply deltamethrin, either as a pre-binning treatment inside a grain bin or elevator silo or as a residual treatment inside a milling or production facility.