Impact of high temperatures on efficacy of cyfluthrin and hydroprene applied to concrete to control Tribolium castaneum (Herbst)

In laboratory trials, concrete was treated with cyfluthrin wettable powder (WP) at 40 mg active ingredient AI] cyfluthrin WP/m², then heated for 4, 8, or 16 h at either 45°C or 55°C, or treated but not heated (seven treatment combinations). Bioassays were conducted by exposing adult Tribolium castaneum (Herbst) for 0.5, 1, and 2 h. Survival of T. castaneum was generally greater on unheated concrete compared with the heating treatments, and survival appeared to decrease as heating time increased at both 45°C and 55°C. In a second laboratory trial, concrete was treated with hydroprene (Gentrol) at the label rate of 1.9×10⁻³ mg AI]/cm², and bioassayed by exposing late-instar T. castaneum larvae on the treated surface. There were significant differences between untreated controls and the heat treatment regimes (P<0.05) with respect to the percentage of live emerged adults, the percentage of those adults with deformities, and the percentage of dead adults, but heating did not reduce efficacy of hydroprene. In a field trial, concrete was treated with cyfluthrin at 2 mg AI] cyfluthrin WP/m², and placed in a flour mill undergoing an experimental heat treatment and in an unheated office. Treated concrete was bioassayed by continually exposing adult T. castaneum for 0.5-120 h. The effect of heating time on insect mortality was not significant (P?0.05). Except for T. castaneum exposed for 0.5 h, the percentage of beetle survival on unheated concrete was greater (P<0.05) than survival on concrete that had been heated in the mill, indicating a possible beneficial effect on cyfluthrin toxicity due to heating. Results of these studies show that short-term exposures to high temperatures may have no appreciable effect on efficacy of either cyfluthrin WP or hydroprene, and combination treatments of heat plus either of these insecticides may be effective alternatives to methyl bromide for disinfesting milling facilities.