Residual Studies with Cyfluthrin Wettable Powder: Toxicity Toward Red Flour Beetles (Coleoptera: Tenebrionidae) Exposed for Short Intervals on Treated Concrete

Abstract

Red flour beetles, Tribolium castaneum (Herbst), were exposed for 0.5, 1, 2, and 4 h on concrete treated with 20% cyfluthrin wettable powder at rates of 100, 150, and 200 mg (20, 30, and 40 mg [AI]/m2). Beetle recovery was assessed at 0, 24, 48, and 168 h postexposure, and residual bioassays were conducted at 3-wk intervals for 24 wk after treatment. At the low application rate of 100 mg/m2, initial knockdown after exposure increased as the exposure interval increased, but by week 18, 60-80% of the beetles had recovered and were mobile after 168 h postexposure. As the application rate increased to 150 and 200 mg/m2, initial knockdown increased as the exposure interval increased, and survival decreased after 168 h postexposure. The percentage of beetles that remained mobile after they were exposed on the treated concrete was usually correlated with the percentage that were active at 168 h postexposure. Of the 48 possible concentration-exposure-recovery combinations, 4 were described by nonlinear regression, 33 were described by linear regression, and regressions on week were not significant for the remaining 11 combinations (P ≥ 0.05). The period during which survival was <10% was 3.7-10.5 times longer for beetles exposed to the maximum label rate of 200 mg/m2 compared with the minimum label rate of 100 mg/m2.