Food source effect and residual efficacy of chlorfenapyr as a surface treatment on sealed and unsealed concrete

• Presence of food reduces efficacy of the insecticide chlorfenapyr.
• Sealing the concrete testing substrate did not provide a beneficial effect.
• Loss of residual efficacy in the presence of food became more pronounced over time.

Adults of Tribolium castaneum (Herbst), the red flour beetle, were exposed at 1 day, and 2, 4, and 6 weeks post-treatment on sealed and unsealed concrete arenas treated with chlorfenapyr at rates of 2.8, 6.9, 13.8, 20.6, 27.5 mg active ingredient/m2. Beetles were held either with or without flour, and assessments were done of the percentage of mobile beetles after 24 h and after 1 wk, and the percentage of beetles knocked down and dead after 1-wk. Although the percentage of adults that were still mobile after 24-hr of exposure increased on sealed and unsealed concrete with increasing post-treatment interval, there were less mobile adults on the arenas without flour compared to those with flour in week 0, but the opposite was true at weeks 2, 4 and 6. At the one week assessments, there were usually more beetles remaining mobile and more beetles knocked down on arenas with flour compared to those without flour, and more dead beetles on arenas without flour compared to those with flour. Sealing did not have a clear beneficial effect. The presence of the flour food source generally decreased efficacy of the insecticide, regardless of concentration.