Efficacy and sub-lethal effects of methoprene and pyrethrin aerosol treatments on Tribolium castaneum

Aerosol applications, such as methoprene (an insect growth regulator) with synergized pyrethrins, are often used to suppress the red flour beetle (Tribolium castaneum) populations in food-processing facilities. In this study, we explored the impact of these chemicals individually with the carrier, isoparM, and in combination on T. castaneum by measuring the adult survivorship and their progeny production. After 50 males or females were treated with the labeled rates for space spray, one male and one female were paired by placing them in a plastic Petri dish containing 5 g of flour. Mortality was assessed for two weeks. Exposures of the insect to the mixture of methoprene, pyrethroid and isoparM resulted in significantly lower survivorships (males 73%, females 87%) than the other treatment combinations. There was no significant difference in the survivorship between the male and female. After two weeks, adults were removed and the flour was used to rear the progeny for six weeks to determine sub-lethal effects. Relatively fewer adult progeny were produced in the mixture of methoprene, pyrethrin and isoparM (33.73±6.37) than in the other treatments. These results indicate that the efficacy of the mixture of methoprene, pyrethrin, and isoparM is higher than the individual components. However, such an effect does not appear to affect the following generation. These results may be explained by the fact that the labeled rate for space sprays is about three times lower than those for surface sprays which are typically used for direct mortality efficacy tests.