DIFFERENTIAL TOXICITY OF PYRETHROID AND ORGANOPHOSPHATE INSECTICIDES TO THE HONEY BEE, APIS MELLIFERA AND THE YELLOW FEVER MOSQUITO, AEDES AEGYPTI
Six insecticide active ingredients (AIs) and five commercial insecticide formulations were applied by topical application and onto filter paper strips to determine differential toxicity to Aedes aegypti (L.) and Apis mellifera (L.), and to evaluate their potential use in future insecticide resistance monitoring surveys. For topical application, 0.1 or 1 µl of the technical insecticide solution was applied to the Ae. aegypti and A. mellifera thorax, respectively. For insecticide-impregnated strips the insecticide amount varied, according with the commercial formulation. By topical application deltamethrin was the most toxic AI (LD 50 = 0.057 µg/g) to Ae. aegypti and prallethrin was least toxic (LD 50 = 19.42 µg/g). For A. mellifera, the most toxic AIs were deltamethrin (LD 50 = 0.013 µg/g) and bifenthrin (LD50 = 0.156 µg/g); and the least toxic was chlorpyrifos (LD 50 = 3.246 µg/g). When the insecticide-impregnated papers method was used, Mosquitomist Two (chlorpyrifos 24.6%) was the most toxic insecticide for Ae. aegypti (LC50 = 0.024 µg/cm2 ), and Aqualuer (permethrin 20.6%, PBO 20.6%) was least toxic (LC50 = 0.408 µg/cm2 ). For A. mellifera the most toxic commercial insecticide formulations were Talstar (bifenthrin 7.9%; LC50 = 0.288 µg/cm2 ) and Mosquitomist Two (LC50 = 0.299 µg/cm2 ), with no significant differences, and the least toxic commercial formulation was Deltagard (deltamethrin 2.0%; LC50 = 15.084 µg/cm2 ). By topical application, more than 28 times of chlorpyrifos was needed to obtain the same mortality in A. mellifera as in Ae. aegypti. When using the insecticide-impregnated paper method, more than 206 times of Deltagard was needed to obtain the same mortality in A. mellifera as in Ae. aegypti. Even though Mosquitomist Two was the most toxic insecticide for both insect species, the honey bees were >12 times more tolerant to this insecticide, compared with the mosquitoes.