Synergistic and antagonistic effects of insecticide binary mixtures against house flies (Musca domestica)

Abstract

The house fly, Musca domestica Linnaeus, 1758 (Diptera, Muscidae), is known as a globally distributed parasite with veterinary and medical importance and the ability to develop resistance to insecticides Insecticide mixtures can contribute to enhancing the effectiveness of existing insecticides against house flies and to implementing insecticide resistance management. The present study was conducted to assess the efficacy of four insecticides with different modes of action, applied alone and in binary mixtures, against adults of the M. domestica laboratory strain by no-choice feeding bioassays. The interaction patterns of neonicotinoid acetamiprid, phenylpyrazole fipronil, avermectin ivermectin, and pyrrole chlorfenapyr in the binary mixtures were likewise analyzed by calculating the combination indices to find out combinations with the synergistic effect. The analysis of values of insecticide lethal concentrations for 50% mortality revealed that the toxicity of acetamiprid, fipronil, and ivermectin increased in the binary mixtures compared to when they applied alone, while the toxicity of chlorfenapyr depended on the second insecticide in the mixtures. The combination index values of five insecticide mixtures, fipronil/acetamiprid (1:10), fipronil/chlorfenapyr (1:4), ivermectin/acetamiprid (1:2.5), ivermectin/chlorfenapyr (1:3 and 1:10) were <1, which displays a synergism. Three insecticide mixtures, acetamiprid/chlorfenapyr (1:4), fipronil/ivermectin (1:4), fipronil/chlorfenapyr (1:40), had combination index values >1, which indicates an antagonism. The fipronil/chlorfenapyr (1:4) mixture was the more toxic to adults of M. domestica. The ivermectin/chlorfenapyr (1:10) mixture and the ivermectin/acetamiprid (1:2.5) mixture produced the highest synergistic effects. The results of the present study suggest that the interaction patterns (synergistic or antagonistic) in the insecticide mixtures can depend on both the combination of insecticides and their ratio. Further studies are required in order to evaluate the synergistic combinations against field populations of M. domestica.