Abstract
Fipronil is a widely used phenylpyrazole insecticide with an environmental and mammalian safety profile that limits its use in agricultural systems, including livestock production. Ethiprole, an alternative phenylpyrazole insecticide, is used in crop protection because of its more favorable safety profile but it is not currently utilized in livestock systems. The aim of this study was to evaluate the toxicity of ethiprole in insecticide susceptible and multi-insecticide resistant strains of the house fly (Musca domestica), a major pest in numerous livestock systems. A secondary aim was to assess the effects of an Rdl target-site mutation on ethiprole using Drosophila melanogaster. Ethiprole and fipronil were essentially equivalent in toxicity in both topical and feeding assays for both strains of M. domestica. Compared to fipronil, ethiprole elicited a significantly greater increase in firing frequency during the rising phase of nerve excitation in larval CNS of susceptible M. domestica, but only at the highest concentration tested (10 μM). In a glass contact assay, the Rdl mutant D. melanogaster had a 50.3-fold resistance ratio compared to the susceptible strain with ethiprole, while only 3.7-fold was observed with fipronil. Recovery of nerve activity from GABA-induced silencing in larval D. melanogaster CNS was more pronounced in the Rdl mutant than the susceptible strain and dependent on insecticide and concentration. These findings are in support of ethiprole being pursued as an M. domestica control insecticide in animal agriculture with some caution should an Rdl mutation arise in M. domestica populations.
