Differential mechanisms of action of the novel γ ‐aminobutyric acid receptor antagonist ectoparasiticides fluralaner ( A1443 ) and fipronil

BACKGROUND Fluralaner ( A1443 ) is an isoxazoline ectoparasiticide that is a novel antagonist of γ ‐aminobutyric acid ( GABA ) receptors ( GABARs ), with a potency comparable to that of fipronil, a phenylpyrazole ectoparasiticide. To clarify the biological effectiveness of fluralaner against fipronil‐resistant pests, differences in the actions of fluralaner and fipronil on GABARs that possess resistance to dieldrin ( rdl )‐type mutations were evaluated. RESULTS Fipronil had neither pest control nor GABAR ‐antagonistic activities against two‐spotted spider mites ( Tetranychus urticae ) that had two different rdl ‐type amino acids ( A 301 → H and T 350 → A: Drosophila melanogaster GABAR numbering) and against small brown planthoppers ( Laodelphax striatellus ) that had a novel rdl ‐type ( A 283 → N) mutation in GABARs . In contrast, fluralaner showed not only high pest control activities against these pests, but also excellent antagonistic activities for these rdl ‐type GABARs . CONCLUSION The findings indicate that rdl ‐type fipronil‐resistant pests do not show cross‐resistance to fluralaner owing to the differential actions of fluralaner and fipronil on the GABAR . © 2014 Society of Chemical Industry