Influence of temperature on knockdown, toxicity, and resistance to pyrethroids in the house fly, Musca domestica

Abstract

Knockdown (KD), toxicity, and resistance to bioallethrin, permethrin, flucythrinate, and cypermethrin in Musca domestica were examined at 18, 25, and 32°C in a susceptible strain (NAIDM), a resistant strain (KDR) with a known resistance mechanism ( kdr), and a multiple resistant strain (Learn) with unknown resistance mechanism(s). Penetration and recovery from KD occurred more rapidly at higher temperatures. All four pyrethroids showed greater kill at 18 than at 32°C, although the differences varied with the compounds and, to a lesser extent, with the strains. Two main reasons are implicated for this observed negative temperature coefficient (negative TC): rate of metabolism/excretion/redistribution (MER) and reactivity at the site of action. The negative TC of permethrin and bioallethrin appears due to both MER and target site interactions, while that of flucythrinate and cypermethrin is likely due primarily to increasing MER with increasing temperature. Analysis of KD data in the KDR strain indicates that the kdr mechanism itself probably has no TC. There was a negative TC to resistance based on 24-hr LD 50s in both the KDR and Learn strains to flucythrinate and cypermethrin while the effect of temperature on resistance to bioallethrin and permethrin varied. The relevance of these findings on the field use of pyrethroids is briefly discussed.