Phenotypic susceptibility to pyrethroids and organophosphate of wild Stomoxys calcitrans (Diptera: Muscidae) populations in southwestern France.

Abstract

Stomoxys calcitrans (Diptera: Muscidae), is an important vector of lumpy skin disease and bovine besnoitiosis in Europe. Control of this biting fly could represent a keystone in the containment of this emerging disease. Reports of insecticide resistance in S. calcitrans are scarce in Europe. Therefore, the purpose of this study was to evaluate the phenotypic susceptibility to deltamethrin, cypermethrin and phoxim of five wild S. calcitrans populations from southwestern France, where transmission of bovine besnoitiosis is very prevalent. Adult S. calcitrans were caught at each study site and exposed to insecticide-impregnated filter papers under laboratory conditions. Quantities of active ingredients on filter papers corresponded to the recommended doses proposed by the manufacturers (37.5mg a.i./m2 of cattle's skin, 125mg a.i./m2 and 750mg a.i./m2 for deltamethrin, cypermethrin and phoxim respectively) were tested. Knock-down effects (KD) (1h after the onset of exposure) and mortality rates (24h and 48h after exposure) were evaluated. Phoxim showed a rapid and full efficacy in all populations. However, the KD effects (37.5 to 97.5%) and the mortality rates at 48h (10 to 91.25%) induced by the exposure to pyrethroids varied greatly according to the study site but none of the populations showed full susceptibility. Therefore, the current recommended doses of these pyrethroids are probably less efficient than expected in the field and should be considered with caution in the control of bovine besnoitiosis in France.