Changes in Culicoides sonorensis feeding behaviour following sublethal insecticide exposure.

Culicoides biting midges (Diptera: Ceratopogonidae) are economically important biting flies known for transmitting pathogens like bluetongue virus to livestock. In order to control these insects and the diseases they are associated with, livestock producers employ a variety of preventive practices which commonly include insecticide use. The efficacy of insecticide treatments can wane over time as insects either develop resistance or the active ingredient is degraded in the environment. Sublethal insecticide exposures can change vector behaviour in ways that affect vectorial capacity. To determine whether Culicoides feeding behaviour is altered by sublethal exposure to commonly used agricultural insecticides, we exposed female C. sonorensis Wirth and Jones to permethrin and coumaphos at lethal concentrations (LC) ranging from LC₁₀ to LC₃₀. We also exposed midges to fluralaner at 100 mg/mL. Midges were offered a blood meal at 6, 12, 18 and 24 h post-exposure, and blood-feeding success was measured. We identified a significant inhibition of engorgement by permethrin up to 12 h post-exposure as well as by fluralaner up to 6 h post-exposure. Engorgement after coumaphos exposure was paradoxically higher in the LC₃₀ group after 18 and 24 h post-exposure, but decreased at the same timepoints for the LC₂₀ group. The different modes of action of each of these insecticides may account for their differing effects on Culicoides feeding.