Changes in Culicoides sonorensis feeding behavior 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 behavior in ways that
affect vectorial capacity. To determine whether Culicoides feeding
behavior is altered by sublethal exposure to commonly used agricultural
insecticides, we exposed female C. sonorensis to permethrin and coumaphos
at concentrations ranging from LC10-LC30. We also exposed midges to
fluralaner at 100 mg/mL. Midges were offered a blood meal at 6, 12, 18,
and 24 hours post-exposure, and blood feeding success was measured. We
identified a significant inhibition of engorgement by permethrin up to 12
hours post-exposure, as well as by fluralaner up to 6 hours post-exposure.
Coumaphos engorgement rates were paradoxically heightened in the LC30
group after 18 and 24 hours 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.