<i>Culicoides insignis</i> Lutz and <i>Culicoides stellifer</i> (Coquillett) (Diptera: Ceratopogonidae) are more active at canopy height than ground level throughout the night in Florida

Culicoides biting midges (Diptera: Ceratopogonidae) are important, yet understudied vectors of animal and human pathogens. Many biting midge species reach significantly higher densities at tree canopy height (10-20 m), compared to ground level (1 m), which may compromise the effectiveness of space spray ground adulticiding. Timing adulticide applications to coincide with the hour(s) of greatest midge density at ground level could ameliorate this issue. However, the circadian activity patterns for most vector species remain poorly understood, especially in regard to vertical movement (between ground and canopy). This study investigated the circadian flight patterns and vertical stratification of two vector species (Culicoides insignis Lutz and Culicoides stellifer [Coquillett]) using a novel hourly sampling light trap operated at ground (≈1 m) and canopy (≈11 m) heights from 1700 h to 0800 h on two Florida deer farms. Both C. insignis and C. stellifer exhibited strong vertical stratification, with significantly more midges collected in the canopy than at ground level, up to 7.4-fold and 11.5-fold differences, respectively. Peak flight activity was not crepuscular, but occurred between 0028 h and 0103 h for C. insignis, and between 2240 h and 0234 h for C. stellifer, varying somewhat by location and height. The circadian and vertical activity patterns observed here contrast with assumptions of crepuscular activity in Culicoides spp. This suggests that the current timing of ultra-low volume insecticide applications on deer farms (typically dusk) is not aligned with peak Culicoides activity (2200 h-0200 h), reducing efficacy of control measures. To optimize Culicoides control outcomes, adulticides should be applied when Culicoides activity peaks.