Culex erythrothorax (Diptera: Culicidae): Activity periods, insecticide susceptibility and control in California (USA).

The mosquito Culex erythrothorax Dyar is a West Nile virus (WNV) vector that breeds in wetlands with emergent vegetation. Urbanization and recreational activities near wetlands place humans, birds and mosquitoes in close proximity, increasing the risk of WNV transmission. Adult Cx. erythrothorax abundance peaked in a wetland bordering the San Francisco Bay of California (USA) during the first 3 hours after sunset (5527 ± 4070 mosquitoes / trap night) while peak adult Culex tarsalis Coquillett abundance occurred during the subsequent 3 h period (83 ± 30 Cx. tarsalis). When insecticide resistance was assessed using bottle bioassay, Cx. erythrothorax was highly sensitive to permethrin, naled, and etofenprox insecticides compared to a strain of Culex pipiens that is susceptible to insecticides (LC50 = 0.35, 0.71, and 4.1 µg/bottle, respectively). The Cx. erythrothorax were 2.8-fold more resistant to resmethrin, however, the LC50 value was low (0.68 µg/bottle). Piperonyl butoxide increased the toxicity of permethrin (0.5 µg/bottle) and reduced knock down time, but a higher permethrin concentration (2.0 µg/bottle) did not have similar effects. Bulk mixed-function oxidase, alpha-esterase, or beta-esterase activities in mosquito homogenates were higher in Cx. erythrothorax relative to the Cx. pipiens susceptible strain. There was no difference in the activity of glutathione S-transferase between the two mosquito species and insensitive acetylcholine esterase was not detected. Larvicides that were applied to the site had limited impact on reducing mosquito abundance. Subsequent removal of emergent vegetation in concert with larvicide applications and reduced daily environmental temperature substantially reduced mosquito abundance. To control Cx. erythrothorax in wetlands, land managers should consider vegetation removal so that larvicide can efficiently enter the water. Vector control agencies may more successfully control adult viremic Cx. erythrothorax that enter nearby neighborhoods by applying adulticides during the 3 h that follow sunset.

Assessing Mosquito Breeding Sites and Abundance Using An Unmanned Aircraft.

An unmanned aircraft system (UAS; i.e., drone) with an attached multispectral camera was used to quantify accumulated surface water on a 0.54-km2 tidal marsh that abuts San Francisco Bay, CA, USA. The results of the survey showed unequal accumulation of surface water and provided information for focused inspections of potential mosquito breeding areas and identified areas where existing ditches needed improvement for increasing water circulation in the marsh to reduce mosquito breeding. The UAS was also outfitted with a high-magnification zoom video camera and piloted at varying heights to measure the video camera's ability to visualize immature mosquitoes in 2 small containers of contrasting colors during simulation tests in a marsh habitat. Immature mosquitoes could be seen clearly in white or black containers at heights up to 14 and 8 m, respectively. An artificial intelligence algorithm identified mosquito larvae and pupae in videos of the white tray with 94.1% and 52.8% accuracy, respectively. Together, our studies show that an UAS equipped with multispectral and zoom cameras provides a means for vector control agencies to rapidly and quantitatively assess the landscape for the presence of surface water and mosquito larvae.