In situ marking of Culex tarsalis larvae (Diptera: Culicidae) with nitrogen-15: A novel technique in mosquito mark-capture studies

The Wyoming communities of Lander and Torrington have been areas of high West Nile Virus (WNV) incidence and both have sizeable populations of Culex tarsalis Coquillett, the primary vector of WNV in Wyoming. Cx. tarsalis larval habitats near these two communities were labelled with 15N enriched ammonium chloride (NH4Cl). Subsequent collections of adult Cx. tarsalis were conducted using dry ice-baited CDC light traps over four consecutive trap nights and analyzed for 15N enrichment. A single "central" trap was placed next to the isotopically labelled larval habitats at each location. Eight hundred and twelve mosquitoes were analyzed yielding eighteen 15N enriched specimens coming from the central trap at the Lander study site. Four hundred and forty-seven mosquitoes were analyzed from the traps located 2.5 km from the Lander 15N marked pond yielding two potentially marked mosquitoes at very low levels of enrichment. A total of 540 mosquitoes were analyzed from the Torrington study site yielding 10 marked mosquitoes from the central trap. Successful marking indicates that the 15N labelled NH4Cl was incorporated into the tissue of adult mosquitoes from their larval habitat. This also demonstrates, to the best of my knowledge, the first evidence of in situ mosquito marking with 15N stable isotope. This technique allows for the natural emergence of mosquitoes in their habitat eliminating the potential for behavioural bias which can be introduced in other, more common, marking techniques. This technique has a potential not only for use in ecological and behavioural studies of mosquitoes but with other insects with aquatic immature stages.