Prevalence of parasitism of adult Aedes vexans by a mermithid (Nematoda: Mermithidae) in Oklahoma.

During the past 20 years, considerable effort has been directed toward development ofcontrol of mosquitoes by using mermithid nematodes as biological agents (Petersen 198b). Still, httle is known about the distribution of this parasitehost relationship. With the exception of studies with Perutilimermis cullos (Nickle), a parasite of adult Aedes sollicitans (Walker) along the Gulf and East Coast salt marshes (Petersen et al. 1967, Stiles 1903), and Octomyornermis troglodytis Poinar and Sanders, a parasite of immature and adult stages of the tree hole mosquito Aedes sienensis (Ludlow) in California (Poinar and Sanders 19?4), little is known about the occurrence of mermithids that mature in adult mosquitoes in the U.S. (Mermithids parasitize mosquitoes in the early larval stage, but some species do not mature until the host develops to the adult stage.) During studies on the transmission of the dog heartworm, Dirofilaria immitis (Leidy) near Stillwater, Oklahoma (Afolabi 1985)a in 1983. a number of adult Aedes uex,ans (Meigen) captured in light traps and animal-baited traps were found to be parasitized by an unidentified species of mermithid. This is the first reported observation of adult Ae. uexans being parasitized by mermithids in the US. Parasitism of adults of this species have been observed in British Columbia and Manitoba. Steiner (1924) reported that in 1920 ca.80% of both sexes captured in a sweepnet collection near Vancouver were parasitized by a mermithid described as Poramermis canadensis Steiner (described from immature stages). Parasitism was not observed in other species in the same collection except for a single specimen of Aedes sticticus (Meigen). The following year, levels of parasitism did not exceed ca.20%. Trpis et al. (1968) reported high levels of parasitism where all Ae. uexans females were parasitized,but Ae.