Infection of the western treehole mosquito,Aedes sierrensis (Diptera: Culicidae), with Lambornella clarki (Ciliophora: Tetrahymenidae)

Lambornella clarki was a common parasite of Aedes sierrensis immatures collected from treeholes in Mendocino County, California, in 1982–1983. The ciliate was not found in mosquitoes from treeholes with water having the most extreme values of electrical conductivity (<0.23 and >1.74 mmhos/cm) and pH (<6.5 and >7.7). Infection rates for individual monthly samples from L. clarki-positive treeholes ranged from 1 to 75%; 67% of all infections were observed in 4th-instar larvae. Infection with pathogens and parasites such as L. clarki, Ascogregarina clarki, Octomyomermis troglodytis, and unidentified bacteria and fungi, appeared responsible for high mortality rates (21–76%). Parasitism with L. clarki did not always result in death of the mosquito host; 7% of adults emerging from samples held in the laboratory were found to be infected. Ciliates were restricted to the host hemocoel except in older females where they invaded the ovaries, resulting in parasitic castration. This phenomenon may be associated with parasite dispersal.