Bionomics of Romanomermis sichuanensis, a Mermithid Parasite of Anopheles sinensis

In May 1982 a new mermithid nematode, Romanomermis sichuanensis was found in Leshan district, Sichuan, China. Anopheles sinensis and A. gigas baileyi were naturally infected. From May 1982 to September 1984, we collected An. sinensis larvae monthly from the same breeding sites in Leshan to determine the prevalence of mermithid infections and the effects of several environmental parameters on the prevalence of this mermithid nematode. An. sinensis was collected monthly from four sites that included four habitat types: paddy fields with standing or flowing water, abandoned fields, ponds, and streams. Mosquito larvae were sampled by a 400 ml ladle or a nylon sweep net at fixed places in the sites. The host density was calculated as mean number of larval mosquitoes per ladle. The water temperature and rainfall were recorded. The prevalence of parasitism was determined by dissection of mosquitoes or by holding the larval mosquitoes until they pupated or nematodes emerged. R. sichuanensis was found commonly in a hilly site occupying ca. 4 km super(2) in Leshan. Most paddy fields in this region are irrigated with spring water and the water remains in most fields all year. An. sinensis) is the most abundant mosquito species during the year. An. gigas bailegi was also present but at very low levels. The prevalence of parasitism in An. sinensis by R. sichuanensis fluctuated yearly.