AUTUMN SOUTHWARD RETURN MIGRATION OF THE MOSQUITO CULEX-TRITAENIORHYNCHUS IN CHINA

Direct evidence for a southward 'return' migration in autumn of the mo squito Culex tritaeniorhynchus in China was obtained by aerial samplin g with a net suspended from a balloon. In a preliminary study between 2 and 20 September 1990 at Jiangpu, near Nanjing, in Jiangsu Province, 11 females and 4 males of this species were taken at heights of 150-2 50 m. During 17-26 October 1991 at Dongxiang in northern Jiangxi Provi nce, 44 mosquitoes (8 males, 36 females) were caught in the aerial net at heights of 80-380 m in northeasterly winds (E-NNW). Most of the sp ecimens were flying within the subsiding air-mass behind a cold front. Cx tritaeniorhynchus was the only species identified (31 females) amo ng the mosquitoes from Dongxiang. Of 24 females dissected, 17 had N st age ovaries - interpreted as diapause, five had stage I ovaries, one h ad stage II ovaries, and one was gravid (stage V), but none was freshl y blood-fed. Cx tritaeniorhynchus is the main vector of Japanese viral encephalitis in China, and it is possible that the virus is reintrodu ced to northern temperate areas in spring by northward migration of in fected Cx tritaeniorhynchus females.