Mosquito (Diptera : culicidae) dispersal: Implications for the epidemiology of Japanese and Murray Valley encephalitis viruses in Australia

One hypothesis to explain the southern extension of Japanese encephalitis ( IE) virus from Papua New Guinea into the Torres Strait islands in 1995 and to mainland Australia in 1998 is the dispersal of infected mosquitoes, part icularly Culex annulirostris Skuse from which JE virus has been isolated re peatedly. To investigate whether this species disperses in this manner, mos quitoes were identified from 368 aerial kite trap collections operated at 5 0-310 m (altitude) at inland New South Wales between November 1979 to Decem ber 1984. Forty samples (9 during daylight and 31 at night) contained mosqu itoes, of which 221 could be identified as Culex australicus Dobrotworsky & Drummond (58.8%), Culex annulirostris (21.3%), Anopheles annulipes Walker s.l. (10.4%), Aedes theobaldi (Taylor) (7.2%), Aedes rubrithorax (Macquart) (1.4%), and Aedes sagax (Skuse) (<0.9%). During the night, mosquitoes were found in 22.6% of the collections at a mean density (+/-SD) of 91.3 +/- 15 1.7/10(6) m(3) of air sampled. During the day, only 3.8% were positive at a mean density 125.3 +/- 152.1. When examined in relation to possible flying time and wind speed, mean +/- SD dispersal distances by day and night were 23.9 +/- 15.3 km and 152.4 +/- 116.3 km,respectively. These data provide c ircumstantial evidence that aerial carriage southward <approximate to> 200 km from Papua New Guinea to Cape York peninsula is feasible, but that south ern dispersal of Murray Valley encephalitis virus infected mosquitoes from tropical to temperate Australia is unlikely.