CHANGES IN MOSQUITO POPULATIONS WITH EXPANSION OF THE ROSS RIVER RESERVOIR, AUSTRALIA, FROM STAGE-1 TO STAGE-2A

Female mosquitoes were collected at 4 sites around the Ross River rese rvoir (Stage 2A) from 484 carbon dioxide-supplemented light traps. The seasonal abundance from these collections during 1991-93 was compared statistically with that for similar collections done for the Stage 1 reservoir in 1984-85. Principally due to clearing of the forest prior to the inundation of the Stage 2A, several tree hole/plant axil and sh aded pool species are no longer present or are rare. Due to extensive loss of marginal emergent vegetation and creation of expanses of shall ow muddy pools, mean number per trap of Anopheles amictus and Aedes no rmanensis increased up to 36- and 282-fold, respectively, from Stage 1 to 2A. For Culex annulirostris, mean abundance did not exceed densiti es recorded for Stage 1. However, from examination of trends from 1991 to 1993, mean catches of Culex, Anopheles spp., and Mansonia uniformi s were increasing despite the progressive reduction of the inundated a rea of the reservoir. Cluster analysis of species abundance indicated broad similarities with Stage 1 data, and differences in faunal compos ition of the reservoir area compared with that around Townsville. In v iew of the continuing stabilization of the Stage 2A reservoir area, co ntinued surveillance of major vector species is recommended.