POSSIBLE CULEX-PIPIENS PALLENS CONTROL BY IMPROVEMENT OF FLOW-RATES IN WATER CHANNELS OF SAGA CITY, SOUTHWEST JAPAN

Water levels and flow rates (no. censuses with flow/no. censuses per y ear) were analyzed for 208 mosquito-productive and 422 mosquito-free c hannel segments during 1986-88 in Saga City, southwest Japan. Mean wat er levels tended to be higher at mosquito-free segments than at mosqui to-productive segments, but the differences were <5 cm and usually not significant. Flow rates exceeded 80% at 60-67% of mosquito-free segme nts. In contrast, flow rates were <20% at 49-62% of mosquito-productiv e segments. Expected flow speeds at cement-lined segments exceeded 20 cm/sec (a flow speed required for mosquito control) for water levels o f >15 cm. Most mosquito-productive segments had mean water levels of > 15 cm, indicating that water stagnancy at those segments was due not t o low water levels but to their structure. Engineering is necessary to yield flow speeds high enough to prevent mosquito breeding at mosquit o-productive segments. Alternatively, engineering to prevent wastewate r discharge into open channels may improve water quality, leading to m osquito suppression through colonization of larvivorous predators.