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