By sampling a total of 6 rice fields and 5 fallow fields (approximately 15 sample dates each) during the 1977 rice season species and population density of mosquitoes that breed in the riceland agroecosystem of Louisiana were determined. Six species were collected from producing rice fields. Three species, Psorophora columbiae (Dyar and Knab). Anopheles crucians Wiedemann, and Uranotaenia sapphirina (Osten-Sacken), were collected in all 3 rice producing regions of the state. Larvae of Culex erraticus (Dyar and Knab) were collected from the producing rice fields in the northern and middle producing regions, while larvae of Cx. salinarius Coquillett were collected from rice fields in the middle and southern regions of the state. Larvae of An. quadrimaculatus Say were collected in the northern and southern regions. In the southern region An. crucians, Ur. sapphirina, and An. quadrimaculatus were the predominant species collected during the rice production season. In the middle region of the state. An. crucians was the predominant species collected, while in the northern region, Cx. erraticus and An. crucians predominated. In post harvest fields flooded by rainfall in the southern region, Cx. salinarius increased by 99.7% over the mean number/dip collected during the rice producing season. Floodwater fluctuation caused soil exposure along levees and in areas having higher elevation in the fields thus producing egg deposition habitats for Ps. columbiae. Due to this fluctuation, population of Ps. columbiae were produced in all 3 regions during the rice producing season. Ps. columbiae and An. crucians were significantly correlated (P<0.05) and highly significantly correlated (P<0.01), respectively, to both soil and water temperatures. Cx. erraticus were significantly (P<0.01) correlated to water salinity. The data indicated that as plant density increased in the fields the larval An. quadrimaculatus populations decreased. Four floodwater mosquito species were collected from the 5 fallow rice fields sampled. Larvae of Aedes sollicitans (Walker) were collected from the southern region only, while larvae of Ps. discolor (Coquillett) were collected from the middle region only. Larvae of Ps. ciliata (Fabricius) and Ps. columbiae were collected from fallow rice fields in all rice producing areas of the state. Eggs of Ps. columbiae were the most abundant and adult females showed a significant oviposition preference (P<0.01) for cattle hoof prints while adult female Ae. sollicitans showed a significant preference (P <0.01) for flat pans (areas between the levees). The relative abundance of Ps. columbiae eggs was significantly correlated (P <0.05) to rainfall (r = 0.5247.