Culex vishnui larvae were most common in fallow rice fields, Culex pseudovishnui and Culex tritaeniorhynchus larvae in planted rice fields. Large numbers of C. tritaeniorhynchus were also found in wells, ponds and ditches. In ploughed, flooded fallow fields and in fields with young paddy, C. vishnui larvae were dominant. By the time the paddy reached about .3 m (1 ft) high, C. pseudovishnui and C. tritaeniorhynchus began to replace C. vishnui. No statistically significant differences could be demonstrated between numbers of larvae from the edges of fields and from the interiors, but individual fields showed larvae to be concentrated in the area of the field furthest from water inlets.