There is a great deal of variation in the location and dimensions of Psorophora columbiae (Dyar and Knab) egg horizons on riceland levees in Texas. This variation appears to b the result of differences in soil moisture content at given points on levee slopes at different times of the year as influenced by irrigation water and rainfall. Data presented herein indicate that virtually any point along a levee slope is subject to having eggs deposited on it provided the soil moisture conditions preferred by Ps. columbiae females are satisfied. The presence of irrigation water and/or heavy rainfall results in eggs being deposited at the higher elevations on the levees and in greatest numbers at locations on the levees that are 0-4 in. (10cm) in vertical elevation above the surface of standing water when it is present in a field. At times when there is no irrigation water or when there is little or no rainfall, the zones of maximum egg deposition for Ps. columbiae tend to be at the lower elevations on levees. For example, the zone of maximum egg deposition on levees in the field used in this study was 0-6 in. (0-15 cm) in elevation above the bottoms of the levees during the year that the field was used as a pasture and not subject to irrigation.
