The fecundity, insemination status, oviposition rate and fertility of females from crosses with laboratory colony and/or field-collected populations of Culex tarsalis were determined. The insemination rate was highest for inbred laboratory females (96%), less for laboratory females outcrossed to field-collected males (78%), still less for field-collected females outcrossed to laboratory males (47%), and least for inbred field-collected females (28%). The oviposition rate for inseminated field-collected females was 73% compared with 98% for laboratory females. While 77% of the eggs developed in ovaries of inbred laboratory females hatched. Intermediate percentages of developed eggs hatched in the 2 types of outcrossed females.