Male insemination capacity and the incidence of multiple insemination was studied using a wild-type, laboratory strain and a recessive eye color mutant of Cx. tritaeniorhynchus. Sexually mature, wild-type males inseminated an average of 5.1 mature females during a 4-day test period with most inseminations occurring the 2nd night. Multiple insemination was detected in 8 of 389 fertile egg rafts and occurred most frequently in small cages having high pair densities. No preferential mating was observed among the mutant males and females, and progressively more wild-type matings occurred at lower pair densities and in larger cages.