Virgin females of Glossina morsitans Westw. derived from pupae collected on the field were exposed in the laboratory to virgin sterile males and later to virgin normal males; the resulting productivity was an indication of multiple mating by females. Females inseminated once with sterile sperm and then held for 0, 24 or 96 hr. before being allowed to mate with fertile males produced about equal numbers of progeny 29–56 days later; however, subequal numbers of progeny were produced the first 28 days after the initial mating because of the relationship between the time of the second insemination and ovulation. Females given the opportunity to mate repeatedly for 96 hours with their first mates also mated again with new groups of males, but the incidence of this second mating was lower. Thus, multiple mating of females in the laboratory is established, but its frequency in nature is unkown.

When groups of males were exposed to successive new groups of virgin females, the minimum mean number of females inseminated per male renged from 4.9 to 5.6. However, the later inseminations were progressively less effective, and once the complement of sperm of an individual male was depleted, fertility was not recovered. The multiple mating of male and female G. morsitans is not expected to affect the use of sterile males for population control.