Hemizygotes have no abnormal visible morphological phenotypes. The accessory glands are normal in morphology and size. Hemizygous males produce abundant, morphologically normal, motile sperm. Eggs fertilised by these sperm survive to adulthood and the number of progeny produced by hemizygous males is proportional to the number of sperm stored by their mates, indicating that the sperm are functional. The time spent in copulation is not significantly different for hemizygous or control males. The males appear to transfer sperm normally to females. At 6 hours after mating, on average 17% as many sperm are stored in the seminal receptacles of females mated to hemizygous males compared to females mated to control males. The few sperm that are present in the seminal receptacles are in disorganised clumps, with the sperm heads in twisted disarray, in contrast to the more parallel arrangement of sperm from control matings. At 6 hours after mating, spermathecae of females mated to hemizygous males contain only 11% as many sperm as those of females mated to control males. Although the primary effect of Acp36DE^N1 appears to be on the number of sperm that are initially stored by females, there is also an effect on the retention of sperm in the seminal receptacle by day 2 after mating. The localisation of sperm in females mated to hemizygous males does not differ from that of females mated to control males. Hemizygous males are not sterile, but their mates produce only 10% as many progeny as females mated to control males. Although the mates of hemizygous males lay nearly normal numbers of eggs on the first day after mating, only 33% of these eggs ultimately give rise to adults, suggesting that the remaining eggs are unfertilised. Very few progeny result from eggs laid 3 or more days after mating, in contrast to mates of control males, where 80% of eggs laid on each of the first through ninth day after mating give rise to adults. The high rate of egg laying seen in the mates of hemizygous males on the first day after mating is not maintained. By the third day after mating, the number of eggs laid by mates of hemizygous males is intermediate between and significantly different from the number laid by mates of controls and that of virgins. On the fourth and subsequent days after mating, the number of eggs laid by mates of hemizygous males is indistinguishable from that of virgins and significantly less the number laid by mates of controls. The mates of hemizygous males remain unreceptive to remating on the first day after mating (as do the mates of control males). The mates of hemizygous males become receptive starting on the second day after mating and remate at frequencies similar to those of virgin females by the third day after mating. There is no significant difference in life span between females mated to hemizygous males and females mated to control males.