SPERM NUMBERS, THEIR STORAGE AND USAGE IN THE FLY DRYOMYZA-ANILIS

In the fly Dryomyza anilis females have two kinds of sperm storage org ans: one bursa copulatrix and three spermathecae (two spermathecae wit h a common duct form the doublet, and the third is a singlet spermathe cal unit). At the beginning of a mating the male deposits his sperm in the bursa copulatrix. After sperm transfer the male taps the female's abdomen with his claspers. This behaviour has been shown to increase the male's fertilization success. After mating, the female discharges large quantities of sperm before oviposition. To find out where the sp erm remaining in the female are stored, I counted the number of sperm in the droplet and in the female's sperm storage organs after differen t types of mating. I carried out three mating experiments. In experime nt 1, virgin females were mated with one male and the matings were int errupted either immediately after sperm transfer or after several tapp ing sequences. The results show that during male tapping more sperm mo ved into the singlet spermatheca. In addition, the total number of spe rm correlated with sperm numbers in all sperm storage organs, and male size was positively related to the number of sperm remaining in the b ursa. In experiment 2, females mated with several males. The number of sperm increased with increasing number of matings only in the doublet spermatheca. No increase in the number of sperm in the singlet sperma theca during consecutive matings suggests that sperm were replaced or did not reach this sperm storage organ. In experiment 3, virgin female s were mated with a single male and half of them were allowed to lay e ggs. The experiment showed that during egglaying, females primarily us ed sperm from their singlet spermatheca. The results from the three ex periments suggest that sperm stored in the singlet spermatheca is cent ral for male fertilization success and male tapping is related to sper m storage in the singlet spermatheca. The different female's sperm sto rage organs in D. anilis may have separate functions during sperm stor age as well as during sperm usage.