Eupyrene sperm migrates to spermatheca after apyrene sperm in the swallowtail butterfly, Papilio xuthus L. (Lepidoptera : Papilionidae)

When swallowtail butterflies, Papilio xuthus, are mated by the hand-pairing method, both types of sperm, eupyrene and apyrene sperm, are transferred f rom the male to the spermatheca via the spermatophore in the bursa copulatr ix. This mechanism is demonstrated by two different kinds of Experiments. T he first set of experiments employed interrupted copulation, and the second set was examination of the Sperm in the spermatophore and spermatheca afte r the termination of copulation. The sperm was transferred 30 min after the start of copulation. The eupyrene sperm was still in the bundle; the numbe r of the bundles ranged from 9 to 108 (mean, 42.7; n = 27). The bundles wer e gradually released alter the completion of copulation, and the free eupyr ene spermatozoa then remained in the spermatophore at least 2 h before migr ating to the spermatheca. On the other hand, about 160 000 apyrene spermato zoa were transferred to the spermatophore and remained there for more than 1 h. We observed 11 000 apyrene spermatozoa in the spermatheca 12 h after t he completion of copulation, but most of this type of sperm disappeared sho rtly thereafter. In contrast, the eupyrene sperm arrived in the spermatheca more than 1 day after the completion of copulation and remained there at l east 1 week. Therefore, these findings suggest that apyrene sperm migrate f rom the spermatophore to the spermatheca earlier than eupyrene sperm. Accor dingly, if females mated multiply. the time difference might avoid the mixi ng of sperm. In addition, the predominance of sperm from the last mating se ssion may occur not in the bursa copulatrix but in the spermatheca.