The Effect of Repeated Matings on Sperm Numbers in Successive Ejaculates of the Cabbage White Butterfly Pieris rapae (Lepidoptera: Pieridae)

The effect of repeated matings on sperm numbers in successive ejaculates of the cabbage white butterfly, Pieris rapae, was examined. First ejaculates were larger than successive ones, which did not differ among themselves. Moreover, the cumulative mass of previous spermatophores was not correlated with that of the last mating. The number of eupyrene sperm bundles in the ejaculate did not differ between first and successive matings. Multiplying by 256, a male transfers about 11,000 eupyrene sperm at every mating. First ejaculates contained about 46,000 apyrene sperm, whereas successive ejaculates contained higher numbers. The sperm density increased after the first mating, though the spermatophore mass decreased. The significance of change in sperm quantity with mating number is discussed from the viewpoint of male investment.