Spermatophore size and multiple mating: Effects on reproductive success and post-mating behaviour in the Indian meal moth

Ensuring fatherhood is an important issue in polygamous species. In many le pidopteran species, the male inserts a large package (spermatophore) consis ting of sperm, accessory gland fluids and nutrients into the female's bursa copulatrix during copulation. In most species it has been shown that a lar ge mate donation causes females either to stop calling, or to prolong the t ime until re-mating, hereby ensuring fatherhood. We investigated the change s in size of the donation in multiple mating and how the size affected the female post mating behaviour in the Indian meal moth, Plodia interpunctella . In concordance with other previous studies, we found that a male inserted a significantly larger donation during the first mating compared to follow ing mating occasions. The larger donation was not coupled with larval outpu t since it did not decline during mating occasions. Some males were able to mate at least eight times and male fitness, counted as larval output, show ed no association with sequence of mating number. Even though females recei ved larger donations during the first mating, there was no effect on female post mating behaviour in terms of pheromone production and calling behavio ur. The weight of the mated female's bursa copulatrix decreased linearly ov er the first eight days after mating, suggesting that females absorb materi al other than sperm. We discuss the female advantage of receiving a large d onation and why males invest more energy into the first mating while female post-mating behaviour is not affected.