The question of paternal investment in Lepidoptera: male-contributed proteins in Plodia interpunctella

In Plodia interpunctella, radioactive labelling techniques indicate that male-derived substances, transferred to the female during copulation, enter unfertilized eggs. These substances are proteinaceous and the cumulative amount of material entering the unfertilized eggs increases with time since mating. Following courtship, smaller males complete coupling with females at a lower frequency than larger males. Smaller males also transfer smaller (by weight) ejaculates than larger males. Ejaculate weight is about 4% of male body weight in P. interpunctella. However, neither fecundity nor the number of deposited eggs are a function of ejaculate weight. Consequently, ejaculate materials cannot be designated a form of paternal investment, despite the observed transfer to unfertilized eggs.