Fed males increase oviposition in female hawkmoths via non-nutritive direct benefits

Direct benefits provided by males have large effects on the fitness of females and their offspring in many species. Here, we examined whether mating or feeding experience of male Carolina sphinx moths, Manduca sexta (Sphingidae), affects the quality of direct benefits that males provide to their mates. We mated virgin females with fed and unfed, virgin and previously mated males. Feeding experience affected male mating success, spermatophore size and flight muscle size. In addition, females mated to fed males laid more eggs than females mated to unfed males, and females mated to virgin males laid more eggs than females mated to previously mated males. Using ¹³C-enriched glucose in the nectar of the fed males, we found that the second and third spermatophores of males were strongly labelled, but this labelled glucose was not present either in the female's fat body or in her eggs. Therefore, although fed males provided females direct benefits from the sugar in the nectar, the sugar was not used as a nutrient by females. We suggest that in short-lived species, where females mate singly and males mate multiply, and where nectar availability is highly variable, males may be selected to conserve their resources to maintain flight capability and to invest in sperm performance and, thus, provide only limited (non-nutritive) direct fitness benefits to their mates.