Male guarding behavior of Trypoxylon opacum (Hymenoptera; Crabronidae): an adaptation to maximize its paternity?

Large numbers of male Trypoxylon species guard nests during building and provisioning. This behavior likely serves multiple purposes: the male defends its position from other males; it mates with the resident female; and protects the nest from other species, as well as predators and parasites. Here we describe the behavior of male and female Trypoxylon opacum during their nest building. We show that T. opacum males guard the nest, while females search for trophic resources. In this cooperation, both sexes gain fitness by protecting the nest against natural enemies and ensuring paternity. In this process, some males can occupy a position as satellite males, which may give them the chance to mate. We observed that satellite males also have opportunities to mate and sometimes can also expel parasites. Field-based studies, such as this study, provide an important counterpoint to laboratory experiments. Understanding mate guarding may benefit from an approach that considers the benefits and costs to both sexes, while fully accounting for both conflict and cooperation scenarios. This observation can improve our understanding of how parental care may evolve in Hymenoptera species and how individuals may improve their fitness in different contexts.