The influence of horn and body size on the reproductive behavior of the horned rainbow scarab beetle Phanaeus difformis (Coleoptera: Scarabaeidae)

The reproductive behavior of horned rainbow scarab beetles, Phanaeus difformis, was studied to determine the influence of morphological traits on intersexual and intrasexual interactions. Phanaeus difformis is a sexually dimorphic dung beetle in which males possess much larger horns than females, and males can be grouped into "major" and "minor" male morph categories based on horn size. Male-female pairs cooperated in nest construction and provisioning. In the laboratory, males of both morphs assisted females and were equally successful at copulating. However, in the field larger individuals had a pairing advantage due to greater success in intrasexual competition. Some males used an alternative mating tactic which involved sneaking copulations with paired females. In most cases the sneak male was smaller than the paired male.