A test of sexual dimorphism in deactivating plant defense and attraction of conspecifics in the four-eyed red milkweed beetle (Tetraopes tetrophthalmus)

Abstract

Abstract Herbivorous insects frequently exhibit sexual dimorphism in body size and a variety of other traits. Such differences often lead to distinct behaviors, which may present themselves in insect responses to conspecifics, plant defenses, and feeding. Based on a previous study of a congeneric species, we hypothesized that sexual dimorphism may yield differences in how the host-specific red milkweed beetle Tetraopes tetrophthalmus (Coleoptera: Cerambycidae) deactivates milkweed defenses, a leaf trenching behavior in which beetles cut veins (laticifers) prior to feeding. We also predicted that beetles would display differences in their subsequent feeding patterns and attraction of conspecifics. Although beetles were size dimorphic (females were larger than males), we did not find consistent differences in the rates of trenching or feeding between males and females. Females did, however, cut more milkweed veins and attract more conspecifics than males. Sex differences in size and other traits were thus associated with some differential behaviors, but not strongly associated with the deactivation of plant defense.