Sexual Dimorphism, Deactivation of Plant Defense, and Attraction of Conspecifics in the Four-Eyed Red Milkweed Beetle (Tetraopes tetrophthalmus)

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 behavior in which beetles cut latex-delivering veins 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 vein cutting or initiation of feeding between males and females. Females did, however, cut more milkweed veins per leaf, and attracted more conspecifics than males. Sex differences in size and other traits were thus associated with differential attraction, but not strongly associated with the overall deactivation of plant defense.