Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2006
Publication Date: 1/22/2007
Citation: French, B.W., Hammack, L. 2007. Sexual Dimorphism in Basitarsae of Diabrotica and Cerotoma spp. (Coleoptera: Chrysomelidae). Annals of Entomological Society of America. 100:59-63.
Interpretive Summary: In North America corn rootworms and bean leaf beetles are significant pests of corn and soybeans. Due to their invasiveness into new habitats and adaptability to management practices, there is a renewed interest in their basic biology. For modeling and management purposes, the sex ratio of experimental insects generally needs to be determined. Sex determination is often associated with secondary sexual characteristics, and here we describe sexual differences in the external basitarsal structure of three species of corn rootworm beetles and the bean leaf beetle. The tarsal sexual dimorphism in question comprises the presence in males but not females of hairless patches on the proximal ventral surface of the basitarsus or first tarsomere. This specialization occurs on prothoracic and mesothoracic legs of Diabrotica males but only on the prothoracic legs of the bean leaf beetle. Even in the Diabrotica species examined, however, the patches are somewhat larger on the prothoracic than the mesothoracic legs. We relate this sexual dimorphism in tarsal morphology to mating behavior and the propensity for diabroticite males to retain tarsal contact with the elytra of females during copulation.
Technical Abstract: Sexual dimorphism in basitarsal pad morphology is described for prothoracic and mesothoracic legs of Diabrotica virgifera virgifera LeConte, Diabrotica barberi Smith and Lawrence, and Diabrotica undecimpunctata howardi Barber and for prothoracic legs of Cerotoma trifucata (Forster). On the indicated legs of these diabroticite beetles, the typical structure of the hairy tarsal pads of chrysomelid beetles is replaced proximally on tarsomere one of males by a hairless planar ovoid patch that may facilitate maintenance of the mating posture of males upon the elytra of females. This basitarsal patch proved as reliable as the standard supra-anal plate character for establishing sex of these important crop pests.