Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 8, 2003
Publication Date: April 1, 2004
Citation: Cosse, A.A. 2004. The presence of tibial spurs as a male sexual character for Galerucella calmarienis (Coleoptera: Chrysomelidae). J. Entomol Sci. 39(2):281-283. Interpretive Summary: The leaf beetle, Galerucella calmariensis, is an effective biological control agent of the introduced perennial wetland plant, purple loosestrife (Lythrum salicaria L.). The beetle is native to Europe but has been established in the United States. A pheromone could be a useful tool in monitoring the dispersal of G. calmarienis, especially during the early stages of beetle introductions in unpopulated stands of purple loosestrife. During our investigation into possible pheromone component(s) for G. calmariensis, by chemical and electrophysiological comparisons of male and female emissions, it was imperative to correctly identify and separate the sexes prior to emissions collection. Galerucella calmariensis can be sexed using general guidelines, but this can be time-consuming work and the guidelines are somewhat subjective and not completely reliable. The discovery of male-specific tibial spurs will benefit researchers and land managers involved in biological control of loosestrife by making the sexing of G. calmariensis a simpler and 100% reliable process.
Technical Abstract: Close examination (20-30X) of tibia of Galerucella calmariensis (L.) (Coleoptera: Chrysomelidae) showed that some of these leaf beetles had a single black-colored spur at the distal end of the tibia. These spurs were only observed on the meso- and metatibia and were clearly contrasted against the light brown color of the legs. Those beetles that showed tibial spurs were determined to be all males; those without the spurs were determined to be all female, following dissection and examination of the genitalia. Scanning electron micrographs showed that the male tibial spur can be clearly observed as a curved cone-shaped structure in between the hairs on the apex of the tibia. These striated spurs (ca. 60 micrometers in length) were absent on the female tibia. Sexing 500 beetles using the male-specific tibial spur character resulted in 100% accurate sex determination.