Chemical-Mediated Mate Attraction in Clover Root Curculio (<i>Sitona hispidulus</i> F.), A Belowground Pest of Forage Crops

Curculionid beetles are well known for their production of semiochemicals, including contact (e.g. cuticular hydrocarbons) and volatile pheromones that mediate conspecific attraction and mating. Clover root curculio (CRC; Sitona hispidulus) in particular is an emergent, soil-borne pest of significant concern to producers of alfalfa and other leguminous crops in the United States. Producers have few control options for CRC and a greater understanding of chemical-mediated attraction in this species can potentially improve the sustainability of its management. To examine which chemical cues are important for affecting the behavior of CRC and whether there are sex-based differences in response, I performed behavioral assays using an olfactometer (i.e., Y-tube). This effort was complemented with solvent-based extractions of cuticular hydrocarbons and analysis via Gas Chromatograph Mass Spectrometer (GC-MS) to characterize contact chemicals that can also contribute to conspecific recognition and attraction. Olfactometer assays suggest that CRC most likely has a male-produced, volatile aggregation pheromone, as females exhibited a strong preference for male odors. In contrast, our cuticular hydrocarbon data suggest a lack of sex differences in their epicuticular wax layer. Knowledge of chemicals involved in mediation of Curculionidae mating interactions is essential for the development of ecologically sound strategies for the control of below-ground pests. Once semiochemicals are identified and behaviors observed, we can use this knowledge to develop a cost-effective detection method, such as semiochemical-baited traps. These traps could alert growers of the presence of CRC in their fields, disrupt mating, as well as draw some away from their crops.