Identification and field testing of ester sex pheromone components of the click beetles Dalopius maritimus and Dalopius asellus

The Nearctic click beetles Dalopius maritimus and Dalopius asellus are common on agricultural land in western North America but their sex pheromones were not known. Here we report the identification of the major sex pheromone components of these species. Gas chromatographic-mass spectrometric (GC-MS) analyses of sex pheromone gland extract of female D. maritimus revealed seven compounds of which ( Z,E)- and ( E,E)-farnesyl octanoate were deemed candidate pheromone components based on their terpenoid structure, which is common among click beetle pheromones. In field experiments, traps baited with synthetic ( Z,E)-farnesyl octanoate captured many male D. maritimus, whereas ( E,E)-farnesyl octanoate was neither attractive on its own nor did it enhance the attractiveness of ( Z,E)-farnesyl octanoate, indicating that ( Z,E)-farnesyl octanoate is the major pheromone component of D. maritimus. Gas chromatographic-electroantennographic detection (GC-EAD) analyses of pheromone gland extract of female D. asellus revealed a single compound that elicited responses from male antennae. GC-MS analysis determined that this compound was neryl octanoate, and that the second-most abundant compound in gland extracts was ( E,E)-farnesyl octanoate. In field experiments, traps baited with synthetic neryl octanoate captured many male D. asellus, whereas ( E,E)-farnesyl octanoate—which was tested singly and in binary combination with neryl octanoate—had no pheromonal function. These data indicate that neryl octanoate is the major pheromone component of D. asellus. Our findings add to the knowledge of sexual communication systems in click beetles. Synthetic pheromone lures can now be developed to monitor the abundance of these species on agricultural land.