Identification of a hyperactive pheromone analog in field tests of pheromone mimics for two click beetle species in the genus Cardiophorus (Coleoptera: Elateridae)

Females of two click beetle species, Cardiophorus tenebrosus and C. edwardsi (Coleoptera: Elateridae), produce methyl (3R,6E)-2,3-dihydrofarnesoate as their sex pheromone. We had serendipitously discovered that males of both species were also strongly attracted to (R)-fuscumol acetate ((E)-6,10-dimethylundeca-5,9-dien-2-yl acetate), a known longhorned beetle (Coleoptera: Cerambycidae) pheromone, due to its structural similarities to the click beetle pheromone. To further investigate the specificity of the responses of Cardiophorus males, additional analogs with different chain lengths and structural relationships compared to the natural pheromone were synthesized and tested. In field and electroantennogram bioassays, only fuscumol propionate ((E)-6,10-dimethylundeca-5,9-dien-2-yl propionate) elicited strong responses from Cardiophorus males, indicating that they were able to distinguish chain length and spatial relationships between the structural elements. In field trials, C. tenebrosus males were attracted equally to the analog and their natural pheromone, but the pheromone elicited stronger antennal responses from males. In contrast, traps baited with fuscumol propionate caught approximately 26 times as many C. edwardsi males compared to traps baited with the natural pheromone, although the analog elicited significantly smaller antennal responses from C. edwardsi males. Thus, in terms of behavioral responses, fuscumol propionate appears to be acting as a hyperactive pheromone mimic, a phenomenon which has rarely been observed in insect semiochemistry.