Antennal Responses to Volatiles Related to Host Location in the Ambrosia Beetle Platypus quercivorus (Murayama)

The ambrosia beetle Platypus quercivorus (Murayama) is a vector of Japanese oak wilt, a fungal pathogen that causes mass mortality of Fagaceae trees. The male locates and lands on the host tree and releases an aggregation pheromone that attracts both males and females. Thus, aggregation pheromones and host tree volatiles are important chemicals for host location. However, the antennal responses to these volatiles have not yet been examined. To obtain physiological property of P. quercivorus antennae, we electrophysiologically recorded the antennal responses of this beetle to candidate volatiles, including isoprene and other leaf volatiles (1-hexanol, 2-ethyl-1-hexanol, trans-2-hexenal, decanal, and benzaldehyde) of the host trees, as well as quercivorol (aggregation pheromone) and ethanol (widely used for trapping this insect in the field). Electroantennograms (EAGs) exhibited clear dose-dependent responses to the tested volatiles, but antennae did not respond to decanal. Sexual differences in responses were not observed for almost all volatiles. However, the EAGs suggested that the quercivorol and trans-2-hexenal sensitivity of males was higher than that of females. Ethanol elicited a large EAG amplitude in both sexes, but the sensitivity of males or females to ethanol was lower than that to the other volatiles. EAGs showed a very weak response to isoprene only in males, although isoprene is considered a possible attractant for host location. Our study will facilitate to understand the mechanism of the host location ecologically and neurophysiologically.