Sound production in Scolytidae: Rivalry and premating stridulation of male Douglas-fir beetle

The previously reported attractant chirp of male Dendroctonus pseudotsugae changed to a distinctive long interrupted chirp after several minutes in the female gallery, and the same chirp occurred during fighting with another male. It was experimentally evoked by synthetic 3-methylcyclohex-2-en-1-one and frontalin, both known pheromone components of the male. A different, short, uninterrupted male chirp emitted shortly before copulation, was not evoked by these pheromones. It is suggested that chemostimulus allows or maintains dual contexts for the interrupted chirp. Observation of premating and mating behaviour showed some initial male aggressiveness with the female that subsided as gallery cooperation was established before mating and as the uninterrupted chirp replaced the interrupted chirp.