Acoustic structures and signals in the larger Mexican pine beetle, Dendroctonus approximatus.

We investigated the relationship between body size, acoustic structures and chirp characteristics in the larger Mexican pine beetle, Dendroctonus approximatus.  Bark beetles use acoustic signals at close range during pair formation, male-male competition and when disturbed.  Dendroctonus spp. produce sound via stridulation, during which the abdomen is scraped across an elytral file.   Acoustic communication in D. approximatus, one of the largest bark beetles in North America, has not been investigated, nor do any studies exist describing the stridulatory structures or signals.  Male and female acoustic signals were recorded in the laboratory in disturbance and mating contexts.  Acoustic structures were imaged and measured using a scanning electron microscope and image processing software.  Acoustic characteristics such as chirp duration, number of pulses per chirp, pulse rate, peak frequency, and median frequency were analyzed with respect to body size and size of acoustic structures.  Males produced short chirps in disturbance and premating contexts, as well as longer multi-component chirps prior to mating.  Multi-component chirps were significantly longer in duration compared to other chirps produced by males.  Females produced chirps in response to disturbance and male stridulations. Female disturbance chirps differed from those given by males in both temporal and spectral characteristics.  Among males, temporal characteristics of chirps were related to features of the acoustic structures.  For chirps given in a disturbance context, the number of pulses scaled positively with the number of ridges in the stridulatory file.  Ultimately, these results will contribute to our broader knowledge of how bark beetles use acoustic communication and be incorporated into a comparative study of bioacoustics across bark beetle species.