Acoustic signalling in the destructive bark beetle genus Dendroctonus (Curculionidae: Scolytinae) with emphasis on Dendroctonus valens

Acoustic signalling is common in bark beetles (Curculionidae: Scolytinae) but has been underappreciated in the literature, resulting in many unanswered questions regarding their acoustic ecology. The goal of this work was to answer some outstanding questions in the economically important Dendroctonus genus using mainly Dendroctonus valens. Dendroctonus spp. produce complex and variable acoustic signals in many contexts. Addressing the question of why they signal, I found that during courtship the ultimate function of signals was linked to female mate choice. Not only did chirp characteristics correlate with signaller fitness, but females differentiated between and made decisions about potential mates based on chirp variability in courtship song performances. The question of how chirp variability is produced was then addressed. I found the proximate mechanism of chirp production is a form of ‘spring stridulation’, where elastic potential energy is stored as fuel for stridulation. Altering the number of times the energy store was reloaded during a chirp led to the variable pulse pattern of the distinct chirp varieties. Finally, I addressed the question of sexual dimorphism in sound production. I noted that females produced sound in the contexts of disturbance and territoriality and further that they do so by way of an alternative mechanism to that of sound production in males. However, female sounds were erratic and rare, and their presence did not evoke a conclusive behavioural response in conspecifics, leading to an overall lack of support for a communicative function of female sound. My thesis research forms the most comprehensive story of the ultimate and proximate nature of sound production in both sexes of a destructive group of tree-killing bark beetles.