Vibration-mediated territoriality in the warty birch caterpillar Drepana bilineata

The warty birch caterpillar Drepano bilineata produces two distinct types of vibrational signals (mandible drumming and anal scraping) during interactions with conspecifics. Vibrational signalling is characterized using standard and high-speed videography synchronized with laser-doppler vibrometry, and behavioural experiments test the hypothesis that signalling functions to advertise occupancy of birch (Betula) leaves. Drumming involves raising the head and striking the leaf with the sharp edges of the open mandibles. Anal scraping involves dragging a pair of specialized oar-shaped setae against the leaf surface. Staged encounters between leaf residents and conspecific intruders result in the resident signalling, with rates increasing as the intruder moves closer. Intruders signal significantly less often than residents. Conflicts are typically resolved within a few minutes, with the resident winning in 61 % of the trials, and the intruder winning in 6%. Contests that last more than 30 min are deemed 'ties' and comprise the remaining 33% of trials. The results support the hypothesis that vibrational signals function to advertise leaf occupancy. Vibrational communication is believed to be widespread in Drepanoidea caterpillars, but has only been described in two species to date: D. bilineata (present study) and Drepana arcuata. It is proposed that differences in territorial behaviour and signalling between these species are related to their relative investments ill silk leaf mats and shelters. The proximate and ultimate bases for the evolution of vibrational communication in caterpillars are discussed.