Feeding behaviour in Australian gregarious Lophyrotoma sawflies (Hymenoptera: Pergidae)

Details of feeding behaviour of Australian sawfly species on eucalypt hosts are not well known. In this study, we report new findings on two pergid sawflies, Lophyrotoma interrupta and an unidentified species of Lophyrotoma, after observing larvae feed. We confirmed both daily and nightly feeding regimes, with L. interrupta and Lophyrotoma sp. engaged in feeding-related activities 92.2% and 67.0% of the time, respectively. A colony sometimes splits into subcolonies as a leaf depletes; individuals leave singly and explore surrounding leaves before joining the rest of the colony feeding on the new leaf. As a specific feeding behaviour, the larvae of both species cut midveins on surrounding leaves in one of several ways before and during feeding. Larvae used pre-processed cut leaves at a ratio ranging from 0.64 to 0.88 of the whole leaves eaten. Of the leaves cut prior to feeding, approximately half were not consumed, whereas the remaining were consumed 2 days after cutting (median time). We observed a decreasing trend of further cuttings when the proportion of damaged leaves in the surrounding area was increased. Feeding of Lophyrotoma sp. followed a clear pattern: Usually, the last individual remaining on the leaf severed the leaf petiole as it left. This petiole snipping occurred in over half the leaves that larvae had used; however, this behaviour was not observed in L. interrupta.