Mass emergence of a specialist sawfly species on unpalatable herbs under severe feeding pressure by sika deer

摘要

In recent years, the increase in sika deer populations has had a significant impact on forest ecosystems. Many studies have reported that this increase has led to the dominance of plants unpalatable to the deer; however, few studies have investigated the effects of this dominance on the specialist sawfly species that feed on the unpalatable plants. We observed the mass emergence of Aglaostigma amoorensis (Hymenoptera: Tenthredinidae), a rare specialist sawfly of the false helleborine Veratrum plants unpalatable to sika deer, in areas under severe feeding pressure by sika deer. An exponential increase in the number of emergent A.amoorensis adults was observed to occur with an increase in Veratrum album patch sizes. In addition, the increase in the A.amoorensis density had a negative effect on reproductive success of V.album. Our findings suggest that the relative abundance of specialist sawfly to the host-plant abundance has changed for successive years after sika deer irruption.