Seasonal prevalence of the invasive rusty-spotted longhorn beetle, Apriona swainsoni (Coleoptera: Cerambycidae), adults in Fukushima Prefecture, Japan

Invasive longhorn beetles are serious pests of tree stands worldwide. The rusty-spotted longhorn beetle, Apriona swainsoni (Hope) (Coleoptera: Cerambycidae: Lamiinae), is native to continental Asia, where it is a significant pest of legume trees. Its invasion into non-native ranges and damage to the local legume tree, Maackia amurensis, were first reported from Fukushima Prefecture, Japan, in 2021. This study investigated the biology of A. swainsoni in relation to adult emergence in Japan. Preliminary observations confirmed that A. swainsoni larvae create planned emergence holes on the host surface in late May. By exploiting these planned emergence holes, the adult emergence period was investigated in a field promenade of M. amurensis during the summer of 2022 and 2023. The researchers plugged the holes and recorded plug removal, resulting in the observation of 60 and 227 putative emergence events in respective years, with the majority occurring in early to mid-July. Further, during the summer of 2022, a periodic field survey of adult emergence was conducted, obtaining eight adults. Furthermore, a supplementary survey using infested logs maintained in a field cage demonstrated that the emergence period does not differ between sexes and the male-to-female ratio is one:one. Our results suggest that control efforts to suppress A. swainsoni adults in the field, such as insecticide spraying, should be prioritized in the relatively short, peak emergence period. This work indicates that the plug survey is useful for detecting the emergence period.