An invasive population of Roseau cane scale in the Mississippi River Delta, USA originated from northeastern China

Intense infestations of roseau cane scale, Nipponaclerda biwakoensis, have contributed to widespread dieback of Phragmites australis reeds in the Mississippi River Delta since 2016. In Louisiana, P. australis communities protect the marsh ecosystem from erosion and storm-related impacts, stabilize shipping channels, and shield oil and inland infrastructure. Identifying suitable biological control agents from the source population is key to managing the invasive population of N. biwakoensis and protecting the delicate marsh ecosystem. We used mitochondrial COI sequence data from collections of N. biwakoensis spanning the native and invasive range to identify the origin of the invasive population. Network analysis revealed a rich diversity of 57 unique haplotypes distributed across the native range in East Asia. One haplotype, restricted to northeastern China, is identical to the dominant USA haplotype, indicating that N. biwakoensis was introduced from northeastern China to the United States. In contrast, ecological niche modeling of habitat suitability from across East Asia identified southeastern China as the best location to search for natural enemies to match the climatic conditions in the Mississippi River Delta. These two pieces of evidence provide critical guidance to focus future biological control efforts, and we discuss the importance of examining both genetic and environmental data when searching for potential biological control agents. Additionally, we identified two cryptic species of Nipponaclerda on Phragmites, one in Japan and another in Viet Nam. This research offers new depths of perspective on population structure for a rarely studied group of scale insects, the flat grass scales (Aclerdidae).