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

The recent decline of Phragmites australis stands in the Mississippi River Delta is due, in part, to damage from herbivory by the non-native roseau cane scale, Nipponaclerda biwakoensis. In Louisiana, P. australis communities, known locally as roseau cane, protect the marsh ecosystem from erosion and storm-related impacts, stabilize shipping channels, and shield oil and inland infrastructure. Intense infestations by N. biwakoensis have contributed to widespread dieback of reeds in this region since 2016. 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. Therefore, we used mitochondrial COI sequence data, drawn from collections of N. biwakoensis spanning the native and invasive range, to identify the origin of the established population in Louisiana and Texas. Network analysis using TCS 1.21 revealed a rich diversity of 57 unique COI haplotypes distributed across the native range in East Asia. Relationships among the sampled haplotypes indicate that N. biwakoensis was likely introduced to the United States from northeastern China. Specimens from the USA are nested among a group of haplotypes all originating from China, and the samples belong to a haplotype that was otherwise only collected in Beijing and Hebei. In contrast, modeling of habitat suitability based on host plant records from across East Asia, using MaxEnt 3.4.4, identified southeastern China as the best location to search for potential 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). Together the evaluation of scale insect genetics and ecological niche modeling will optimize foreign exploration efforts for biological control agents.

Automated summary

The damage caused by non-native roseau cane scales has led to the decline of Phragmites australis stands in the Mississippi River Delta. Identifying the origin of the invasive population and finding potential biological control agents through genetic and environmental data is crucial. This research also discovered two cryptic species of scale insects on Phragmites, providing new insights into population structure.