Natural enemy exclusion studies and field surveys of the roseau cane scale (Nipponaclerda biwakoensis) in the native range of Taiwan and adventive Louisiana

Nipponaclerda biwakoensis is an invasive scale found in the Mississippi River Delta (MRD) and parts of southern Louisiana. Its host, the common reed (Phragmites australis), is the dominant vegetation of the MRD providing numerous ecological benefits. Dense infestations of the scale are implicated in the die-back of Phragmites observed since 2016. There are currently three encyrtid parasitoid wasp species found in Louisiana. These parasitoids are the only natural enemies from the native range in Louisiana. Working with collaborators in Taiwan, we collected data on scale population metrics, host plant health, and parasitism rates through field surveys in both the MRD and native range in Taiwan. Following the enemy release hypothesis, we would expect the population density of N. biwakoensis to be higher in Louisiana Phragmites due to the lower numbers of natural enemies present in the MRD. Natural enemy exclusion studies were performed at experimental sites in both countries to test the enemy release hypothesis. Scale infested Phragmites were placed into treatment groups of total natural enemy exclusion, predator exclusion with parasitoid inclusion, or open access for predators and parasitoids. Data presented were collected over two field seasons in 2021 and 2022. Effects of natural enemy exclusion on population dynamics and host plant health were compared within the same site and across countries. Additional range surveys were performed in fall 2021 across the gulf coast and an updated Nipponaclerda invasion range will be presented. Results of the studies will be discussed in the context of scale management in Louisiana.