Species-specific PCR primers provide insights into spatial distributions and interspecific interactions of Roseau cane scale parasitoids in Louisiana

The roseau cane scale (RCS), Nipponaclerda biwakoensis (Hemiptera: Aclerdidae), is a pest of Phragmites australis (Poales: Poaceae) in the Mississippi River Delta. Three encyrtid (Hymenoptera) species, Neastymachus japonicus, Astymachus lasallei, and Boucekiella depressa, have been observed parasitising RCS across southeastern Louisiana; however, little is known about their potential as biological control agents. The use of species-specific primers presents a tool for rapid and accurate assessment of parasitism. The objectives of this study were to (1) sequence candidate gene regions of the three encyrtid parasitoid species and develop species-specific PCR primers for multiplex PCR; (2) compare the detection of the three encyrtid parasitoid species using multiplex primers with detection via rearing and morphological characters; and (3) use these tools to describe patterns in parasitism by these encyrtids along RCS-infested stems. Species-specific PCR primers were developed from sequences of the D2 region of nuclear ribosomal RNA. We compared the PCR-based detection method with rearing and morphological identification. The multiplex PCR assay increased the detection of encyrtid wasps 2.2-times over detections of emergent adults. Among the three wasp species, B. depressa and A. lasallei were more frequently detected in RCS at the bottom 50 cm of stems as emergent adults, but this was not observed in the PCR assay. Based on these results, we confirmed that PCR-based detection is more rapid and sensitive than traditional rearing and identification. Due to their abundance in Louisiana, the impact on scale populations by local parasitoids must be considered for any future biological control programme of RCS.