Intrinsic competition between parasitoid wasps of the roseau cane scale (Nipponaclerda biwakoensis) during multiparasitism events

Roseau cane scale, Nipponaclerda biwakoensis, is an invasive species from East Asia currently damaging stands of roseau cane, Phragmites australis, in the Mississippi River delta of Louisiana. Management relies on biological control by four species of parasitoid wasp that arrived fortuitously from the native range: Boucekiella depressa, Neastymachus japonicus, Astymachus lasallei, and an undescribed species of Aprostocetus. Multiparasitism is a frequent occurrence within the system, with every combination of species having been successfully reared from parasitized scale. During multiparasitism, larvae of two or more species must compete for food and space with mortality being a known occurrence within the host. A system of superior and inferior competitors likely exists between the species of the parasitoid complex. The research discussed utilizes PCR with species-specific primers as a forensic tool to identify the parasitoid wasp species that were present within a host mummy. Upon emergence, adults parasitoids were identified and DNA from the leftover mummy was extracted. Detection of DNA not of the emerging species, indicates that the additional species did not survive the multiparasitism event. For each species pair, the frequency at which that species successfully reaches adulthood can be used to generate a dominance hierarchy within the parasitoid complex. Understanding how intrinsic competition works informs the mechanisms at work during biocontrol of RCS and potential avenues for improving management.