Presence of native and introduced hyperparasitoids raises concerns for the biocontrol of the planthopper Metcalfa pruinosa in Europe

Metcalfa pruinosa (Hemiptera, Flatidae) is a Nearctic planthopper that has become an invasive pest in Europe since the late 1970s. It is highly polyphagous, and causes significant damage through sap-sucking, honeydew excretion, and the developmentof sooty mould. To counter its spread, the Nearctic parasitoid Neodryinus typhlocybae (Hymenoptera, Dryinidae) was introduced as a biological control agent. In this two-year study, the mortality of N. typhlocybae cocoons, was investigated. Analysis of over 4800 cocoons collected from 14 sites in northeastern Italy (the area of the parasitoid’s first introduction in Europe) revealed a high cumulative mortality (>70 %), primarily due to predation and hyperparasitism. Nine hyperparasitoid species were identified, with the native Pachyneuron muscarum and the Nearctic Cheiloneurus swezeyi emerging as dominant species. C. swezeyi, reported for the first time in Europe, is known as the primary antagonist of N. typhlocybae in its country of origin. Our study demonstrated a close synchronization with the life cycle of the primary parasitoid and molecular analyses revealed five haplotypes. Emergence patterns highlighted different life strategies between C. swezeyi and P. muscarum, suggesting potential ecological niche partitioning. The specificity of C. swezeyi raises concerns about the long-term efficacy of N. typhlocybae as a biological control agent of M. pruinosa. These findings un derscore the complexity of multitrophic interactions in biological control systems and the need for a continuous monitoring of hyperparasitoid communities to assess their impact on M. pruinosa control. Further research is necessary to determine the extent of C. swezeyi distribution across Europe.