Symbionts mediate oviposition behaviour in invasive and native woodwasps.
Globalization leads to the introduction of invasive species that are often accompanied by associated microorganisms, and this can lead to homogenization of both introduced hosts and microbes with the native biota. One such example is the invasive Eurasian woodwasp Sirex noctilio, which inoculates pines with an obligate nutritional mutualist, the white rot fungus Amylostereum areolatum. Although S. noctilio has been previously introduced outside of its native range, its arrival in North America was the first time that it was introduced to communities hosting native Sirex species and Amylostereum strains. We conducted experiments aiming to investigate acceptance versus avoidance of native and non-native Amylostereum strains and species during ovipositor drilling by females of S. noctilio and a native congener, Sirex nigricornis. Sirex noctilio preferred wood without prior fungal emplacement, whereas S. nigricornis preferred wood inoculated with one of the strains of Amylostereum that putatively invaded with S. noctilio. Drilling and presumed oviposition by both woodwasp species were highly aggregated. Based on the responses of these two Sirex species to the fungal strains and species included in the present study, the invasive S. noctilio would continue its present symbiont associations, whereas the native S. nigricornis would partly use the strain of fungal symbiont putatively introduced with S. noctilio.