Comparing functional traits and abundance of invasive versus native woodwasps

Abstract

Functional traits are useful for comparing the resource use of invasive and native species, with goals of identifying resource overlap to predict competitive interactions. The invasion of northeastern North America by the woodwasp Sirex noctilio has resulted in competition with the native congeneric Sirex nigricornis for suppressed and weakened pines. We compared sizes of adults, venom glands, fecundity, tree species use, voltinism and abundance of the invasive woodwasp S. noctilio with the native S. nigricornis in northeastern North American pines. Rearing adults from attacked pines showed that these species used the same tree species but S. noctilio were far more abundant, especially with increasing time since establishment. Adults of the invasive S. noctilio were larger than S. nigricornis, female S. noctilio had larger glands carrying phytotoxic venom in relation to body size, average-sized S. noctilio females carried more eggs, and S. noctilio developed faster than S. nigricornis. Sirex noctilio was the dominant woodwasp infesting suppressed pines in our study areas. We hypothesize that the future abundance of S. nigricornis could depend in part on the availability of wood for oviposition by this native that is not available or acceptable to the earlier-emerging S. noctilio.