Host Use Patterns by the European Woodwasp, Sirex noctilio, in Its Native and Invaded Range

Abstract

Accelerating introductions of forest insects challenge decision-makers who might or might not respond with surveillance programs, quarantines, eradication efforts, or biological control programs. Comparing ecological controls on indigenous vs. introduced populations could inform responses to new introductions. We studied the European woodwasp, Sirex noctilio, which is not a pest in its native forests, is a serious invasive pest in the southern hemisphere, and now has an uncertain future in North America after its introduction there. Indigenous populations of S. noctilio (in Galicia, Spain) resembled those in New York in that S. noctilio were largely restricted to suppressed trees that were also dying for other reasons, and still only some dying trees showed evidence of S. noctilio: 20–40% and 35–51% in Galicia and New York, respectively. In both areas, P. sylvestris (native to Europe) was the species most likely to have attacks in non-suppressed trees. P. resinosa, native to North America, does not appear dangerously susceptible to S. noctilio. P. radiata, which sustains high damage in the southern hemisphere, is apparently not innately susceptible because in Galicia it was less often used by native S. noctilio than either native pine (P. pinaster and P. sylvestris). Silvicultural practices in Galicia that maintain basal area at 25–40 m2/ha limit S. noctilio abundance. More than 25 species of other xylophagous insects feed on pine in Galicia, but co-occurrences with S. noctilio were infrequent, so strong interspecific competition seemed unlikely. Evidently, S. noctilio in northeastern North America will be more similar to indigenous populations in Europe, where it is not a pest, than to introduced populations in the southern hemisphere, where it is. However, S. noctilio populations could behave differently when they reach forests of the southeastern U.S., where tree species, soils, climate, ecology, management, and landscape configurations of pine stands are different.

Comparing functional traits and abundance of invasive versus native woodwasps

“…Largely based on the southern hemisphere where many North American pines have been introduced, susceptibility of pine species to S. noctilio varies by tree species (Ryan and Hurley 2012;Nahrung et al 2015). Our result was somewhat unexpected because P. sylvestris is native to Europe, where it is assumed to have coevolved with S. noctilio (Ayres et al 2014). However, we do not know exactly where the genotypes of S. noctilio introduced to New York and Pennsylvania originated and, given the broad native geographic range of S. noctilio, it is possible that these genotypes of this woodwasp did not co-evolve with P. sylvestris (Boissin et al 2012;Bittner et al 2017).…”

“…However, S. nigricornis could have an advantage in situations where pines unacceptable to S. noctilio for some reason could be available for use by S. nigricornis or when pines could become weakened (e.g., by lightning strikes) after the main flight of S. noctilio adults and before or during the S. nigricornis flight time. In addition, the fact that the transient resource of suppressed trees are often patchily distributed (e.g., Ayres et al 2014) could lead to coexistence of these species via differential spatial distribution of use of suppressed pines. Monceau et al (2015) have shown that some degree of niche differentiation between native and invasive hornets can minimize competition.…”

“…Established populations of S. noctilio were first reported in northeastern North America in 2004 (Hoebeke et al 2005) and this invasive now occurs in eight eastern US states (CERIS 2017) and two eastern Canadian provinces (de Groot et al 2006, CFIA 2009 and it is expected to continue to spread. In the southern and northern hemispheres, S. noctilio typically oviposits in suppressed pines (Neumann andMinko 1981, Dodds et al 2010;Ayres et al 2014). However, populations can increase and, especially in overstocked stands and during droughts, S. noctilio can kill pines that are considered healthy (Madden 1988).…”

SirexWoodwasp: A Model for Evolving Management Paradigms of Invasive Forest Pests

“…This also plays an important role in populations in natural woody ecosystems (4,27,37,66,90,106,128).…”

“…A suite of other natural enemies associated with native siricids is also attacking S. noctilio in North America (4,27,37,66,128). Thus, additional biological control, at least given the current distribution of the wasp, seems unnecessary (32).…”