A comparison of control results for the alien invasive woodwasp, Sirex noctilio, in the southern hemisphere

Abstract

1 Sirex noctilio has resulted in one of the most damaging biological invasions of pine forestry in the southern hemisphere. 2 An intensive, integrated control programme has been developed for this pest and is generally considered very successful. However, a critical comparison of S. noctilio infestations and control efforts throughout the southern hemisphere reveals that control has not been uniformly effective. Of particular concern is the apparently unexplained variability in establishment and success of biological control agents, including various parasitic wasps and the parasitic nematode Deladenus siricidicola . 3 An overlooked aspect in the establishment of the biological control interventions for S. noctilio is the potential influence of genetic bottlenecks on the ability of the agents to adapt to different environments and different populations of S. noctilio . 4 Despite established biological control agents, stress in forests caused by silvicultural practices or the environment will predispose trees to heavy infestation. Unfortunately, improved silvicultural practices are not always economically feasible and environmental changes are often unavoidable. 5 Sirex noctilio continues to pose a serious threat to pine forestry in many areas.Despite extensive earlier research into a single integrated control for S. noctilio , it is important to recognize that such a strategy will probably require significant local adaptation in new areas of infestation and over time.

Anthropogenic effects on interaction outcomes: examples from insect-microbial symbioses in forest and savanna ecosystems

“…This species has rarely been viewed as a serious threat to forests or plantations of pine in its region of origin. In contrast, S. noctilio has caused serious damage to pine plantations in the southern hemisphere where it has been accidentally introduced several times (Neumann and Minko 1981;Haugen 1990;Hurley et al 2007). In the Southern Hemisphere, up to 80% mortality has been recorded in outbreaks in plantations.…”

Lack of fidelity revealed in an insect–fungal mutualism after invasion

“…In the Southern Hemisphere, the invasive wood-boring wasp Sirex noctilio and its obligate nutritional fungal mutualist Amylostereum areolatum is a highly aggressive pest complex infesting and killing healthy plantation pines [4]. In its native range in Eurasia and North Africa, this complex is a secondary pest, infesting dead or dying conifers, primarily in the genus Pinus [5].…”

Performance of Sirex noctilio ’s biocontrol agent Deladenus siricidicola , in known and predicted hosts

“…If the lower survival of D. siricidicola in hybrid taxa is explained by the lower growth of A. areolatum in that taxon as occurred in the laboratory, it is possible that the large variation in parasitism rates reported globally (Hurley et al, 2007Slippers et al, 2012) could be the result of differential fungal growth on different genotypes, phenotypes or chemotypes of trees. Breeding pines for resistance to Sirex has not been a focus of management because of the success of existing management strategies (Slippers et al, 2015), but it is possible that germplasm could be selected that would promote nematode survival.…”

“…Barrett and Golfari) (Pinales: Pinaceae) and their hybrids, are grown in large-scale plantations (Gavran, 2014). No Pinus species are known to be resistant to Sirex, although the level of susceptibility varies between species (Ryan and Hurley, 2012): it is likely that these hybrids will be suitable hosts but uncertain how host characteristics may interact with biological control (Bedding, 2009 The parasitic nematode, Deladenus (=Beddingia) siricidicola Bedding (Tylenchida: Neotylenchidae), is the most effective biological control agent used in S. noctilio management worldwide, but shows very variable and inconsistent parasitism rates within and between regions (Hurley et al, 2007). Mechanisms behind the variation in biological control success using nematodes have not been clearly explained (Hurley et al, 2008;Slippers et al, 2012).…”

“…The freeliving form is thus spread naturally when infected S. noctilio females lay packets of nematodes in place of viable eggs into trees, and operationally by inoculating laboratory-cultured nematodes into felled trees. The success of the biological control program is influenced by interactions between wasp, nematodes and fungal strains (Morris et al, 2012;Slippers et al, 2015), other insects and fungi (Yousuf et al, 2014), climatic conditions (Hurley et al, 2007) and host tree characteristics (Bedding, 2009).…”