Managing Sirex noctilio populations in Patagonia (Argentina): silviculture and biological control

VILLACIDE JOSE; FISCHBEIN DEBORAH.; JOFRE NELIDA; CORLEY JUAN

Annapolis, Maryland, USA

Jornada; 21st US Interagency research forum on invasive species; 2010

Sirex noctilio is primitive wood boring solitary wasp with a univoltine life cycle. Characteristic of this species is the occurrence of severely damaging, pulse-like eruptive population outbreaks. It is during outbreaks, that the damage to pine plantations can be severe; tree mortality may reach levels close to 80%. Outbreak behavior is thus important when the design of management strategies to minimize the impact of woodwasps on the forest resources is developed. Essentially, the aim of any management plan consists in either reducing the intensity of the outbreaks (also minimizing spread) and/or pushing outbreak probability away from the plantation cycle (Corley and Villacide 2005).  In Patagonia (Argentina), as in other Sirex affected regions, remarkable outbreaks have been observed. Based on empirical and simulation modelling studies, silvicultural treatment of plantations including usual thinning practice (removing stressed and/or suppressed trees) and sanitary thinning have resulted in a strong reduction in the intensity of damage and/or its occurrence (Villacide and Corley 2006). In turn, biological control by the nematode Beddingia siricidicola, has reported highly variable parasitism rates, reaching in some sites an 80% (Villacide and Corley 2008). However, these values do not appear to be directly linked to the effective Sirex decrease in tree mortality. A significant Sirex impact has been recorded in Patagonian plantations, even in the presence of high levels of parasitism by the nematode (between 60-80%). Parasitism rates by parasitoids have been reported only for the Ibalia leucospoides. In field conditions, Ibalia may parasitize up to 40% of its hosts. Because of this, I. leucospoides is generally reported as a successful control agent of S. noctilio. Still, some studies suggest that under some environmental conditions its regulatory role is secondary to that of other parasitoids. Because the parasitoids Rhyssa persuasoria and Megarhyssa nortoni have been introduced recently, their contribution in the Sirex control has not been reported yet. Despite this, M. nortoni was found in other sites considerably far from the original release points and can prove a significant contribution to woodwasp mortality in Patagonia (Corley and Bruzzone 2009). We note that among an array of tools used for the management of woodwasp populations, it is via an integrated pest management protocol, with strong involvement of silviculture practices that the best results are likely to be obtained. REFERENCES Corley JC. and JM. Villacide. 2005. Una visión dinámica del manejo de la plaga forestal Sirex noctilio. IDIA XXI 8:136-138. Corley JC and OA Bruzzone. 2009. Prolonged diapause and the success of parasitoids in biological control. Biological Control 51(3) 471-474. Villacide JM and Corley JC. 2006. Control de niveles poblacionales endémicos de la avispa de los pinos Sirex noctilio (Hymenoptera: siricidae) mediante el raleo sanitario de hospederos atacados. RIA-Revista de Investigaciones Agropecuarias 35 (1): 121-134. Villacide JM and Corley JC. 2008. Parasitism and dispersal potential of Sirex noctilio: implications for biological control. Agricultural and Forest Entomology 10: 341-345.