Economic appraisal of Sirex Wood Wasp (Sirex noctilio) control in Australian pine plantations

Sirex noctilio (Sirex) is an exotic wood wasp and a pest of Pinus that has been in Australia for 65 years. Our study quantified expenditure on Sirex control between 1952 and 2014 through the National Sirex Control program, and costed the impact of three major outbreaks where large-scale tree mortality occurred. We estimate the combined cost of the program and the outbreaks at $34.5 million (net present value using a 1952 baseline and a 5% discount rate). Expenditure on the program was estimated at $24.8 million, while the combined plantation timber losses from the three studied outbreaks — Pittwater, Delatite and the Green Triangle — were valued at $9.7 million. Much higher expenditure values were generated when discounting was limited to the year that the outbreaks commenced. The outbreak at Pittwater, Tasmania commenced in 1952 and had estimated losses of $5.7 million or $5161 ha−1. This outbreak provided the best insight into the potential of Sirex to impact timber values under a 'no control' scenario. The Sirex outbreak in the Green Triangle, which commenced in 1987, was costed at $21.6 million. It was Australia's largest outbreak and occurred at a time when proven control methods were available. Study of the National Sirex Control program highlights the threats that exotic pests pose to Pinus plantations in Australia. Where realised, these threats can translate to major timber loses and costly control programs.