Estimating the potential geographical range of Sirex noctilio: comparison with an existing model and relationship with field severity

Abstract

The Sirex woodwasp, Sirex noctilio, is a significant pest of exotic stands of Pinus species in the southern hemisphere, and an emerging threat in north-eastern America. The potential global distribution of S. noctilio was assessed using the process-oriented niche modelling software CLIMEX. Model parameters were inferred from S. noctilio’s known native distribution in Eurasia and northern Africa, its exotic range in Brazil, New Zealand and South Africa, and from ecophysiological laboratory observations of both S. noctilio and its symbiotic wood-decay fungus, Amylostereum areolatum. Model predictions were validated using independent distribution data from Australia, New Zealand, South Africa and the Americas. Damage significance and spatial distribution data of S. noctilio infestations in New Zealand were compared with growth and suitability outputs of the model, to explore if the impact of S. noctilio could be related to climate. However, no correlation between modelled climate suitability and field infestation severity were found. The resulting model indicated that S. noctilio is currently occupying a fraction of its potential climatic niche in the regions it has invaded. Taking into account areas where suitable hosts occur, results suggest that S. noctilio could further extend its range into additional plantations in southern Queensland in Australia and central Brazil, and into native and exotic stands of Pinus throughout north-east America. Stands of Pinus that are isolated at present from current S. noctilio infestations, such as those in California, Central America and Western Australia, may also be at risk if control measures are ineffective in preventing its spread. Differences in parameter selection and risk projections of our model and a previously published CLIMEX model of S. noctilio are discussed.