Distribution and rapid range expansion of the introduced willow sawfly Nematus oligospilus Forster (Hymenoptera: Tenthredinidae) in Australasia

Abstract

The willow sawfly, Nematus oligospilusFörster (Hymenoptera: Tenthredinidae), has been introduced inadvertently across temperate regions in the Southern Hemisphere, including New Zealand and Australia, where it has dispersed extremely rapidly. A host specialist herbivore, at high population densities it can defoliate and damage introduced willows (Salix spp.), many species of which are invasive weeds in Australasia. In this study, we show that in just 10 years, the distribution of N.oligospilus has expanded across most of south-eastern Australia and south-western Western Australia and, in less than 15 years across both the North and South Islands of New Zealand. The relative population densit..