Willow sawfly, which can defoliate willow species, was first confirmed in Australia in 2005.
31 October 2008 | Updated 8 February 2013
In 2005 CSIRO Entomology confirmed the establishment of the willow sawfly, Nematus oligospilus (Hymenoptera: Tenthredinidae) on willows (Salix spp.) around Lake Burley Griffin, Canberra, in the Australian Capital Territory (ACT).
They found that this species, previously unknown in Australia, was well established in the ACT and surrounding areas (Queanbeyan, Braidwood and Cooma) of south-east New South Wales (NSW).
There are also reports from the south coast of NSW and the Adelaide Hills of South Australia. It is highly likely that N. oligospilus is, or will become, established in other areas of southern Australia.
Willow sawfly attacks both pest and amenity willows.
It is not known how this insect arrived in Australia but it has not been introduced as part of any official bio-control program for willows.
Anecdotal evidence suggested it had been in the Canberra area since at least the summer of 2003-04.
About willow sawfly
N. oligospilus is of temperate northern hemisphere origin, where it occupies a wide range of latitudes. Recently it has become established in temperate areas of the southern hemisphere (Argentina, Chile, South Africa and New Zealand).
In New Zealand, it was first sighted in 1997 on the North Island between Auckland and Rotorua. By 2004 it had spread throughout both islands.
Sawflies tend to show high host specificity and N. oligospilus is restricted to willows and (so far only in South America) poplars. Willows in New Zealand and Australia are exotic and were originally introduced for soil stabilisation, river erosion control and as shade for stock.
Whilst some, such as Salix babylonica, are still valued for these purposes and for amenity and ornamental use, others, such as Salix nigra and Salix fragilis have spread rapidly and are now considered by many to be serious weeds of riparian environments. It is likely that perception of the arrival of this exotic insect will differ between stakeholder groups.
In their region of origin, outbreaks of these sawflies tend to be short-lived, although repeated total defoliation may slow tree growth and even cause mortality, especially under drought conditions. The severity of outbreaks of this sawfly in Australia, where it probably lacks its natural enemies, is as yet unknown.
However, in New Zealand N. oligospilus has caused severe damage to willow plantings used for river bank stabilisation to a point where authorities are investigating resistant varieties or use of alternative species.
In Canberra, N. oligospilus appears to be continually brooded in summer and resultant heavy infestations are leading to repeated and severe defoliation of both unwanted weed willows and desirable amenity and shade plantings.
CSIRO Entomology is not currently researching willow sawfly. This fact sheet is provided for information only.
State museums and Canberra Connect in the ACT will usually provide identification and advice for the general public.
Read about the Ecology and management of Australian weeds.