Update on Leaf-Feeding Willow Sawfly: the Arrival of Nematus Oligospilus in Australia

This document was originally published on the website of the CRC for Australian Weed Management, which was wound up in 2008. To preserve the technical information it contains, the department is republishing this document. Due to limitations in the CRC’s production process, however, its content may not be accessible for all users. Please contact the department’s Weed Management Unit if you require more assistance. factsheet Update on leaf-feeding willow sawfly: the arrival of Nematus oligospilus in Australia Background Impact in the southern hemisphere Willow sawfly In the southern hemisphere countries, Two species of willow sawfly have been the sawfly has caused widespread known from Australia since 1994, the defoliation of willow trees when first willow gall or bean gall sawfly Pontania observed, and spread very fast, proxima, and the willow bud sawfly covering all of New Zealand within ten Amauronematus viduatus, both years. Several species of Salix are accidentally introduced from the attacked, including crack willow, Adult willow sawfly willow sawfly northern hemisphere (Naumann et al. weeping willow, pencil willow and Photo: http://www.hortnet.co.nz/publications/ 2002). golden willow. It seems likely that all guides/willow_sawfly/wsawfly.htm tree willows in the subgenus Salix will Leaf-feeding willow sawfly be attacked but not Populus species. As it is now present in the ACT, The leaf-feeding willow sawfly is a new southern New South Wales and the introduction to Australia, first recorded Arrival in Australia Adelaide hills, eradication is out of the here in 2003 though the identification The introduction of biological control question. It can be expected to turn up has only been confirmed this year. It is agents into Australia is a rigorous and in Victoria and Tasmania fairly soon, also native to the northern hemisphere, lengthy process in place to protect and eventually in Western Australia. where it is found from Ireland through Australia’s unique and valuable continental Europe to the Himalayas, environment and agricultural systems. and also occurs in North America from Impact in Australia However, it is not known how willow Alaska to Mexico. It was first recorded The extent of defoliation in particular sawfly reached Australia, but it is likely in the southern hemisphere in years will probably depend on climatic to have come from New Zealand where Argentina in 1980, in southern Africa conditions. In warm conditions, the it has been widespread in the North in 1993/94 and in New Zealand in sawfly can have up to four generations Island for at least eight years. It may 1997. per season, but may be stressed by dry have come over as pupal cocoons in seasons. There is no information on the willow foliage in cut flowers which Biology sawfly's ability to tolerate high summer were inadequately treated or inspected. temperatures. Climatic predictions Eggs are laid and larvae feed on the Given that cocoons can form in any would require accurate distribution leaves. Pupation takes place in cocoons loose material they may have attached information from the northern on the tree or in the soil under trees. to packaging or other materials. hemisphere, eg the exact localities in Winter is passed as diapausing mature Alternatively it is possible that adults Mexico and the USA where it is found, larvae or pre-pupae in cocoons. The were blown across the Tasman in the with their altitude. southern hemisphere populations easterly wind systems associated with reproduce asexually and males have major cyclonic weather patterns in late However, it is likely that N. oligospilus is never been seen; this promotes rapid summer. a complex of sibling species which may spread and increase of populations. have different climatic tolerances, so Cooperative Research Centre for Australian Weed Management • Fact Sheet any distribution information from the greatest in cool wet summers and least northern hemisphere may not refer to in hot dry summers. Large trees will not the subspecies present in Australia. In be killed but are likely to suffer severe practice, therefore, the northern limits defoliation, which may ultimately kill of this species in Australia cannot be trees if repeated over several years. predicted without laboratory Smaller trees and seedlings may be experiments to determine the upper killed. Larva (15 - 20 mm when fully grown) temperature thresholds of the Photo: D Allan subspecies found here. Impact on willows http://www.hortnet.co.nz/publications/guides/ willow_sawfly/wsawfly.htm Some willows, including crack willows willow sawfly Native parasites and and weeping willows, are serious predators weeds and willows are one of the 20 some districts, it may be necessary to It is also impossible at this stage to Weeds of National Significance or use insecticide treatments to protect predict whether native parasites and WONS. Damage to these will be highly the trees. Any treatments should be predators will transfer over to attack beneficial and will support and assist applied early in the summer as soon as this species. There are very few native the efforts of local government, the first larvae appear (probably Australian species in this sawfly group regional groups, and landcare and October) as treatments are not effective (Tenthridinidae) (Naumann et al. 2002) rivercare groups to control and destroy once heavy defoliation is already so there is probably only a small pool of willow infestations. present. Unfortunately if defoliation parasites available. However, there may occurs every year, annual treatment will However, rapid defoliation of willows in be generalist parasites and predators also be necessary. If this happens, in mid-summer leads to loss of shade and, that will attack this species. If there is the long term land owners might be where willows are the only tree along significant attack, this may limit the advised to replace the willow trees. river banks, may cause increased water populations and, therefore, impact of temperatures in summer. Defoliation the sawfly. will also reduce the effectiveness of Reference It would be useful to start gathering foliar spray herbicide treatments used Naumann ID, Williams MA & Schmidt some information on parasitism and to control willows, though stem S. 2002. Synopsis of the Tenthredinidae predation of the different life stages injection, basal bark and cut stump (Hymenoptera) in Australia, including (egg, larvae and pupae) in the different treatments should not be affected. On two newly recorded, introduced sawfly regions of Australia. the other hand, severe willow species associated with willows (Salix defoliation will also create an spp.). Australian Journal of Entomology opportunity for rivercare groups to Implications for land 41, 1-6. managers gradually replace willows through plantings of native trees under and Pictures and more information are If the New Zealand experience is among the willows. available from HortResearch on repeated here, we can expect severe www.hortnet.co.nz/publications/ Where willows are valued or heritage defoliation of most species of tree guides/willow_sawfly/wsawfly.htm. trees, such as old weeping willows in willows each summer, with effects For further information visit the Weeds CRC’s website: www.weeds.crc.org.au CRC for Australian Weed Management Written by: Dr Rachel Mcfadyen, CEO, Weeds Waite Road, Urrbrae CRC Established and supported PMB 1, Waite Campus Acknowledgements: Photos courtesy of under the Australian Glen Osmond, SA 5064 HortResearch on www.hortnet.co.nz/publications/ Government’s Cooperative T 08 8303 6590 guides/willow_sawfly/wsawfly.htm Research Centres Program F 08 8303 7311 E [email protected] Ref: 40/2005/fs Disclaimer: This publication is provided for the purpose of disseminating information relating to scientific and technical matters. Participating organisations of the Weeds CRC do not accept liability for any loss and/or damage, including financial loss, resulting from the reliance upon any information, advice or recommendations contained in this publication. The contents of this publication should not necessarily be taken to represent the views of the participating organisations. Cooperative Research Centre for Australian Weed Management • Fact Sheet .

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