Jones, Peter ORCID: 0000000295669393 and Comfort, Daphne (2019) Elm Trees Under Attack Again. Town And

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of Gloucestershire Research Repository This is a peer-reviewed, final published version of the following document and is licensed under All Rights Reserved license: Jones, Peter ORCID: 0000-0002-9566-9393 and Comfort, Daphne (2019) Elm trees under attack again. Town and Country Planning. pp. 71-74. ISSN 0040-9960 Official URL: https://www.tcpa.org.uk/ EPrint URI: http://eprints.glos.ac.uk/id/eprint/6552 Disclaimer The University of Gloucestershire has obtained warranties from all depositors as to their title in the material deposited and as to their right to deposit such material. The University of Gloucestershire makes no representation or warranties of commercial utility, title, or fitness for a particular purpose or any other warranty, express or implied in respect of any material deposited. The University of Gloucestershire makes no representation that the use of the materials will not infringe any patent, copyright, trademark or other property or proprietary rights. The University of Gloucestershire accepts no liability for any infringement of intellectual property rights in any material deposited but will remove such material from public view pending investigation in the event of an allegation of any such infringement. PLEASE SCROLL DOWN FOR TEXT. elm trees under attack again Peter Jones and Daphne Comfort outline the potential environmental impact of a new threat to elms in Britain, and look at current control treatments English elms in Cuckmere Valley in East Sussex The ConservationThe Foundation From the late 1960s onwards, Dutch elm disease there is no evidence from Europe to date of even spread rapidly within southern Britain,1 devastating severely defoliated elms dying. This article describes the elm population, killing an estimated 20 million the characteristics and breeding cycle of the elm elms by 20102 and leading to dramatic changes in zig-zag sawfly, reports on current control treatments, the appearance of many landscapes. While elms are and reviews its potential environmental impact still an environmentally important species within within Britain. some parts of Britain, half a century later, the elm zig-zag sawfly, first identified in Britain in 2017, Elm zig-zag sawfly poses a new threat to surviving elm populations. The female adult zig-zag sawfly measures The elm zig-zag sawfly is a highly invasive Asian 6-10 millimetres in length and is brownish to black insect which was identified attacking elm trees in in colour, with brownish translucent wings and Poland and Hungary in 2003 and which has since white legs and antennae. No males have ever been spread to 17 countries on mainland Europe. It feeds recorded and the insects reproduce asexually. The on all three species of elm trees commonly found females lay up to 50 eggs, which are light green in Britain – namely, English elms, wych elms and in colour and less than 1 millimetre long, into the small-leaved elms – and large populations of the serrated edges of elm leaves. Within four to eight insect can lead to extensive defoliation. However, days, the larvae hatch and feed on the leaf tissue Town & Country Planning February 2019 71 between the main veins, and in so doing produce throughout the country’. During the last decade, the characteristic zig-zag pattern of feeding damage the insect has been reported in Croatia, Germany, on the leaf. As the larvae become more mature, Slovenia, the Netherlands, Belgium, the Czech they eat almost the entire leaf, thus eliminating the Republic, Latvia, Bulgaria, Switzerland, and Britain. initial zig-zag pattern. The larvae pass through a number of growth Control and management stages and then pupate, building either a loosely Attempts to control, manage and treat the elm spun reticular cocoon on the underside of the leaf zig-zag sawfly face a number of challenges. In or, later in the year, a more substantial cocoon to general terms, even in the event of the identification protect the sawfly during the winter. These latter of the larvae or their characteristic feeding patterns, cocoons are usually found in the leaf litter or in the the quick dispersal of the females makes eradication soil underneath affected elm trees. or containment very difficult. At the same time, The life cycle takes about four weeks, although chemical control by insecticides is likely to be in colder temperatures it can take up to 12 weeks, ineffective in the medium to long term, because and the elm sawfly may be able to complete four treated elm trees may quickly become re-infested generations in a single summer. The short and rapid from untreated trees nearby, thus necessitating succession of life cycles, which also reflects the further treatment. Furthermore, chemical control may elm sawfly’s parthenogenic method of reproduction, have unacceptable impacts on other invertebrate can lead to the large-scale build-up of the insects species that are harmless or even beneficial. and their larvae, which, within a locality where Indeed, the Forestry Commission has suggested significant numbers of elm trees are present, might that ‘chemical control is therefore likely to be limited be seen to amount to an infestation within a year. to the protection of individual elm trees, or groups of elm trees, of aesthetic or cultural importance’.7 The spread of the insect The Forestry Commission suggested a number of A number of vectors seem to be responsible control measures that are likely to be most effective for the spread of the elm zig-zag sawfly. Natural in the management of the problem.7 These measures spread via the flight of the adult females, which are include limiting the movements of elm plants to the reported to have an outstanding flying ability, and minimum number and distance necessary; inspecting passive distribution by the wind are perhaps the elm plants, and any soil and leaf litter with them, principal vectors. Blank et al.3 have estimated a self- before moving them on, and again before planting; dispersal speed of 45-90 kilometres per year. At the destroying elm material arising from tree surgery or same time, long-distance dispersal can be caused felling; and buying British-grown elm plants rather by the adult insects being carried on cars and than risking the introduction of the insects or larvae lorries, as evidenced by the frequent occurrence of by purchasing imported plants. elm zig-zag sawflies along roads and major arterial routes. The long-distance spread of the insects Potential landscape and environmental impacts could also occur in the transport of elm plants for in Britain planting. While heavily infected trees are likely to The presence of the elm zig-zag sawfly in Britain be rejected for sale, where the larvae are in the was confirmed in Britain in 2017, following the growing medium or the leaf litter the spread of the discovery of the larvaes’ distinctive feeding traces insect may occur. near Dorking in Surrey. Since then the insect has Geographically, the elm zig-zag sawfly is native to been reported in a number of locations in the South East Asia and is found on the two largest Japanese East and the East Midlands of England, and there islands of Hokkaido and Honshu and also in Gansu are fears it could spread more widely. Indeed, Province in North West China.4 The insect was the Department for Environment, Food and Rural first recorded in Europe in 2003, in all probability Affairs has claimed that ‘the whole of the UK is having been spread on imported plants for planting. endangered by the pest’,4 and the Forestry The first recorded occurrences in Europe were in Commission has suggested that the insect ‘could Hungary and Holland in 2003, and by 2009 the survive in all parts of the country’.7 insect had been recorded in Romania, Moldova, Despite the devastation of Britain’s elm population Ukraine, Slovakia, Austria, Serbia, and Italy. by Dutch elm disease, elms are still an environmentally In Italy, for example, Zandigiacomo et al.5 reported important species within Britain. Joan Webber, that the elm zig-zag sawfly was observed at five Principal Pathologist for Forest Research, has sites in the Friuli-Venezia Giulia region of North suggested that ‘in Britain we probably have more Eastern Italy and that within a year the insect had elm trees now than we did before the current spread across an area of 1,200 square kilometres epidemic which we think started in the late 1960s’.8 and to the neighbouring Veneto region. From their The vast majority of Britain’s elm population are study in Hungary, Vetek et al.6 reported that ‘the young trees, often found in hedgerows and field pest may be confirmed to be widely distributed margins and sometimes in woodlands. In Wiltshire, 72 Town & Country Planning February 2019 Ptelea/Wikipedia English elm, and leaf damage caused by the elm zig-zag sawfly for example, there are English elms in many how often mass occurrences of the pest occur’, hedgerows, because of their ability to produce and has reported that mass occurrences of the vegetative suckers, while some wych elms are insect can lead to ‘complete defoliation of elms’ and found in mixed broadleaved woodlands. Hedgerows ‘a significant reduction in the aesthetic value of the in parts of Cornwall have elm colonies and some trees’.4 trees are over 10 metres high. More specifically, Zandigiacomo et al.5 reported However, while the vast majority of the mature that a mass occurrence of the elm zig-zag sawfly stately elms that once graced many urban and larvae in Canal de Ferro Valley in Northern Italy rural landscapes have been lost, some pockets of led to the elm trees being ‘severely damaged or resistance remain.

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