Proceedings Crop Protection in Northern Britain 2014

THE SPREAD AND MOVEMENT OF THE NEW ZEALAND ( TRIANGULATUS) IN SCOTLAND

B Boag and R Neilson The James Hutton Institute, Invergowrie, Dundee, DD2 5DA Email: [email protected]

Summary: It is now over 20 years since the was identified as an alien organism which could potentially have a detrimental impact on Scotland’s soils and wildlife. Since then, over 2000 records have been received by the James Hutton Institute (formally SCRI). These reports strongly suggest it was introduced into Scotland via botanic gardens, then from commercial outlets to domestic households. More recently, it has spread to farmland. The mechanism by which it is spread between domestic gardens is still probably via containerised plants but other potential routes may occasionally occur e.g. on the fur of dogs and cats. In rural areas, have been found attached to silage and hay bales, on the ground sheets of tents and in kick samples from streams. Once established in a field, the New Zealand flatworm has the capacity to migrate up to one metre each day.

INTRODUCTION

The mechanism by which potentially harmful alien species are introduced and spread must be understood if future introductions are to be stopped and the detrimental impacts of those organisms already here are to be minimised or reduced (Manchester & Bullock, 2000). The New Zealand flatworm has possibly been introduced into the British Isles on at least two separate occasions (Dynes et al., 2001). The fact that in Scotland it was first found at Edinburgh Botanic Gardens suggested it could have been introduced when plants were collected in New Zealand. However, Willis & Edwards (1977), Bloch (1992) and Blackshaw & Stewart (1992) suggested it may have come in on ornamental plants. The senior author has found it in a rhododendron nursery on the Banks Peninsula, New Zealand, which exported plants to Scotland. To date, Arthurdendyus triangulatus has only been recorded from agricultural fields in western Scotland.

A retrospective survey, undertaken using a questionnaire, showed that in Scotland, until 1970, the New Zealand flatworm had only been found in botanic gardens and garden centres. From 1971 onwards, it was recorded in domestic gardens and only a decade later, it was found in agricultural land (Boag et al., 1994). Samples and records received by the senior author for the last 22 years have been mainly from domestic gardens and are lodged with NBN (National Biodiversity Network; http://www.nbn.org.uk/; Figure 1).

The rate at which the New Zealand flatworm can move was investigated by Mather & Christensen (1995) who found a maximum rate of 16.9 m h-1 under artificial conditions in the Faroe Islands, while Gibson & Cosens (1998) reported a more realistic maximum rate of 1.8 m

55 d-1 in an allotment in Edinburgh. However these results were not obtained under field conditions and therefore extrapolation of these findings to what happens in farmland in the west of Scotland could be misleading.

The purpose of this paper is to use data collated over 20 years from records sent to the James Hutton Institute to investigate how the New Zealand flatworm had been, and is being, spread and to assess the rate of migration, once it has become established, under field conditions.

MATERIALS AND METHODS

The data used in this paper were mainly obtained from the general public (usually gardeners) contacting the senior author over the last 22 years after they were made aware of the New Zealand flatworm via posters, TV, radio and press interest. A retrospective survey was undertaken in 1992-1993 by sending questionnaires to those who had previously identified and left records with a number of organisations e.g. National Museums of Scotland, BRISC (Biological Recording in Scotland), Edinburgh University etc.

A field experiment on the movement of the New Zealand flatworm was undertaken in 1999 in an uninfested part of a field (which already had a part infested with flatworm) at a farm at Sandbank, near Dunoon on the west coast of Scotland (Ordnance Survey Grid Reference NS 145 819). The experimental design was in the form of a cross. Traps (black polythene bags 600 mm x 300 mm filled with 5 kg of sand) were laid out at distances of 1, 3, 6, 9, 12, 15, 18, 21 and 24 m from the centre in a north, south, east and west directions. After being set out for a month and no flatworm being found associated with these traps, 154 flatworms were released under the central trap on 16th October and their movement to other traps monitored until 7th January. A repeat experiment was undertaken using 231 flatworms starting on May 10th and finishing on 13th June of the following year.

RESULTS

Data collected from the general public

The data from the records sent to the James Hutton Institute (formerly the Scottish Crop Research Institute) were of a similar nature over the 20 year period. Confirmation of the identity of the specimens was a major concern and initially many specimens were sent by post but more recently photos attached to emails are the norm. Misidentifications of specimens sent to the institute included over 100 specimens of horse-leech (probably Haemopis sanguisuga), numerous earthworms and even a slow worm (Anguis fragilis) which had been run over by a car. Accompanying notes submitted with records indicated that the respondents had few earthworms in the soil and enquired as to how to control the flatworms and increase earthworm populations. Records also highlighted unexpected modes of spread e.g. flatworm being found on the fur of cats and dogs, in kick samples from rivers and on the underside of tent ground sheets. In rural areas where agricultural fields are known to be infested with New Zealand flatworms, silage bales and hay bales were found to have the flatworm adhering to them, suggesting it could be spread when these bales are relocated to other fields/farms. The most recent NBN map showing the distribution of the New Zealand flatworm indicates that it has

56 continued to spread in Scotland and now can be found in all the major Hebridean Islands as well as in Orkney and Shetland.

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0 9 0 1 2 3 4 5 6

Figure 1. Distribution of New Zealand flatworm, (Arthurdendyus triangulatus) in the British Isles at 10km grid resolution.

Flatworm migration experiment

The results of the flatworm migration experiment indicated that, under field conditions, the New Zealand flatworms released on 16th October 1999 migrated 24 m in 26 days (0.92 m d-1) while comparable data for those released on 10th May 2000 showed they migrated 24 m in 21 days (1.14 m d-1) (Table 1). Within both experiments the fastest recorded movement of a single flatworm was 15 m in 7 days (2.14 m d-1).

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Table 1. Rate of movement of the New Zealand flatworm, Arthurdendyus triangulatus, in a field in western Scotland, 1999 and 2000.

Oct–Jan 16 22 28 04 11 17 26 06 07 Oct Oct Oct Nov Nov Nov Nov Dec Jan

Max distance 0 9 12 15 24 24 24 24 24 travelled (m)

Mean 0 0.9 1.6 2.9 5.7 4.1 5.3 6.5 4.3 distance travelled (m)

May-June 09 16 22 30 07 13 14 May May May May Jun Jun Jun

Max distance 0 15 18 18 24 24 24 travelled (m)

Mean 0 2.7 4.7 5.9 6.7 8.6 11.1 distance travelled (m)

DISCUSSION

The results from scrutinising 2000 records sent to the institute confirm that the New Zealand flatworm is still mainly a problem confined to domestic gardens. In Scotland, in 1991, 56 of the 217 botanic gardens, nurseries and garden centres (26%) were infested with New Zealand flatworm (Boag et al., 1994). Since then, anecdotal evidence suggests that, as the reputations of these establishments were at stake, the proportion of infested botanic gardens, garden centres and nurseries decreased and the main conduit of spread of the New Zealand flatworm is now via containerised plants being exchanged between neighbours, relatives and friends. However, the number of fields/farms infested in Scotland is probably underreported as farmers are often unaware of the presence of the New Zealand flatworm. In Northern Ireland, a survey undertaken in 1991 found 4% of fields infested but a repeat survey in 1998/1999 found 70 % of the same 60 farms surveyed were infested (Murchie et al., 2003). No comparable follow up, second survey has been undertaken in Scotland.

The results of the flatworm migration experiment indicated that the New Zealand flatworm is relatively mobile and has the potential to colonise fields relatively quickly. The rate of movement recorded after the May release was faster than after the October release. This may have been due to higher temperatures over the spring/summer, which concurs with Yeates et al. (1998) who suggested that the rate of movement was greater with elevated temperatures. Under

58 artificial laboratory conditions, the New Zealand flatworm has been recorded as travelling up to 12 m h-1 (Gibson & Cosens, 1998) and 17m h-1 (Mather & Christensen, 1995). However these data are of theoretical interest only. The rates obtained by Gibson & Cosens (1998) in an Edinburgh allotment varied between 3.9 m d-1 and 0.4 m d-1, which is similar to those recorded during the field experiments, with 0.92 m d-1 and 1.14 m d-1. There is also evidence to suggest that the spread of the New Zealand flatworm within a field may not be uniform. A survey of the distribution of the flatworm in an infested field in the west of Scotland has shown its spread to be patchy (Boag et al., 1999). The reason for this is not clear but may be due to the lack of refugia or the moisture content of the soil (Boag et al., 2005).

ACKNOWLEDGEMENTS

We thank all those who sent in samples/records and Mr. Tom Hill who allowed us to use his land for the migration experiment.

REFERENCES

Blackshaw RP, Stewart VI, 1992. triangulata (Dendy, 1894), a predatory terrestrial and its potential impact on lumbricid earthworms. Agricultural Zoology Reviews 5, 201-209. Bloch D, 1992. A note on the occurrence of land in the Faroe Islands. Frodskaparrit 38, 63-68. Boag B, Deeks L, Neilson R, 2005. A spatio-temporal analysis of a New Zealand flatworm (Arthurdendyus triangulatus) population in western Scotland. Annals of Applied Biology 147, 81-88. Boag B, Jones HD, Neilson R, Santoro G, 1999. Spatial distribution and relationship between the New Zealand flatworm Artioposthia triangulata and earthworms in a grass field in Scotland. Pedobiologia 43, 340-344. Boag B, Palmer LF, Neilson R, Chambers SJ, 1994. Distribution and prevalence of the predatory planarian Artioposthia triangulata (Dendy) (Tricladida: Terricola) in Scotland. Annals of Applied Biology 124,165-171. Dynes C, Flemming CC, Murchie AK, 2001.Genetic variation in native and introduced populations of the “New Zealand flatworm”, Arthurdendyus triangulatus. Annals of Applied Biology 139, 165-174. Gibson PH, Cosens DJ, 1998. Locomotion in the terrestrial planarian Artioposthia triangulata (Dendy). Pedobiologia 42, 241-251. Manchester SJ, Bullock JM, 2000.The impacts of non-native species on UK biodiversity and effectiveness of control. Journal of Applied Biology 37, 845-864. Mather JG, Christensen OM, 1995. Surface movement rates of the “New Zealand flatworm” Artioposthia triangulata: potential for spread by active migration. Annals of Applied Biology 126, 563-570. Murchie AK, Moore JP, Walters KFA, Blackshaw RP, 2003.Invasion of agricultural land by the New Zealand flatworm, Arthurdendyus triangulatus (Dendy). Pedobiologia, 920-923. Willis RJ, Edwards AR, 1977. The occurrence of the land planarian Atioposthia triangulata (Dendy) in Northern Ireland. Irish Naturalists Journal 19, 112-116. Yeates GW, Boag B, Johns PM, 1998. Field and laboratory observations on terrestrial planarians from modified habitats. Pedobiologia 42, 554-662.

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