Use of an individual-based model to forecast the effect of climate change on the dynamics, abundance and geographical range of the pest slug Deroceras reticulatum in the UK JENNA C. WILLIS *, DAVID A. BOHAN *, YOON H. CHOI w , KELVIN F. CONRAD * and MIKHAIL A. SEMENOV * *Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK, wCentre for Infections, Health Protection Agency, 61 Colindale Avenue, London NW9 5HT, UK Abstract Slugs are serious agricultural pests and their activity is strongly driven by ambient temperature and soil moisture. The strength of this relationship has been shown through the development of a deterministic model, based upon temperature and soil moisture conditions alone, which accurately describes the population dynamics and abundance of Deroceras reticulatum. Because of this strong climatic dependence, slug abundance and dynamics are likely to be affected by climate change. We used a validated individual- based model (IbM) of D. reticulatum, to assess the effects of climate change on the abundance of this species in the UK. Climatic scenarios were based on the UKCIP02 predictions and constructed using the LARS-WG stochastic weather generator. The IbM of slugs predicted population dynamics at three time slices (2020s, 2050s and 2080s), and two scenarios of greenhouse gas emissions. The maximum generation number, the number of population peaks, the number of slug-days in each season, the percentage of years when the population passes over a threshold for damage and the percentage of years in which populations go extinct were investigated. Currently, the south-west of the UK has the best conditions for D. reticulatum to thrive, with the north-east of Scotland having the most adverse. By 2080 under both low- and high-emissions scenarios, the north and west of Scotland will have the most favourable conditions for the survival of this species and the east of the UK and Scotland will have the harshest. By 2080 the climate in the north-west of Scotland will become more like the current climate in south- east England, which explains the shift in the pattern of abundance. The north-west of Scotland will have increased slug damage and south-west England and west-Wales will have decreased slug damage with some changes becoming evident by 2020. Keywords: climate change scenarios, slug population dynamics, stochastic modelling, UKCIP, weather generator Received 24 October 2005; revised version received 19 December 2005; accepted 20 December 2005 Introduction Deroceras reticulatum (Genus Deroceras), the grey field slug, is a major agricultural pest, thriving in the disturbed environments created in agricultural fields (Barker, 1991). D. reticulatum is found across the UK and much of the rest of the world, having been introduced into North America, Peru, Tasmania, New Zealand and Central Asia (Yildirim & Kebapc ¸i, 2004), as it is a highly successful invader. Slugs cause economic damage to crops by eating the shoots and endosperm of germinating seeds, occasion- ally causing whole areas of the field to be resown. This results in the application of d10 million of slug pellets each year in field crops in England and Wales alone (Garthwaite & Thomas, 1996). Slugs can also cause cosmetic damage; the presence of slugs themselves can devalue the crop. Potatoes and winter wheat are Correspondence: Mikhail Semenov, tel. 1 44 1582 763 133 (Ext. 2395), fax 1 44 1582 760 981, e-mail: mikhail.semenov@bbsrc.ac.uk. Global Change Biology (2006) 12, 1643–1657, doi: 10.1111/j.1365-2486.2006.01201.x r 2006 The Authors Journal compilation r 2006 Blackwell Publishing Ltd 1643