MODELING TOPOCLIMATIC PATTERNS OF EGG MORTALITY OF EPIRRITA-AUTUMNATA(LEPIDOPTERA, GEOMETRIDAE) WITH A GEOGRAPHICAL INFORMATION-SYSTEM - PREDICTIONS FOR CURRENT CLIMATE AND WARMER CLIMATE SCENARIOS

1. Our aim was to quantify the effects of a warmer winter climate on t he egg mortality (and, consequently, the risk of an outbreak) of Epirr ita autumnata, a serious defoliator of mountain birch. 2, The egg surv ival of E. autumnata was studied in northernmost Finland from 1993 to 1996, when minimum temperatures were also recorded. Utilizing a digita l elevation map with a GIS (Geographical Information System), models w ere developed for egg survival and minimum temperature, taking into ac count altitude, local topography and temperatures at a meteorological station-in the study area. 3. Areas of high egg mortality of E. autumn ata can be modelled in the GIS with reasonable accuracy by the model d escribing areal distribution of minimum winter temperatures, taking ac count of the fact that the critical limit for egg survival of E. autum nata in midwinter is about -35.5 degrees C. The approach can be applie d in short-term forecasting of outbreak areas when previous year popul ation densities and minimum winter temperatures at meteorological stat ions are known. 4. In our study area, from 1961 to 1991 more than one- third of the years were egg-killing winters in the mixed birch-pine fo rests zone, and 15% of years in the birch forest zone. In order for an outbreak to take place, at least three consecutive seasons with a hig h population growth rate are needed; in the mixed birch-pine forests t he possibilities of an E. autumnata outbreak during the period 1961-91 were very rare, while in the birch forest zone outbreak possibilities were also noticeably restricted by winter minimum temperatures. 5, If winter warming takes place according to the scenarios presented, by t he middle of the next century the birch-growing areas in our study are a protected by low temperatures from outbreaks of E. autumnata will be only one-third as great as those of today, and by the end of the next century only one-tenth of those of today. 6. The models and methods d escribed in this paper can be applied to other ecological processes. T he modelling strategies and techniques described here serve as interme diate tools for linking large scale climate models (general circulatio n models, GCMs) and ecological processes happening at a smaller scale.