Minimum Winter Temperature as a Limiting Factor of the Potential Spread of , an Alien Pest of Ash Trees, in Europe.

The emerald ash borer, EAB () is a devastating alien pest of ash trees. It is spreading in European Russia and Ukraine and will appear in other European countries. Our aim was to determine the regions of Europe where the winter temperature drops low enough to prevent establishment. We calculated the minimum daily air temperature from 2003-2019 for each grid square (0.5° × 0.5°) in East Asia, North America and Europe and determined the minimum daily temperature in the grid squares where was recorded. Temperatures of -30 to -33 °C occur in the northern portions of the pest range on all continents. No established population has been recorded in localities where temperatures below -34 °C occur. This temperature is close to the absolute supercooling point of larva (-35.3 °C). It is unlikely that low temperatures could prevent the spread of in northern Western Europe (Sweden, Norway, Finland, etc.), since the temperature in this area did not fall to -34 °C from 2003-2019. However, such temperatures are not rare in eastern European Russia (Kostroma, Vologda, Orenburg regions, etc.), where and occur. These regions could potentially become refuges for these ash species.