1. It has been predicted that temperature increases of 3.6–5.8 ∘C would shift
the northern distribution limit of Lymantria monacha (Linnaeus) and Lymantria dispar
(Linnaeus) by 500–700 km, but these predictions ignore the effects of minimum winter
temperatures. It was hypothesised that winter cold can limit range expansion due to high
egg mortality in cold temperatures.
2. The present study determined the supercooling points of overwintering eggs of these
forest pests, and compared these with recent minimum winter temperatures in the areas
of origin of three populations. Eggs from one L. monacha and one L. dispar population
from the species’ core distribution area inGermany were included, as well as L. monacha
eggs from Finland, near the northern border of the species’ distribution.
3. The median supercooling points of both species were more than 10 ∘C lower than
the median minimum winter temperatures of their areas of origin, and the median
supercooling points of Finnish and German L. monacha eggs did not differ significantly.
The median supercooling point of German L. monacha eggs differed from that of
German L. dispar eggs.
4. Previous literature on the topic is referenced, and translations of the old German
and Russian sources are given. Based on these results, it is argued that the frequent claim
that L. monacha eggs can survive cold down to −40 ∘C is unsupported, with a value near
−30 ∘C being a more likely limit.
5.Winter cold alone can limit the predicted range shifts of these species to 200–300 km
under 3.6–5.8 ∘C increase scenarios, which is less than half the value of earlier estimates.