Rock Microhabitats Provide Suitable Thermal Conditions for Overwintering Insects: A Case Study of the Spongy Moth (Lymantria dispar L.) Population in the Altai Mountains

Abstract

Many insect species overwinter in various rock shelters (cavities and crevices), but the microclimates of rock biotopes remain poorly understood. We investigated the temperature dynamics in rock microhabitats where clusters of egg masses of the wintering spongy moth Lymantria dispar L. (SM) were observed. Our research objective was to find the relation between the ovipositing behaviour of females and the landscape features in different parts of this species’ range. Studies of the ecology of the SM are important from a practical point of view, as the moth causes significant economic damage to forests of the Holarctic. We found that the average monthly temperature of rock surfaces in the studied microhabitats was 2–5 °C above the average air temperature. More importantly, the minimum temperatures in these microhabitats were 4–13 °C higher than the minimum air temperature. These results help to reassess the role of the mountain landscape in the spread of insect species. Rock biotopes provided a significant improvement in the conditions for wintering insects. We believe that, when modelling the spread of invasive species (such as the SM), it is necessary to account for the influence of rock biotopes that may facilitate shifts in the northern boundaries of their range.