Adaptive capacity of Asian populations of Lymantria dispar to non preferred plants during northward expansion.

The spongy moth (Lymantria dispar) is one of the most widespread insect defoliators in the Holarctic, with a capacity to form regular large-scale outbreaks. In the context of global climate change, the geographic range of this species is undergoing a shift that necessitates adaptation to novel host plants, including conifers. The present study assessed the capacity of insects from two L. dispar populations to use pine and larch as hosts, namely Pinus sylvestris and Larix sibirica, as compared to their habitual birch host, Betula pendula. The survival rate of larvae from a Novosibirsk population (south Siberian steppe) was similar on birch and larch, but lower on pine. In contrast, the survival of larvae from an Altai population (south Siberian mountainous landscape) was similar on all three hosts. However, females from both populations exhibited a reduced tendency to oviposit on pine compared to birch and larch, with no discernible differences observed between larch and birch. Hatching success was found to be independent of the host plant. Feeding on pine significantly reduced pupal mass and prolonged larval development compared to birch and larch in both populations. Physiological correlates of adaptation to new host plants were also examined. In 4th instar larvae, alkaline protease activity increased on larch and pine compared to birch but decreased on pine relative to larch, showing no population-specific tendency. Esterase activity exhibited variation exclusively in males, while malondialdehyde accumulation increased for both populations on larch. The findings reported here show that the spongy moth exhibits sufficient physiological adaptability to utilize coniferous hosts, thus highlighting its potential to expand into new ecological niches under changing environmental conditions.