Native boxwood across Europe has been destroyed by the invasive moth Cydalima perspectalis. To date, climatic conditions and natural enemies have not been able to contain the pests. Increases in temperature due to climate change (CC) may affect insect development and voltinism, with species-specific effects. Its spread across European countries indicates that the expansion of C. perspectalis is not limited by cold winters. However, in southern Europe, rising maximum temperatures can affect pests and their host plants. Despite this, the effects of high temperatures on herbivorous pests have been studied far less extensively than those of low temperatures. Our results show that elevated temperatures accelerate egg development but prolong larval development, reduce adult longevity and fertility, and substantially increase mortality across the egg, larval, and pupal stages. These findings indicate that spring–summer temperatures in the Mediterranean Basin are approaching the upper thermal limits of this species and that further warming is unlikely to facilitate its expansion in this region. Although high temperatures did not reduce diapause induction, they increased larval mortality, and field monitoring showed that altitude, more than thermal time, dominated the patterns of first-flight emergence. Habitat orientation (North or South) may further mediate pest–host coexistence. Overall, this study contributes to the literature by clarifying how this pest responds to the warming conditions associated with CC in southern Europe.
