The role of host resource dynamics in shaping life-history evolution of pine processionary moths

Synchronization between larval development and peak resource quality drives life-history evolution in forest defoliators from cold-temperate regions but is less considered in other ecosystems, such as those in the Mediterranean region. Studies on Thaumetopoea pityocampa , the main Mediterranean pine defoliator, which typically develops during winter (winter population [WP]), have mostly focused on climate. In the present work, the hypothesis that resource matching drives the evolution of this defoliator was tested, alongside the alternative hypothesis that climatic factors are the primary drivers. Seasonal changes in pine foliage quality and defoliator phenology were examined across WPs and a recently evolved summer population (SP) restricted to a section of an otherwise WP-occupied continuous forest. All studied forests consisted of Pinus pinaster monocultures in coastal Portugal, where P. pinaster is the only host available for T. pityocampa . In WP distribution areas, larval development coincided with increasing foliage nitrogen and declining C:N ratios during autumn and winter. In contrast, the SP forest was characterized by poor winter foliage quality, which did not exceed summer leaf quality. Overall, WP development aligns with Mediterranean pine physiology, and the shift in the life cycle to summer in a region with low winter leaf quality provides some support for the resource-matching hypothesis. The mild climate of central coastal Portugal does not appear to constrain life history in this moth. This work provides evidence that interactions between resource availability and climate may contribute to life-history evolution in this forest defoliator. It illustrates a pathway through which insects can diversify life cycles to optimize resource use.