João Campôa

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.

Forest decline is a complex phenomenon; however, there is often a tendency to oversimplify by attributing it to a single cause, neglecting the interaction of multiple factors. Ever since the detection of the pinewood nematode (PWN), Bursaphelenchus xylophilus , in Portugal (and in Europe) over two decades ago, pine wilt cases in the country have been primarily attributed to this pathogen, leading authorities to enforce strict containment and control measures. Other contributing factors are generally overlooked, with the system being easily overwhelmed by disturbances such as droughts and fires. In this study, a physiographic approach was used to assess multiple factors potentially affecting tree wilting, including environmental parameters in the landscape, alongside other biological agents, and infestation by the PWN. The study area is a highly managed production forest where control measures have been implemented since the detection of PWN in the 1990´s. Pine decline was found to be aggregated in the landscape, with topographic parameters associated with water availability playing a significant role. Wilting trees were affected by multiple biological agents, even though the density of PWN was positively correlated with the decline. However, B. xylophilus was also found to be present in asymptomatic hosts, suggesting an ability to persist for some time in healthy trees within the forest. This research illustrates the multifaceted nature of pine forest decline and the limitations of managing it as originating from a single cause. A critical overview of current PWN management measures is provided, along with proposals for a more heuristic and holistic approach.