Pine wilt disease is an increasing threat to pine forests, particularly under climate change scenarios, where water stress and rising temperatures may increase tree susceptibility to infection by plant-parasitic nematodes. This study evaluates and compares the pathogenicity of the pinewood nematode, Bursaphelenchus xylophilus, and the closely related, generally considered non-pathogenic B. mucronatus in Pinus pinaster and P. pinea under different temperature and water regimes. Two- to three-year-old seedlings of both pine species were inoculated with 3,000 nematodes (B. xylophilus or B. mucronatus) and maintained at two temperatures (25°C or 30°C) and two water regimes (water-stressed or well-watered). Disease symptom progression was monitored for 40 days, and soil water content was recorded throughout the assay. At the end of the experiment, nematodes were extracted from aerial parts and roots and quantified per gram of dry wood. The results showed a clear host-dependent response. Pinus pinea remained symptomless throughout the assay, with low nematode recovery for both nematode species. In contrast, P. pinaster was highly susceptible to B. xylophilus, with symptoms appearing a few days after inoculation and high nematode numbers recovered. Importantly, B. mucronatus also caused symptoms in P. pinaster at 30°C under water-stressed conditions, accompanied by nematode recovery at the end of the assay, indicating that environmental stress can substantially increase its pathogenic impact. These findings highlight the importance of temperature and water availability in modulating nematode pathogenicity and host response. They also suggest that B. mucronatus, despite being generally regarded as a non-pathogenic or weak pathogen, may pose a significant risk for pine forests under climate change conditions. Based on these findings, advanced differential and targeted proteomic analyses are being conducted on Pinus spp. tissues. This will allow the characterisation of the biological functions of differentially expressed proteins under climate change scenarios and identify key biomarkers linked to nematode infection. Research funded by FEDER-Portugal2020, COMPETE2020; FCT projects (PTDC/ASP-SIL/3142/2020; UIDB/04004/2025; UIDB/04539/2020; LA/P/0092/2020); Instituto do Ambiente Tecnologia e Vida. Hugo Silva funded by FCT (PhD Grant-2023.03527.BD-https://doi.org/10.54499/2023.03527.BD).