Resource quality has direct or indirect effects on female oviposition choice, offspring performance, and ultimately on body size and sex ratios. We examined these patterns in Sirex noctilio Fabricus, the globally invasive European pine woodwasp, in South African Pinus patula plantations. We studied how natural variation in biotic and abiotic factors influenced sex-specific density, larval growth rates, and survival. Twenty trees infested trees divided into top, middle, and bottom sections were sampled at three time points during larval developmental. We measured moisture content, bluestain colonization, and co-occurring insect density and counted, measured, and sexed all immature wasps. A subset of larval tunnels was measured to assess compensatory feeding and growth efficiency. Wasp density increased from the bottoms to the tops of trees for both males and females. However, the largest individuals and the longest tunnels were found in bottom sections. Male bias was strong (~10:1) and likewise differed among sections, with the highest proportion in the middle and top sections. Sex ratios became more strongly male biased due to high female mortality, especially in top and middle logs. Biotic and abiotic factors such as colonization by Diplodia sapinea, weevil (Pissodes spp.) density, and wood moisture explained modest residual variation in our primary mixed effects models, generally between 6-12%. These findings contribute to a more comprehensive understanding of sex-specific resource quality for S. noctilio and of how variation in key biotic and abiotic factors can influence body size, sex ratio and survival in this economically important woodwasp.