We assessed the effects of chronic defoliation on host plant quality and larval performance of a pine sawfly. Neodiprion autumnalis larvae were reared on ponderosa pine (Pinus ponderosa) that had experienced moderate to severe defoliation (>50%) of mature foliage for at least 15 yr and on trees sustaining no observable defoliation during the same time interval. N. autumnalis performance was 23% (total instar survival) to 12% (potential fecundity) higher on chronically defoliated trees compared with non-defoliated trees. Perennially attacked trees had reduced dry matter (an estimate of total carbon) content of mature needles, higher foliar nitrogen, and a 10% lower carbon/nitrogen balance compared with non-defoliated trees. No differences were detected in foliar toughness. Based on these findings, we maintain that chronic defoliation of evergreen conifers reduces the production of carbon-based secondary compounds in foliage and increases plant nutrition resulting in a positive feedback loop.