Maritime pine (Pinus pinaster Ait.) is currently threatened by the scale insect Matsucoccus feytaudi Duc., which feeds exclusively on this species. Some P. pinaster provenances from the western Mediterranean are known to be resistant to M. feytaudi. The primary resistance mechanism is the existence of anatomical defenses (i.e., resin ducts), but the production of these defenses may come at the cost of resource allocation trade-offs with other functions, including growth. We analyzed a multienvironment trial in central Italy including eight representative provenances of P. pinaster. Trees at one trial were severely attacked by M. feytaudi, whereas those at three trials remained insect-free at tree age 20. Genotype × environment interactions for growth and mortality were analyzed using the additive main effects and multiplicative interaction (AMMI) model. Strong correlations were found between AMMI genotypic scores for tree height and diameter and M. feytaudi nymph density at the infested trial site. In particular, provenances exhibiting specific adaptation to near-optimal conditions showed high susceptibility to the insect; conversely, those origins better adapted to poorer conditions were much less affected by the outbreak. This study demonstrates that a potentially adaptive divergence in aboveground growth among P. pinaster provenances is related to resistance to the insect M. feytaudi.