Pine or spruce? Comparison of stump suitability for the large pine weevil Hylobius abietis (L.) development

The Norway spruce Picea abies (L.) H.Karst. and Scots pine Pinus sylvestris L. are both species with high economic potential; as a result, they are widely cultivated on plantations. Replanted coniferous seedlings in clearings are threatened by the large pine weevil Hylobius abietis (L.), one of the most prevalent pests in European forests. This weevil develops in fresh conifer stumps, which can be exploited to suppress its population. This study asks whether tree species and stump diameter influence the number of hatched adults, their sex, and their body size. During the two years after the forest was logged, we captured beetles using emergence traps installed on 18 Scots pine and 18 Norway spruce stumps. Generalised linear models used for the data analysis showed that the tree species (pine or spruce) significantly affects the number of beetles and their body mass. The vast majority of beetles left the stumps in the first year after felling. Beetles hatched in spruce stumps were less abundant and had a higher mass and longer devel??? opment time. The sex of the beetles did not depend on either tree species or stump diameter. These results can be explained by the greater attractiveness and higher substrate suitability of pine wood. The increased weevil larvae mortality, as well as the higher body mass and longer devel??? opment of the beetles, could be attributed to the less suitable properties of spruce wood, which is of lower nutritional quality. The lower mass of beetles in pine stumps may also be ascribed to their higher abundance and greater competition for resources. The results of this study did not provide a clear view of the comparative risks of spruce and pine stumps. While more beetles hatch from pine stumps, beetles from spruce stumps are larger, contributing to their higher fitness. Moreover, larger beetles with greater food consumption will likely cause more damage.