The large pine weevil (Hylobius abietis L.) is a major pest in European and Asian coniferous forests, particularly in managed plantations where clear-felling practices create ideal conditions for its population growth. Traditional management practices involving synthetic insecticides have limited efficacy in terms of reducing pest populations and pose environmental risks. This study evaluated the effectiveness of a wild entomopathogenic fungus (EPF) and the commercial entomopathogenic nematode Steinernema carpocapsae (EPN) as biological control agents (BCAs) against H. abietis in clear-felled spruce plantations in Wales and Scotland. Field trials used a randomised block design with three treatments (EPN full dose, EPF full dose and a combination of EPF+EPN at half doses each) compared to a control. Emergence trapping and destructive sampling were employed to assess treatment efficacy. All treatments significantly reduced weevil emergence, with the mixed treatment showing the greatest impact. Destructive sampling revealed strong associations between treatment type and infection outcomes in H. abietis, with a small but significant relationship between weevil developmental stages and infection types. Importantly, the treatments had no significant impact on the total abundance or taxon richness of non-target invertebrates. These findings suggest that wild EPFs alone and combined with EPNs are effective and environmentally safe alternatives to synthetic insecticides for managing H. abietis populations in managed forests.

The forest regeneration phase in Sweden commonly involves mechanical soil preparation followed by the planting of Scots pine (Pinus sylvestris L.) or Norway spruce (Picea abies (L.) Karst) seedlings. The prepared soil offers planting positions with different properties, including reduced damage by pine weevils (Hylobius abietis L.). Nitrogen fertilization can be applied at the time of planting to aid establishment of the seedlings. In this study, we compared the effects of different planting positions, organic nitrogen fertilization, and different seedling sizes on the early survival and growth of Scots pine and Norway spruce seedlings. The main planting positions were capped mound, hinge, and mineral soil. Seedlings planted close to organic material were categorized as being in low-quality positions, since proximity to organic material increases pine weevil attraction. Higher mortality rates related to pine weevil damage were recorded for the seedlings planted in the low-quality positions, regardless of seedling size or N fertilization. Pine weevil attack rates increased with increasing seedling size. Growth was, in general, lowest in the mineral soil positions. The effect of organic N fertilization on growth was positive for the spruce regardless of the planting position or seedling size, while it depended on the planting position and seedling size for the pine, indicating that the effects of organic N fertilization depend on the seedling species, seedling size, and planting position.