Feeding in the Crowns of Scots Pine Trees by the Pine Weevil Hylobius abietis
Hylobius abietis (L.) (Coleoptera:Curculionidae) is the major insect pest of forest regeneration in Europe, where adult weevils kill conifer seedlings by feeding on the bark. This study demonstrates that pine weevils also feed extensively in the crowns of mature coniferous trees. Crown feeding primarily took place during a limited period immediately after the migration to new breeding sites (roots of freshly cut coniferous trees). The weevils reached the crowns mainly by flight and tended to concentrate on trees in freshly cut-over areas. The proportion of sexually mature females successively increased during the crown-feeding period, indicating that they require a certain period of maturation feeding. The pine weevils fed on twigs of 3–20 mm thickness, and they consumed about 0.2–0.3% (200 cm2) of the total bark surface in the crowns of mature Scots pine trees. Calculations suggested that the amount of food consumed in the trees surrounding a fresh clear-cutting should have met the nutrient requirements of the weevil population in the area during the maturation feeding period. In the crowns of shelterwood trees, about 50 cm2 of the bark was consumed per tree (0.63 m2 ha-1). This level of consumption is not believed to be high enough to relieve the feeding pressure on seedlings and thereby explain the low level of damage usually found under shelterwoods.