Feeding on roots in the humus layer by adult pine weevil, Hylobius abietis

Abstract

Abstract1 The consumption by adult pine weevil, Hylobius abietis, of the bark of roots present in the humus layer was assessed in a field study conducted in southern Sweden during two years (1998 and 2002). The study sites were divided into two areas: (i) a shelterwood where 80–100 mature Scots pine trees per hectare remained after cutting and (ii) a clearcut where no trees were left.2 On average, 3741 m2 per hectare of root bark was present in the humus layer, of which 135 m2 was not coniferous but comprised species such as bilberry and broadleaved trees.3 The mean area debarked by pine weevils was 2.9 m2 per hectare; 2.6 m2 of conifer roots and 0.3 m2 of bilberry roots. Roots of broadleaved trees were almost never consumed. No clear preferences for roots of a specific level of vitality were observed.4 No consistent difference between the shelterwood and clearcut was found, either in the amount of root bark area available or in the extent of root feeding by pine weevil.5 A weak negative correlation between debarked areas on roots and seedlings was found, indicating that root feeding may have reduced damage to seedlings.6 It is concluded that conifer roots in the humus layer constitute a major food source for the pine weevil and can be utilized for a considerable period in both clearcuts and shelterwoods.