Control of the Large Pine Weevil and Bark Beetles of the Genus Hylastes

Abstract

Since 1968 a water-based formulation of gamma BHC (Gammacol) has largely replaced DDT as a plant-dipping treatment against the large pine weevil Hylobius abietis L. and Hylastes spp. beetles. With Sitka spruce in high rainfall areas, BHC at 1⋅6 per cent is as effective as DDT at 2⋅5 per cent in controlling these insects. Neither chemical has proved adequate where exceptionally high populations of Hylobius occurred, though control of Hylastes has been very good. Plants were dipped in Gammacol, and then stored in sealed polythene bags for 28 days. Provided that the plants were dried sufficiently before storing, they subsequently suffered only a slight reduction in height-growth but received adequate protection against beetles. This technique should enable forest nurseries to supply ready-treated planting stock. Chlorpyrifos (Dureban) may prove a useful alternative to BHC.