Effect of Timber Condition on Parasitization of Pine Weevil ( Hylobius abietis L.) Larvae by Entomopathogenic Nematodes under Laboratory Conditions

The large pine weevil ( Hylobius abietis L.) is one of the most important pests in coniferous reforestation in Europe. Larvae develop in the stumps of recently felled trees; the emerging adults feed on the bark of seedlings and may kill them. The ability of the entomopathogenic nematodes Heterorhabditis megidis and Steinernema carpocapsae to invade pine weevil larvae in Sitka spruce ( Picea sitchensis ) buried in moist sand was evaluated. Overall, four times as many H. megidis as S. carpocapsae invaded pine weevil larvae. The two species of nematode differed in their response to timber condition. The number of S. carpocapsae invading pine weevil larvae was twice as high in billets inoculated with the wood-rotting fungus Phlebiopsis gigantea as in fresh timber, while the number of H. megidis invading was reduced by 25%. Invasion into non-feeding insects (larvae of the wax moth Galleria mellonella ) contained in timber disks was also affected by timber quality, indicating that nematode behaviour was affected directly by the physical or chemical condition of the timber, though trophically mediated effects may also have been involved