THE ROLE OF MICRO ARTHROPODS IN THE DEFACEMENT OF SAWN LUMBER BY SAP STAIN AND MOLD FUNGI

Fungal sap stain, mould, and basidiomycete defacement of boards sawn f rom the sapwood of freshly felled logs of Corsican pine (Pinus nigra v ar. maritima (Aiton) Melville) was assessed during a 14-week field tri al at a sawmill in southern England. The boards were placed in nonstic kered stacks to reduce moisture loss, and stacks were constructed in a nest arrangement to allow experimental untreated board samples to be positioned centrally in each stack. The experimental samples were plac ed in plastic tanks, and the open tank faces were left either uncovere d or were covered with a fine-mesh nylon screen to prevent entry of mi croarthropods. All the experimental samples were sterilized by gamma-r adiation prior to the tanks being installed into the board stacks. The outer casing boards, which surrounded the experimental tanks in each stack, were dip treated with a fungicide, a broad-spectrum insecticide -acaricide, a combination of the fungicide and the insecticide-acarici de, or water, which served as a control. After 8 and 14 weeks of expos ure, casing beards were inspected for fungal infestation. The experime ntal sample boards removed from the centre of the stacks at the 8-week inspection were also assessed for fungal infestation. Boards that wer e accessible to arthropods (i.e., in open tanks surrounded by non-inse cticide-treated boards) suffered severe sap stain. Experimental boards protected from arthropods by a mesh screen and (or) casing timbers tr eated with the insecticide chemical had minimal sap stain. In contrast , colonization by moulds was not reduced when either physical or chemi cal barriers were in place, suggesting that mould spores were mainly t ransmitted by air currents. Micro-arthropods were clearly implicated a s primary agents of sap-stain transmission on green sawn lumber. They may also graze the moulds and therefore limit the intensity of defacem ent by these fungi.