Resistance of modified wood to marine borers

• Wood modification can confer marine borer resistance to non-durable timber species.
• Efficient resin treatments deposit the resin in the cell wall.
• Similar protection mechanisms seem to effect resistance against both types of borers.
• Resistance seems to require modification on cell wall level.

The resistance of differently modified wood to the common shipworm, Teredo navalis, and the wood boring crustacean, Limnoria quadripunctata, was assessed in a field trial and by means of a short term laboratory assay, respectively. Scots pine (Pinus sylvestris) sapwood was treated with TEOS (tetra-ethoxy-ortho-silane) and different thermosetting resins, namely phenol formaldehyde (PF) and methylated melamine formaldehyde (MMF). Additionally, acetylated and untreated Radiata pine (Pinus radiata) was included. In the field trial according to EN 275 in the Baltic Sea over a period of six years the specimens were exclusively attacked by T. navalis. For the laboratory assay, matchstick-sized samples cut from spare panels prepared for the field trial were subjected to individuals of L. quadripunctata; faecal pellet production served as a measure of feeding rate. Treatments that prevented shipworm attack in the field also reduced feeding of L. quadripunctata in the laboratory assay: efficacy of resin treatments was enhanced by parameters that increase the amount of resin in the cell wall (i.e. high WPG and dry curing conditions); acetylation resulted in high resistance; and TEOS treatment was not effective. The results suggest that modification on cell wall level is required to impart marine borer resistance.