Contribution of hardness to the natural resistance of a range of wood species to attack by the marine borer Limnoria

This study set out to determine whether wood surface hardness plays a role in determining the resistance to Limnoria attack. The feeding rates of the wood-boring crustacean Limnoria quadripunctata on matchstick-sized samples of a range of timbers were assessed by measuring the production of faecal pellets under forced feeding conditions. Pellet production rates varied significantly between wood species, with production on Lophira alata (ekki) 25-fold lower than that on non-durable Scots pine (Pinus sylvestris) sapwood. The surface hardness of the timbers was measured for air-dry and seawater-soaked samples using a microindentation technique. The force required for a universal testing machine to drive a 150-μm-diameter pin 1.2 mm into the samples was measured. For all wood species, the hardness of seawater-soaked wood was lower than that of air-dry wood. Hardness was found to correlate positively with density. Pellet production rates showed a significant negative correlation with hardness across the range of species used, but if the denser species alone were considered, wood species significantly affected the rate, but hardness did not. In view of these observations, tests on resistance to attack by Limnoria should include a denser, non-durable wood species for comparison, as its hardness would likely be more similar to that of the durable species.