The effectiveness of silica treatments against wood-boring invertebrates

Abstract

Abstract Timber specimens were impregnated with the organo-silicate tetraethyl orthosilicate (TEOS) in an effort to deposit hard silica granules and improve resistance to wood-borers. Trials were conducted against marine borers (teredinids and Limnoria ), the termite Coptotermes acinaciformis , and the wood-boring beetle Lyctus brunneus . A 14-week laboratory bioassay against C. acinaciformis showed that treated Pinus radiata containing 16.7 wt.% silica was as readily attacked as untreated timber. However, a 3-year laboratory trial of treated Castanospermum australe showed that attack by L. brunneus was prevented by 10.3 wt.% silica, and reduced by 0.7 and 3.4 wt.% silica. A trial of wood treated with copper-chromium-arsenic followed by silicon was conducted in the sea at Townsville, Australia for 7 years. Double treatment with 6.7 or 19.2 wt.% silica prevented attack in P. radiata by teredinids, while for CCA alone some replicates failed. In the same trial, double-treated Corymbia maculata with lower silica retention failed. Silica granules may overwhelm the food and waste-sorting mechanisms in teredinids and lyctine larvae, whereas borers, requiring less intimate contact with granules ( Limnoria and termites), or those that do not ingest wood for food ( Sphaeroma and Martesia ), are little affected.