Laboratory and field data reported in the literature are confusing with regard to ‘adequate’ protection thresholds for borate timber preservatives against subterranean termites. The confusion is compounded by differences in termite species, timber species and test methodology. Laboratory data indicate a borate retention of 0.5% mass/mass (m/m) boric acid equivalent (BAE) would cause > 90% termite mortality and restrict mass loss in test specimens to 5%. Field data generally suggest that borate retentions appreciably in excess of 0.5% m/m BAE are required. We report a field experiment with varying amounts of untreated feeder material in which Coptotermes acinaciformis (Froggatt) responses to borate-treated radiata pine (Pinus radiata D.Don) were measured. In the absence of untreated feeder material, retention of 0.5% BAE provides adequate protection from Coptotermes sp., whereas in the presence of untreated feeder material, increased retentions are required. Furthermore, the retentions required increase with increased amounts of susceptible material. The apparently conflicting results between the laboratory and the field data are explained by the presence or absence of untreated feeder material in the test environment. Further investigation to determine how widespread this phenomenon is with different timber preservatives is suggested.

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