Susceptibility of envelope-treated softwood to subterranean termite damage

Abstract

Two field trials were conducted to determine the aboveground effectiveness of envelope treatments of deltamethrin and permethrin for the protection of two softwood framing timbers, radiata pine, Pinus radiata D.Don, and slash pine, Pinus elliottii Englem., against damage by Australia's most economically important species of termite, Coptotermes acinaciformis (Froggatt). Specimens were treated with Tanalith® T (a novel solvent) to achieve 5-mm-depth envelopes. Details of a 12-month field trial in the wet/dry tropics of northern Australia (Darwin, Northern Territory) and of a 7-month trial in subtropical eastern Australia (Beerburrum, Queensland) using a different test method are presented. At the conclusion of the field trial in the Northern Territory, all timber specimens had evidence of contact by C. acinaciformis. Both the deltamethrin (0.002% mass/mass ovendried [m/m OD]) and permethrin (0.02% m/m OD) envelope treatments were completely successful. Similarly, the fully impregnated LOSP reference treatment containing permethrin (0.02% m/m OD) was also successful. Damage to the untreated and solvent (Tanalith® T) control specimens was variable due to the inclusion of both sapwood and heartwood specimens of radiata pine and slash pine in the trial. The Tanalith® T appeared to contribute to the overall effectiveness of the deltamethrin and permethrin envelope treatments. Similar results were obtained from the field trial in southeast Queensland using a different test protocol. C. acinaciformis and Schedorhinotermes seclusus (Hill) provided termite foraging pressure to most timber specimens. All treatments protected the test specimens. Termites did not cause damage to test specimens via untreated cut ends. Consequently, with regard to C. acinaciformis or S. seclusus, there appears to be no need to apply a supplementary treatment to exposed cut ends of Tanalith® T treated softwood framing material up to the profile dimension examined. The direction for further work is indicated.