Results of a laboratory bioassay on the efficacy of two preservative formulations (chlorothalonil in oil; chlorothalonil plus chlorpyrifos in oil) to the Australian subterranean termite Mastotermes darwiniensis Froggatt are given. Specimens of Pinus radiata D. Don sapwood were treated to three retentions of each formulation to achieve 3.2, 6.4 and 12.8 kg/m³ of chlorothalonil a.i. and 3.2 + 0.2, 6.4 + 0.4 and 12.8 + 0.8 kg/m³ of chlorothalonil plus chlorpyrifos a.i. All specimens (including controls) were subjected to an artificial leaching/volatilisation weathering schedule prior to the bioassay. Results showed that all three retentions of each formulation were successful in protecting specimens from significant attack by Mastotermes darwiniensis. The results also indicated that the chlorothalonil in oil formulation appeared to have had an antifeedant effect on Mastotermes darwiniensis. The results of the bioassay were sufficiently encouraging to warrant an evaluation of the two preservative formulations in the field.

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