In this paper the protective efficacy of S-421 (Octachlorodipropylether) against termites (Coptotermes formosamus Shiraki) was investigated by the laboratory tests of soil- and wood- treatments, comparing with Chlorpyrifos, Phoxim and Chlordane etc. Various weathering procedures were also applied to the treated soil or wood for evaluation of the durability of chemicals.
The results obtained were as follows:
1. The S-421 treated soil (sandy loam or clay loam) could be prevented from the termite penetration in the almost same level of treating concentration with Chlordane before and after weathering. When compared with Chlorpyrifos or Phoxim, S-421 undoubtedly showed the inferior effects to them in soil treatment, however it held the higher retention of the efficacy after weathering than those organophosphorous compounds, especially in clay-loam treatment because of its high durability.
2. In the feeding tests by termites, the consumption of the S-421-treated wood was almost the same with that of the Chlordane sample showing the similar level of efficacy. Although Chlorpyrifos and Phoxim caused the lesser wood-consumption and the more termite-mortality than S-421 and Chlordane in the same chemical concentration, the weathering procedure more extensively decreased the protective effects of the former compounds than the latter ones. After weathering the treated wood at 60°C at 100% RH for 8 and 16 weeks, Chlordane showed the most stable efficacy among tested chemicals, and S-421 was superior to Chlorpyrifos or Phoxim in the effectiveness when used at 2% solution.
From the results obtained here and the low mammalian toxicity, S-421 is expected to be one of promising chemicals as the alternative of Chlordane.

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