This paper describes the results from bioassays using Hylotrupes bajulus, and chemical analyses, of pyrethroid-treated wood samples following storage for up to 3 years. A range of four storage environments was used consisting of combinations of two temperatures (20°C and 40°C) and two relative humidities (60% and 90%). It is concluded from the chemical analyses that, although losses at room temperature were small, at the higher temperature used in this study loss of insecticide was accelerated. Exposure of treated wood to high relative humidity did not appear to result in increased loss of insecticide. The bioassay results confirmed these conclusions. The significance of the bioassay results in relation to the long term efficay in service of preventive treatments is discussed and a logic proposed for deriving a service life on the basis of which an estimate of up to 58 years protection from current commercial formulations is derived.

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