By means of controlled laboratory experiments it was established that timber treatment fluids containing g-HCH and pentachlorophenol (PCP) and used according to manufacturers recommendations rapidly cause the death of pipistrelle bats roosting in contact with timber treated between six weeks and 14 months previously. The chemicals responsible are presumably ingested when the bats groom their fur after they have been in contact with the treated timber. Bats prevented from establishing such bodily contact took longer to die indicating that absorption of the vapour phase of the tested chemicals also takes place across the skin or respiratory epithelium. Acrylic resin reduces the lethal effect when used as a sealant over wood treated with g-HCH and PCP, but polyurethane varnish does not. It has also been established that no obvious harm is caused to bats roosting for 16 to 22 weeks in contact with timber treated with the synthetic pyrethroids permethrin, cypermethrin and deltamethrin at concentrations which have previously proved effective for the control of woodboring beetles. Similarly, no obvious harm is caused to bats roosting for 14 weeks in contact with timber treated with the fungicides borester-7 and zinc octoate. However, greater mortality was recorded in bats housed in cages treated with the fungicide tributyltin oxide than in control groups. It is clear from these results that synthetic pyrethroids should replace g-HCH for the treatment of wood-boring beetles in bat roosts. A high priority should be accorded to replacing PCP with a fungicide which is not toxic to bats.

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