Plaster beetle (psocid) infestation in buildings : Environmental management and control — a pragmatic approach

Plaster beetles (psocids) are active stocky and soft-bodied insects that are commonly found in new-build apartments, flats and housing blocks. They are also commonly called barklice or booklice because of their superficial resemblance to certain species of lice, and because they are found, sometimes in very large numbers, on mouldy books and papers in damp buildings or their basements and under loose, damp bark. Plaster beetles are either pale grey or pale brown in colour and may or may not have wings. They are common but harmless, unpleasant nuisance pests. Many live on bark and leaf surfaces feeding on algae, fungi or lichens. Others are found in leaf litter or in caves. A small number have extended their range to include buildings and building materials such as thatch, stored food stocks and museum exhibits. Plaster beetle infestation is mainly caused by damp and residual moisture, resulting in high levels of relative humidity (> 65–75 per cent) in the structural voids, ducting and insulation thereby allowing mould infestation. Psocids primarily feed on fungi and moulds for a few months in newly built houses after the completion of a building. Spraying with chemical treatments will deal with the symptoms of the problem but will not deal with the underlying causes of the infestation, namely damp, residual moisture and moulds. Heating treatment offered by some companies, whereby the building is heated to 45°C, should kill off psocids in the building; however, this does not address the underlying cause(s) of the problem and there is a risk of reinfestation. The author has advocated non-destructive investigations of buildings combined with correct diagnosis and identification of type and viability of both plaster beetle and mould infestation, as not all mould infestations are equally toxic or pathogenic. The author strongly believes, based on scientific, practical experience and successful case studies over the last 35 years, that environmental control of plaster beetle infestation and preventative maintenance are preferable to remedial conventional chemical spraying treatments. Rectifying building defects combined with drying out the building fabric and preventative maintenance should in most cases forestall the need for major interventions, and it is beyond doubt that these steps reduce the risk of reinfestation in buildings. The environmentally sustainable approach and the ongoing monitoring of the environmental conditions in buildings ensures the long-term health of building materials, health of the occupants and structures.