THE Central Science Laboratory has been funded by the Ministry of Agriculture, Fisheries and Food, with a contribution by the Scottish Executive Rural Affairs Department, to study one of the most important challenges faced by sheep farmers in the UK - the sheep scab mite.

This astigmatid mite lives on the skin of the sheep and causes sheep scab, a highly contagious condition which can result in the emaciation and death of sheep.

There is increasing interest in finding a new method of control that is more effective for the sheep and safer for workers and the environment.

The remedy has usually been to dip sheep in baths of insecticidal chemicals, usually organophosphates (OPs). There is mounting evidence that repeated exposure by sheep dippers to OPs causes chronic neuropathy, depression and anxiety.

Disposing of chemicals used in sheep-dipping may result in environmental contamination of rural water supplies, and new legislation introduced in 1999 will make it increasingly difficult for users to dispose of spent dip-wash legally and effectively.

Some recently introduced alternatives to OPs (eg synthetic pyrethroids) are implicated in harming various aquatic fauna. Also mites may be developing resistance to some of the currently used chemical insecticides.

The development of new biological control measures, or those using chemicals that are non-toxic to non-target organisms, requires a suitable and reliable bioassay.

Developing any bioassay depends on supplies of mites in good condition and in sufficient numbers to permit experiments to be conducted to high standards with the necessary replication.

Currently, scab mites are usually obtained from deliberately infested sheep.

However, this has animal welfare implications, is cumbersome and produces a supply that is unpredictable and inherently variable due to interactions with the host.

CSL has over 30 years of experience culturing and studying mite biology.

This equips the researchers to design studies in vitro that will allow them to improve animal welfare and reduce variability.

Through a better understanding of the complex conditions that support sheep scab mites, it will be possible to design strategies to control mites by controlling their environment or by affecting their endocrine system, an approach in which CSL has a track record of success.

This work represents an essential and major step towards finding alternatives to dipping, which is causing concerns about human health and environmental damage.