House Doctor

THERE ARE some insects to whom evolution has entrusted the important task of recycling wood. So when trees die and fall to the forest floor, wood-boring beetles lay their eggs in the bark, and their larvae get to work munching their way through the timber, helping to return the wood to soil, and enabling the nutrients to be taken up by new tree growth. If wood-boring insects did not exist, then neither would we, because the primeval forest would have choked to death under a mountain of its own dead wood.

These days, of course, the insects are in competition with humans for timber, and so their vital recycling function is seen in a different light. In fact, wood-boring insects get such a bad press that most people think their homes must be periodically sprayed with insecticides to keep the little critters at bay. And anyone, including this column, who questions this blanket chemical warfare approach gets roundly upbraided by the timber treatment industry. But now it appears that chemical timber treatment is not only a potential health threat, but it may not even do what it is sold to do - ie get rid of the insects.

According to a report published in New Scientist, chemical spraying for deathwatch beetle infestation in old churches has actually had the opposite effect to that intended. Scientists found that the chemicals failed to kill off any of the beetle larvae but instead killed the spiders which are the beetles' natural predators. So the emerging adult beetles, without any spiders to control their numbers, were able to breed unmolested, and lay the next generation of eggs in those areas of wood unaffected by the spraying. The result?

A huge increase in the beetle population.

The fact that modern man's attempts to deal with the perceived insect pest should be so unsuccessful should come as no surprise. Insects are the most successful group of animals on the planet; there are millions of different species, they breed and multiply at an amazing rate, and they are fantastic at adapting to changing conditions. The idea that insects inside buildings are A Bad Thing is based partly on the annoyance factor of flies and mosquitoes buzzing around the home, but chiefly upon the marketing clout of the chemical companies.

However, there is mounting evidence that the insecticides - all of which are nerve poisons - may be far more dangerous than previously realised. Permethrin, the latest so-called safe pesticide, has recently been linked with Gulf War syndrome and multiple chemical sensitivity.

The scientists' answer to the deathwatch beetle problem, by the way, was very, very simple.

Like all wood-boring insects, the beetle larvae can only survive in damp timber, so fixing leaks and drying the place out was found to account for most of them. But do not expect the timber treatment companies to tell you any of this.

Jeff@doctoronthehouse. demon.co.uk