Plant pests have natural enemies which help keep them in check. In the protected environment of a garden, greenhouse or conservatory, pests can breed so rapidly that their enemies cannot reduce them in sufficient numbers.

Many gardeners resort, often reluctantly, to chemical pesticides. A better option is to tip the balance in favour of the natural enemies - through boosting their numbers so that the pest population can be effectively reduced without chemicals.

This method is called "biological control" - simply using one organism to control another. A wide range of pests is now controlled this way under glass. Certain biological controls can be used outside, for instance, to keep slugs and vine weevil at bay.

First developed over 75 years ago, biological control is widespread in commercial horticulture. Over 1,000 acres of UK glasshouse grown tomatoes, cucumbers and sweet peppers are protected using these natural control agents.

Growers in this country are world leaders in the use of biological control, and today an increasing number of proven products are available to gardeners. These controls can be parasites, which live on or within another organism, or predators that prey on others. All are natural species which have not been genetically engineered.

Times are changing. Today, increasing numbers of garden chemicals are being withdrawn on grounds of safety. Registration of new chemicals is increasingly complicated and expensive, and pests are becoming resistant to frequently applied pesticides.

Biological control has proved itself to be an effective and environmentally safe alternative to chemicals, providing a long term solution to controlling pests.