Plants must compete against insects and weeds the latter being suppressed using herbicides or hoeing between the plants. Stan Finch and Rosemary Collier of Horticulture Research International, Wellesbourne, have demonstrated  that specialist insects, those that feed on specific plant species, can be prevented from finding their host plants if other plants are grown alongside. The precise type of 'decoy plant' is irrelevant, since green cardboard models also have the same effect. It appears that insects fly onto and off of a plant several times to check its suitability for egg-laying. A plant surrounded by bare soil is therefore likely to be found by an insect more easily and more times than one surrounded by other green plants. In addition, insects are more successful in a carefully weeded crop field than in one containing weeds. Since insecticides kill only a fixed percentage of insects, more insecticides may have to be applied to a weeded crop to maintain the current level of pest control. The solution? Cultivate your weeds!  June issue of "Biologist" Institute of Biology. Contact Christine Knott tel  020 7581 8333 ex 256 E-mail:   c.knott@iob.org  www.iob.org