The experimental manipulation of insect herbivore load by the use of an insecticide (malathion): The effect of application on plant growth.

The effects of insect herbivores on natural communities of plants may be demonstrated by manipulative experimetns. Such experiments, which reduce the natural levels of herbivory by application of insecticide, incorporate the assumption that the insecticide has no direct effect on the vegetation. A test of this assumption should therefore be an integral part of any study of herbivory employing chemical exclusion. Here a single compound (Malathion-60), which is commonly used in such studies, is tested both in the field and on selected plant species under controlled conditions. It was found to have no effect on a range of early successional plant species. The limitations of the tests are discussed.