INTRODUCTION

In Chapter 1 it was pointed out that many of the striking advances in knowledge over the last 10–15 years regarding pesticide impact have been the outcome of field studies in practical pest control programmes. In all these projects, the environmental studies relate to the known chemical and formulation which is either applied directly to the stream at a predetermined application rate calculated to produce the desired concentration of the chemical in the water, or which contaminates the stream indirectly as a result of aerial application of pesticide to control terrestrial pests in the environs of the stream or river, and where the dosage rate in terms of kilograms per hectare has again been predetermined. In both instances the actual time of application is also known precisely.

The object of these environmental studies is to find out the extent to which the pesticide treatment produces significant changes in the composition of stream fauna produced by mortality or downstream movement, with particular reference to the macroinvertebrates which are the subject of this review. In order to measure these effects and to ascertain significant population changes among the different organisms of running water community – both in the short term and the long term – pesticide ecologists have to rely on a variety of sampling methods. It is these various capture or trapping techniques which provide the essential data for measuring changes in population density or in population composition attributable to pesticide impact.