Interactions between insecticides and soil microbes

Abstract

The widespread use of insecticides over the past 30 years has resulted in problems caused by their interaction with natural biological systems. The complex interrelationship of these systems is illustrated in Figure 1. A problem due to contamination by residues may appear far removed from the initial point of introduction into the environment. For example, while some insecticides are intentionally applied directly to the soil to control soil insects, the soil is also a repository for chemicals from drift during foliar application, plant residues containing insecticides and their degradation products, and chemicals deposited by atmospheric precipitation. The persistence of insecticides and their degradation products depends on how deeply they are mixed into the soil; even the most persistent compounds disappear relatively quickly when on the soil surface, yet when incorporated into the soil they are very persistent (Edwards 1966). Generally insecticide residues will occur in the top 6 in. of soil (Chisholm et al. 1950, Harris and Sans 1969, Lichtenstein et al. 1962). This is also the region of greatest activity of soil fauna and flora (Alexander 1961), thus setting the stage for interaction of insecticide residues with the fauna and flora of the soil ecosystem. Recent monographs have considered the effects of insecticides on soil fauna (Edwards and Thompson 1973) and aquatic microorganisms (Ware and Roan 1970).