Environmental actions of agrochemicals. 1. Side-effects of the herbicide 3-amino-1,2,4-triazole on a laboratory acarine/host-plant interaction (Tetranychus urticae/Phaseolus vulgaris) as revealed by electron microscopy.

Foliar and soil application in concentrations below the recommended rate of the herbicide 3-amino-1,2,4-triazole to the host plant Phaseolus vulgaris L. results in structural alterations of the protein-synthesizing apparatus of midgut and salivary-gland cells of the phytophagous spider mite Tetranychus urticae Koch (Acari: Tetranychidae) independent of its mode of application. With prolonged incubation times cytological defects become more intense, and spread to more cells and tissues. Resultant effects on yolk and egg formation were expressed as an inhibition of egg deposition that led to a decrease in the reproduction rate of T. urticae. Consequences of 3-amino-1,2,4-triazole action on T. urticae are discussed with regard to its value to a host-plant/parasite model, agricultural practices and environmental impacts.