Environmental actions of agrochemicals 2. Histological effects of the herbicide/insecticide dinoseb-acetate (2-sec-butyl-4,6-dinitrophenyl acetate) on the spider miteTetranychus urticae (Acari: Tetranychidae) reared on herbicidetreatedPhaseolus vulgaris

Abstract

The pure herbicidal compound dinoseb-acetate (2-sec-butyl-4,6-dinitrophenyl acetate) and its commercial formulation Aretit^® were tested for their effects on the spider miteTetranychus urticae L. (Acari, Tetranychidae) following post-emergence application to the host plantPhaseolus vulgaris L. under laboratory and semi-field conditions.

Mites which fed on beans treated with the pure compound produced a lower number than those feeding on untreated control plants. Mite quantity on Aretit-treated plants remained behind the control 6 days post-treatment but did not differ significantly from the control 21 days post-treatment. There were no indications for a specific sensitivity of single developmental stages. External as well as internal changes in mite morphology were not obvious independent of the kind of treatment.

Effects of herbicide application became undoubtedly obvious at the electron-microscopy level, although the pattern of cellular alterations was very unspecific. Tissue changes exceeding normal variance can be demonstrated in more than 50% of the investigated individuals of each short-term test variant. They are manifest in mitochondrial swelling and disruption, especially in cells of the midgut caeca and prosomal glands, and a disarrangement of the RER, especially in the pure-compound treatment. Cellular changes are more pronounced and polymorphological in the pure-compound test variant than in the commercial formulation variant. At 21 days post-treatment, frequency of tissue alterations exceeding normal variance was reduced, with the exception of the diluted Aretit treatment where it remained at a high level.

Consequences of cellular changes on individual and population development and dynamics ofT. urticae are estimated on the basis of dinoseb-acetate risk in agricultural practices. Results are discussed with respect to the use of electro microscopy in elucidating herbicide action, to the influence of formulation, and the need for a test system enabling a prediction of ecotoxicological actions of biocides prior to their admission for use in the field.