Toxic effects of phosphamidon to insects and mites

Abstract

Research on the toxicity of an insecticide to insects and mites can have two major goals. One of them is to develop reproducible criteria of poisonous effects by applying exact methods of dosing and evaluation. The resulting data can serve as a basis for a variety of comparative investigations. The other goal is to predict a poisonous effect under practical conditions, with a high degree of reliability, by exploiting reliable analogies or by exact reproduction of criteria which are decisive for the toxic effect in practice. Both trends in entomological work are interesting, the first for a solid foundation of knowledge on a pesticide, the second for its use. The ways in which to reach both aims differ mainly in the methods of experimentation. Classical toxicological work is based on the dosage- or time-response of test animals to doses of a poison which are measured out exactly and applied to the candidate. Criteria of intoxication are commonly LD₅₀ or LT₅₀ values. In entomological practice the standardized method of topical application anwers to these specifications. As an equivalent in mite work the slide-dip technique has become the method of choice. It produces an unknown, but constant dosage of the toxicant as a deposit on immobilized individuals. Greater variability than with the above methods must be expected when insects are tested on living plants, because secondary contact through movement on residues or feeding on poisoned parts make the dosage response dependent on individual behaviour patterns of test animals. The further the imitation of field conditions goes, the greater is the variability to be expected. For example, it is very difficult to establish a dosage-mortality relationship between different quantities of granulated insecticide in soil and the response of aphids on a plant rooting in the treated soil sample. Thus, with increasing realism of testing arrangements, the judgement of results becomes a problem requiring statistical interpretation.