A biological assay technique for the assessment and comparison of systemic insecticide residues

A technique is described using mortality of aphids on excised leaf samples to assess residual systemic insecticides within the leaf or on its surface. Residues in crops or soil can also be assessed by keeping aphids on leaf samples treated with solvent extracts of contaminated material. Little or no pre-treatment for the removal of potentially interfering materials co-extracted from the crop is required. Comparison of mortalities caused by unknown residues with mortalities caused by known amounts of insecticide enables the technique to be used quantitatively. The sensitivity of the technique varies with the toxicity of the compound being assayed. With most of the insecticides tested, extract solutions down to about 10 ppm may be assessed directly; weaker solutions must first be concentrated.