Toxicity evaluation tests with insects

As the value of these two new chemicals for insecticides became more evident, the need for extended experimental and test work was definitely established. It was necessary to determine chemical formulas, work out analytical methods, obtain knowledge of various physical and chemical characteristics, and complete evaluation of insecticidal action as well as toxicity and effect of residues. Toxicity was concerned with not only insects but humans and other warm-blooded animals. Residual studies included information on persistence and type and amount of residue. This information, once accumulated, must be correlated with similar information on other insecticides. 

As in other areas of natural products chemistry, studies on insect chemical defenses comprise several different aspects first come the isolation and structure determination of the compound(s) responsible for the defensive activity. The next step is the total synthesis of the identified compounds, in order to confirm the proposed structure, usually deduced from spectroscopic data only, and to get enough material for biological testing. Biosynthetic studies to determine the origin of the active compound(s) (biosynthesis by the insect itself or sequestration from the diet with or without metabolization) are sometimes performed. In some cases, the biological activities of the isolated compounds (repellency, toxicity...) and their possible pharmacological activities are also evaluated. This chapter is divided into four sections treating those different topics. 

This method is suitable for stored-product pests. The evaluation of toxic vapor is a somewhat similar operation. The insecticide is introduced into a sealed container along with the insects and mortality is recorded at different intervals. Various fumigation techniques were described by Busvine (1971), including (1) small-scale techniques for measuring the susceptibility of exposed insects and (2) semipractical tests using large fumigation chambers. 

Insecticidal Activity. Adult houseflies and 3rd instar com earworm larvae were used to evaluate the light induced toxicity of a-T. Rose Bengal was used as the standard. Both species were treated with a series of doses of the test compounds by feeding. In addition, a-T was tested by topical application. Two sets of insects were treated, one of which was kept covered to serve as a dark control. 

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