Insect tests, toxicity evaluation

The laboratory testing of these molecules was carried out on four insects, the housefly, Musca domestica. M.d., the pea aphid, Aerythoslphon pisum. A.P., the corn earworm, Hellothis zea, H.z., and the two-spotted spidermite, Triticum urticae, T.u. In all toxicity test evaluations, parathion was employed as a standard. Therefore, any compound having a Toxicity Index (TI) of 100 is equal to parathion. The data for the laboratory toxicity evaluation of these molecules are collected in Tables 1 and 2. 

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. 

Traditionally, the discovery process begins when a chemist synthesizes a new compound. The chemist may choose to make compounds based on an understanding of vertebrate pharmacology, biologically active natural products, or proven insecticidal chemistry or he may choose to make completely novel structures for which no biological information is available. In any case the compounds are evaluated for toxic effects in insect species which usually represent desirable insecticide markets. The objective of this initial testing is to eliminate inactive compounds from further tests, and to roughly define the species spectrum of activity. 

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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