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UBC Theses and Dissertations

A method of bioassay for the residual contact toxicity of insecticides Harris, Charles Ronald


A method of bioassay distinguishing residual contact from fumigant toxicity is described. Basically the apparatus consists of a series of Buchner funnels set up in series. Woven fiberglass cloth was selected as the substratum. By substitution of a dye in place of Insecticide, it was possible, using colorlmetric analysis, to calculate the total milligrams of dye adhering to the cloth. It was assumed that proportionate amounts of dye and insecticide would be picked up. Musea domestica L.was used as the test insect. Two strains of flies, designated as the SES and Ottawa cultures, were used. Fumigant effect was eliminated by application of negative pressure. Since fumigant effect is proportionate to vapour pressure, the rate of evacuation varied for each insecticide. Elimination of fumigant effect brought about a corresponding decrease in mortality. Dosage-mortality data are given for six insecticides in comparison to a "standard" insecticide (dieldrin) utilizing the concept of toxicity index ( Sun, 1950). Statistical analysis of the data indicate significant heterogeneity in eleven out of twenty-four experiments. An analysis of the Chi-square function is presented. Dosage-mortality data for DDT are given. The SES culture was determined to be 141x as resistant for females and 67x as resistant for males as the Ottawa culture, by topical application. Residual contact application indicated that females of the SES culture were 252x as resistant compared to the Ottawa culture. Variation within the SES culture is discussed as a factor in demonstrating the sensitivity of the technique.

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