THE STANDARDIZING OF A LABORATORY METHOD FOR COMPARING THE TOXICITY OF CONTACT INSECTICIDES

Abstract

Toxicity tests were conducted with nicotine sulphate and nicotine alkaloid using Drosophila melanogaster as the test animal, with a modified Tattersfield atomizer spray machine, and by an immersion technique. One hundred and fifty flies were treated at each concentration each day. Each experiment was replicated 8 or 10 times using 3 to 22 concentrations. Data were analysed by the method of analysis of variance and by means of probits.It appears from the data secured that careful standardization of any technique will be needed to secure comparable results. Results from spraying were the more uniform and consistent. Saponin spreader had a synergistic action with nicotine sulphate. It complicates results and its effect cannot be separated from that of the insecticide. Variations in observed mortalities result from different rates of spray application (slower applications were better), different ages of test animals (day-old flies and flies over four days old were most susceptible), different numbers of test animals per container (increased numbers increased the kill), different populations (these vary greatly in susceptibility), differences in larval and adult nutrition, and the use of different sized fly containers. All these factors must be standardized or accounted for. When this was done variations due to different experimenters were not significant.In general six or eight replications were enough to establish a curve. Analysis of variance on angular transformation values gives a good test for consistency and the method of probits reveals much heterogeneity in the data.