Evaluation of Toxicity in Insects

Abstract

The susceptibility of an insect population to a poison is assessed by constructing a dosage-mortality curve in which the dosage is plotted against the percentage mortality at a given period of time. Such a plot produces a sigmoid curve whose asymptotic approaches at the regions of zero and 100% mortality are difficult to define without extensive testing. The use of probit transformation in which the sigmoid curve is converted to a straight line by plotting the logarithm of the dosage against the probit value of percent mortality (Log-Probit paper is available commercially for making these plots) is recommended. This method of computation yields a straight line which greatly facilitates the determination of the LD₅₀ and other values on the plot (Fig. 6.1). Detailed discussions of this method are available in specialized books (Finney 1949, 1952; Swaroop and uemura, 1956; Busvine 1971).