SOME FACTORS AFFECTING THE TOXICITY OF HYDROCYANIC ACID FOR INSECTS

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Abstract
A detailed study was made of the toxicity of HCN for certain insects. The insects used in this work were two species of aphids, Aphis rumicis and Macrosiphoniella sanborni, one species of thrips, Thrips tabaci, and two species of grain beetles, Sitophilus granarius and S. oryza. Apparatus by which all factors can be controlled or varied was employed. The results of over a thousand experiments indicate that, within certain limits, concentration and length of exposure are inversely related or that toxicity = concentration x the time. The higher the temperature, the more susceptible were the insects; this susceptibility was more pronounced with the shorter exposures. Present indications are that humidity is not an important factor affecting the toxicity of HCN. Comparative studies on calcium cyanide and liquid cyanide show that the liquid HCN is more toxic than the gases from hydrolysis of calcium cyanide. A small amount of methyl acetate added to liquid HCN seemed to increase the toxicity of the gas arising from the liquid HCN, which may be due to the fact that a small amount of methyl acetate kept the spiracles open, while in pure HCN the spiracles were quickly closed.

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