Factors affecting the resistance of the flour beetle, tribolium confusum duv., to hydrogen cyanide1

1 Two types of apparatus for exposing insects to known concentrations of toxic gases, under controlled conditions, were constructed and are described. 2 The relative resistance of different stages of the flour beetle, Tribolium confusum Duv., to hydrogen cyanide was determined, the results being treated by Bliss's method. The order of resistance was pupa (most resistant), adult, larva, egg. The difference in resistance at different ages was found for the pupa, adult and egg. The application to all these results of Cotton's theory of the relation of rate of metabolism and susceptibility to fumigants is discussed. It is considered that this theory might hold for stages other than the egg. 3 A series of experiments was carried out to discover whether individual resistance to hydrogen cyanide was inherited. It was found that the offspring of resistant individuals were significantly more resistant than the offspring of susceptible individuals, and that this difference was maintained over several generations. 4 A considerable increase in resistance was found to occur if adult beetles were removed from their flour about an hour, instead of immediately, prior to their fumigation. The reason for this increase was not determined, but various suggestions to account for it are discussed. 5 It was noted that under certain conditions, adult beetles emitted a volatile substance which was self-toxic, and also appeared to react with cyanide. 6 The dosage-mortality curves for all the experiments are discussed and possible reasons for their apparent abnormality put forward. 7 The experiments here described, which must only be regarded as preliminary, emphasize i. The complexity of the problems arising in the study of the resistance of living organisms to toxic substances. ii. The need for carrying out such experiments under as natural conditions as possible. iii. The importance of a careful analysis of factors which affect the resistance of the organism.