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S ummary The orders of resistance of four different species of insects are shown to be different towards hydrogen cyanide, ethylene oxide and sulphur dioxide. The different circumstances to be considered in fumigation research are surveyed with a view to ensuring reliable results. They can be grouped as: (a) Factors which may influence absorption of poison. ( b ) Factors which may influence toxic processes and degree of poisoning. These factors are assessed and each aspect of technique is described with an estimate of the extent to which it has been controlled. The arrangement of experiments to provide as much information as possible is described and the limits of accuracy defined. Details of the rearing and treatment of insects are given. Difficulties of estimation of mortality are considered and a relation between severity of fumigation and incidence of death or recovery from stupefaction is demonstrated. The dose‐kill data are treated by Bliss's Method of Probits and tables of statistics for each set of data are appended. Various time‐concentration relations are considered, and from these the empirical formula c n t = W has been adopted. A statistical analysis shows no serious deviation from this relationship. The need for uniformity in expression of toxicity is stressed, and the following criterion of resistance proposed: “The 5‐hr. concentrations ( mg./ l. N.T.P.) for 50 and 99% kill and the value of n”. The values of the criteria for the four species used ( Calandra granaria. C. oryzae. Triboliun castaneum and Cimea: lectularius ) are given.
J. R. Busvine (Mon,) studied this question.