Adults of Calandra granaria and C. oryzae have been fumigated with hydrogen cyanide by the methods of sustained pressure reduction and preliminary pressure reduction, the main criterion of response being death. Of the factors studied, starvation and sex of the insects are without influence. With pressure reduction, Haber's Rule relating mortality, concentration and period of exposure is not followed; for a given concentration-time product, the mortality is higher, the shorter the period of exposure.

Preliminary pressure reduction increases mortality much less than sustained pressure reduction. With the latter the mortality of C. oryzae is higher than that of C. granaria. The increases in susceptibility are largely accounted for by increases caused by pressure reduction alone in the absence of fumigant. The number of eggs laid by untreated females and by females surviving treatment was excessively variable and no discrimination between factors could be made.