Wheat of three moisture contents was fumigated with ethylene oxide, methyl bromide and hydrogen cyanide. Both chemical and biological assays were used to follow the changing distribution of the fumigant when applied with sustained vacuum, in a vacuum fumigation with simultaneous admission of air and fumigant, or at atmospheric pressure.
As these various factors were altered, in a multifactorial experiment, the changes in the fumigant distribution were also recorded chemically, and then analysed statistically. Changes in the mortality of both species of Calandra, either buried in a one-cwt sack of wheat or in the free-space, were estimated so that that part of the changes which was associated with the altered fumigant distribution was segregated by a covariance analysis and the remainder formed an estimate of the direct influence of the experimental Conditions on the susceptibility of the weevils to the fumigants.
When either ethylene oxide or methyl bromide is used as a fumigant for wheat, vacuum fumigation with simultaneous admission of air and fumigant gives results, in terms of the control of Calandra spp., which are almost indistinguishable from those obtained at atmospheric pressure under comparable conditions. When hydrogen cyanide is the fumigant, atmospheric fumigation is superior, quite apart from the capital expense and other practical disadvantages of fumigations at reduced pressures.