Problems in the laboratory investigation of the toxicity of phosphine to stored product insects

The principles to be observed in determining the toxicity of fumigants to stored product insects by means of laboratory experiments, and the circumstances in which these must be modified for phosphine are discussed. After assessing the published literature two kinds of experiment are recommended, to imitate the levels of concentration and exposures used in practice and to limit the exposure period to 8 or 24 hr. For the latter exposures higher concentrations than are used in practice would be required and it might not be possible to achieve complete mortality of test samples. However, this technique should separate the tolerant and susceptible stages of the life cycle and reveal any stages of intermediate susceptibility. The maximum duration of the developmental period of the tolerant stages would represent the minimum exposure period for phosphine desirable in practice provided all the individuals in a tolerant stage developed and reached a susceptible one.