Responses of Pests to Fumigation. I. Toxicity of Mercury Vapour to the Eggs of Calandra granaria (L.).

Abstract

Wild populations of Calandra granaria were allowed to oviposit on clean wheat and the tolerances of the eggs to mercury vapour were estimated. For six such populations the median lethal doses ranged from 55 mg.hr./m.3 to less than 1.0 mg.hr./m.3. A laboratory strain of grain weevils has developed resistance to mercury vapour in the egg stage, probably from contamination of an incubator. Such evidence as is available suggests that this resistance is associated with reduced chorion permeability rather than enhanced metabolic ability. The increase in resistance is such that no attainable concentration × time product will kill more than half the resistant egg population which is thus virtually in equilibrium with air saturated with mercury vapour. Fumigation of gravid females, or of wheat prior to oviposition, does not reduce the viability of any eggs subsequently laid.