The Fumigation of Insects with Hydrocyanic Acid: Effect of Different Air Pressures

The direct action of reduced pressures, in the absence of any fumigant, on C. oryzae and C. granaria have been investigated in glass chambers of about 1 litre capacity. C. oryzae is sufficiently sensitive to make the direct effect of reducing the pressure within the range 2 to 10 cm. mercury of some practical importance, but C. granaria is more resistant. Mortality of both species increases for exposure periods of up to 8 hr. and for increased temperatures from 20°C. to 28°C. A large part of the observed mortality must be associated with enhanced water-loss from the insects at reduced pressures, as little response occurs when the atmosphere is kept saturated with water-vapour.

Section: Discussionmentioning

confidence: 93%

Responses of Pests to Fumigation. IV.—The responses of Calandra spp. to Reduced Pressures

Nahal¹

1953

“…In all situations explored here, the method of sustained pressure reduction is superior to the other two, although when the fumigant is methyl bromide, which is only slightly sorbed, this superiority is less marked except at low doses of fumigant, becoming negligible at higher dosages. Of the many changes brought about by the sustained pressure reduction, there is undoubtedly a direct enhancement of the susceptibility of insects to fumigation (Moore & Carpenter, 1938) and it is thought probable that there is a component of the resultant mortality which may be attributed to the effect of the reduced pressure, when no fumigant is applied. Investigations of these problems have been done and will be reported separately by various workers.…”

Section: Resultsmentioning

confidence: 99%

Responses of Pests to Fumigation. III.—The Fumigation of Wheat containing Calandra spp.(Curculionidae) with three Fumigants, under Reduced Pressure

Nahal¹

1953

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.

“…The effect of very low pressures is harder to explain. Moore & Carpenter (1938) found that at 1-2 mm. pressure some, though not all, species of insects were much less susceptible than at 6 cm., and they also made the important observation that sorption of hydrogen cyanide on insects at 1-2 mm.…”

Section: Discussionmentioning

confidence: 96%

Responses of Pests to Fumigation. VI.—Water Losses and the Mortality ofCalandraSpp. at reduced Pressures

Bhambhani¹

1956

In Part IV of this series, El Nahal (1953) reviewed the evidence which shows that the amount of water lost by insects at reduced pressures is an important faetor contributing to the death of the insects. El Nahal further showed that the mortality of both Calandra oryzae (L.) and G. granaria (L.) increased with the exposure period (range 0-8 hr.) and temperature (range 20-28°C.) when the pressure was reduced to between 2 and 8 cm. mercury. Within this pressure range, C. oryzae was more susceptible than G. granaria, and for both species this susceptibility increased as the pressure was reduced. El Nahal confirmed that when the air in the chamber in which the weevils were contained was kept saturated with moisture, mortality at low pressures was greatly reduced.