In a recent paper on “Recent Developments in Fumigation of Buildings, Stored Foods, and other Materials,”' published in “Chemistry and Industry” on November II, 1939. an attempt was made to cover a wide field. The present paper deals, in more detail, with certain experimental work, much of which has been carried out at the Biological Field Station of the Imperial College of Science and Technology.
Laboratory experiments show that effective control of stem eelworms, removed from plant debris, can be obtained by fumigation under conditions which do not reduce either the germination of seed or the yield of lucerne grown from seed similarly fumigated.A practical fumigation of six tons of seed under a gas-proof sheet is described. IntroductionThe incidence and distribution of stem eelworm in young lucerne stands strongly suggests that it is seedb0rne.l In laboratory experiments other races of stem eelworm occurring on onion,2 teazle3 and red clover4 have been controlled by fumigating the seed with methyl bromide and it was decided therefore to attempt to obtain control of the lucerne race by fumigating the imported seed. The work described here deals with the effect of methyl bromide fumigation on eelworm larvae extracted from stems, the germination of lucerne seed and the growth of lucerne raised from fumigated seed. Field evidence on the nematicidal effects of the treatments has been reported previously by Br0wn.l
A bioassay system for the pyrethrins is discussed in which the quantity of toxicant that flying insects accumulate is measured, as well as the responses of the insects. T h e determination of spray pick-up from water-base sprays is described, and the use of primary responses, such as activation and paralysis, in biological assays is advocated. T h e test system is discussed in detail for Aedes aegypti L. and the special characteristics of some other species of flying insects noted. I t is considered that the location of the site of action of the pyrethrins under these conditions is at the peripheral nervous system of the test insects. WATER-BASE SPRAYS AND AIDES AEGYPTI L. Relation between toxicity and pick-up of insecticides applied as aqueous spraysMuch published work has been based on the tacit assumption that the quantity of insecticide accumulated by an insect flying in a spray is proportional to the concentration of insecticide in the spray fluid and to the volume sprayed into the air space occupied by the insects. Published statements that wasps, horseflies and blowflies are more sensitive than houseflies to pyrethrins, based on the concentrations used, ignore the fact that the first-mentioned insects, which are hairy, pick up far more spray liquid in flight or when stationary than the houseflies. We have shown that the weight of insecticide acting on the insect is proportional to the product of the volume of spray liquid accumulated by the insect and the concentration of insecticide in the liquid.If the volume of liquid picked up by the insect is plotted against the concentration of insecticide in the spray liquid, the points representing the acquisition of a constant quantity of insecticide by the insect should then lie on arectangular hyperbola. This has been shown to be true for a number of insects, using their responses to the weights of pyrethrins accumulated. Any variation of the conditions which alters the quantity of spray liquid accumulated, such as a change of nominal spray dosage, or humidity, also alters the concentration at which any particular response occurs and alters it in such a way that the threshold weight of the insecticide causing the response is maintained.
In June 1935, certain problems arose concerning the fumigation of houses with hydrogen cyanide for the destruction of bedbugs. Workmen reconditioning houses in Rochester, which had been given the customary 24 hr. aeration after fumigation with hydrogen cyanide “disks”, had complained of sickness during their work. The walls, cavities and floor spaces of some of these houses had been tested by Mr Topping, the Chief Sanitary Inspector of Rochester, who, using benzidine acetate-copper acetate paper, had obtained a strong positive reaction indicative of the presence of hydrogen cyanide after 24 hr. aeration.
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