The Acaricidal Effects of Compressed Gas Treatments on the Grain Mite, Tyrophagus putrescentiae

Abstract

Experiments were carried out on the acaricidal effects of the treatments of stored food with four kinds of compressed gases under various conditions, as a possible measure for the control of mites with non-poisonous materials. The gases used in the experiments were carbon dioxide, dinitrogen monooxide (laughing gas), nitrogen and hydrogen, all in high pressure bombs. Samples of the grain mite, Tyrophagus putrescentiae were placed in high-pressure resistant autoclave for chemical synthesis (200ml capacity) together with the culture medium (dried yeast), and were treated with these gases under various pressures and temperatures for different time lengths. The materials after treatment were incubated in a chamber regulated to 21°C and 85-90% R.H. for two months, and the treatment conditions, in which no survival and no breeding of the mites was confirmed, were regarded as the effective dose.The results indicate that the acaricidal effects were highest in carbon dioxide, while dinitrogen monooxide was slightly effective, and almost no effects were observed with nitrogen and hydrogen even when these gases were applied under high pressures. With carbon dioxide, for example, the minimum effective dose at 40°C was 10 minutes at 16kg/cmcm2 (absolute), 20 minutes at 11kg/cmcm2 and 65 minutes at 6kg/cmcm2. Under lower temperature conditions, higher pressure was necessary to obtain the same effects with the same exposure time, as shown in Table 2 and Fig. 3. It was observed through these experiments that effective control of the mites in stored food could be achieved by application of high pressure carbon dioxide for a certain length of time under a given temperature.