The Influence of Atmospheric Humidity on the Thermal Death Point of a Number of Insects

THIS work is an attempt to investigate the eflfects of various atmospheric humidities on the death points of insects at high temperatures. A number of species of insects were used, and an attempt made to correlate the results with those of previous workers. The apparatus used was similar in essentials to that previously used by Beattie (1928) and by Buxton (1931 b). It is shown in Fig. 1. The whole apparatus was submerged in a tank of water heated electrically, and thermostatically controlled to within a fifth of a degree centigrade. Compressed air blown through the water kept it well stirred. The insects were placed in the Woolfe's bottle A, which was kept well submerged below the water. It was found that if only the necks of the bottle were above the surface, the air in A might be several degrees cooler than the water. The total submergence of A made it more difficult to introduce the insects, and the method is unsuitable for very large insects. A broad glass tube, B, was introduced into the middle neck of A. A small bag of bolting silk, D, containing the insects, was put down the tube B on a thin glass rod. The humidity in A was controlled by means of a layer of an appropriate mixture of sulphuric acid and water at the bottom, and fresh air could be blown in through C, another Woolfe's bottle containing pumice and the same acid as A. At the outlet, E, there was a piece of capillary glass tube to prevent undue backward diffusion.