AN APPARATUS FOR TESTING AND COMPARING THE BIOLOGICAL ACTION OF INSECTICIDES ON FLYING INSECTS AND A METHOD FOR SAMPLING THE CONCENTRATION OF THE ATOMIZED INSECTICIDE

S ummary1 An apparatus and method for testing the effect of atomized sprays on flies and mosquitoes are described. The apparatus consists of a revolving wire gauze cage placed in a thermostatically controlled chamber, the whole of which may be easily cleaned and freed from toxic residues. The insecticide is sprayed into the chamber by means of an Aerograph MP gun and distributed by means of a slow‐moving fan. When the insecticide has been injected and an interval allowed for the initial rapid fall of concentration, the movement of the cage is stopped and the insects are introduced into it by means of a special tube and plunger. The time required for paralysis to take place is recorded. After a given interval the insects are removed from the gauze cage and kept to ascertain the mortality. 2 A technique for sampling the concentration of insecticide in the air space is described. The insecticide carrier is coloured with a dye, Sudan III for petroleum oil bases and methylene blue for water bases. The percentage of atomized material remaining in the atmosphere at any given time is determined by aspirating a known quantity of the atmosphere of the chamber through a sintered glass filter. The dye is retained in the filter, it is washed out with a measured quantity of liquid and compared with known standards. Reasons are given for the assumption that the dye molecules will behave in the same way as the insecticide molecules. This sampling method has been used to study the behaviour of a light oil, a heavy white oil and water at different degrees of atomization. Tables and graphs are given which show that, except with a fine atomization where most of the insecticide remains suspended for a considerable time, there is an initial rapid fall, which varies in amount with the degree of atomization. This initial fall is followed by a much more gradual decrease of concentration. The experiments show clearly that oil bases of different physical properties cannot be compared adequately unless a sampling method is used to ascertain the quantities of material remaining suspended. Where water bases are used it is shown that the time concentration curve varies not only with the degree of atomization, but also with the degree of saturation of the atmosphere before spraying. The concentration remains higher in an unsaturated atmosphere than in a saturated one.