Action of Inert Dusts on Insects

Abstract

IN his recent letter Dr. Wigglesworth¹ has explained the desiccating action of inert dusts on insects by the abrasion and perhaps adsorption of waxy substances forming a thin layer on the cuticle. The following results, which appear to confirm his conclusions, were obtained while comparing the dust resistances of various races and species of Drosophila, and spraying dust on some other animals. Of the various dusts tested, the loss of water was most accelerated by shaking the insects with charcoal of plant or animal origin. At 25° C. and 40–50 per cent relative humidity, Drosophila melanogaster flies were dead after eleven minutes, and D. subobscura after nine minutes, whereas in an atmosphere saturated with moisture, they survived for many hours. Mosquitoes, house-flies and house-spiders dusted with charcoal and kept in a centrally heated room died in less than an hour, and a young newt died in about two hours. Earthworms and slugs, on the other hand, were not killed by the dusts.