THE SIGNIFICANCE OF DDT-IRRITABILITY TESTS ON MOSQUITOS: WITH AN ANNEX ON RESULTS OBTAINED WITH THE IRRITABILITY TEST METHOD RECOMMENDED BY THE WHO EXPERT COMMITTEE ON INSECTICIDES.

The author reviews various laboratory investigations of the effects of insecticides on mosquito behaviour. The only extensive data on this subject concern the effects of DDT on irritability. The measurement of this response is discussed, and information is collated on the factors affecting it, such as the type and state of the insecticide, the species and physiological state of the mosquito and environmental factors including temperature, humidity, light and crowding. The author concludes that, despite the numerous difficulties associated with this subject, a sound technique (such as that recommended by the WHO Expert Committee on Insecticides) should be adequate to detect inherent differences in irritability between mosquito colonies, of a magnitude likely to be important in practice.An annex describes tests carried out by the author on strains of two anopheline and four culicine species with the irritability test method recommended by the WHO Expert Committee on Insecticides. Four DDT-resistant strains were less irritated by DDT than normal colonies, the difference being significant in the two culicine resistant strains.