Relation of DDT-Irritation Threshold to Knockdown of Three Species of Anopheline Mosquitoes1

Abstract

The threshold of irritation was determined for bloodfed and unfed females of Anopheles albirnanus Wiedemann, A. aztecus Hoffmann, and A. quadrimaculatus Say taken from laboratory colonies. By means of a special device each mosquito which flew off from the DDT-treated surface was trapped in a container, where it remained in almost continuous contact with the insecticide until knockdown occurred. When the exposure times which provoked a response to irritation (thresholds) were compared with the exposure times resulting in knockdown, no correlation was found between the records for the same specimen. But summarizing all the observations (made 5 times with 20 mosquitoes of each species, with bloodfed or unfed females) the collective results indicate that the most irritable species, A. albimanus, is also the most susceptible one to the knockdown effect. The comparison of the thresholds of irritation between unfed and bloodfed females showed that nourishment influenced the various species to a different degree. Among A. aztecus almost no decrease of irritability was caused by the replete stomach, whereas bloodfed A. albimanus, as well as bloodfed A. quadrimaculatus, were approximately one-half as irritable as unfed females.