A Study of Mosquito Behavior. An Experimental Laboratory Study of the Sexual Behavior of Aedes aegypti (Linnaeus)

Abstract

Exptl. evidence is presented to confirm Johnston''s and Mayer''s hypothesis that in Culicidae Johnston''s organ is aural in function, an assumption previously based chiefly on morph. evidence. Expts. also proved that the males perceive vibratory stimuli as had been hypothesized in the literature. The front and middle tarsi of the male are structurally suited for seizing and holding the female. The hind tarsi take little part in mating. The female tarsi are not suited for seizing and she does not cling to the male or hold him to her during copulation. Knab''s hypothesis that the positions assumed by mosquitoes during cop-ulation are correlated with the female tarsal claws is unfounded. The hypothesis is suggested that the face-to-face and end-to-end positions assumed by different spp. of mosquitoes during copulation might be correlated with the degree of development of the last tarsal segments and claws of the male''s front and middle legs. The sound produced by the female of A. aegypti in flight is the external stimulus which attracts and induces the male to copulate. Odor and sounds other than those made by the female in flight play no role in the mating behavior. The male attempts to copulate when a sufficient number of antennal fibrillae are ex-tended making possible the perception of the sound of the flying female. This occurs about 15 to 24 hrs. after emergence and by this time the hypopygium has rotated sufficiently so that copulation can be successfully completed. Copulation occurs only when the female begins to fly voluntarily at least several hrs. after emergence. By this time she becomes "attractive" because the sound she makes in flight falls within the range which will stimulate the male. Sexually active males cannot differentiate between recently emerged males and old females. The male responds to a range of sound frequencies rather than to a single fixed frequency; thus aegypti males attempt to copulate with males and females of several different spp. of Culicidae because the sounds made by these mosquitoes fall within a stimulating range. The instinctive mating behavior of aegypti males whether elicited by a female mosquito or by mechanically produced sounds, as by tuning fork, is basically the same. The seizing response elicited by the sounds of tuning forks or an audio oscillator-speaker consists of clinging with the front and middle legs to the cloth of the cage, and vibrating the wings rapidly. The clasping response usually follows the seizing response and consists of flexing the abdomen ventrad. The upper and lower limits of sound frequencies which will induce a mating response from aegypti males are about 100 and 800 cycles per sec. The limits vary with the age and virginity or non-virginity of the males. With increase in age both virgin and non-virgin males respond to a wider range of sound but the range of non. virgins which have copulated repeatedly is narrower than that of virgin males kept isolated from females. The practical application of the response of mosquitoes to sound is discussed and it is concluded that, at present, it appears unlikely that a killing device employing sound as an attractant would be a more efficient or economical substitute than the present methods of mosquito control.