The Sterile-Male Technique for Control of Mosquitos: A Field Cage Study with Anopheles Quadrimaculatus

The use of sterile males to control a cage population of a laboratory strain of Anopheles quadrimaculatus was not successful, even though 80 to 90% of the females laid sterile egg clutches. At the ratio of sterile males to normal males being used, complete sterility should have been quickly achieved. Subsequent studies of the survival and sexual vigor of these sterile males indicated that only a small number, about 5%, of the released males were actually competing with normal males for the uninseminated females. Thus, until a more hardy and sexually vigorous male A. quadrimaculatus can be reared in the laboratory, the use of the sterile-male technique to control this insect seems impractical. Research was begun several years ago to adapt the technique of releasing sterile males to the control or eradication of mosquitoes. Davis et al. (1959) showed that doses of 8,865 to 12,000 R applied in the adult or pupal stage caused complete sterility in males and females of Anopheles quadrimaculatus Say. However, in the laboratory, males sterilized by gamma irradiation were not as competitive as normal males in inseminating females, although at high ratios of sterile to fertile males (6:1 and 10:1) production of viable eggs decreased more than 80%. In contrast, Weidhaas et al. (1962) were unsuccessful in either suppressing natural populations of A. quadrimaculatus or in causing a significant degree of sterility in wild females by the release of males sterilized by gamma irradiation. Also, when Dame et al. (1964) studied the behavior of released sterile A. quadrimaculatus from the laboratory colony and that of wild mosquitoes in the field, they concluded that the behavioral deficiencies of colony males prevented them from effective sexual competition for wild females though they were capable of mating effectively with released colony females. To gain a better insight into the problems associated with the release of sterile male mosquitoes, we decided to release sterile males into a population of A. quadrimaculatus breeding in a large outdoor cage. By using the caged population, we could study both the efficacy of the induced sterility and also the behavior and survival of a strain exposed to semi-natural conditions. The regular Gainesville laboratory colony of A. quadrimaculatus was used as a source of the sterile males and to start the cage population since it was difficult to establish a wild strain in the cage (several attempts had little success). METHODS AND MATERIALS The cage used for the experiment was 40 x 16 ft, and 12 ft high, and consisted of an aluminum frame covered by 20-mesh plastic screen. It The Florida Entomologist, Vol. 51, No. 2 (Jun., 1968), pp. 77-82 Published by Florida Entomological Society