Genetic control of insects of public health importance.

During recent years many advances have been made in the development of insect control by genetic manipulation. These methods include the sterile-male technique, now well known, which depends on ionizing radiation or chemosterilization. The recent field experiment carried out by WHO in Rangoon, Burma, on Culex fatigans has demonstrated that naturally occurring cytogenetic mechanisms such as cytoplasmic incompatibility can be used successfully without the use of radiations or chemosterilants. The paper not only describes the experiment on Culex fatigans but also discusses basic concepts and theoretical considerations involved in genetic control of insects of public health importance. The possibility of using genetic mechanisms for the control of other vector species is also discussed. There are a number of problems which require study before genetic control can be used on an operational scale. These problems and suggestions for future research in this field are also outlined.

A possible model for speciation by cytoplasmic isolation in the Culex pipiens complex.

Evidence so far available indicates that in the Culex pipiens complex there exists a genetic system with unique properties not comparable with those of the chromosomal gene system and probably involved in a mode of speciation peculiar to this complex. In a long series of backcrosses it has been shown that probably every Culex pipiens population contains a factor that is inherited through the cytoplasm, the only phenotypic expression of which is the crossability or non-crossability (incompatibility) of a given strain with other strains. That there is a whole series of such cytoplasmic factors is indicated by the twenty or so crossing types of Culex strains found throughout the world.In closed populations it seems likely that, as a result of genic diversification, a modification occurs that will eventually lead to differences in traits determined by genes.