The prevalence of Aedes aegypti in early summer in Texas cities is very variable. Only in the Lower Rio Grande Valley is the winter climate mild enough to allow this mosquito to survive, without protected hold-over places, in sufficient numbers to produce a high incidence of breeding early in the season every year. In other cities early prevalence of breeding is associated with abundance of protected winter hold-over places, especially cisterns, fire-protection barrels in compresses and warehouses, or shallow wells. In cities having only a few such hold-over places, a high breeding index does not develop until late summer, and in many smaller cities such an index may not develop at all unless the mosquitoes are imported from elsewhere in automobiles or freight cars. In such cities the occurrence and prevalence of Aedes aegypti may vary from year to year depending on whether or not such an importation occurs early in the season. In coastal cities, alternation of cold and warm periods during the winter has a harmful effect on the survival of Aedes aegypti, and may be more important in holding the insect in check than the extremes of cold, or the total amount of cold weather.
Special Consultant, Malaria Control in War Areas, U. S. Public Health Service, Rice Institute, Houston, Texas.