B. DeMeillon in 1936 and P. F. Russell and F. W. Knipe in 1939 reported their experiments in Africa and India, respectively, where the number of malaria cases was reduced by killing adult mosquitoes with sprays. In 1940 F. L. Soper and D. B. Wilson showed how they had been able to exterminate Anopheles gambiae in Brazil, partly at least, by using a spray containing pyrethrum, carbon tetrachloride, and kerosene. This eradication of an insect from a country is one of the most interesting chapters in medical history.

In 1940 W. N. Sullivan, L. D. Goodhue, and J. H. Fares published their first report on a new method for dispersing insecticides in air. This method suggested to Goodhue an entirely new and revolutionary approach to insecticide dispersal. The aerosol bomb they developed provided in a small package the most effective means known for killing adult mosquitoes within enclosures the release of the aerosol for a few seconds in 1,000 cubic feet of air space will kill all the mosquitoes in it.

When in June 1943 it had been shown that very small quantities of DDT sprays applied from the ground were effective against adult mosquitoes, the Orlando entomologists immediately started tests with aircraft. Aircraft had not previously been employed for controlling adult mosquitoes. If usable, this could be the means for reducing the adult mosquito population within a matter of hours, thereby immediately checking the spread of malaria and dengue among our military forces in various places. Special spray equipment was designed by Husman and the initial tests made against salt-marsh adult mosquitoes on the Florida Keys in November 1943. The results indicated that practically all adult mosquitoes could be killed by spraying 2 or 3 quarts of a 5 percent DDT oil solution per acre over dense vegetation. In December of the same year, the first tests were made with large combat planes, using Chemical Warfare Services M-10 tanks. Similar tests were followed in Panama in April 1944 where Lindquist and Husman practically eliminated the adults of Anopheles albimanus in jungle forest at 0.4 pound of DDT per acre with a10 percent DDT spray.

Their early research established the value of DDT aerial sprays for controlling adult mosquitoes and stimulated world-wide investigations by the Allied Forces. Airplanes became one of the most effective ways of controlling mosquitoes and mosquito-borne diseases wherever our troops were located.

Early in 1943, A. W. Lindquist, J. B. Gahan, B. V. Travis, F. A. Morton, Wisecup, Eide, and others at the Orlando laboratory found that the new DDT insecticide possessed unusual residual properties. Following intensive laboratory tests, their first field tests were made near Tallahassee, Fla., in August 1943. DDT applied in sprays on the interior surfaces at the rate of about 200 milligrams per square foot protected buildings for at least 70 days against infestations of the common malaria mosquito, the most important vector of malaria in the Southeastern States. Here was born the most important method yet devised for controlling malaria. The Orlando entomologists recommended this method of mosquito control to the Armed Forces who were experiencing many cases of malaria in various parts of the world.

In 1944 the Orlando entomologists tested two formulations under practical conditions near Stuttgart, Ark., a rice-growing area heavily infested with Anopheles mosquitoes. In two areas, each 9 miles square, the interior of every outbuilding was sprayed with an Oil solution containing 5 percent of DDT. The experiments confirmed the Tallahassee tests and recommendations were made for using 5 percent DDT sprays at the rate of 200 milligrams per square foot. The information was sent to our allied countries. Further large-scale tests were started by C. B. Symes, A. B. Hadaway, and G. Giglioli, in January 1945 in British Guiana, and by Gahan in New Mexico in April. The experiments were aimed at two very efficient but different vectors of malaria and were successful.

This research has been of great benefit to practically all peoples of the globe. In 1950 more than 800,000 homes in the Southeastern States were treated by Federal and State public health agencies employing DDT residual sprays. Elsewhere the World Health Organization reports a total of about 50 million persons as now being protected against malaria by this residual insecticide alone.

Military pickets, night laborers, explorers, and other personnel working in areas heavily infested with mosquitoes have sought constantly for some means of protecting their persons from mosquito bites. In 1910 Howard listed several essential oils for this purpose. Of these, the oil of citronella Was the most widely known repellent. It was effective for a few minutes to an hour, but some people preferred the stings of mosquito bites to the odor of citronella.

The first extensive research on mosquito repellents was begun by Phillip Granett of New Jersey in 1935. In 1940 he had developed a repellent that was greatly superior to all others. Unfortunately, however, this material, after being tested on experimental animals, was declared unsafe for use on humans.

When the United States entered the Second World War the need for a mosquito repellent became acute. The military services were particularly insistent on knowing of a good protective agent against mosquito bites. With funds allotted by the Office of Scientific Research and Development, the Department of Agriculture initiated an extensive research program in April 1942 at the Orlando laboratory. Many industrial companies and manufacturers cooperated in the investigations. Subsequently more than 10,000 synthetic organic chemicals in various formulations were tested against hungry mosquitoes by Travis, Morton, and their associates on the skin and clothing of men. Promising materials were also tested for their toxicological effects by the Food and Drug Administration.

Three materials and combinations of them were recommended to the military services dimethyl phthalate, Rutgers 6-12 (2-ethyl-I,3-hexanediol), and indalone (n-butyl mesityl oxide oxalate). These and a mixture of them, commonly known as 6-2-2, were standard insect repellents in 1952.

HEALTH CONDITIONS in many parts of the world have been revolutionized by mosquito control. Vast regions are now healthier, safer habitations for men as a result of the tremendous amount of research that has been carried on during the past 75 years. Today more than 25 million people of the United States live in areas where mosquito-control programs are in progress.

One of the world's most effective malaria-carrying species of mosquito was eradicated from Brazil between the time of its discovery in March 1930 and November 1941. Other eradication projects have been undertaken.

Still, mosquito research is far from finished. Each year, workers all over the world add hundreds of articles on mosquito investigations to a considerable bibliography already available. All this information is immediately put to practical use by the 250 separate local, city, county, State, and Federal mosquito-control agencies.

HARRY H. STAGE is assistant leader of the division of insects affecting man and animals, Bureau of Entomology and Plant Quarantine. After completing work at Syracuse University in 1917 and subsequent mosquito control work in the Navy in the First World War, he was employed as entomologist of the St. Louis Southwestern Railway Lines and actively participated for 10 years in malaria control in the area served by that railroad. From 1931 to 1940 he was in charge of the Bureau's northwestern laboratory on mosquito investigations. Since 1940 he has traveled extensively in the Arctic and the Tropics on various kinds of mosquito-control research.