MOSQUITO CONTROL TESTS — STAGE 357 



alhimanus Weid., an efficient vector of malaria in Panama, likes to 

 breed in large unshaded bodies of water where the mosslike aquatic 

 plant Naids comes to the surface. This plant forms a mat of vegeta- 

 tion that protects the larvae from wave action and from predaceous 

 fish. In preparation for the Gatun Lake test such an area was 

 found, several acres in size. Technicians from the Anny School of 

 Malariology took 200 half-pint samples of water from the "breeding 

 ground" and reported an average of a dozen mosquito larvae per 

 sample. A stable trap was set up on the adjacent shore line and baited 

 with a pony. At dawn of the day when the B-25 was to put out, 

 several officers and others visited the trap and estimated that about 

 15,000 mosquitoes had been caught, about half of them Anopheles al- 

 himanus. The pony was then taken out of the trap, the mosquitoes 

 were liberated, and the signal was given for the B-25 to put out the 

 spray. Five-percent DDT oil solution was applied at the rate of 2 

 quarts per acre. That evening the pony was returned to the trap. 

 The next morning we found 86 mosquitoes in the trap and found not 

 a single larva in 200 samples of water. Again, the kill appeared to 

 have been more than 99 percent (13) . 



The Army and Navy lost no time in getting this new technique 

 out to the islands of the Pacific. Thereby a great deal of suffering 

 on the part of our troops was prevented and many, many man-hours 

 were saved that would otherwise have been lost to the war effort. 



Our tests yielded valuable information on the kinds of weather 

 conditions that are favorable for spraying and on the desirable size 

 and distribution of particles of the different sprays. An Army officer 

 trained in biochemistry devised an ingenious method for collecting 

 droplets of the spray at 10- foot intervals of elevation from the ground 

 to the tops of trees about 125 feet high. He tied several large balloons 

 to the end of a stout cord, and at 10-foot intervals along the cord he 

 secured petri dishes in which glass slides had been fastened. Each 

 glass slide was covered with magnesium oxide. The pattern of the 

 pink- or blue-tinted spray was easily seen on the white-coated slides. 

 The size of the DDT particles and their distribution were recorded. 

 From this information we could check the amount of spray dispersed 

 per acre. 



DDT RESIDUAL SPRAYS IN MEXICO AGAINST ANOPHELES 

 PSEUDOPUNCTIPENNIS 



It was suggested by A. W. Lindquist and others of the Orlando 

 laboratory that malaria might be controlled by spraying DDT on 

 the walls and ceilings of dwellings and farm buildings. Laboratory 

 tests of pyrethrins against bedbugs by Lindquist and associates in 

 1942 demonstrated the soundness of the residual principle and the 

 feasibility of malaria control with residual treatments employing 



