356 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



plot the mosquitoes landing on them in a 2-minute period at dusk and 

 another at dawn. Twice daily for about 5 days before the plots were 

 treated and for 14 days after treatment trained members of the Medi- 

 cal Corps made such counts. The well-defined trails and labeled 

 stakes made it easy for these men to find their stations, where they 

 promptly began counting mosquitoes when a signal gun was fired. A 

 total of 5,501 man-days were employed in preparing for and com- 

 pleting the tests'. The second method was use of stable traps. A m.odi- 

 fied stable trap of a design conceived by E. H. Magoon, of the Rocke- 

 feller Foundation, was placed in the center of each of the plots. Sev- 

 eral times before the spraying was begun we placed a Panamanian 

 pony in each trap at dusk and next morning counted the mosquitoes 

 that had been caught in the trap during the night. On the morning 

 of our first trial, the stable trap in the plot that was to be treated con- 

 tained so many mosquitoes that an actual count was impossible. 

 The estimate agreed upon was 10,000. The mosquitoes were allowed to 

 escape. Thirty minutes later a B-25 roared overhead spraying a 5- 

 percent DDT fuel-oil solution at the rate of 2 quarts per acre. Next 

 morning some 30 of us — Army medical officers, entomologists, techni- 

 cians, and others — left Panama City at 4 a. m. and were at the stable 

 trap before daybreak. With the aid of flashlights we peered into the 

 trap to see how many mosquitoes had turned up to feed on the pony 

 the night after spraying. We located just 1. The counts were con- 

 tinued for about 2 weeks and the numbers of mosquitoes rose slowly 

 to 200 during that time. The numbers of mosquitoes recorded in one 

 plot left untreated were then compared with the numbers recorded 

 in the five treated plots. 



For the first time, specific data were available on the effectiveness 

 of DDT spray applied at a known rate upon a population of Anoph- 

 eles^ Mansonia^ Aedes, and Culex adults. It appeared that within 

 24 hours we had reduced by more than 99 percent the adult mosquito 

 population within an area of dense jungle 1 mile long and ^ mile 

 wide. With that kind of result there was every reason to believe we 

 could control the spread of malaria, dengue, or any other mosquito- 

 borne disease within a matter of hours. 



Before the treatment, members of the Army School of Malariology, 

 C. Z., had put in several places on the ground small buckets of water 

 containing Aedes aegypti (L.) larvae. Twenty-hour hours after the 

 treatment, 70 to 90 percent of these larvae were found dead. Some of 

 the buckets had been placed under heavy or wide-spreading leaves, 

 but this protection had not saved the larvae. The results seemed really 

 too spectacular ; some of the experimenters were skeptical of them until 

 subsequent tests gave approximately the same results. 



Two or three weeks after these tests we sprayed an isolated section 

 of Gatun Lake and the adjacent shore line from a B-25. Anopheles 



