MIGRATION OF INSECTS TO REBECCA SHOAL LIGHT- 

 STATION AND THE TORTUGAS ISLANDS, WITH SPECIAL 

 REFERENCE TO MOSQUITOES AND FLIES. 



BY S. C. BALL. 



INTRODUCTION. 



For the purpose of determining whether mosquitoes can, either by 

 their own powers of flight or with the aid of favorable winds, migrate 

 across the sea for considerable distances, the writer spent the period 

 from June 26 to July 18, 1917, upon the Rebecca Shoal light-station. 

 The work was undertaken under the auspices of the Carnegie Institu- 

 tion of Washington, Hon. G. R. Putnam, Commissioner of Lighthouses, 

 having kindly granted permission to study at Rebecca Shoal light- 

 house. Moreover Dr. L. 0. Howard has kindly made timely sugges- 

 tions respecting classification, but he is in no sense responsible for 

 statements expressed herein. Except Stegomyia, the names of mos- 

 quitoes used are from Howard, Dyar and Knab, 1917. 



The circumstances which suggested the desirability of such investi- 

 gations were the repeated experiences of Dr. Mayer and other scientists 

 at Tortugas, Florida, in connection with the occurrence there of mos- 

 quitoes. It appeared that these insects were abundant on Loggerhead 

 Key only after northerly winds of several hours' duration in other 

 words, under conditions favorable to their migration from the mainland 

 of Florida. Owing to the care which would be necessary in order to 

 prevent absolutely the breeding of mosquitoes on the several keys of 

 the Tortugas Group, particularly at Fort Jefferson on Garden Key, it 

 was thought advisable to make observations at the nearest point to 

 Tortugas where this difficulty could be overcome. 



Rebecca Shoal light-station was chosen (1) because of its isolation 

 from the mainland and other keys, and (2) because of its freedom 

 from all except easily controllable breeding-places for mosquitoes. 

 The lighthouse stands in 12 feet of water upon Rebecca Shoal, a small 

 and entirely submerged part of the Florida Reef, 12 miles east of the 

 Dry Tortugas and 48 miles west of Key West. The nearest point upon 

 the mainland of Florida is Cape Sable, 105 miles northeast. Havana 

 lies 95 miles to the south on the Cuban coast, while Cape San Antonio, 

 at the western end of Cuba, bears southwest from Rebecca Shoal at a 

 distance of 230 miles. Cardenas Bay lies 135 miles to the southeast. 



Between Rebecca Shoal and Key West several keys of the Florida 

 Reef intervene. Most important in relation to insect migration is the 



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