Insects Taken at Rebecca Shoal from June 26 to July 18

The conditions on another of the Tortugas Islands are interesting in this regard. East Key lies 6 miles east of Loggerhead and is the most isolated of the group as well as least frequently visited by man. Although it has a fairly luxuriant growth of bay cedars and xerophytic shrubs, there is not a drop of water on the key, and hence no possi bility of mosquitoes breeding. On July 20 and found Aeries niger so numerous at dusk and daybreak that as many as 4 females would be attempting to bite at one time. A walk through the grass at sunset was sure to arouse several of the insects. As to the origin of the mosquitoes found on East Key, two or three sources may have con tributed. We have seen that on east winds a few of the Aeries niger migrated to the Rebecca Shoal light-station. Since East Key is only 12 miles farther west it seems likely that a few may also reach this island from Marquesas, but, no doubt, the greater number came in the migrations of July 5 and 11. It is known that they are capable of living for some time in captivity, and so may well have survived on plant juices from July 11 to 21.

On July 23 an examination of the fresh-water reservoirs at Fort Jefferson was undertaken to determine the extent to which mosquitoes were breeding there. It was found that all except one of the tanks

had been treated a short time before with kerosene, but this one con tained large numbers of larvae and pupae. Several hundred were transferred in glass jars to Loggerhead Key, where some were pre served and the others allowed to mature.

Since

Stegomyia calopus used to breed in the reservoirs at Fort Jeffer son it was expected that at least a part of these would prove to be of that species. But all larva and adults reared from them proved to be Culex pipiens Linnaeus. Not a single adult of this had been, or was later, taken either at Rebecca Shoal or at Tortugas. It is probable that the adults had been introduced by vessels visiting the fort and had deposited eggs in this reservoir. That the imagoes emerging from this source do not fly to other keys of the Tortugas 2 and 3 miles away is not surprising; Culex pipiens does not fly far from its breeding-place.

Unfortunately I did not succeed in determining the origin of the specimens of Stegomyia calopus which were taken on Loggerhead Key. The fact that the majority were males indicates that the breeding place was not far away; indeed, it is known that this species seldom flies more than a few hundred yards.