274 MOSQUITOES OF NORTH AMERICA 



It would seem as if in this discussion the possibility of the conveyance of mos- 

 quitoes to ships by means of lighters for the discharge of cargo could not be 

 omitted. This is the common method of exchanging cargo in many tropical 

 ports and furnishes a ready means of transferring mosquitoes from the shore to 

 the ship. 



At an earlier date this question of distance of flight was considered by one 

 of us (Howard), and he endeavored to induce several surgeons in the U. S. Navy 

 to make observations. A series of notes were sent in by Surgeon A. H. Eussell 

 of the Navy, who made some interesting observations. With a vessel anchored, 

 say a mile from shore, and constant boat parties going to and fro between the 

 vessel and the shore, there is always the chance that Aedes calopus may be carried 

 under the coat lapels or even in the pocket of passengers. Therefore the occur- 

 rence of a few individuals on shipboard at this distance, and vsdth constant 

 traffic going on, is inconclusive. Eussell (in litt.) observed one instance, and 

 investigated all factors carefully, in which he apparently proved a flight from 

 shore to a vessel anchored a mile out, but it would be practically impossible to 

 eliminate all chances of error in such a case. 



Bearing upon the question of the origin of calopus on board ships the obser- 

 vations of Durham at Para are significant. 



*' It is said by captains that mosquitoes only commence to come on board when 

 the lighters which are used for the discharge of the cargo are brought alongside. 

 Seeing that the anchorage for the large ships is some two miles below the city, 

 and the lighters lying about the neighbourhood of the city are brought to wharf- 

 sides for discharge, they are a means of bringing city mosquitoes to the ships. 

 On examination, several of the large barges (which are covered with a rain- 

 proof metal cover) were found to harbour a certain number of the insects, both 

 S. fasciata and C. fatigans were found in the adult condition and a few larvae 

 of the former in the bilge water ; but these lighters had recently been cleaned up 

 and painted ; open lighters are also used, these were seen to contain abundant 

 rain water and tar and oily material from the coal for which they are used ; no 

 larvae were found in them. 



" During my trip up to Manaos, indiscriminate collection of all and any mos- 

 quitoes that could be found on board was made. Although a number were col- 

 lected it was not until after anchoring at Manaos and the lighters came alongside 

 that the species 8. fasciata was taken. It appears that the method of discharge 

 by means of lighters may be almost as risky for the importation of mosquitoes 

 infected in the city, as if the vessel was actually brought to the wharfside." 



Busck, on the occasion of his visit to Trinidad, made an observation which 

 bears upon the distance of flight of calopus. He states that at La Brea there is 

 a long pier, built by the asphalt company, near the end of which the superin- 

 tendent erected his house in order to be free from mosquito molestation. The ex- 

 periment was successful, and he lived in peace, until, later, another official, for 

 similar purposes, built a house in the middle of the pier. This apparently 

 afforded just the right interval for calopus to spread from the shore to the house 

 in the middle of the pier, and from that house to the one on the end of the pier, 

 and both houses became infested. The entire length of the pier was about 400 

 feet. 



