68 The Control of Mosquitoes 



granted that Anopheles are absent. There are 

 some prolific breeding areas whose importance 

 cannot be determined without a thorough and 

 painstaking examination. 



Many lagoons, ponds, etc., have been seen 

 where larvae were not present near the shore line, 

 but were very numerous in protected portions of 

 deeper water. Water more than a foot deep, free 

 from vegetation, debris, algae, etc., is generally 

 non-productive. It often happens that numerous 

 larvae are present only in particular parts of a large 

 and apparently suitable breeding place, and it 

 should be thoroughly investigated before any 

 conclusions are drawn regarding its possibilities. 



Again, some areas may produce a species of 

 Anopheles larvae only at certain times, and it is 

 wrong to conclude that because results are nega- 

 tive to-day the conditions will not change sooner 

 or later. Seasonal changes have an important 

 bearing upon mosquito propagation. 



In clear water such as reservoirs with clean 

 edges and abrupt banks, more or less finely divided 

 debris collects and is often removed from one side 

 of the lake to the other by winds. Larvas are 

 frequently present in this mass, and apparently 

 the small fish cannot reach them. Marked wave 

 action prevents mosquito production. If the 



