CHAPTER XIII 



ATTACK ON PROPAGATION AREAS BY CLEARING 

 BODIES OF WATER 



DY removing vegetation, algae, and drift from 

 '-^ bodies of water, much of the food and most 

 of the protection of Anopheles larvae are withdrawn. 

 Under normal conditions these larvae prefer to 

 remain at the surface of the water where they find 

 their food. 



Where vegetation in the water is plentiful, it is 

 difficult to use oil effectively, and in order not to 

 leave any air holes large quantities must be used. 

 Vegetation interferes with the spreading of the oH 

 film; it also interrupts the action of the larvacide. 

 When rank grasses come up through the water it is 

 not easy to see if the oil film is satisfactory or not. 

 In moving water, such as ditches and streams, where 

 the vegetation is removed the current velocity is in- 

 creased, and tends toward washing the larvae away ; 

 and by leaving no hiding-place during rainstorms, 



the stream or ditch can be swept clear of larvae. 



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