186 MOSQUITOES 



of the water b}^ means of cloths tied to tlie end of a long' 

 stick and saturated with kerosene. The use of such a 

 mop may be desirable, even where a straight discharge 

 pump has been used, in order to commingle two surface- 

 sheets of oil. 



The question as to the frequency of application of 

 kerosene is an imi^ortant one. In my earl}^ experiments 

 I found that the kerosene was effective for some days 

 after the odor had disappeared and after the iridescent 

 effect upon the surface of the water had ceased to be per- 

 ceptible to the ejQ. A single application to a small pool 

 was certainly effective from twelve to fifteen days. The 

 persistence of the oil, however, will undoubtedly vary 

 with the temperature and with the character of the pool 

 — whether exposed to the direct rays of the sun or shaded 

 by trees. It is, at all events, safe to say that it will be j)er- 

 fectly effective under nearly all circumstances, for at least 

 a week, and probably longer. That means that for a Aveek 

 no mosquito can alight upon the surface and succeed in 

 depositing eggs, and that even if she could do so the 

 larv?e hatching from such eggs would be killed. There- 

 fore we must calculate from the end of such an effective 

 period to the end of the growth of larval and pupal life, 

 and just before this second period is reached the applica- 

 tion should be renewed. Under the most favorable cir- 

 cumstances it will take from seven to ten days for a mos- 

 quito larva to reach full growth, and the pupa to become 

 ready to give out the adult. Therefore, to the kerosene 

 week must be added at least a week of larval and pupal 

 growth, which would require a second application of kero- 



