186 MOSQUITOES 



of the water by means of cloths tied to the end of a long- 

 stick and saturated with kerosene. The use of such a 

 mop may be desirable, even where a straig-ht discharge 

 lium[) has been used, in order to commingle two suiface- 

 sheets of oil. 



Tlu^ question as to the frequency of application of 

 kerosene is an important one. In my early 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 tlie water had ceased to be per- 

 ceptiV)le to the eye. A sing-le 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 tlie 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 per- 

 fectly effective under nearly all circumstances, for at least 

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

 no mosquito can alight upon the surface and succeed in 

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

 larvjc hatching from such eggs Avould be kilhnl. There- 

 fore we must calculate from the end of such an etVective 

 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- 

 (jnito hirva to reacli full growth, and tlie i)upa to become 

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

 week must be added at least a W(>ek of larval and ])upal 

 growth, wliich Avould require a second application of kero- 



