DESTROYING AND REPELLING MOSQUITOES 89 



elusion, after many experiments in small ponds, that a 

 combination of the goldfish, which is ornamental and useful 

 in the open water, the roach or shiner, which is a very 

 active species, two small species of sunfish, which live 

 among plants, and the top-minnow would probably prove 

 to be more effective in preventing mosquitoes breeding 

 than any other fishes." 



OIL AS A REMEDY FOR MOSQUITOES 



The power that oil has to kill the larvae and pupae of 

 mosquitoes has been known for some time. Its practical 

 use against these insects has been of comparatively recent 

 date. 



How it kills. — If oil be poured upon water, it will sooner 

 or later spread evenly over the surface in a thin film. 

 This film has a comparatively strong tension, and speak- 

 ing from the standpoint of an insect, is very difficult to 

 break. The larvae and pupae of the mosquitoes, as we 

 have already shown, breathe air direct by thrusting the 

 ends of the respiratory tubes out of the water. As they 

 come up beneath the oil film, to obtain air, they are unable 

 to push their tubes through the oil, and thus are completely 

 shut off from the air and in a short time drown from suffoca- 

 tion. It may also be said that the oil, as it comes in con- 

 tact with the respiratory tubes, produces injury which 

 hastens death. If any eggs are lying on the surface of 

 the water and are touched by the oil, they are destroyed. 

 Likewise the adult female mosquitoes are caught in the 

 oil and killed when depositing eggs. 



Kinds of oil to use. — In all my experiments ordinary 

 kerosene oil, such as is used for illuminating purposes, 



