290 THE MOSQUITOES OF NEW JERSEY 



saturated. The former is chemically inactive, the latter chemically 

 active. 



Saturated oils kill mosquito larvae largely by suffocation. Unsatu- 

 rated oils kill the larvae by chemical attack on the protoplasm of the 

 wriggler. Destructive effects of unsaturated oil are correspondingly 

 greater to aquatic plants and other animals. In making up a set of 

 specifications for an oil larvicide, therefore, the degree of saturation 

 had to be taken into consideration. 



For efficient mosquito eradication oil must possess the following 

 properties : 



1. It must kill larvae and pupae within a short time after application. 



2. It must spread rapidly on the water surface in order to penetrate 

 all the hiding places of the larvae and pupae. 



3. It must produce a uniform, unbroken film on the surface so that 

 no wriggler can escape it. 



4). It must remain on the water for a comparatively long time in or- 

 der to kill the newly hatched larvae and to prevent the adult mosquito 

 from laying eggs. 



Experiments conducted at the New Jersey Agricultural Experiment 

 Station have shown that fractions of petroleum boiling at 200°-550°r. 

 are very toxic to larvae and pupae, giving complete kill within thirty 

 minutes. The higher boiling fractions possess lower toxicity, requiring 

 several hours to kill, meanwhile allowing mature pupae to develop into 

 adults. On the other hand, the low boiling fractions possess high vola- 

 tility and rapidly evaporate from the surface of the water, whereas the 

 high boiling fractions do not volatilize and only slowly decompose, 

 leaving an oil film on the water for a long time, thus preventing ovi- 

 position and hatching of mosquito eggs. 



A mixture of these fractions in proper portions produces an oil which 

 is highly toxic to larvae and lasts for eight days or longer. An oil of the 

 following specifications was found very efficient : 



Type of Oil Distillate Fuel 



Specific gravity 27°-33° Be. 



Flash point 130°F. (P.M.) or higher 



Viscosity 35-40 S.U. (a) 100°F. 



Odor Sweet (non-offensive) 



Distillation range, Degrees F 10 per cent — 430-450 



50 per cent— 510-550 

 90 per cent — 630 or higher 



