138 AGRICULTURAL EXPERIMENT STATION. 



sand tlie material is fatal to many fish and harmless to most larvae, 

 hence the results of the application might be contrar}^ to what was 

 intended. 



Salt to check breeding- in fresh water areas was tried because 

 ia many places water barrels and casks are placed on bridges and 

 trestles by railroad companies and others to provide material for 

 putting out fires. Fire buckets partly filled with water are also 

 placed in the halls of hotels, and all of these furnish excellent 

 breeding places for C. pmigens and restiians, as well as, occasion- 

 ally, some other species. If the simple addition of salt would 

 prevent breeding it would be easy to secure its addition to the 

 water on the double pleas that it would keep off mosquitoes, add 

 to the eft'ectiveness in fire fighting and retard freezing in winter. 

 Unfortunately, while the saUed pails were not so readily selected 

 for oviposition, yet, unless the salting was very heavy, they did 

 appear in small numbers. On the other hand, the addition of 

 salt to water in which larvae were already present exercised no 

 bad influence upon them. They simply matured a little faster. 



Lime is another common, easily obtained and cheap material 

 and its general sanitary effect is desirable even if as a larvicide it 

 is not quite so active as some others. I found that in pails and 

 tubs into which a lump of lime was thrown, the water would stand 

 for weeks without becoming infested by wrigglers, while neigh- 

 boring pails were swarming, and I have often observed that in old 

 lime buckets where there was an icing of lime over the surface no 

 larvae were ever found. Lime then, used freely in the barn yard 

 and in offensive or muddy pools will sweeten the surroundings 

 and check moscjuito breeding to a verv considerable extent. It 

 will not answer where there is much addition of water and it must 

 be used in considerable amounts to be effective. 



Chloride of Lime is much more active and even so small a quan- 

 titv as fourteen grains in one quart of water will kill all stages 

 except pupae ready to transform in a few hours. This makes an 

 excellent material for treating gutters and drainage ditches. It 

 should be finely divided for this purpose and should be spread 

 or dusted freely over the surface. Used as it is ordinarily ap- 

 plied for disinfecting purposes, it is quite sufficient to destroy 

 mosquito larvae. 



It will be noticed on reading over this section that there are 

 really two different tvpes of materials that are used as larvicides ; 

 those that make a film on the surface through which the larvae and 

 pupae cannot safelv penetrate to breathe, and those which mix 

 with the water itself and either poison it or destroy the food of 

 the larva. Each type has its advantages and its limitations. The 



