CONTROL OF FLIES 255 



applied repeatedly with continuous expenditure of time, labour 

 and money. Temporary methods must, however, sometimes be 

 employed, and various workers, mainly in America, have carried 

 out extensive investigations on the use of insecticides for 

 destroying larvae in their breeding places. 



Howard (191 1, p. 194) found it to be " perfectly impracticable 

 to use air-slaked lime, land plaster, or gas lime with good results. 

 Few or no larvae were killed by a thorough mixture of the 

 manure with any of these substances. Chloride of lime, however, 

 was found to be an excellent maggot killer," in the proportion 

 of one pound to eight quarts of horse manure. Ninety per cent, 

 of the larvae were kijled in less than twenty-four hours. 



While kerosene gives good results in small experiments, "on 

 a large scale this substance cannot be used with good effect," 

 owing to the difficulty of obtaining thorough mixing. 



Hermes found that fly larvae in manure are very tenacious of 

 life, and " that insecticides which will kill them must be strong, 

 in fact from two to five times as strong as those which are useful 

 against other insects." 



Howard (191 1, p. 197) quotes some unpublished experiments 

 by Forbes, of Illinois, which show that " the breeding of the 

 house-fly in manure can be controlled by the application of a 

 solution of iron sulphate — two pounds in a gallon of water for 

 each horse per day — or by the use of two and one-half pounds of 

 dry sulphate per horse per day." It is stated also that iron 

 sulphate has the advantage of completely deodorising the manure, 

 and does not appear to injure it or the soil to which it is applied. 



Any attempt to control the breeding places of flies in cities 

 must be regulated to some extent by local bylaws, which 

 might with advantage be based on the excellent regulations 

 enforced in the District of Columbia. Much can also be done 

 by suitable posters and leaflets, and by interesting the people and 

 educating the children. 



In camps and stations, where the night soil is buried in 

 trenches, special care is necessary in making the trenches suffi- 

 ciently deep, and in covering the excreta immediately after 

 deposition in the trenches with a sufficient quantity of soil. 

 The mere presence of dry earth over the excreta will not prevent 



