Common Insect Enemies 111 



fly lays its eggs in manure and decaying vegetation; the stable 

 fly lays its eggs in fermenting plant produas; and the horn 

 fly lays its eggs only on fresh cow manure. A knowledge of 

 their breeding habits is of considerable help in the control of 

 these inseas: treat manure piles and decaying vegetation 

 with DDT and keep down the fly population. 



To kill the flies around the barn, both the building it- 

 self and the cattle should be treated. A residual spray ap- 

 plied to the walls of the barn twice a year — May and August 

 for best results — will reduce the fly population to a very low 

 figure, for all flies that touch the treated surface will die. A 

 5 % DDT-kerosene spray, a 5 % emulsion, or a 2/4% disper- 

 sion of wettable powder (approximately 2 pounds of 50% 

 wettable powder to 5 gallons of water) are all satisfaaory 

 for application to barns, but of these three, the wettable pow- 

 der is perhaps the most popular, for it is nonflammable and 

 it is not readily absorbed by porous surfaces — rough wood 

 and concrete — such as are found in barns. For best results, 

 a gallon of the 2 % % dispersion should be used for approxi- 

 mately each 300 square feet of surface. 



For direct application to the animals, the oil solution, 

 of course, should not be used, but either the emulsion or the 

 dispersion of wettable powder can be applied without harm 

 to the animals. A single application of about a 2% % emul- 

 sion or dispersion of wettable powder, applied as a spray at 

 the rate of about 1 quart per adult horse or cow, will effec- 

 tively control the horn fly as well as other flies for a few 

 weeks or more. When applying the spray, particular at- 

 tention should be paid to the belly, rump, and back. 



An alternative method of applying DDT to animals is 

 by means of a dip, but when a dip is used the concentration 

 of DDT should be much lower than when a spray is used: 



