40 



CIRCULAR 14 8, U. S. DEPARTMENT OF AGRICULTURE 



the eggs are laid. Each female may lay from 10 to 25 eggs during 

 the egg-laying period, which probably lasts from 12 to 15 days. When 

 that period is completed the female dies in her burrow. The entire 

 life cycle is passed on the bod} 7 of the host animal. The eggs hatch 

 in from 3 to 10 days, and the young mites after passing through 

 several molts reach maturity and begin laying eggs in 10 or 12 days. 



As the average period of incubation on the animal is about four 

 days, and the average period after hatching until egg laying begins is 

 11 days, a new generation of mites may be produced in about 15 days. 

 If the first treatment or dipping could be depended on to kill all the 

 mites on the animal the time for the second treatment could be calcu- 



Hea 



and shoulders involved 



lated accurately. Unfortunately, the first treatment usually does not 

 kill all the sarcoptic mites on the animal because of the difficulty of 

 getting the dip or other insecticidal substances into the burrows and 

 in contact with the mites. Practical experience has shown that the 

 interval between treatments or dippings should be from five to seven 

 days. 



Symptoms. — In the early stages of sarcoptic mange in horses the 

 first visible lesions usually occur on the neck or shoulders or around 

 the head, but the disease may start on the breast, flanks, sides, or other 

 parts of the trunk. From these parts the disease spreads until the 

 entire surface of the body may become involved. 



