78 Gerald F. Hill : 



(5) The period of viability of the insect when removed from the 



host, (a) when under one day old and unfed, (b) Avlien be- 

 tween tiiree and seven days old, and (e) in the adult con- 

 dition. 



(6) The period of viability of the pupa when removed from the 



host and kept under varying conditions. 



Historical. 



The sheep Louse-tiy is one of the best known external parasites 

 of the sheep, and has long been known in Europe and America as a 

 pest of some considerable importance. The life history and habits 

 -of thei fly are referred to briefly and more or less vaguely in many 

 text-books and" other publications. In many of these tlie writers 

 express widely different views upon such important details as the 

 length of life of the female Louse-fly, the number of pupae extruded 

 by the female and the intervals between each extrusion. Dr. Cooper 

 Curtice (189U), however, gives a more detailed account of the habits 

 of the parasite, and some of his observations will be referred to 

 later on in this Report. 



The records of investigations and observations by Dr. L. D. 

 Swingle (1913) are the most complete so far published. This inves- 

 tigator, after simie initial failures, was able to obtain precise infor- 

 mation on many points in the life-history of the parasite, which 

 appear to have been merely conjectured hitherto. He showed that 

 the period which elapsed between the deposition of the pupa, or 

 more correctly the larva, to the emergence of the young Louse-fly 

 was 19-23 days in summer, and 19 to 36 days in winter. Young 

 males and females, he found, are capable of copulating Avithin 

 -three or four days after their emergence, and the female reaches 

 maturity, i.e., extrudes the first pupa, fourteen to thirty days after 

 its emergence from the puparium. There is great mortality among 

 the young " ticks " before they take their first meal, but he was 

 able to keep female *' ticks " under observation for five and a-half 

 months, and considered that some of them probably live much 

 longer, although many die earlier. 



The rate of pupa laying, counting from the deposition of the 

 first one, was found to be one pupa every seven or eight days. The 

 number of pupae laid by an individual female depends upon the 

 length of her life. For a female living four months, which he 

 considered might be regarded as an average life-time, the number 

 is about ten to twelve pupae. For one living six months the 

 number is fifteen or inoi-e. 



