Insects and Parasitic Diseases. 77 



PART 11. 



Certain points in the Life-History of Melopliagus oviniis, Linn.^ 

 the Sheep Louse-fly, or " Sheep-Tick." 



Introduction. 



The life-history and habits of the Sheep Louse-fly, or " Sheep- 

 Tick '' (Melophagus ovinus Linn.) have been known for many years^ 

 as a result of investigations carried out in Europe and U.S.A. 

 Prior to 1916 there do not appear to have been any similar investi- 

 gations carried out here, and as there was no known marked dif- 

 ference in Australia from the life-history of the pest as known 

 elsewhere, legislation for the control of the Sheep Louse-fly by dip- 

 ping was introduced accordingly. The enforcement of the Sheep' 

 Dipping Act, however, has not had the effect of eradicating the 

 pest. Many sheep-owners contend that this failure is due to the- 

 fact that the Louse-flies and their pupae become dislodged from 

 the fleece of the host and remain viable in the grass, brushwood, or 

 elsewhere, for a longer or shorter period, during which the pupae 

 develop into young Louse-flies, which, Avith similarly dislodged 

 adults, subsequently infect " Tick ^'-free sheep. 



In view of the importance of this contention it seemed desirable 

 that the points in question as well as others in the life-history and 

 habits of this pest should be investigated. With this object in view, 

 certain experiments were begun by Sweet and Seddon in this Insti- 

 tute in the summer of 1916, but though they showed some difference 

 from observations elsewhere they were still incomplete, and re- 

 quired confirmation and extension. The present writer therefore- 

 commenced a series of observations and experiments in May, 1917, 

 to verify under a. variety of conditions, the work of Swingle in 

 U.S.A. and Sweet and Seddon in Victoria, and also to determine 

 the period of viability of the pupa when removed from the ho'st. 

 The chief subjects upon which further information was sought 

 were : — 



(1) Incubation period of the pupa on the host. 



(2) The period required by the young Louse-fly to reach maturity 



— i.e, the period elapsing between its emergence from the 

 parent and the extrusion of the fii'st offspring. 



(.3) The length of life of the female fly. 



(4) The number of pupae extruded by an individual female and 

 the time elapsing between each extrusion. 



