I UNIVERSITY OF WYOMING Agricultural Experiment Station LARAMIE, WYOMING. BULLETIN NO. 99 JULY. 1913 UBRARY O"TH~ UIJV£RSITY Of WYOMIN8 LARAMIE The Life-History ot the Sheep-Tick Melophagus ovinus LEROY D. SWINGLE. Par.. ito!ogiot Bulletins will be sent free upon request. Address Director Experi- ment Station, Laramie, Wyoming. UNIVERSITY OF WYOMING Agricultural Experiment Station LARAMIE. BOARD OF TRUSTEES. Officers. TIMOTHY F. BURKE, 1,1,. B President ARTHUR C. JONES Treasurer FRANK SUMNER BURRAGE, B. A Secretary Executive Committee. A. B. HAMILTON T·. F. BURKE W. S. INGHAM Members. Term Appointed Expires 1908 HON. GIBSON CLARK 1915 1911 HON. W. S. INGHAM, B. A 1915 1913 HON. C. D. SPALDING 1915. 1911 HON. ALEXANDER B. HAMILTON, M. D 1917 1911 HON. LYMAN H. BROOKS 1917 1913 I-ION. CHARLES S. BEACI I. ... .1917 1895 HON. TIMOTHY F. BURKE, LL. B 1919 1913 HON. MARY B. DAVID 1919 HON. ROSE A. BIRD MALEY, State Superintendent of Public Instruction Ex officio PRESIDENT C. A. DUNIWAY, Ph. D Ex officio STATION COUNCIL. C. A. DUNIWA Y, Ph. D , .. President HENRY G. KNIGHT, A. M Director and Agricultural Chemist A. NELSON, Ph. D Botanist and Horticulturist F. E. HEPNER, M. S Assistant Chemist J. A. HILL, B. S '" Wool Specialist O. L. PRIEN, M. D. V Veterinarian A. D. FAVILLE, B. S. , Animal Husbandman J. C. FITTERER, M. S., C. E , Irrigation Engineer S. K. Loy, Ph. D , Chemist T. S. PARSONS, M. S Agronomist L. D. SWINGLE, Ph. D Parasitologist KARL STEIK, M. A , Engineering Chemist JAMES McLAY Stock Superintendent C. D. MOIR , : Clerk F. S. BURRAGE, B. A ' , Secretary The Life-History of the Sheep-Tick Melophagus ouinu» BY LEROY D. SWINGLE. INTRODUCTION. This investigation of the life-history of the sheep-tick was made not only because of its scientific importance but also for :l basis upon which to determine effective methods for the utter eradication of the tick. It was the hope of the writer to publish at this time a complete paper on the life-history and eradication of this obnoxious associate of sheep, but owing to failure in . securing a large number of sheep for dipping experiments, it was decided to publish at this time only the results obtained i-i the investigation of the life-history, leaving for a later bulletin the eradication of the tick, which, however, has been worked out except for the practical dipping tests just mentioned. Let it he kept in mind that the life-history has been studied not so much from the purely scientific point of view, as from the standpoint of the eradication of the tick. The sheep-tick, a common and familiar pest, while known 10 biologi ts for many years, has not, so far as I am aware, re- ceived the attention that has been given to many other insects no more common and no more harmful. On this account prac- tical and unfailing methods of eradication have not been prac- ticed in this country. To be sure, many or perhaps most of the sheep-raisers dip their sheep yearly to destroy the tick, yet by the middle of the winter hundreds of these lance-armed pests are to be found living upon a single sheep. The reason is that the dipping was merely of temporary benefit, the life-history of the tick not being sufficiently known to constitute a basis for in- telligent dipping. 4 Wyo. Aqricultural Experiment Station. BUL. 99 The sheep-tick, contrary to general opinion, is not a true tick, such for example as the cattle-tick. Its whole life is spent on the sheep and therefore its life-history is less complex than of the true tick. The sheep-tick is more like a fly than a true tick. It possesses, as do flies, six legs; the true tick has eight. Zoologists regard it as a kind of fly that has lost its wings; it needs no wings, being parasitic during its whole life upon ani- mals that come in close contact with each other. Some authors claim that in addition to its bloodsucking habit, it eats the yolk matter in the wool. I have never seen' any signs of such a habit and am inclined to doubt that such is the case. However, a careful examination of the stomach contents. might show that such material is ingested. It is certain that the flagellates contained in their stomachs are generally obtained by eating the excrement from other ticks which are infected, and so it may be possible that the yolk matter is also sometimes eaten. LIFE-HISTORY. It is convenient for our purposes to divide the life-history into three stages, namely, the pupa, the young tick sexually im- mature, and the adult capable of reproduction . Yet this is a more or less artificial division. In the case of most insects, such for example as the house fly, there are four natural divi- sions, namely, the egg, the larva which hatches from the egg, the pupa, and the imago, or adult fly. In the sheep-tick there are present these natural stages, but they are not all apparent except when carefully studied by means of the microscope. The reason lies in the fact that the egg is not laid as in the case of the house fly, but is retained in a uterus where it undergoes development after fertilization, and forms a larva, this larva being nourished in the uterus by a kind of milk secreted by .glands which open into the uterus in the region of the larva's mouth. According to my own observations, the period required for the development of the larva is generally not over a week. When the larva has become so large as to greatly distend the The Life-History of the Sheep-Tick. 5 abdomen, it is born. According to Pratt (1889), the puparium" is completed about twelve hours after the larva is born, and it is not proper to say that the tick gives birth to a pupa. After a variable period of development, the pupa hatches into a young tick, which soon becomes capable of reproduction. These then are the natural stages in the life-history, but for convenience I shall use the term pupa to designate the offspring from the time of birth till it hatches into the young tick pos- sessing the external characters of the sexually mature, or adult tick. In external appearance the larva, as soon as it is born, is the same as the true pupa. The pupa when laid is covered with a white chitinous membrane which soon turns dark brown and hard and is then known as the puparium. Along with the pupa is deposited a gelatinous substance which serves to glue the pupa to the wool. This glue is readily soluble in water yet when dry constitutes a firm cement. FIG. 1. Enlarged drawing of pupa. a. Lid which ope n s , allowing young tick to es- cape. FIG. 2. Enlarged draw- ing of adult female sheep- tick. The two stages, pupa and adult tick, are represented in the figures 1 and 2 respectively. The natural sizes are approxi- mately represented by the lines at one side. The pupae can readily be found by anyone who will examine ticky sheep by separating the wool along the neck, shoulders, belly and thighs, ·Pratt and otbers quoted In this paper use the term puparlum to denote the pupal stage. Packard (1898) uses tbe term in a narrower sense, desig- nating merely the old larval hardened skiilwhlch surrounds the aott pupa within. 6 WyQ -, Aqricultural Experiment Station. BUL. 99 They are rarely found high up near the back region of the sheep. The main objects of this investigation of the life history were: To determine the incubation period of the pupa, i. e., the time elapsing between the laying and the hatching of the pupa; To determine the time required by the young tick to reach sexual maturity, i, e., the time elapsing between its hatching and the laying of its fir t pupa; To determine the length of life of the female tick; To det~rmine the number of pupae laid in a life time, and the rapidity with which they are laid.* The methods used to determine the incubation period of the pupa were such as to place the pupae under quite normal conditions. As far as I have been able to discover from the literature available, the incubation period is known only for pupae kept in boxes in the laboratory. In the fir t method to be tried several females containing large larvae were collected. The larvae are readily recognized as large white bodies distending the abdomen. These ticks were placed in cups on the sheep made in the following man- ner. A ring was sheared in the wool close to the skin, the wool in the center of the ring being left. Then a muslin band was pasted by means of Le Page's glue perpendicular to the skin and against the outer wall of the furrow made by shearing the wool. A vertical section through the area is shown in figure .t. FIG. 3. Vertical sectlon showing breeding cup. a. Wool. b. Skin of sbeep. c. Oloth cover. d. OJoth band pasted to the wool. To the top of this band a cheese cloth or muslin cover was sewed, the ticks having been placed within the cup thus formed. 'The egg and intra-uterine tages of the tick have been accurately worked out by Pratt (1893 and 1899). The Life-History of the Sheep-Tick.