Because of its ability to cany diseases, the sheep tick should be classed as one of the most important ectoparasites of British sheep. No reason for the differences between individual susceptibility to infestation has been found.

Commercial arsenical dips are excellent acaricides, but give little protection from reinfestation, and are no better than watery solutions of sodium arsenite at the same concentrations of arsenic. In the work reported, addition of derris to the commercial dip did not improve it.

Coal-tar fractions which were tested were of little value in tick control, and five finely divided inert powders were not acaricidal.

D.D.T. and B.H.C. give promise of being of real value in controlling ticks; since the former is not effective against sheep scab, it is suggested that future research on anti-tick dips be confined to preparations containing B.H.C., the γ content of which is probably about as effective as D.D.T. against ticks when used at a 5 times greater dilution. Two commercial dips containing B.H.C. were found to be of little value.

A method of anti-tick treatment which involves walking sheep through a shallow bath of dip holds great promise.

Treatment of pastures with D.D.T. appeared to have no effect upon the tick population, and neither D.D.T. nor B.H.C. was effective against ticks when administered to sheep per os.

By stocking a pasture with sheep which were dipped sufficiently often to prevent any female tick from engorging, the tick population was almost completely eradicated in one year. Sheep which were born in the pasture in April 1948, and remained there until October 1949, were not dipped during 1949 and, as far as is known, were not at any time infested by ticks. Pastures from which all sheep were excluded gradually lost their tick populations, but a few ticks remained at the end of 3 years. This may be because, in the main enclosure, almost every tick would have an opportunity of attaching on a dipped sheep, and would be killed; in the unstocked enclosures, lack of opportunity to attach on sheep would result in a larger number of ticks infesting wild animals and so a few ticks would be carried over from year to year. This result is unlikely to have any practical application at present, because ridding a small area (e.g. a farm or a valley) of ticks would result in the sheep of that area losing their immunity to tick-borne diseases, and re-introduction of ticks might bring disastrous results. Also, it should be pointed out that work quoted in the text gives the result of an attempt at eradication in one county of Britain. Among other things, the fact that cattle, hare, and deer were absent immediately prohibits application of the results to many other areas of Great Britain. However, it appears that, in the absence of hare and deer, it might be possible to rid an area of ticks by adequate treatment of domestic animals.

It is a pleasure to acknowledge the helpful advice received from Dr H. H. Green of the Veterinary Laboratory at Weybridge, during the course of this work. The work was carried out under the auspices of a coordinating committee of the Agricultural Research Council and is published by permission of that Council, and of the Veterinary Laboratory of the Ministry of Agriculture.