THE SHEEP BLOWFLY.

New Zealand Herald, Volume LXI, Issue 18709, 15 May 1924, Page 12

THE SHEEP BLOWFLY.

' RAVAGES of the PEST. ; .<5 -yfci /j ■■■ ■". '£*' •' V /v V. • 1 ORIGIN and: treatment. METHODS OF PREVENTION. ; A most extraordinary theory i& being advanced regarding the cause of the ravages by the sheep . blowfly, and an equally extraordinary remedy (remarks Dalgety's Review) is being propounded for its cure. It appears that this theory was set out by Dr. W. M. Sinclair, who, in the course of some extensive investigations on cell structure, was attracted to the problem. The blowfly he considers is, on the whole, beneficial in - removing offal, which without its agency would render patts iof the earth' almost uninhabitable. > .. ' '' .

The source .of blowfly attraction .• ,tt sheep, as is generally known, lies ii the skin of the animal, and this is suffi ciently easily demonstrable to render ii uiiT»cessary to; ascribe the condition ,tc any changing habit of the fly. If unchecked no doubt in time fly larvae would develop the ability to digest flesh.. At present, however, these ; latter, although they swallow blood and other flesh juices in his opinion depend absolutely for their digestion on certain bacteria engulfed with the food, or supplied by the fly from its filthy feeding grounds. If fly larvae an freed from .bacteria they die, even in the presence of an abundance of fresh isterile food: '■•-'■ ; f ,'-. :'• i -'■' ■* . ' , These bacteria, always present on the skin of the sheep, are held in check by the normal greasiness of the fleece, but where' moisture occurs they multiply rapidly, decomposing certain scurfy waste and "creating more by irritation, thus supplying not only a suitable food for fly larvae, but bv the odour of decomposition both . attracting the fly and stimulating it to -deposit its larvae on the sheep. How to Remove Attraction.

In order to starve the larvae and render the sheep unattractive to the fly all that is necessary, Dr. " Sinclair states, is to prevent bacterial multiplication in the fleece, in spite of any moisture. This latter, of course, ■: cannot he prevented under natural conditions, as the better the sheep from a commercial point of view the more liable is its fleece to become moist. It has been found : possible, he asserts, to prevent: this v, bacterial overgrowth by certain chemicals, prepared in ; such ,/, a , manner that whan placed on the unbroken skin they are readily absorbed into the blood'of the sheep, and are thrown out bv the sweat and yolk ; glands to the extent of the wool, a"nd j there uniting with the skin scurf are retained at the point where bacterial multiplication commences and .from its nature prevents the overU : growth., < . •If the animal is already struck and the skin, broken direct application to the moist area : is necessary, owing oto the already large bacterial .flora. ' The larvae ' it is claimed, then immediately ceas« irritating the sheep, and soon, drop off,, the sore healing rapidly. - As the' sheep sheds the skin scurf after shearing owing to exposure to i cold, only then is the protection removed,, and a fresh application '.' is necessary about ' three • weeks, after shearing. •'.{;?:. . .Kl ; -It has 'been ; found that a form.of mercury in the proportion of 1 to 500.000 '■ prevents the multiplication of '% bacteria, and can be deposited on the skin of the sheep from the -- blood in a 1 proportion of 1:; to 10,000, thus c : effectually .preventing germs- growth. ''-r' : .:. : ■::.;;.■? ] Tests are - being , conducted on fly-in-fested, sheep at the Homebush. (N.S.W.) sateyards to ascertain'^ the'effects of v the" new? treatment, and arrangements .are being made to' conduct exhaustive-trials. on some of the experiment farms under Government supervision. -y. ; - . - \ r . 1 Advice to Sheep-Owners.

Dr. , Sinclair may be' solving the problem, 1 but in 1 the meantime sheep-owners are well ; advised to continue the means for controlling the ■. pest : as " previously pursued \by them, and as recommended by the New South. Wales Government ■ Entomologist arid Pastoral Fly Committee. . Tne > dryness of the „ season keeps .the sheep ] blowfly from increase in ;; many districts. '''i s W'* ? ,. ": ':•'.'" ■ ■''' ■"/-*- \ The chief lines of attack 1 upon r this pest, have" hitherto been:—The - reduc- „■"-' tion •»; of the various species of' blowflies by the propagation of parasitic enemies (chiefly minute .wasps): ; the ; capture ; of . the flies -in baited traps; • the destruction of ':■ the larvae by means of;poisoned- carcases and ; the poisoning of the larvae on the sheep itself - by > means , of .dipping •or jetting with -an '-, arsenical v preparation. ' •' -■ ~ '~ ..-, . : The choice of a:poison and; the strength at which it can be applied are largely - governed % by: - two 4f actors--— effects on >: the living animal and the effect on the colour and texture of the wool, quite, .■;■■•'--apart ;; from :.. its success in dealing with the pest itself. In addidition, the ease with "which the spray can 'be applied 'is important, as it is not always ' possible, to ensure sufficient ■ water for the pur- ,;'-.; pose. The continual growth;'{ of the' wool, however, provides a constantly re-; newed sphere in which the,larvae can work without check, and a second or ; ; third dipping, spraying, or, jetting may. be necessary under sonic, conditions ' to : "'prevent reinfestation.', '.I *« r