ARCHIVE FILE
This article was published in 1954
See the original document
INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Dieldrin for Control of Blowfly Strike in Sheep
N. P. H. GRAHAM, B.V.Sc., Technical Adviser, Wm. Cooper & Nephews (Aust.) Pty. Ltd.
N. P. H. GRAHAM, B.V.Sc., Technical Adviser, Wm. Cooper & Nephews (Aust.) Pty. Ltd.
In recent years we have seen the development of a new type of insecticide which has been given the loose family name of the chlorinated hydrocarbon insecticides. All these insecticides possess to a greater or less extent two characteristics, they are potent contact insecticides and they are very persistent.
One member of this group is Chlordane, which consists of a mixture of isomers. During the investigations of the chemical composition of chlordane, four new insecticides were evolved — these were Aldrin, which is a hexachloro hexahydro dimenthano naphthalene, Dieldrin which is a hexachloro, octahydro dimenthano naphthalene, and Isodrin and Endrin, which are stero isomers of Aldrin and Dieldrin respectively.
These four have a contact toxicity of much the same order as gamma isomer of BHC, i.e., very much higher than DDT and Toxaphene. Of this group Dieldrin is the material on which most work has been done.
Attention was first drawn to Dieldrin as an insecticide for use against fly strike in a series of papers by Fidler and du Toit, in South Africa in 1952, who showed that Dieldrin was the most toxic of the chlorinated hydrocarbon insecticides against larvae of L. cuprina. They also treated sheep with a suspension of 0.5 per cent, concentration of insecticide and found that DDT, DDD and methoschlor gave about nine weeks, Toxaphene 13 weeks, Chlordane 19 weeks, gamma isomer of BHC 33 weeks, Dieldrin 37 weeks and Aldrin 39 weeks protection when challenged by artificial strikes. However, the concentration of BHC, Dieldrin and Aldrin were high in relation to their cost and it was doubtful if such concentrations could be used in the field.
As the result of the tests carried out in England in an insectary, the firm with which I am associated found that Dieldrin and Aldrin still gave remarkably long protection at much lower concentrations. Concentrations of 0.15 per cent. Dieldrin gave 21 weeks protection against artificial strikes and 0.05 per cent. gave over 18 weeks protection.
Arrangements accordingly were made to carry out a series of field trials in Australia and other countries in which Blowfly strike is a problem.
In Australia, we decided that Dieldrin might be used to protect theep from fly strikes which could not be controlled adequately by the Mules and Tail operation, and trials were arranged to test its value in protecting weaners from body strike and rams from head strike. It was considered also that as most owners are reluctant to Mules their lambs at marking time, we should test its value in protecting suckling lambs by applying it as a dressing at marking time and as a normal jetting mixture to protect unmulesed weaners.
In view of the information available of the cost of the material, we decided to use a basic concentration of 0.05 per cent. Dieldrin and wherever possible to test concentrations above and below this.
The following is a brief summary of the results which were obtained in trials carried out since January, 1953:
BODY STRIKE:
We were fortunate in being able to test this material during a severe wave of body strike in January - April, 1953. During the first five weeks of the trial, sheep treated with 0.05 per cent. and 0.1 per cent. Dieldrin remained virtually free of body strike, whereas about 30 per cent of the control group were struck. During the next nine weeks, 2 per cent of the sheep treated with 0.1 per cent. Dieldrin were struck on the body, as against 15 per cent of the controls, and 9 per cent. of the sheep treated with 0.05 per cent. Dieldrin as against 50 per cent. in their corresponding control group. Running with these latter groups for the second portion of the trial was a group of sheep which had been sprayed with 0.5 per cent. BHC seven weeks after the Dieldrin treatments were made. This BHC group received 15 per cent. of body strikes over this period. The treatment consisted of jetting cach sheep from the poll to the rump: using about 1/5th gallon per sheep.
This trial indicated that Dieldrin was able to protect sheep from body strike under severe conditions for periods of up to 3 months, so that a single treatment carried out in January or February would give adequate protection for the rest of the season.
CRUTCH STRIKE:
To protect suckling lambs by means of a dressing applied at lamb marking required a high degree of efficiency over a long period, so it was decided to use concentrations of 0.1 per cent., 0.2 per cent. and 0.3 per cent. Dieldrin. Of these, the 0.3 per cent treatment gave the best results. The dressing was applied by means of a knapsack spray at the rate of about 4 fl. OZS. per lamb.
Unfortunately, in this type of trial it is not possible to muster and examine the lambs frequently, so a single examination was made 14 weeks after treatment; when 12 per cent of the lambs treated with 0.3 per cent. Dieldrin were struck as against 26 per cent of the controls. The strikes on the Dieldrin group were all small, whereas many of the strikes on the control sheep were extensive.
These results suggest that it may be possible to get a reasonable degree of protection for lambs during suckling, if high concentrations of Dieldrin are used as a dressing at lamb marking.
A preliminary jetting trial was carried out on unmulesed Merino weaners in January, 1952. Unfortunately, the control group was lost but there was general evidence of moderate fly activity over the period of the trial. Concentrations of 0.025 per cent. and 0.05 per cent. Dieldrin were used. The treated sheep were free from strike for ten weeks; when the protection broke down rapidly.
This test was repeated in the early summer of 1952. In one trial unmulesed Merino stud weaners were jetted at the rate of 1/5th gallon per sheep with 0.05 per cent. Dieldrin. There was little fly activity over the first nine weeks of the test, but 12 per cent. of the control sheep were struck during the tenth week and none of the treated sheep. From 11th to 14th week, 14 per cent of the treated sheep were struck, and a further 34 per cent. of the control sheep.
In a second trial unmulesed flock Merino ewe weaners were treated in the same way with concentrations of 0.025 per cent., 0.1 per cent, and 0.15 per cent. Dieldrin. Over the first 12½ weeks of the trial no strikes occurred in the treated groups and 33 per cent in the control groups. From 13th to 18th week, 7 per cent of the sheep treated with 0.025 per cent. were struck and 2 per cent of the sheep treated with 0.015 per cent.; while another 40 per cent. of the controls were struck over this period.
These trials indicate that when used for jetting against crutch strike Dieldrin will give nine-ten weeks complete protection and still will give some protection for up to 14 to 18 weeks. Increasing the concentration did not increase markedly the period of immunity, but did decrease the incidence of strike.
HEAD STRIKE:
Unfortunately, the head strike trials have not been satisfactory for various reasons, and we have to rely largely on the experience of graziers. If the rams' heads are saturated thoroughly with Dieldrin at 0.05 per cent. or 0.1 per cent. they are given almost complete protection from head strike for about six months.
HAND DRESSING:
Dieldrin has been used at this range of concentrations for hand dressing sheep, both when the struck area has been shorn and when it has been left unshorn, with excellent results.
DISCUSSION:
The main virtue of Dieldrin lies in the extraordinary long periods for which it protects sheep from fly strike. We have still much to learn in the use of the material in the most economical manner, but even as described above the treatments have been cheap.
Although flies which alight on treated areas will absorb toxic doses of insecticide, they are in no way repelled by the insecticide. They move round freely and frequently will oviposit on treated areas. These eggs, however, do not develop into strikes; the larvae being killed as soon as they emerge.
Dieldrin at the concentrations used is inexpensive. Using the product my firm has been marketing, a gallon of mixture containing 0.05 per cent. Dieldrin costs about 10d. per gallon, allowing for freight,etc.; so that, with the treatments outlined above, the cost of material has been of the order of 1d. to 4d. per sheep, depending on the concentration used.
TOXICITY:
Finally, a few words on the toxicity of Dieldrin.
Dieldrin is absorbed readily through the intact skin, even when it is applied in the form of dry-powders, and for this reason care should be exercised in handling the material; particularly the concentrates. As far as the sheep are concerned, they are unlikely to absorb a toxic dose from the concentrations normally used.
Groups of sheep have survived dipping in concentrations up to 1 per cent. Dieldrin with no ill-effects. When given multiple dippings in 0.5 per cent. Dieldrin, followed 14 days later by a dipping in 0.75 per cent. Dieldrin and followed 21 days later by a dipping in 1 per cent. Dieldrin, one out of five died.
Although, as far as is known, there have not been any reported cases of Dieldrin poisoning in man, it has been estimated that the dermal application of 250 ccs. of a 10 per cent. emulsion would cause toxic symptoms.
We recommend that if any concentrate is spilt on the skin, it should be washed off immediately, and that clothing which becomes saturated with wash during spraying or jetting should be changed as soon as possible.
The toxic symptoms are typical of chlorinated hydrocarbon insecticide poisoning, starting with tremors and developing into tetanic convulsions. As a rule, the only lesions seen on post-mortem examination are the injuries received during the convulsions.
Dieldrin, however, shows one particular feature in that the toxic symptoms may be delayed for a considerable period after application. The animal often appears normal for some days; then suddenly develops fatal symptoms.