The Use of Treatments Containing Methoxychlor Against Biting Flies on Cattle and the Determination of Methoxychlor Residues in Milk1

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Abstract
Experiments on the use of treatments containing methoxychlor against biting flies on cattle and the determination of methoxychlor residues in milk were conducted in Centre and Northumberland Counties, Pennsylvania, during the summer of 1957. Treatments were administered once a day to three herds of lactating Holsteins by two self-treating devices, the electric-eye-controlled sprayer and the cable-type back rubber. Populations of the horn fly (Siphona irritans (L.)), stable fly (Stomoxys calcitrans (L.)) and horse flies (Tabanus sulcifrons (Macq.) and T giganteus (DeG.)) on treated and check groups were counted once or twice daily to determine the effectiveness of the treatments. Milk samples were collected from the two groups of animals to determine methox:rchlor residues in milk. Results of the spraying experiments made in Centre County over a period of 68 days showed that an oil-base spray, containing methoxychlor in combination with Lethane 384, synergized pyrethrins and butoxy polypropylene glycol applied at the rate of 120 ml. per animal, provided excellent control of horn and stable flies, and was significantly more effective than a water-base spray consisting of methoxychlor and diethyltoluamide (N,N-diethyl-m-toluamide). The addition of Thanite to the water-base spray tended to increase its effectiveness appreciably. In Northumberland County, spraying experiments were carried on for 66 days. Results indicated that methoxychlor and Thanite in a water-base spray, applied at the rate of 75 ml. per animal, failed to provide satisfactory control of the horse and stable flies but the effectiveness of the combination was markedly increased by the addition of butoxy polypropylene glycol. Observations on the effectiveness of treatments containing methoxychlor applied on a back rubber were continued for 73 days. An oil-base mixture of 1% methoxychlor, butoxy polypropylene glycol and Thanite did not achieve effective control of the horn and stable flies but the efficiency of the mixture was significantly enhanced when the concentration of methoxychlor was increased to 4%. The treatments employed in both the spraying and back rubber experiments were, in general, much more effective against the horn fly than the stable fly or horse flies, when the data for each species were treated separately. None of the cattle employed in the experiments was adversely affected by the treatments. Milk samples collected from the cows sprayed with the oil-base spray containing 1% methoxychlor showed a maximum of 0.1 p.p.m. with a mean of 0.03 p.p.m. Water-base sprays, applied to two herds over periods of 33 and 66 days, respectively, showed a maximum of 0.09 p.p.m. of methoxychlor in the milk, with a mean of 0.04 p.p.m. Cows having access to back rubbers treated with a formulation containing 1% methoxychlor did not excrete measurable amounts of the compound in their milk; the same cows exposed later to a back rubber treated with 4% methoxychlor showed a maximum of 0.03 p.p.m. and a mean of 0.01 p.p.m. in their milk. The presence of pyrethrins, piperonyl butoxide, butoxy polypropylene glycol, organic’ thio(yanates, and diethyltoluamide did not appear to affect the excretion of methoxychlor by the treated cows.

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