Systemic Insecticides for Control of Cattle Grubs in Virginia1

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Abstract
Widespread investigations by industrial, federal and state research workers have resulted in the development of several systemic insecticides for control of cattle grubs, Hypoderma lineatum (De Vill.) and H. bovis (L.). Materials have been found that result in excellent control when applied orally to the animal. Others have shown equal effectiveness when applied dermally in the form of a spray. Investigations were carried out in Virginia during the 1957-58 cattle grub season to evaluate these newer systemic insecticides applied orally and dermally. Another test was set up to determine the most effective time to apply a systemic insecticide to the animal. Certain economic benefits resulting from grub control were also investigated. The test using insecticides applied orally by means of a bolus or oblet showed that control of the cattle grubs was quite satisfactory using Dowco 109 (Phosphoramidothioic acid methyl, O-(4-terts butyl-2-chlorophenyl)O-methyl ester) (15 mg./kg.) and Dow ET-57 (110 mg./kg.), but Am. Cyanamid 12,880 (O,O,dimethyl-5-(N-methylcarbamoylmethyl) phosphorodithioate) (8 and 15 mg./kg.) resulted in only moderate control. The spray treatments resulted in excellent control of the grubs using either Dowco 109 or Bayer 21/199. In the timing experiment, a new group of animals was treated each month with an oral application of Dowco 109. No difference in effectiveness resulted due to time of application. The studies on the gain in weight indicated that the type of. feeding of the animals had a great deal to do with the benefits that were derived from cattle grub control. The average gain in weight of animals which were on a winter subsistence diet showed no benefits resulting from the control of cattle grubs. On the other hand, the average gain in weight of the animals which were fed on a fattening or full ration showed a significant increase in the treated animals over the untreated animals. Comparison of the bides of slaughtered animals that had been treated with systemic insecticides with the hides of untreated animals indicated that the use of systemic insecticides greatly reduced the number of grub holes and fresh scars in the hides of animals that were being marketed in the late winter and spring.

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