Tests to Control Horn Flies with New Insecticides

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Abstract
In laboratory knock-down tests against Siphona irritans small screen-wire cages were dipped in preparations containing 0.5% of different chlorinated hydrocarbon insecticides. Methoxychlor caused complete knock-down in 5 min., DDT in 8, TDE in 17, chlordan in 53, and toxaphene in 73 min. in tests made 24 hrs. after the cages had been dipped. After 2 months'' exposure, the methoxychlor, DDT, TDE, toxaphene, and chlordan caused complete knock-down of flies in 12, 62, 152, 248, and 360 to 720 min., respectively. The cage treated with methoxychlor apparently lost little of its effectiveness. The knock-down of flies exposed to animals treated with the insecticides was the same as that detd. in the laboratory, except that a longer time was required. In semi-field tests best results were obtained with DDT and toxaphene. In most of the tests, wettable powders proved superior to emulsions regardless of the concn. of insecticide tested. DDT was more effective at 1.5% concn. than at 0.5 and 0.25%. The 0.5% concn. gave only slightly better results than 0.25%. In comparative tests with different breeds of cattle, DDT retained its effectiveness much better on Herefords than on Jerseys or Brahmans. The difference between the Jerseys and Brahmans was not great.

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