Effectiveness of Piperonyl Butoxide and Pyrethrum as a Practical Treatment for Hog Lice

Abstract

The hog louse, Haematopinus suis (L.), is of widespread occurrence on hogs and it is said to be, next to cholera, the worst enemy of swine. It is the largest bloodsucking louse found on any farm animal. It causes needless irritation and loss of blood and makes the animals restless so that they fail to gain in weight in a normal manner. The habits of hogs in sleeping and eating together enhances the rapid spread of lice from one animal to another until the entire herd is soon infested. Application of a thin even coat of oil over the whole body of the hog, either by brushing or by dipping has been the usual measure recommended for control of hog lice. Several kinds of oils, especially crude petroleum, raw linseed oil, equal parts of kerosene and lard, equal parts of kerosene and cottonseed oil, and processed fuel oil, have been recommended as treatments. Also coal tar-creosote dips and pine tar dips have been used for control of hog lice. When oil treatments are used, however, it is necessary to treat every animal present and to repeat the application in two weeks in order to kill the newly hatched lice before they are capable of laying eggs. Following this treatment, the hogs should be kept out of the sunlight and not driven or excited, for at least a day after oiling. Results of certain phases of extensive studies on the human louse have furnished basic information which has been applied to the control of hog lice. The human body louse, Pediculus humanus corporis Deg., is considered to be highly resistant to insecticides. Finely ground pyrethrum flowers and derris powder were found by Bushland, McAlister, Eddy, Jones, and Knipling (1944), to be comparatively ineffective, but powders prepared by depositing pyrethrum extract on an inert diluent were highly effective. Certain synergists used with powders impregnated with pyrethrum extract increased the effectiveness of pyrethrins against body lice approximately 100 times. Impregnation of underwear with pyrethrum extract and a suitable synergist with as little as 0.28 gm of pyrethrins per suit has been shown by Jones, McAlister, Bushland, and Knipling (1944) to be effective against nymphs and adults of the body louse introduced after the garments had been worn for six weeks following treatment. Subsequent to this work, piperonyl butoxide has been found to increase the effectiveness of pyrethrins against body lice to a much greater extent than that indicated for the synergist used in war-developed pyrethrum louse treatments.