Introduction to the study of tsetse-fly repellents in the field of veterinary science

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Abstract
A technique was worked out whereby the action of any substance in repelling tsetse flies can be compared with that of pyrethrum, which is the only one of about 150 substances that gave any promise of practical efficacy in the veterinary field. A freshly prepared emulsion containing 0·2 per cent. pyrethrins can be applied with the utmost freedom to any animal without danger, and it is probable that an animal so treated will not be fed upon by tsetse flies within the next 24 hours if it remains in subdued light. Direct sunlight, however, quickly reduces and eventually destroys this protective action. In the case of zebu cattle exposed to normal African sunlight, tsetse will feed within 24 hours of the drug's application. In the case of donkeys, however, complete protection against the feeding of tsetse during more than 24 hours can be obtained by spraying or washing with a pyrethrum preparation. Many kinds of pyrethrum preparations were tried, but in the end we found we could not improve on a freshly made emulsion consisting of 2 per cent. pyagra in weak (0·2 per cent.) solution of soft sopa. But although tsetse will not feed on a donkey sprayed recently with 2 per cent. pyagra or similar pyrethrum preparation, they may probe, and experiments with rats showed that this may be sufficient to set up infection. However, reasons are given why one cannot argue directly from tame flies and white rats to wild flies and large domestic animals. A field trial gave inconclusive results because although the three treated donkeys remained healthy, only one of the three untreated animals became infected. However, while the controls were worried by tsetse, the treated animals were apparently undisturbed by the flies.

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