The reactions of blowflies to organic sulphur compounds and other materials used in traps

Abstract

1. Seven organic sulphur compounds likely to be produced in the breakdown of cystine have been tested under field conditions as blowfly attractants. Two of them, ethyl mercaptan and dimethyl di-sulphide, when mixed with hydrogen sulphide or carbon dioxide formed powerful attractants for females of the blowflies Lucilia caesar (and L. illustris) and L. sericata.2. In the majority of trials 10 ml. 0·2% ethyl mercaptan mixed with 10 ml. freshly saturated hydrogen sulphide solution was used as the control attractant. As a standard in field-trapping studies this material overcomes many of the disadvantages of meat baits.3. Sodium carbonate, sodium bicarbonate, ammonium hydroxide, ammonium carbonate and indole, at various concentrations, did not activate the organic compounds. Furthermore, when added to the ethyl mercaptan-hydrogen sulphide preparation they did not increase its activity.4. In the present experiments oviposition was rarely induced. When it did occur it was associated with the presence of indole.5. L. caesar responded to attractants placed 2 ft. from the ground as well as to the same materials placed on the ground. Height alone, therefore, was not responsible for the fact that L. caesar did not respond to the attractants when they were placed on sheep.6. The responses of blowflies to chemical attractants was linked with climatic conditions. Thus, under certain conditions Calliphora spp., particularly C. vomitoria, responded to these attractants.7. The results obtained in the present investigation emphasize the attractive nature of sulphur-containing compounds and the possible importance of hydrogen sulphide and carbon dioxide as sensitizing agents of such compounds on sheep.