Research into the Application of the Sterile-Male Release Technique to the Rhinoceros Beetle (Coleoptera:Scarabaeidae)

The control of the Rhinoceros beetle, which causes considerable damage in palm and coconut plantations in the tropical regions of the world, meets with difficulties resulting from the habits of the insects. Chemical and biological control methods have not yet produced economically worthwhile results. It was therefore proposed, under the Joint Project established by the UN Special Fund and the South Pacific Commission for devising a method of controlling the main pest in this group, Oryctes rhinoceros, that the possibility be investigated of using against these coleoptera the technique of releasing males sterilized by radiation. Studies have been made involving the two most important species O. monoceros Ol. and O. rhinoceros L. The first stage was the development of a continuous breeding method, which had not hitherto been possible because of the large-scale slaughter arising from fungus attacks by Metarrhizium anisopliae Metsch. For the larvae the technique used involved first individual rearing, followed by group rearing tests with 100 or so insects in tanks. The average temperature in both cases was close to 30°C and the insects were fed on a mixture of rotten wood and leaf mould mixed with the faeces of domestic animals. The adults, fed on banana slices, are placed in troughs or tanks containing sieved-earth. It was thus possible to rear Oryctes in several successive cycles, avoiding the epizooic stage of Metarrhizium, with a multiplication rate from one generation to the next of close on 10, Tests on radiation sterilization procedures taking as variables the gamma-ray dose, the stage of the insect and the physiological state of the imago, showed that O. monoceros adults were sterilized by a single application of 4000 rad, with a slight reduction in their length of life. The same was true of O. rhinoceros, which however required a dose greater than 6000 rad to sterilize it. The mating urge and sexual vigour of the irradiated insects are, however, reduced; competitive trials between irradiated and normal males are described and commented on. Apart from the immediate effects of gamma-rays, a possible deferred effect on the progeny of females mated with partially sterilized males was also envisaged. (author)