Effect of Gamma Irradiation on Fecundity, Sterility, and Female Sex Pheromone Production of Callosobruchus chinensis (Coleoptera: Bruchidae).

Azuki bean beetle, Callosobruchus chinensis (L.) (Coleoptera: Bruchidae), is a field-to-storage pest of legumes and its females produce sex pheromone components with two isomers: (2Z,6E)-7-ethyl-3,11-dimethyl-2,6,10-dodecatrienal (2Z-homofarnesal) and (2E,6E)-7-ethyl-3,11-dimethyl-2,6,10-dodecatrienal (2E-homofarnesal). Two-day-old virgin adults were treated with different doses (0, 200, 300, 400, 500, and 600 Gy) of gamma radiation and the effects on adult survivorship, fecundity, sterility, and pheromone production were studied. The longevity of both sexes and female fecundity were dose dependently affected by the gamma irradiation revealing that the fecundity was more reduced when the female adults were irradiated. Adults of both sexes were totally sterilized by the doses of gamma radiation tested in this study as depicted by the null hatchability of the laid eggs. The results from analyses by gas chromatography-mass spectrometry for solid phase micro-extraction revealed that both of the female sex pheromone components were significantly reduced by 300 Gy. Though significantly less, there was release of some amount of pheromone components by the irradiated female azuki bean beetles revealing the possibility of pheromonal attraction of males to the irradiated females. It is a pre-requisite for the successful sterile insect technology that the sterility of azuki bean beetle is induced without the total disruption of the calling behavior.