Some Effects of Gamma Irradiation on Spodoptera (Laphygma) Exigua Hb. (Lepidoptera: Noctuidae)

A study has been made of the effect of gamma rays from a cobalt-60 source on the eggs, larvae, pupae and adults of Spodoptera exigua Hb., a lepidopteron which is harmful to crops in many climates. The insect was reared on an artificial diet based on powdered cabbage and wheat-germ. The irradiation of one- and four-day-old eggs with 3,6 and 9 krad showed that none of the one-day-old eggs hatched, while the four-day-old ones gave 52, 18 and 0% of adults respectively-. The larvae hatched from irradiated eggs showed retarded development, and the butterflies which developed were listless and of low fertility. Mature larvae irradiated at 3 and 5 krad give 100 and 22. 5% of adults respectively; irradiation at 7 krad or more completely stops the production of adults. Irradiation of young pupae either kills them or leads to the hatching of malformed adults. Irradiation at 50 krad of pupae at the end of their development has no effect on hatching. The adults from nymphs irradiated at 50 krad show a fertility reduced to 0.5%, while the adults which have just hatched show total sterility after irradiation at the same dose. Higher doses reduce the frequency of mating, while females irradiated at 30 krad and mated with normal males lay infertile eggs. (author)