Ionizing radiation for quarantine control of Opogona sacchari (Lepidoptera: Tineidae)

A discriminating irradiation dose of 150 gray (Gy) was used to determine the most tolerant immature stages of Opogona sacchari (Bojer) (Lepidoptera: Tineidae). Based on adult emergence, early and late pupae were determined to be the most tolerant stages, and they were significantly more tolerant than eggs, neonate larvae, and larvae that were 1, 2, or 3 wk old. Irradiation treatment of eggs, neonates, 1-wk-old larvae, 2-wk-old larvae, 3-wk-old larvae, early pupae, and late pupae at 150 Gy resulted in a 96, 96, 95, 73, 61, 8, and 9% reduction in adult emergence, respectively. Pupae were treated with irradiation doses between 60 and 400 Gy. Emergence to the adult stage was significantly reduced by irradiation, averaging 90% in experimental controls and 29% in the 400-Gy treatment. Egg production was also reduced by irradiation, although the average age of pupae at the time of irradiation had a larger effect on fecundity. In total, 2,527 pupae treated with 120 Gy eclosed and produced 47,221 eggs and three F1 larvae. In the 150-Gy treatment, 2,927 adults in total emerged from the 4,626 insects treated as pupae. These adults laid 62,878 eggs, none of which hatched. We conclude that a minimum dose of 150 Gy should be sufficient for sterilization of immature O. sacchari infesting export commodities.