Abstract

The wide variation in irradiation dosage-sterility relationships reported to date for Mediterranean fruit fly, Ceratitis capitata (Wiedemann), in both air and nitrogen gas, made it necessary to define these relationships for Mediterranean fruit fly mass reared in Western Australian facilities. Results demonstrated the characteristic increase in sterility, with increasing exposure to radiation in both air and nitrogen gas, similar to previously reported results. However, 3 basic differences were found between previously reported data and the data for Western Australia. First, the relationship between irradiation dosage and fertility when irradiation was done in air was not parallel to the same relationship in nitrogen gas. The resistance to radiation in nitrogen atmosphere compared with air diminished as irradiation dosage increased. Second, nitrogen offered a much greater protection against the sterilizing effects of radiation; a 2-fold increase in the irradiation dosage was required for sterilization in nitrogen compared with air (7.6-14.3-Krad, more than the 2.5-Krad previously reported). Third, the Western Australian Mediterranean fruit fly was 99.5% sterile when pupae were exposed to 7.6-Krad irradiation dosages in air (between the 6-Krad required in Egypt and the 10-Krad irradiation dosage reported by several others). The use of nitrogen during irradiation was applied to pupae sterilized for a successful eradication of Mediterranean fruit fly program in Western Australia. The average mating competitiveness during the 5-yr program was 52% (compared with an expected 25% in air) and the average sterility was 99.4%.

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