Effect of different radiation doses on Medfly quality

Radiation is used to sterilize Medflies, Ceratitis capitata (Wied.), for SIT programmes. Massreared flies in the Madeira-Med sterile insect technique (SIT) programme are sterilized at the pupal stage about 24 hours before adult eclosion with 100 Gy using a Gamma Cell 220 loaded with Cobalt 60. The pupae are in anoxia/hypoxia when treated. It is known that the higher the radiation dose given to the Medfly pupae, the more the overall quality of the adults is reduced. A series of tests was conducted to determine if we could reduce the radiation dose so as to measurably improve fly quality while maintaining the sterility required for a successful Medfly control (as compared to eradication) programme using SIT. Our target sterility in the irradiated males was 97.5% as measured in mating tests with untreated fertile females. The flies were subjected to standard quality control tests, including field-cage tests. Two series of irradiations were carried out. The first used 0 Gy, 50 Gy, 75 Gy, 100 Gy, 125 Gy and 145 Gy, and the second 0 Gy, 50 Gy, 60 Gy, 70 Gy, 80 Gy, 90 Gy and 100 Gy. In both tests we measured egg hatch, larval production, pupal production, emerged adults and flying adults. In the second test any F1 males that were produced were mated with unirradiated females. Field-cage tests were run with both series of doses to estimate competitiveness of mass-reared flies treated with the various radiation dosages. Results indicated that Medfly control programmes using could use a radiation dosage of 80 Gy.