Comparisons of Cobalt-60 Gamma Irradiation Dose Rates on Grapefruit Flavedo Tissue and on Mexican Fruit Fly Mortality

Percent electrolyte leakage, a measure of membrane integrity, proved to be a good predictor (R² = 0.99) of cobalt-60 gamma irradiation dose injury on mid-season 'Ruby Red' grapefruit Citrus paradisi (Macf.) flavedo tissue (peel). Percent electrolyte leakage on grapefruit peel following a dose-rate of 250 grays/1.0, 2.5, 5.0, and 25.0 min decreased as grays/min (dose-rate) decreased. Total phenols, a biochemical response to irradiation following 250 grays/1.0, 2.5, 5.0, and 25.0 min also decreased as dose-rate decreased, demonstrating that injury to grapefruit peel diminished as 250 grays of gamma irradiation/rate declined. Comparisons of 10 and 20 grays of cobalt-60 gamma irradiation showed that a dose-rate of 10 grays/0.25 min to naked 8-d old Mexican fruit fly Anastrepha ludens (Loew) larvae caused a 90% reduction of adult emergence. Whereas, at 20 grays the reduction was greater than 99% with dose-rates of 20 grays/0.25, 0.5, 1.0, or 100 min. These data show that a gamma irradiation dose capable of reducing fly emergence by >99% will maintain an inhibitory effect even at relatively lower dose-rates. Therefore, once a quarantine security treatment for Mexican fruit fly is established, a lower dose-rate will reduce adult emergence and should impart little damage to grapefruit peel tissue.