Gamma Radiation Doses to Prevent Adult Emergence from Immatures of Mexican and West Indian Fruit Flies (Diptera: Tephritidae)

Abstract

Quarantine treatments against tephritids generally have been concerned only with eggs and larvae because the larva leaves the fruit to pupate in the soil. However, irradiation would usually be applied after fruits are packed, and some packed fruits, such as citrus, could conceivably sit at ambient conditions for a few days before being irradiated, allowing 3rd instars to emerge and pupate within the packaging. Pupae are generally more tolerant of irradiation than are larvae and eggs. This research evaluated tolerance of immatures of Mexican and West Indian fruit flies, Anastrepha ludens (Loew) and A. obliqua (Macquart), respectively, to ionizing radiation from a 137Cs source. Although tolerance to irradiation generally increased with increasing stage of development, the insect immediately preceding 2 developmental milestones (pupariation and larval to pupal molt) was usually more susceptible than 24 h earlier. We recommend that fruits to be irradiated not remain at ambient temperatures for enough time to enable 3rd instars to develop to the phanerocephalic pupal stage, which is ≈3 d at 25°C for the 2 species studied. The 1st d of the phanerocephalic pupa is ≈40% more tolerant of irradiation than the 3rd instar, whereas the insect 24 h earlier is only ≈14% more tolerant. Mexican fruit fly 3rd instars inside grapefruits, Citrus paradisi Macf., were notably more tolerant of irradiation than 3rd instars in ambient air.