Gamma Irradiation as a Quarantine Treatment for Apples Infested by Codling Moth (Lepidoptera: Tortricidae)

Abstract

Codling moth, Cydia pomonella (L.), larvae reared on thinning apples were exposed to gamma radiation at incremental doses up to 138 Gy (gray). Adult emergence from pupae was reduced, and larval mortality increased as dose increased. At a dose of 39.2 Gy, emergence of normal adults from irradiated younger larvae (first through third instars) was reduced, and emergence of physically deformed adults increased. At higher doses, adult emergence was further reduced, the ratio of male to female emergence increased significantly, and overall survival of larvae declined. Similar results were obtained for older larvae (third through fifth instars) except that the doses required for comparable effects were 10-25% higher than those for younger larvae. These data suggest that doses of 372 Gy would prevent first through third instars from maturing and forming cocoons. However, probit analysis showed that a dose of 187 Gy or less gave quarantine security based on preventing adult emergence from fruit infested by larvae. When an estimated 79,540 nondiapausing immature larvae infesting thinning apples were exposed to approximately 153 Gy, only 15,501 formed cocoons; of these, only 256 pupated and none emerged as adults.