Effects of gamma radiation on different developmental stages of the oriental tobacco budworm, H elicoverpa assulta ( L epidoptera: N octuidae)

Ionizing radiation is increasingly used as an alternative to post‐harvest crop fumigation by methyl bromide. We studied the effects of gamma irradiation on H elicoverpa assulta ( L epidoptera: N octuidae) at different stages of development to determine the minimal dose for the prevention of normal emergence of adults. We selected five doses of gamma rays (100, 200, 300, 400 and 500  G y) based on preliminary experiments and irradiated eggs, larvae, pupae and adults. A dose of 100  G y to eggs allowed 21.83% of larvae to pupate, but these all died during the pupal stage. A dose of 100  G y to last‐instar larvae caused larval or pupal death, or the emergence of abnormal adults; no normal adults developed. Irradiation of pupae with doses of 300  G y and above resulted either in their death or emergence of abnormal adults; however, after 100 or 200  G y, normal adults emerged and F 1 eggs were produced, but no eggs hatched. Following irradiation of adults, eggs were produced at all doses, although the numbers were significantly decreased compared to untreated controls ( P < 0.05; 69.45–125.50 vs. 475.05 eggs per female); however, none of the eggs hatched. As prevention of normal emergence is a key outcome for measuring the effectiveness of radiation, then the 100  G y dose was effective for irradiation of eggs and larvae, and 300  G y for pupae.