STERILIZATION OF THE NAVEL ORANGEWORM, PARAMYELOIS TRANSITELLA (WALKER), BY GAMMA RADIATION (LEPIDOPTERA: PHYCITIDAE)

This paper presents fundamental investigations on the navel orangeworm and on its control by the release of sterilized navel orangeworm moths. The first essential for working with this insect was to develop effective techniques for its mass culture. The main problem, to induce mating under laboratory conditions, was solved by providing indirect air circulation, high relative humidity, temperatures between 10° and 16° C, and light intensity similar to that of the early-morning hours. The successful method is described in detail. The effects of gamma radiation were tested on all stages of the navel orangeworm. Mature, eight-day-old pupae were the best able to tolerate dosages sufficient to make all individuals completely sterile. The effective dosage, established at 50,000 rads ± 3.5 per cent, did not affect mating, egg-laying, or longevity of the moths. Treatment with 40,000 rads reduced fertility drastically but did not give complete sterility. Treatment with 80,000 rads reduced the mating capacities of both sexes, and the treated females laid very few eggs. There was no evident difference between the sexes in the sterilizing dosage. The introduction of sterilized female moths reduced the production of viable eggs in untreated laboratory populations at least as much as did introduction of sterilized males. Most significantly, when both sterilized females and sterilized males were added to untreated populations, the result was not to double but to square the amount of control effected by sterile moths of only one sex.