Elvin W. Tilton

Effects of gamma radiation on the larval midgut of the Indian-meal moth, Plodia interpunctella (Lepidoptera: Phycitidae).

The normal midgut consisted of an epithelial layer, a thin basement membrane, an inner circular muscle coat, and outer bundles of longitudinal muscles. The major cytological damage associated with radiation exposure was displayed by the midgut epithelium. Damage ranged from moderate cell disruption 4 days after treatment with 5 krads to almost complete histolysis following 50 krads. The regenerative cells that renew the epithelial lining of the midgut were particularly sensitive to radiation damage resulting in an inability to replace the midgut epithelium.

Gamma, infra-red and microwave radiation combinations for control of Rhyzopertha dominica in wheat☆

Abstract Samples of soft winter wheat containing eggs, larvae, pupae, or adults of Rhyzopertha dominica (F.) were given one of the following treatments: (1) Gamma radiation; (2) infra-red radiation; (3) microwave radiation; (4) gamma + infra-red; or (5) gamma + microwave. The percentage of adult emergence from treated immatures or the mortality and fecundity of treated adults provided a basis for evaluating the effectiveness of the treatments. The average reductions in emergence were 54, 55, and 42 per cent for gamma, infra-red, and microwave treatments, respectively. The reductions in emergence averaged 99 per cent for the gamma + infra-red combination and 96 per cent for the gamma + microwave combination. These mortalities were about 20 per cent higher than predicted. Adult mortality data were inconclusive because of the very low gamma dosage used. However, reductions in adult fecundity for the above combinations were about 95 and 89 per cent, respectively. These were about 22 and 9 per cent greater than the predicted reductions in fecundity.

A method of dosimetry for a bulk-grain irradiator

Abstract This paper discusses the advantages of a lithium fluoride thermoluminescent dosimetry system for use in a bulk-grain irradiator. Unique problems of dosimetry exist because dosimeters must be mixed with the grain, must have the same flow characteristics as the grain and must have adequate resistance to breakage. Tests proved that encapsulated LiF dosimeters provide an accurate record of absorbed dose in a mass of wheat treated by a bulk-grain irradiator. Variations in dosage revealed by the dosimeters showed satisfactory treatment of the majority of the wheat, with overexposure of a small percentage.

Effect of gamma radiation on the metamorphic stages of Dermestes maculatus DeGeer (Coleoptera: Dermestidae).

The effects of gamma-radiation on all stages of the hide beetle Dermestes maculatus, DeGeer were studied. Eggs of D. maculatus were more susceptible to gamma radiation than other stages. Egg radiosensitivity decreased with increasing embryonic development. An absorbed dose of 200 Gy killed the 1st, 6th and 7th instar larvae, but the 4th and 5th instar larvae were more resistant. The developmental period increased in treated larvae. Pupae (24 h) treated with 150 Gy failed to eclose, but eclosion was not affected in older pupae. Adults from female pupae irradiated at 72 h with 150 Gy were infertile, but male pupae required more than 200 Gy for sterilization. The average number of eggs per female decreased with increasing doses when either the male or female of the pair was irradiated as puape or adults. Adult males were sterile after irradiation 300 Gy and adult females treated with the same dose failed to lay eggs. Newly emerged irradiated adults or female adults from irradiated 72-h-old pupae recovered some fertility after treatment with doses as high as 150 Gy. Adult males from irradiated 72-h-old pupae were treated at doses of 50 and 100 Gy showed a higher reproductive capacity at 60 days than at 15 days post-treatment. A dose between 200 and 300 Gy was necessary to provide complete sterility of 24-h-old adults.

Weight loss of wheat infested with gamma-radiated Sitophilus oryzae (L.) and Rhyzopertha dominica (F.)

Abstract Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) adults were treated with 2·5, 5, 10, 25 or 50 krad of gamma radiation and confined on samples of uninfested wheat. Except for those treated at 2·5 krad the amounts of wheat consumed by the adults and their progeny were much less than that eaten by the controls. Five weeks after treatment with 25 krad, total feeding damage by R. dominica and S. oryzae was 11 and 3 per cent, respectively, of the control and most of this feeding occurred during the first week after treatment. The amount of damage caused by live but sterile insects in bulk grain treated with gamma radiation would probably not be a serious problem because of the great reduction in feeding brought about by the radiation.

Sterilization of 4–5-day-old pupae of the Indian meal moth with gamma radiation and its effect on mating competitiveness

Abstract Females of the Indian meal moth, Plodia interpunctella (Hubner), irradiated as 4–5-day-old pupae with an obserbed dose of 35 krad of gamma radiation and confined with unirradiated (U) males were sterile. Male moths treated similarly and confined with U females were only partially sterile. Irradiated (I) males confined with U males and females at a ratio of 1:1:1 caused 18.2% of the eggs produced to be infertile; increasing the ratio to 5:1:1, 10:1:1, 15:1:1 and 25:1:1 caused 48.7, 46.6, 47.7 and 58.9%, respectively, infertile eggs. The calculated competitiveness values (CV) for the 5 ratios were 0.39, 0.70, 0.63, 0.62 and 0.75, respectively. When I females were confined with U males and females in the same 5 ratios: 1:1:1, 5:1:1, etc., 15.6, 66.2, 74.3, 100.0 and 100.0%, respectively, of the eggs were infertile. The CVs calculated for these ratios were 0.73, 1.52, 1.28, 1.50 and 1.30. Thus, I females were more effective in reducing egg fertility than were I males.

Effects of Irradiated Diets on Production of Progeny by Several Successive Generations of the Indian-Meal Moth, Plodia interpunctella (Hübner)

Indian meal moths, Plodia interpunctella, were reared for nine generations on an irradiated whole wheat flour diet or for four generations on irradiated raisins. Diets were treated with dosages of 0, 25, 50, 100, 500, 1000, and 4300 krad of gamma radiation. Each generation was checked for fecundity and for altered sex ratios. No statistically or biologically significant effects on the numbers of progeny or their sex ratio were found. Irradiated flour and raisins appear to be safe as insect culture media.

Radiation sensitivity of successively irradiated generations of Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae), and Sitophilus oryzae (L.) (Coleoptera, Curculionidae)

Abstract Four populations of Tribolium castaneum (Herbst) and of Sitophilus oryzae (L.) were treated with 0 (control), 0·5, 1 or 2 krad of gamma radiation for 7 and 5 successive generations, respectively, and the adults from the subsequent unirradiated generation of each population were checked for fecundity. Groups of 6th generation T. castaneum and S. oryzae adults from each population were tested for resistance to acute radiation by exposure to doses of 16 and 50 krad followed by a check for mortality. No evidence of increased resistance to acute radiation exposures was found. Irradiated T. castaneum populations did not show significant decreases in mean survival time, but some significant decreases in life-span of irradiated S. oryzae populations were found. Fecundity of the 8th generation 0·5 krad T. castaneum was greater than that of the control population, but 1- and 2-krad populations did not show any difference in fecundity. Fecundity of the 6th generation S. oryzae population was not significantly different from that of the control, but 1- and 2-krad populations had significantly reduced fecundities. The test results indicated that possible accidental exposure of some insects to substerilizing doses during commercial radiation disinfestation is unlikely to bring about the development of radiation-resistant insect populations.