Radiation biology and inherited sterility of light brown apple moth (Lepidoptera: Tortricidae): developing a sterile insect release program

The radiation biology of two geographically isolated populations of the light brown apple moth [Epiphyas postvittana (Walker)] was studied in Australia and New Zealand as an initiation of a SIT/F1 sterility program. Pharate and < or = 2 d pre-emergence pupae were exposed to increasing radiation doses up to a maximum dose of 300 Gy. Fertility and other life history parameters were measured in emerging adults (parental) and their progeny (F1-F3 adults). Parental fecundity was significantly affected by increasing irradiation dose in pharate pupae only. For both populations, parental egg fertility declined with increasing radiation. This was most pronounced for the irradiated parental females whose fertility declined at a higher rate than of irradiated males. At 250 Gy, females < or = 2 d preemergence pupae produced few larvae and no adults at F1. No larvae hatched from 250 Gy-irradiated female pharate pupae. At 300 Gy, males still had residual fertility of 2-5.5%, with pharate pupae being the more radio-sensitive. Radiation-induced deleterious inherited effects in offspring from irradiated males were expressed as increased developmental time in F1 larvae, a reduction in percent F1 female survival, decreased adult emergence and increased cumulative mortality over subsequent generations. Males irradiated at > or = 150 Gy produced few but highly sterile offspring at F1 and mortality was > 99% by F2 egg.     

Does exposure of male Drosophila melanogaster to acute gamma radiation influence egg to adult development time and longevity of F1–F3 offspring?

Two‐ to three‐day‐old male Drosophila melanogaster flies were irradiated with 1, 2, 4, 6, 8, 10, 20, 25, 30, 40 and 50 Gy doses of gamma radiation. The longevity and rate of development were observed for three successive generations to assess the impact of irradiation. The mean lifespan of irradiated flies was significantly increased at 1, 2 and 8 Gy, while it was vice versa for high doses at 30, 40 and 50 Gy. Paternal irradiation had an impact on F₁ generation, with significantly increased mean longevity at 2 (female), 4, 6, 8 and 10 and decreased mean longevity at 40 and 50 Gy (male and female). Significant increase in the longevity was observed in the F₂ generation of the 8 (male and female) and 10 Gy (male) irradiated groups, while decreased longevity was observed in F₂ female progeny at 40 Gy. In the case of F₃ progeny of irradiated flies, longevity did not show significant difference with the control. Paternal exposure to radiation had a significant impact on the mean egg to adult developmental time of the F₁ generation; it was shortened at 2 Gy and extended at 25, 30, 40 and 50 Gy compared to the control. Mean development time at 30, 40 and 50 Gy was significantly increased in the F₂ generation, while there were no significant changes in the F₃ generation. The present study concludes that the effect of acute gamma irradiation on longevity and “egg to adult” development time of D. melanogaster may persist to following generations.     

Irradiation of adult Epiphyas postvittana (Lepidoptera: Tortricidae): egg sterility in parental and F1 generations

Adult Epiphyas postvittana Walker were irradiated using a Cobalt 60 source to determine the dose needed to achieve complete egg sterility of mated female moths, and egg sterility of female moths mated to F1 generation males. Adult male and female E. postvittana were irradiated at 100, 200, 250, and 300 Gy and their fertility (when crossed with normal moths) was compared with nonirradiated moths. Viable progeny (determined by egg hatch) were found at doses of 100 and 200 Gy, but very little at 250 and 300 Gy. In particular, there was no survival of female progeny into the F1 generation. Males irradiated at 250 and 300 Gy had very low egg eclosion rates (2.25 and 1.86% at 250 and 300 Gy, respectively) when mated with normal females. The F2 generation from those male progeny had a mean percent hatched of < 1.02%. Based on our results, a dose of 250-300 Gy is recommended for irradiation of E. postvittana adults used for sterile insect technique (SIT) if sterility of parental moths is the desired outcome. Our data also suggests that inclusion of F1 hybrid sterility rather than parental generation sterility into programs using the SIT may allow for doses lower than what we have reported, especially during initial phases of an eradication program where increase fitness of moths might be desirable. Further research is needed to verify the use of F1 hybrid sterility in light brown apple moth SIT programs.     

Fractionated irradiation improves the mating performance of the West Indian sweet potato weevil Euscepes postfasciatus

• 1 The sterile insect technique (SIT) is widely used to suppress or eradicate target pest insect populations.
• 2 The effectiveness of SIT depends on the ability of released sterile males to mate with and inseminate wild females. The use of gamma radiation to induce sterility, however, negatively affects both somatic cells as well as reproductive cells. Consequently, mating performance of sterilized individuals decreases drastically over time. The mating propensity of sterilized Euscepes postfasciatus (Fairmaire) males irradiated with a single dose of 150 Gy (the current standard of the Okinawa Prefecture SIT programme) is equal to that of non‐irradiated weevils for the first 6 days.
• 3 Fractionated irradiation, in which a sterilizing dose is delivered over time in a series of smaller irradiations, reduces the damage of irradiation in insects. In the present study, we evaluated the effect of fractionated irradiation on male fertilization ability, longevity and mating propensity of E. postfasciatus for a period of 16 days after irradiation.
• 4 Although fractionated irradiation totalling 150 Gy was found to induce full sterility regardless of the number of individual doses, the mating propensity of male weevils sterilized by fractionated irradiation was maintained for the first 12 days. These results demonstrate that fractionated irradiation can be highly advantageous in programmes aimed at eradication of E. postfasciatus.

     

Irradiation of Anastrepha ludens (Diptera: Tephritidae) revisited: optimizing sterility induction

Irradiation doses currently applied to sterilize Mexican fruit flies, Anastrepha ludens (Loew) (Diptera: Tephritidae), for release under the sterile insect technique eradication campaign in Mexico, were reviewed in an effort to increase sterile male performance in the field. A dose maximizing sterility induction into wild populations was sought by balancing somatic fitness with genetic sterility. Doses of 40, 60, and 80 Gy induced 95% or more sterility in all males, which in turn induced similar degrees of sterility into a cohort of wild flies in the laboratory. However, a low dose of 40 Gy was sufficient to completely suppress egg production in females. Similarly, a mild carryover of genetic damage might have been transferred to the F1 progeny of males irradiated at 40 Gy crossed with fertile wild females. Our results suggest that the 80-Gy dose currently applied in Mexico can be lowered substantially without jeopardizing program goals. This view could be strengthened by comparing performance of males irradiated at different doses under more natural settings. In general, we discuss the value of determining irradiation doses for pest species where females are more radiosensitive than males, by selecting the dose that causes 100% sterility in females.     

Prolongation of the effective copulation period by fractionated‐dose irradiation in the sweet potato weevil,Cylas formicarius

The sterile insect technique (SIT), based on the principles of population and behavioral ecology, is widely used to suppress or eradicate target pest insect populations. The effectiveness of SIT depends on the ability of released sterile males to mate with and inseminate wild females; however, the use of gamma radiation to induce sterility negatively affects both somatic cells as well as reproductive cells. Consequently, sterilization by irradiation drastically diminishes mating performance over time. It is well known that fractionated‐dose irradiation, in which a sterilizing dose is delivered via a series of smaller irradiations, reduces radiation damage. In the present study, we evaluated the effect of fractionated‐dose irradiation on fertility, longevity, and mating propensity in Cylas formicarius (Summers) (Coleoptera: Brentidae) for 16 days after irradiation. Fractionated‐dose irradiation with 200 Gy induced full sterility regardless of the number of radiation doses. Although the mating propensity of males sterilized by a single 200 Gy dose (the current standard of the Okinawa Prefecture SIT program) was equal to that of non‐irradiated weevils for the first 6 days, the mating propensity of males sterilized by a series of three doses was maintained for at least the first 12 days. These results demonstrated that fractionated‐dose irradiation can be highly advantageous in C. formicarius eradication programs.     

Irradiation of Anastrepha obliqua (Diptera: Tephritidae) revisited: optimizing sterility induction

The effects of irradiation doses increasing from 0 to 100 Gy (1 Gy is energy absorbed in J kg(-1) of irradiated material) on fertility, flight ability, survival, and sterile male mating performance were evaluated for mass-reared Anastrepha obliqua (Macquart). High sterility values (> 98.2%) for irradiated males were obtained for doses as low as 25 Gy. Egg hatch was inhibited for irradiated males crossed with irradiated females at a low dose of 20 Gy. However, we estimated that to achieve 99.9% sterility (standard goal of many sterile insect technique programs), irradiation doses had to be increased to a dose between 50 and 75 Gy. At doses of 25 Gy and greater, we observed a decreasing trend in adult flight ability and an increasing trend in adult mortality. Such differences were greater for pupae irradiated at a young age compared those irradiated 24 h before emergence. Our single most relevant finding was that sterility induction (i.e., oviposition of nonfertilized eggs) was two times greater for males irradiated at low doses (40 Gy) than for males irradiated at high doses (80 Gy) when used at a 3:1:1 sterilized male to fertile male to fertile female ratio. Males irradiated at high doses may have been outcompeted by unirradiated males when courting unirradiated females. Implications of our findings for sterile insect technique programs are discussed.     

Modeling the sterile insect technique for suppression of light brown apple moth (Lepidoptera: Tortricidae)

A population model was derived for light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), subject to the sterile insect technique (SIT). The model was parameterized from the literature and from recent laboratory studies conducted in New Zealand and Australia. Relationships were fitted for several model parameters that vary with irradiation dose, allowing the model to simulate effectively complete sterility at 300 Gy through inherited sterility occurring from lower doses. At 300 Gy, the model suggests that eventual population extinction is 95% probable when the ratio of released to wild males in monitoring traps exceeds 6.4. Higher overflooding rates would be required to achieve eradication more rapidly. The optimal release interval, in terms of minimizing the required rate of production of factory moths, is approximately weekly. There is little advantage in releasing males only compared with releasing both sexes. Female-only releases are unlikely to be a useful tool for inherited sterility eradication because there is no reduction in the fertility of F1 offspring. The critical release rate required to halt population increase declines with decreasing irradiation dose, but at doses of < 171 Gy there is a risk that irradiated-lineage moths may form a self-sustaining population, making eradication by SIT alone impossible. The model suggests that a dose of around 200 Gy may be optimal because the resulting inherited sterility would reduce by a third the number of factory moths required compared with 300 Gy.     

Transmission of genome damage from irradiated male rats to their progeny

The effect of gamma-radiation (3Gy) on slowly proliferating liver tissue of male rats and their progeny was investigated with respect to induction and duration of latent damage. The irradiation caused latent cytogenetic damage in the liver in irradiated males of the F(0) generation, which manifested itself in different ways during proliferation of hepatocytes induced by partial hepatectomy: a reduced proliferating activity, a higher frequency of chromosomal aberrations and a higher proportion of cells with apoptotic DNA fragments were observed, compared with non-irradiated rats. In the progeny of irradiated males (F(1) and F(2) generation), the latent genome damage manifested itself during regeneration of the liver after partial hepatectomy by similar, but less pronounced changes compared with those seen in irradiated males of the parental generation. This finding gave evidence of the transfer of part of the radiation-induced genome damage from parents to their offspring. Irradiation of F(1) and F(2) progeny of irradiated males (their total radiation load being 3 + 3 and 3 + 0 + 3 Gy, respectively) caused less change as irradiation of progeny of non-irradiated control males (their total radiation load being 0 + 3 and 0 + 0 + 3 Gy, respectively).     

Radiation biology and inherited sterility in false codling moth (Lepidoptera: Tortricidae)

False codling moth, Cryptophlebia leucotreta (Meyrick), male and female mature pupae and newly emerged adults were treated with increasing doses of gamma radiation and either inbred or out-crossed with fertile counterparts. For newly emerged adults, there was no significant relationship between dose of radiation and insect fecundity when untreated females were mated to treated males (N female by T male). However, fecundity of treated females mated to either untreated (T female by N male) or treated males (T female by T male) declined as the dose of radiation increased. A similar trend was observed when mature pupae were treated. The dose at which 100% sterility was achieved in treated females mated to untreated males (T female by N male) for both adults and pupae was 200 Gy. In contrast, newly emerged adult males treated with 350 Gy still had a residual fertility of 5.2% when mated to untreated females, and newly emerged adult males that were treated as pupae had a residual fertility of 3.3%. Inherited effects resulting from irradiation of parental (P1) males with selected doses of radiation were recorded for the F1 generation. Decreased F1 fecundity and fertility, increased F1 mortality during development, and a significant shift in the F1 sex ratio in favor of males was observed when increasing doses of radiation were applied to the P1 males.     

Genetic consequences of irradiation of one or both parents (results of experiments on Wistar rats) Exitus lethalis in Wistar rat's progeny after irradiation of one or both parents

Examination of 2563 offsprings of Wistar rats after irradiation of one or both parents with doses of 0.25, 0.5, 1, 2, 3 and 4 Gy was carried out; the manifestation of lethal effects in the progeny of the first generation in ontogenesis was studied. The level of embryonic death was the highest after irradiation of germ cells of parents at stages of spermatids, spermatozoids and matured oocytes. Following irradiation of both parents with doses of 0.25, 0.5 and 1 Gy at these stages of gametogenesis and 4 Gy at the stage of spermatids and matured oocytes there was a trend of increasing radiation effects caused by the participation of two irradiated germ cells. After irradiation of both parents with doses of 2, 3 and 4 Gy the embryonic death F1 was essentially the same as rates for irradiated females and non-irradiated males. The F1 death rate in early postnatal development exceeded the control only after irradiation with doses of 2, 3 and 4 Gy. The increase in radiation effects in the F1 due to the mating of two irradiated parents appears to be associated with a mechanism demonstrating additivity or synergism.     

Mouse hybrid sterility and testicular function

Crosses of BALB/c female mice and inbred wild male mice (PWD, PWK) produce fertile female progeny, but the male offspring are sterile. The hybrid male sterility is a direct action of the hybrid sterility genes Hst-1s and Hstws. Previous reports concluded that spermatogenic arrest effected the sterility. However, the testicular steroidogenesis of hybrid sterile male mice has not been elucidated. In the present report, the steroidogenic capacity of hybrid sterile and parental strain males was directly assessed by quantifying testosterone secretion by maximally stimulated testes perfused in vitro. Additionally, Leydig cell mass and germ cell volumes were morphometrically determined. The experimental results confirm the deleterious impact of the Hst-1s/Hstws genotype on spermatogenesis and demonstrate for the first time that the steroidogenic capacity of hybrid sterile testes is reduced. The biochemical defects that cause the impairment of testicular function are unknown.     

Assessment of effect of partial sterility on mating performance in sweetpotato weevil (Coleoptera: Curculionidae)

The sterile insect technique (SIT) is widely used to suppress or eradicate target pest insect populations. Although the effectiveness of SIT depends on the ability of released sterile males to mate with and inseminate wild females, the use of gamma radiation to induce sterility negatively impacts reproductive cells as well as somatic cells. Consequently, sterilization by irradiation drastically diminishes mating performance over time. In the current study, we evaluated the effect of irradiation dose intensity on fertility, mating propensity, and mating competitiveness in sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Curculionidae), for 16 d after irradiation. Although the mating propensity of males irradiated with 200 Gy, the dose currently used to induce complete sterility of C. f. elegantulus in the SIT program in Okinawa Prefecture, was equal to that of nonirradiated weevils for the first 6 d, the mating propensity of males irradiated with doses between of 75 and 150 Gy was maintained for the first 12 d. The potential fertilization ability of weevils was highly depressed compared with the control weevils, even in those treated with 75 Gy. Mating performance was severely compromised in weevils that were irradiated with a dose of 100 Gy or more. These results demonstrate that partial sterilization can be highly advantageous in eradication programs for the sweetpotato weevil. We discuss the advantages of the application of partial irradiation in insect eradication programs.     

The investigation of the combined effects of gamma irradiation and environmental manipulation on mortality and sterility of Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae)

With respect to the limitations use of methyl bromide and phosphine, employing ionizing radiation to control stored product pests has attracted great attention. The aim of this study is the investigation of the combined effects of gamma irradiation as viable alternatives to synthetic insecticides and environmental management on mortality and sterility of Rhyzopertha dominica (Fabricius) in a wheat cultivar (Gascogen). The effect of doses range from 30 to 2000?Gy gamma irradiation in combination with manipulation of temperature (15, 21, 27 and 32?°C) and relative humidity (20%, 50%, 65% and 85%) on 5–10?days old adults of R. dominica in Gascogen cultivar of wheat were explored. The experiments were repeated three times and conducted in The Nuclear Agriculture Research School in Karaj and laboratory of shahid steki silo in shahre-kord. Probit analysis revealed that both temperature and relative humidity had combined effects when used with gamma irradiation. The lowest doses of gamma ray required to kill 25% (14.2?Gy) and 50% (610.8?Gy) of the population (LD₂₅ and LD₅₀) were recorded at 21?°C and 85% relative humidity respectively. The low dose for 99% mortality (LD₉₉; 2386.7?Gy) was recorded for beetles maintained at 21?°C and 50% relative humidity. The effect of temperature (15, 21, 27 and 32?°C) on sterility caused by gamma irradiation was also investigated. The results showed that the F₁ generation emerged only when the beetles were treated with doses of 0–100?Gy at 32?°C and 0–70?Gy at 27?°C. These results indicate that temperature and relative humidity play an important role in the susceptibility of the lesser grain beetle to gamma irradiation. The results suggest that controlling the efficiency of gamma radiation through environmental control allows the use of low doses of gamma radiation that have a less harmful effect on human health, non-target organisms and seed agronomic features.     

Sterility and Sexual Competitiveness of Tapachula-7 Anastrepha ludens Males Irradiated at Different Doses

A genetic sexing strain of Anastrepha ludens (Loew), Tapachula-7, was developed by the Mexican Program Against Fruit Flies to produce and release only males in programs where the sterile insect technique (SIT) is applied. Currently, breeding are found at a massive scale, and it is necessary to determine the optimum irradiation dose that releases sterile males with minimum damage to their sexual competitiveness. Under laboratory and field conditions, we evaluated the effects of gamma irradiation at doses of 0, 20, 40, 60 and 80 Gy on the sexual competitiveness of males, the induction of sterility in wild females and offspring survivorship. The results of the study indicate that irradiation doses have a significant effect on the sexual behavior of males. A reduction of mating capacity was inversely proportional to the irradiation dose of males. It is estimated that a dose of 60 Gy can induce more than 99% sterility in wild females. In all treatments, the degree of offspring fertility was correlated with the irradiation dose of the parents. In conclusion, the results of the study indicate that a dose of 60 Gy can be applied in sterile insect technique release programs. The application of this dose in the new genetic sexing strain of A. ludens is discussed.     

Physiological and molecular studies on the effect of gamma radiation in fenugreek (Trigonella foenum-graecum L.) plants

This experiment assessed the biochemical changes in fenugreek plants exposed to gamma radiation. Two pot experiments were carried out during two growing seasons of 2015 and 2016. Seeds were subjected to five doses of gamma irradiation (25, 50, 100, 200 and 400?Gy) and were immediately planted into soil pots in a greenhouse. The experimental analysis was performed in M₁ and M₂ generations. Significant differences between irradiated and control plants were detected for most studied characters in M₁ and M₂ generations. It was demonstrated that low doses of gamma irradiation led to gradually increases in growth, yield characters, leaf soluble protein concomitantly with increases in the contents of phenolic and flavonoids compounds particularly at 100?Gy. These changes were accompanied by a substantial increase in ascorbic acid, α-tocopherol and retinol contents. Proline content was increased under all doses of gamma rays in M₁ generation and the highest amount of proline was obtained at 200?Gy with visible decrease in M₂ generation under the same dose. Meanwhile, the highest dose of gamma radiation (400?Gy) decreased all the studied parameters in both mutagenic generations as compared with control plants. In addition, gamma irradiation doses induced changes in DNA profile on using five primers and caused the appearance and disappearance of DNA polymorphic bands with variation in their intensity. These findings confirm the effectiveness of relatively low doses of gamma rays on improving the physiological and biochemical criteria of fenugreek plants.     

Artificial selection,pre‐release diet,and gut symbiont inoculation effects on sterile male longevity for area‐wide fruit‐fly management

Longevity is an important life‐history trait for successful and cost‐effective application of the sterile insect technique. Furthermore, it has been shown that females of some species – e.g., Anastrepha ludens (Loew) (Diptera: Tephritidae) – preferentially copulate with ‘old’, sexually experienced males, rather than younger and inexperienced males. Long‐lived sterile males may therefore have greater opportunity to find and mate with wild females than short‐lived males, and be more effective in inducing sterility into wild populations. We explored the feasibility of increasing sterile male lifespan through selection of long‐lived strains and provision of pre‐release diets with added protein, and inoculated with bacterial symbionts recovered from cultures of the gut of wild Anastrepha obliqua (Macquart). Artificial selection for long‐lived A. ludens resulted in a sharp drop of fecundity levels for F1 females. Nevertheless, the cross of long‐lived males with laboratory females produced a female F1 progeny with fecundity levels comparable to those of females in the established colony. However, the male progeny of long‐lived males*laboratory females did not survive in higher proportions than laboratory males. Provision of sugar to A. obliqua adults resulted in increased survival in comparison to adults provided only with water, whereas the addition of protein to sugar‐only diets had no additional effect on longevity. Non‐irradiated males lived longer than irradiated males, and supplying a generic probiotic diet produced no noticeable effect in restoring irradiated male longevity of A. obliqua. We discuss the need to evaluate the time to reach sexual maturity and survival under stress for long‐lived strains, and the inclusion of low amounts of protein and specific beneficial bacteria in pre‐release diets to increase sterile male performance and longevity in the field.     

Chromosomal principle of radiation-induced F1 sterility in Ephestia kuehniella (Lepidoptera: Pyralidae).

A dose-response analysis of chromosomal aberrations was performed in male progeny of gamma-irradiated males in the flour moth, Ephestia kuehniella. For comparison, several female progeny from each dose level were examined. Aberrations were detected on microspread preparations of pachytene nuclei in the electron microscope and classified according to pairing configurations of synaptonemal complexes (SCs). Fragmentation and various translocations were the most numerous aberrations, whereas interstitial deletion and inversion were rare. At 100 Gy, relatively simple multiple translocations were found. Multiple translocations showing complicated configurations occurred at 150 and 200 Gy, and their number increased with the dose. In males, the mean number of chromosomal breaks resulting in aberrations linearly increased with the dose from 8.4 to 16.2 per nucleus. In females, this value achieved a maximum of 11.2 breaks/nucleus at 200 Gy. Three factors were suggested to contribute to the reported higher level of F1 sterility in males than females: (i) survival of males with high numbers of breaks, (ii) crossing-over in spermatogenesis but not in the achiasmatic oogenesis, and (iii) a higher impact of induced changes on the fertility of males than females. It was concluded that translocations are most responsible for the production of unbalanced gametes resulting in sterility of F1 moths. However, F1 sterility predicted according to the observed frequency of aberrations was much higher than the actual sterility reported earlier. This suggests a regulation factor which corrects the predicted unbalanced state towards balanced segregation of translocated chromosomes.     

Investigation of partial sterility in advanced generation,sodium azide-induced lines of spring barley

Summary The partial sterility found in several advanced generation, sodium azide-induced lines of spring barley (Hordeum vulgare L.) was investigated. Plants of mutant lines were reciprocally crossed with plants of their untreated mother lines. Spike sterility was measured in the selfed offspring of the plants crossed and in F₁ and F₂ progeny. Pollen sterility and endosperm development were analyzed in the selfed offspring of the plants crossed. Results indicated that the sterility was inherited in the mutant lines and was not caused by translocations, inversions, endosperm lethals, embryo-endosperm lethals, or major gene mutations. Furthermore, the sterility was not cytoplasmically inherited, and was essentially eliminated in the F₁ and F₂ of crosses between partially sterile lines and their fertile parents. Results suggest that the sterility may be caused by an environmental interaction with deleterious, homozygous recessive, minor gene mutations that were in the heterozygous condition when the mutant lines were originally selected.Scientific paper No. 7441, College of Agriculture Research Center, Washington State University, Pullman, Wash., USA, Project No. 1006     

Performance of irradiated Teia anartoides (Lepidoptera: Lymantriidae) in urban Auckland, New Zealand

The Australian moth Teia anartoides Walker has been the target of a major eradication program in Auckland, New Zealand. Information on cold torpor and dispersal was needed to help interpret catches of sterile and wild males in female-baited delta traps operated in a grid of up to 1,696 traps at 500-m spacings across the city. Laboratory experiments indicated male flight was enabled at temperatures above 17 degrees C (confirmed by field trapping of wild and recaptured moths). Male survival in the field or in field cages was determined to be limited to approximately 4 d. Sterilization of males for dispersal studies was achieved by exposing male pupae to either 160 or 100 Gy by using 1.25 MeV gamma rays from a Cobalt source, before release as fluorescent-dyed emerged adults. Dispersal was determined by recapture of males in the trapping grid of 1,696 delta traps baited with virgin female moths and placed at spacings of 50-500 m. Irradiated sterile males dispersed up to a maximum recorded distance of 4,500 m (160 Gy) and 10,000 m (100 Gy). At 100 Gy, the median dispersal distance was 300 m, with 90% of males dispersing 1,600 m or less.