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.     

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.

     

Effects of radiation on the fertility of the Ethiopian fruit fly,Dacus ciliatus

The Ethiopian fruit fly, Dacus ciliatus (Loew) (Diptera: Tephritidae), is a significant pest of cucurbit crops in Asia and Africa and is currently controlled with insecticides. The sterilizing effect of gamma radiation on D. ciliatus adults was investigated to assess the suitability of sterile insect technique (SIT) for use as an alternative, non‐chemical strategy for the control of this pest. Late pupae (48 h before emergence) were irradiated with 60, 80, 100, 120, and 140 Gy of gamma rays emitted by a ⁶⁰Co source. Following emergence, the biological characteristics of the experimental cohorts (including all possible male‐female combinations of irradiated and untreated flies) were recorded. No significant negative effects of irradiation on pupal eclosion or the ability of newly emerged flies to fly were observed. Samples of eggs at reproductive fly‐ages (12‐, 15‐, and 17‐day‐old pairs) were collected and their hatch rates were assessed. At 60 Gy, females were completely sterilized, whereas complete sterilization of the males was observed only at 140 Gy (a small amount of fertility persisted even at 120 Gy). In addition to the above experiments, three fruit infestation trials were conducted with zucchini [Cucurbita pepo L. (Cucurbitaceae)] as the plant host and the pupae produced in those trials were collected and recorded. We observed significant (ca. 10%) infestation following treatment with up to 120 Gy and zero progeny only at 140 Gy, mirroring the egg‐hatch results. Our findings support the feasibility of SIT for the control of D. ciliatus.     

Effects of gamma radiation on different developmental stages of the oriental tobacco budworm,Helicoverpa assulta (Lepidoptera: Noctuidae)

Ionizing radiation is increasingly used as an alternative to post‐harvest crop fumigation by methyl bromide. We studied the effects of gamma irradiation on Helicoverpa assulta (Lepidoptera: Noctuidae) 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 Gy) based on preliminary experiments and irradiated eggs, larvae, pupae and adults. A dose of 100 Gy to eggs allowed 21.83% of larvae to pupate, but these all died during the pupal stage. A dose of 100 Gy 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 Gy and above resulted either in their death or emergence of abnormal adults; however, after 100 or 200 Gy, normal adults emerged and F₁ 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 Gy dose was effective for irradiation of eggs and larvae, and 300 Gy for pupae.     

Developmental inhibition of Drosophila suzukii by ionizing radiation

Spotted wing drosophila (SWD) has emerged as a major invasive insect pest of small berry fruits in the Americas and Europe since the late 2000s. Thus, phytosanitary treatment of commodities for export is imperative to prevent the movement of viable SWD to newer areas. In the present study, all developmental stages of SWD were irradiated with different doses of gamma and electron beam radiation to assess developmental inhibition to identify potential quarantine doses of the radiations. Ionizing radiation induced developmental inhibition of all stages of SWD. The effective doses for 99% inhibition (ED₉₉) of hatching, pupariation, and adult emergence from irradiated eggs for gamma radiation were 882, 395 and 39 Gy, respectively, compared with 2849, 687, and 41 Gy, respectively, for electron beam radiation. The ED₉₉ for inhibition of pupariation and adult emergence in irradiated larvae were 703 and 47 Gy, respectively, for gamma radiation, and 619 and 33 Gy, respectively, for electron beam radiation. Pupal irradiation did not completely inhibit adult emergence, even at 300 Gy. However, irradiation with ≥100 Gy of puparia induced adult sterility, with no egg production at all. The ED₉₉ for inhibition of F₁ egg hatchability from adults irradiated with gamma radiation and electron beam radiation was estimated to be 424 and 125 Gy, respectively. The results of the present study suggest that gamma radiation and electron beam radiation are alternatives for phytosanitary treatment. Irradiation with 100 Gy could be suggested as a potential dose for egg, larval, and pupal quarantine treatment of SWD.     

Anastrepha ludens (Loew) (Diptera: Tephritidae) larvae irradiated at higher doses improve the rearing of two species of native parasitoids

Irradiation doses 40, 80, 120 and 160 Gy were used on 6-, 7-, 8- and 9-days-old Anastrepha ludens (Loew) (Diptera: Tephritidae) larvae. The larvae from the different age groups irradiated with different doses were exposed separately to Neotropical-native Doryctobracon crawfordi (Viereck), Utetes anastrephae (Viereck) and the Asian introduced Diachasmimorpha longicaudata (Ashmead) parasitoids (Hymenoptera: Braconidae). A significant increment in parasitoid emergence directly related to radiation increment on parasitoids D. crawfordi and U. anastrephae was observed. This effect was higher on irradiated young larvae; in D. longicaudata, emergence increment was related to age of larva but not with radiation doses. Similar results were obtained for sex ratio. Host larva weight increased with age, and irradiation had no effect on gaining weight of growing larvae. The host larval mortality 72 hr after exposition had an inverse relationship regarding to its age, although it did not have a negative effect as regards radiation doses. Immature stages of parasitoid/larva (>1 = superparasitism) were higher in 8-days-old larvae parasitized by D. Longicaudata, while in D. crawfordi and U. Anastrephae, superparasitism was absent (<1 immature stage per host larva). Superparasitism was not affected by increased radiation dose. No levels of melanin were detected as indicators of immunological reactions. However, these results are considered to be closely related to the lessening of these reactions due to irradiation. The positive relationship between emergence and irradiation dose to host larvae was present in native species D. crawfordi and U. anastrephae, but absent for exotic D. longicaudata. The data presented here are of great relevance for cost effective mass rearing of these parasitoids.     

Effects of X‐ray irradiation on development and reproduction of the oriental tobacco budworm,Helicoverpa assulta (Lepidoptera: Noctuidae)

All stages of the life cycle of Helicoverpa assulta were irradiated with X‐rays to determine the inhibitory dose for development and reproduction to serve as a quarantine treatment. The 100‐Gy dose was effective for irradiation of eggs and larvae, and the 200‐Gy dose was effective for pupae and mixed‐sex adults. When either adult males or females were irradiated, however, 500 Gy was required to prevent the F1 eggs from hatching, and thus single‐sex adults required much higher doses of X‐ray irradiation. To gather confirmatory data applicable to phytosanitary quarantine regulations, pupae—the immature stage most resistant to X‐ray irradiation—were placed inside paprika in boxes for exportation and were irradiated with 300 Gy as a small‐scale confirmatory test. The dose given to 1,007 individual pupae resulted in 12.62 % survival, and 1.79 % of pupae emerged as normal adults; however, these adults produced only a few eggs that did not hatch, suggesting that a minimum dose of 300 Gy of X‐ray irradiation will provide quarantine security for immature H. assulta in paprika exports.     

Evaluation of partial sterility in mating performance and reproduction of the West Indian sweetpotato weevil,Euscepes postfasciatus

The sterile insect technique (SIT) is based on population and behavioral ecology and is widely used to suppress or eradicate target pest insect populations. The effectiveness of SIT depends on the ability of the released sterile males to mate with and inseminate wild females. The use of gamma‐radiation to induce sterility is, however, associated with negative impacts not only on reproductive cells but also on somatic cells. Consequently, irradiation for sterilization diminishes mating performance over time. In this study, we evaluated the balance between the irradiation dose and both fertility and mating propensity in Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) for 22 days following irradiation. The mating propensity of males irradiated with a 150‐Gy dose, as currently used to induce complete sterility of E. postfasciatus in the SIT program in Okinawa Prefecture, was equal to that of non‐irradiated weevils for up to 6 days, and the mating propensity of males irradiated with a dose of 125 Gy was equal to that of non‐irradiated weevils for twice this period (12 days). The fertilization ability of weevils irradiated with a dose of 125 Gy was reduced by 4.6% in males and 0.6% in females, compared to the potential fertilization ability. We also discuss the possibility of the application of partially sterilized insects in eradication programs.     

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.     

Survival and reproduction of Liposcelis paeta (Pearman) (Psocoptera: Liposcelididae) when irradiated by electron beams

Electron beam irradiation has been evaluated for the survival and reproduction of Liposcelis paeta Pearman (Psocoptera: Liposcelididae). All effects increased with increasing doses from 50 to 1000 Gy when the electron energy was 2 MeV. Eggs were unable to develop into adults following a dose of 100 Gy. Complete (100%) mortality was achieved about 5 weeks after adult emergence from nymphs irradiated at 300 Gy, whereas 100% mortality of adults was achieved 9 weeks after irradiation at 300 Gy. The fecundity was greatly reduced to 1.82% of that of control when L. paeta adults were irradiated at 250 Gy. A dose of 300 Gy caused complete reproductive sterility in adults. These results suggest that the most susceptible stage was the egg stage, then nymph and adult stages. A dose of 300 Gy is suggested for quarantine treatment of commodities infested by L. paeta.     

Effect of low temperature between fractionated-dose irradiation doses on mating of the West Indian sweetpotato weevil, <Emphasis Type="Italic">Euscepes postfasciatus</Emphasis> (Coleoptera: Curculionidae)

The effectiveness of the sterile insect technique (SIT) depends on the ability of released sterile males to mate with and inseminate wild females, but the use of gamma radiation to induce sterility negatively affects both somatic and reproductive cells of the sterilized insects. Recently, the effectiveness of fractionated-dose irradiation (FI), in which a sterilizing dose is delivered over time in a series of small irradiations, has been demonstrated in the West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire). FI improves male mating propensity compared with acute irradiation; however, this renewed technique takes a long time (72 h in the present circumstances) compared with the traditional technique (approximately 20 min) using single-dose irradiation (150 Gy) to fully sterilize this weevil. The extra time required by FI might negatively affect the quality of released sterile males, because weevils expend limited resources, such as metabolic energy or sperm, in mating freely in this period. We evaluated whether the temporal storage of weevils at low temperature (5°C and 15°C) improves the quality of sterile males compared with the normal condition (25°C). Temporal storage at low temperature in FI improves male mating propensity. For example, the sexually active phase of males exposed to 15°C was 18 days at least after irradiation. This period was longer than that of normal males (14 days). Meanwhile, this manner delayed male reproductive development and temporarily reduced mating competitiveness ability. If considering the long active phase of sterile males exposed to 15°C, these disadvantage would be cancelled out. We discuss the advantage of FI with temporal storage at low temperature in the eradication program using SIT for E. postfasciatus.     

Induced expression of the IER5 gene by γ-ray irradiation and its involvement in cell cycle checkpoint control and survival

The immediate-early response gene 5 (IER5) was previously shown, using microarray analysis, to be upregulated by ionizing radiation. Here we further characterized the dose- and time-dependency of radiation-induced expression of IER5 at doses from 0.5 to 15 Gy by quantitative real-time PCR analyses in HeLa cells and human lymphoblastoid AHH-1 cells. A radiation-induced increase in the IER5 mRNA level was evident 2 h after irradiation with 2 Gy in both cell lines. In AHH-1 cells the expression reached a peak at 4 h and then quickly returned to the control level, while in HeLa cells the expression only remained increased for a short period of time at around 2 h after irradiation before returning to the control. After high-dose irradiation (10 Gy), the induction of the IER5 expression was lower and delayed in AHH-1 cells as compared with 2-Gy irradiated cells. In HeLa cells, at this dose, two peaks of increased expression were observed 2 h and 12–24 h post-irradiation, respectively. RNA interference technology was employed to silence the IER5 gene in HeLa cells. siRNA-mediated suppression of IER5 resulted in an increased proliferation of HeLa cells. Cell growth and survival analyses demonstrated that suppression of IER5 significantly increased the radioresistance of HeLa cells to radiation doses of up to 6 Gy, but barely affected the sensitivity of cells at 8 Gy. Moreover, suppression of IER5 potentiated radiation-induced arrest at the G2-M transition and led to an increase in the fraction of S phase cells. Taken together, we propose that the early radiation-induced expression of IER5 affects the radiosensitivity via disturbing radiation-induced cell cycle checkpoints.     

Fecundity and longevity of Argentine ant (Hymenoptera: Formicidae) queens in response to irradiation

Irradiation is a post‐harvest quarantine treatment option to control ants and other hitchhiker pests on fresh horticultural products traded between countries. As little is known about irradiation effects on ants, radiotolerance of the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae: Dolichoderinae), was studied to determine a dose sufficient for its control. Queens collected from Buenos Aires, Argentina, were irradiated with 30, 60, 90 Gy or left untreated as controls, and then followed for 8 weeks to evaluate their survival and fecundity. Overall queen survival and brood viability decreased with increasing irradiation dose. The number of eggs was reduced by 50%, 69% and 56% in the 30, 60 and 90 Gy doses, respectively, compared with untreated control queens. The percentage of eggs that developed into larvae decreased from 41.1% in the control to 22.5%, 1.4%, and 0% in the 30, 60, and 90 Gy treatments, respectively. Thus, the number of larvae was reduced by 69% in the 30 Gy treatment compared with the control, only one larva was observed in the 60 Gy treatment, and none in the 90 Gy treatment. Only one pupa was observed in the 30 Gy treatment and none in the 60 and 90 Gy treatments during the 8‐week experiment. Queens irradiated with 60 and 90 Gy had significantly reduced longevity compared with queens treated with lower doses or untreated queens. Radiation dose ≥90 Gy stopped brood development in Argentine ant queens and should be sufficient as a phytosanitary treatment. The radiotolerance of Argentine ant appears to be similar to that of two other important invasive ants.     

Effect of electron beam irradiation on developmental stages of Plutella xylostella (Lepidoptera: Plutellidae)

The effect of electron beam irradiation on each developmental stage of diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), was examined. Eggs, larvae, pupae, and adults were irradiated at target doses of 30, 50, or 100 Gy or they were left untreated as controls in replicated experiments. When eggs and pupae were irradiated with 100 Gy, emergence rates greatly decreased and, although some adults laid eggs, they did not hatch. Egg hatching of irradiated larvae and adult decreased with increasing irradiation doses. However, electron beam irradiation did not kill P. xylostella directly. Adult longevity was not affected. Reciprocal crosses between irradiated and unirradiated moths demonstrated that females were more radiosensitive than males in hatchability; however, the difference was not significant. In addition, electron beam-irradiated larvae showed typical DNA fragmentation in a dose-dependent manner compared with cells from unirradiated larvae. Our findings suggest that electron beam irradiation induces abnormal development and reproduction of P. xylostella; therefore, it may contribute to effective disinfestation and quarantine treatments of P. xylostella.     

X-ray doses to safely release the parasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae) reared on Anastrepha fraterculus larvae (Diptera: Tephritidae)

Diachasmimorpha longicaudata is a koinobiont larval parasitoid that is currently used to control fruit flies of the genera Anastrepha, Ceratitis and Bactrocera. In the rearing process, a fraction of the host larvae that are exposed to parasitoids escape from parasitism and develop into viable and fertile flies. This creates the need to eliminate emerging flies before the parasitoids are shipped for release, increasing costs due to additional handling steps. Exposure of fly eggs or larvae to gamma-irradiation before they are parasitised has been used to reproductively sterilise hosts, or even inhibit their emergence. Our aim was to determine whether X-ray radiation applied to Anastrepha fraterculus third instar larvae before they are exposed to parasitoids, inhibits fly emergence in non-parasitised larvae without affecting the performance of the parasitoids that emerge from parasitised larvae. Three X-ray doses: 6250.2 R, 8333.6 R and 10417 R (equivalent to 60, 80 and 100 Gy, respectively) and one γ-ray dose (100 Gy) were tested. Fly emergence decreased with increasing doses of radiation, showing null values for the higher X-ray dose and the dose of 100 Gy. Irradiation showed either no impact or a positive effect on parasitism rate and fecundity. Sex rate was biased towards females in almost every dose. We conclude that the two types of radiation evaluated here were equally effective in suppressing fly emergence with no detrimental effects on the biological quality of the produced parasitoids. X-rays offer an alternative method of irradiation than the conventional radiation source, i.e. γ-rays. These results represent a significant improvement in the development of a biological control programme against A. fraterculus.     

Effects of X-ray irradiation on male sperm transfer ability and fertility in the sweetpotato weevils <Emphasis Type="Italic">Euscepes postfasciatus</Emphasis> (Coleoptera: Curculionidae) and <Emphasis Type="Italic">Cylas formicarius</Emphasis> (Coleoptera: Brentidae)

Gamma radiation from isotopic sources has been used in sterile insect technique (SIT) programs worldwide, but it might be difficult to continue using these sources in future SIT programs because of social issues. Therefore, an alternative sterilization source to gamma rays, such as X-rays, needs to be developed. The physical properties of radiation are different between gamma rays and X-rays: for example, X-rays have a shorter penetration depth than gamma rays. Therefore, X-rays may not fully confer male sterility, depending on the target pest insects. The present study investigated whether the West-Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) and the sweetpotato weevil Cylas formicarius (Fabricius) are sterilized by X-rays generated in a low-energy X-ray irradiator, without deterioration of male mating ability, at the doses currently used in the eradication programs for E. postfasciatus (150 Gy) and C. formicarius (200 Gy) using gamma rays at Okinawa, Japan. The results demonstrated that it is possible to use X-rays in future SIT programs for E. postfasciatus and C. formicarius, because X-ray irradiated males were almost completely sterilized without deterioration of their mating ability.     

Prematurely condensed chromosome fragments in human lymphocytes induced by high doses of high-linear-energy-transfer irradiation

This study provides a useful biodosimetry protocol for radiation accidents that involve high doses of heavy particle radiation. Human peripheral blood lymphocytes (PBLs) were irradiated in vitro with high doses (5–50 Gy) of charged heavy-ion particles (carbon ions, at an effective linear-energy-transfer (LET) of 34.6 keV/μm), and were then stimulated to obtain dividing cells. PBLs were treated with 100 nM calyculin A to force chromosomes to condense prematurely, and chromosome spreads were obtained and stained with Giemsa. The G2 prematurely condensed chromosome (G2-PCC) index and the number of G2-PCC including fragments (G2-PCC-Fs) per cell for each radiation dose point were scored. Dose-effect relationships were obtained by plotting the G2-PCC indices or G2-PCC-Fs numbers against radiation doses. The G2-PCC index was greater than 5% up to doses of 15 Gy; even after a 30 Gy radiation dose, the index was 1 to 2%. At doses higher than 30 Gy, however, the G2-PCC indices were close to zero. The number of G2-PCC-Fs increased steeply for radiation doses up to 30 Gy at a rate of 1.07 Gy⁻¹. At doses higher than 30 Gy, the numbers of G2-PCC-Fs could not be accurately indexed because of the limited numbers of cells for analysis. Therefore, the number of G2-PCC-Fs could be used to estimate radiation doses up to 30 Gy. In addition, a G2-PCC index close to zero could be used as an indicator for radiation doses greater than 40 Gy.     

Impact of mass rearing and gamma irradiation on thermal tolerance of Eldana saccharina

Mating ability, survival, and fitness of mass‐produced sterile insects when released into the wild, are critical to the success of the sterile insect technique (SIT) as a pest management strategy, but their field performance remains one of the greatest challenges. Thermal stress tolerance by irradiated insects is a determinant of sterile insect quality, hence knowledge of their physiological competitiveness is essential for developing the SIT. Here, we report the results of experiments investigating effects of laboratory rearing and increasing radiation dosage on thermal limits to activity of the adult stage of Eldana saccharina Walker (Lepidoptera: Pyralidae). The critical thermal maximum (CTmax) and critical thermal minimum (CTmin) were assayed using a dynamic method on both sexes of E. saccharina moths in laboratory vs. wild populations (to determine effect of rearing history). Furthermore, the laboratory population was exposed to 150, 200, and 250 Gy, to determine the effect of radiation dose. Laboratory‐reared E. saccharina were more heat tolerant compared to wild moths for both sexes (CTmax = 44.5 vs. 44.3 °C), whereas in the case of CTmin (3.7 vs. 4.4 °C), wild moths were more cold tolerant than their laboratory‐reared counterparts. Irradiation had a negative effect on both CTmax and CTmin. Moths treated at the lowest radiation dose were more cold and heat tolerant than those treated at the highest dosages (CTmin = 4.5 vs. 6.2 °C; CTmax = 43.9 vs. 43.5 °C), thereby reinforcing the importance of lower dosages rather than those that induce full sterility against E. saccharina. In general, sex had no influence on critical thermal limits in all moth treatments except for those irradiated at 150 Gy. The data presented in this article provide evidence that increasing radiation dose impacts on fitness of laboratory‐produced moths relative to their wild counterparts, which in turn could affect the effectiveness of the SIT programme.     

Effects of γ radiation on the reproduction and enteroendocrine cells of the spruce bark beetle <Emphasis Type="Italic">Ips typographus</Emphasis> and prospects for its control

The European spruce bark beetle Ips typographus is one of the most important pests of spruce forests in Europe. The present study investigated the feasibility of a sterile insect technique (SIT) for this pest control. Laboratory-reared males were exposed to various doses of γ radiation (0, 10, 30, 50, 70 and 90 Gy) and allowed to mate with laboratory-reared untreated females. The radiation significantly affected the number of viable offspring. Although females oviposited on average 16.0–18.8 eggs per maternal tunnel in all treatments, the number of larval tunnels per maternal tunnel observed after 4 weeks of development decreased from 17.3 in the control (0 Gy) to 4.5 in the 90-Gy group. Numerous oviposition sites without larval tunnels were observed in galleries when males received high doses (70 and 90 Gy) of γ radiation. Comparison of the sperm viability in the control and irradiated males did not reveal any statistically significant differences. Side effects of the irradiation were examined by immunostaining of the enteroendocrine cells. Two distinct types of cells were revealed with antibodies to neuropeptides allatostatin A and tachykinin in the midgut. The alimentary tracts of males receiving a high dose of radiation (90 Gy) showed a significantly decreased number of tachykinin-like immunoreactive enteroendocrine cells. This observation suggests potential radiation-induced damage of the digestive system, which could lead to a reduction in male fitness. The implications of these findings for successful use of SIT in spruce bark beetle control are discussed.     

‘Fukusensor:’ a genetically engineered plant for reporting DNA damage in response to gamma radiation

Transgenic plants can be designed to be ‘phytosensors’ for detection of environmental contaminants and pathogens. In this study, we describe the design and testing of a radiation phytosensor in the form of green fluorescence protein (GFP)‐transgenic Arabidopsis plant utilizing a DNA repair deficiency mutant background as a host. Mutant lines of Arabidopsis AtATM (At3g48190), which are hypersensitive to gamma irradiation, were used to generate stable GFP transgenic plants in which a gfp gene was under the control of a strong constitutive CaMV 35S promoter. Mutant and nonmutant genetic background transgenic plants were treated with 0, 1, 5, 10 and 100 Gy radiation doses, respectively, using a Co‐60 source. After 1 week, the GFP expression levels were drastically reduced in young leaves of mutant background plants (treated by 10 and 100 Gy), whereas there were scant visible differences in the fluorescence of the nonmutant background plants. These early results indicate that transgenic plants could serve in a relevant sensor system to report radiation dose and the biological effects to organisms in response to radionuclide contamination.