A comparative study on the effects of electron beam irradiation on imidacloprid-resistant and -susceptible Aphis gossypii (Hemiptera: Aphididae)

Effect of electron beam irradiation on the pine wood nematode, Bursaphelenchus xylophilus

PURPOSE

Reproduction inhibition of the pine wood nematode (PWN) by electron beam (e-beam) irradiation both in vitro and in vivo was tested to determine if ionizing radiation could control the PWN by reducing survival and preventing reproduction, thus reducing the risk of pine wilt disease (PWD) spread.

MATERIALS AND METHODS

E-beam (10 MeV) irradiation treatment at different doses (0-4 kGy) was applied to PWNs in a Petri dish. Treatment of pine wood logs infested with PWNs was performed at 10 kGy. Mortality was determined by comparing the survival rates before and after irradiation treatment. DNA damage by e-beam irradiation (0-10 kGy) in the PWN was determined using the comet assay.

RESULTS

E-beam irradiation increased mortality and suppressed reproduction with increasing doses. The lethal dose (LD) values (kGy) were estimated as follows: LD50 = 2.32, LD90 = 5.03, and LD99 = 9.48. E-beam irradiation of pine wood logs significantly suppressed PWN reproduction. Comets of e-beam-irradiated cells showed an increased tail DNA level and moment with an increasing dose.

CONCLUSION

This study suggests that e-beam irradiation could be used as an alternative method for the management of pine wood logs infested with PWNs.

Deleterious effects of electron beam irradiation on development and reproduction of tomato/potato psyllids, Bactericera cockerelli

The potato/tomato psyllid Bactericera cockerelli causes serious damage to several solanaceous crops by direct feeding and vectoring Candidatus Liberibacter solanacearum, a bacterial pathogen. Electron beam (eBeam) irradiation is an environmentally friendly, chemical-free alternative method that is increasing in use for disinfestation of insect pests. We hypothesize that this irradiation technology will have detrimental effects on potato psyllid and thus impede its disease vectoring. To this end, we explored the effects of eBeam treatment ranging from 50 to 500 Gy on survival, development and reproduction of this pest. Impact on psyllids was apparently dose-dependent. When irradiated at 350 Gy, eggs could not hatch, 1st instar nymphs failed to emerge, and although a small portion of irradiated 5th instar nymphs survived, the emerged adults were mostly deformed. Abnormality in eclosed adults suggests harmful effects of eBeam on metamorphosis. Reproduction was seriously impaired when female psyllids were exposed to eBeam at the 5th instar nymphal or young adult stage, presumably due to inability to form oocytes. In addition, reciprocal crosses between irradiated and untreated psyllids indicated that female psyllids were more radiosensitive than males to eBeam. Taken together, these findings indicate that eBeam negatively impacted potato psyllid development and reproduction, which would inevitably compromise its disease transmission capacity. A dose of 350 Gy can be considered as a reference dose for effective control of potato psyllids.

Elucidation of molecular expression associated with abnormal development and sterility caused by electron beam irradiation in Spodoptera litura (F.) (Lepidoptera: Noctuidae)

PURPOSE

The objective of the present study was to elucidate the mode of indirect action of electron beam irradiation at the molecular level against a quarantine pest, Spodoptera litura (F.).

MATERIAL AND METHODS

Electron beam irradiation (50-200 Gy) was applied to S. litura eggs, larvae, pupae, and adults, after which the feeding area, body weight, deformity of pupae and adults, ovarian development, expression levels of vitellogenin (Vg) and vitellogenin receptor (VgR) genes, and protein levels were analyzed.

RESULTS

The amount of feeding by S. litura larvae and the synthesis level of 70 kDa storage protein significantly decreased as the electron beam dose increased. When larvae were treated with the electron beam, morphological deformities appeared in the pupae, and abnormal wing disc (AWD) expression significantly decreased. Ovarian development was completely inhibited in emerged adults that had undergone 200 Gy electron beam irradiation as pupae. Quantitative real-time PCR (qRT-PCR) assays showed significant downregulation of the Vg and VgR genes due to electron beam irradiation; whereas the synthesis level of Vg protein (190 kDa) did not decrease with time in eggs unlike in non-irradiated (control) S. litura eggs, exhibiting irradiation induced impairment of Vg functioning.

CONCLUSIONS

These findings of radiation-induced abnormal development and sterility in S. litura together with the correlated changes at the molecular level may facilitate the development of a phytosanitary strategy against this quarantine pest using electron beam irradiation.

Electron Beam-Induced Sterility and Inhibition of Ovarian Development in the Sakhalin Pine Longicorn, Monochamus saltuarius (Coleoptera: Cerambycidae)

The Sakhalin pine longicorn, Monochamus saltuarius (Gebler; Coleoptera: Cerambycidae), is an insect vector of the pine wilt nematode (PWN), Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle, and is widely distributed in central Korea. M. saltuarius is a forest pest that seriously damages Pinus densiflora (Siebold et Zucc, Pinales: Pinaceae) and Pinus koraiensis (Siebold & Zucc, Pinales: Pinaceae) forests. We examined the effect of electron beam irradiation on the mating, DNA damage and ovarian development of M. saltuarius adults and sought to identify the optimal dose for sterilizing insects. When the adults were irradiated with electron beams, both females and males were completely sterile at 200 Gy. In a reciprocal crossing experiment between unirradiated and irradiated adults, the reproductive ability of wild adults was recovered by crossing with wild adults even after crossing previously with sterile adults. When a pair of unirradiated adults (♀- × ♂-) and 10 or 20 irradiated adults (♀+ or ♂+) were kept together, the control effect was as high as 80~90%. After electron beam irradiation at 200 Gy, the DNA of M. saltuarius adults was damaged, the ovarian development of female adults was inhibited, and the level of vitellogenin was significantly decreased compared with that in unirradiated female adults. These results suggest that pine wilt disease can be effectively controlled if a large number of sterilized M. saltuarius male adults are released into the field.

X-ray Irradiation Control of Frankliniella occidentalis and Frankliniella intonsa (Thysanoptera: Thripidae) in the Exportation of Freshly Cut Lily Flowers

Lily (Lilium longiflorum Thunb.) is the most representative bulb flower, and it is the third most important flower in the flower industry of South Korea after rose and chrysanthemum. To determine the efficacy of X-ray irradiation for use in quarantine processing, two species of flower thrips (Frankliniella intonsa (Trybom) and Frankliniella occidentalis (Pergande)) were placed in the top, middle, and bottom locations of lily boxes and irradiated with different X-ray doses. After irradiation with an X-ray dose of 150 Gy, the egg hatching of the two flower thrips was completely inhibited at every location in the lily boxes, and the irradiated F. intonsa and F. occidentalis nymphs failed to emerge as adult in every location of the lily boxes. When the adults were irradiated at 150 Gy, the fecundity of the two flower thrips was markedly lower than that of the untreated control groups. The F1 generation failed to hatch at the top and middle locations, whereas the F1 generation of both F. intonsa and F. occidentalis was not suppressed at the bottom locations, even at 200 Gy. However, hatching was perfectly inhibited at 300 Gy of X-ray irradiation. Also, X-rays did not affect the postharvest physiology of cut lilies. Therefore, a minimum dose of 300 Gy is recommended for the control of F. intonsa and F. occidentalis for the exportation of lily.