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.
Keywords: Tobacco cutworm; abnormal wing disc; electron beam; vitellogenin.