Isolation And Identification Of Summer Diapause-associated Genes In The Rice Water Weevil, Lissorhoptrus Oryzophilus Kuschel (Coleoptera: Curculionidae)

The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae) is an alien insect in China which invaded this country in later 1980s. Adults feed on leaf epidermis of rice plants; larvae cut roots. Adult damage is generally of minor importance, and it is the larval feeding that causes economic losses. In some regions of China where rice is planted only for one season, the weevil has only generation, and the newly-emerged adults move to aestivating sites following a brief feeding where they maintain in diapause state. However, in the regions such as southeast Zhejiang, China where rice is planted for two consecutive seasons, the weevil can complete two generations: more than 90% of first-generation "summer" females enter summer diapause, and the rest reproduces on late-season rice leading to a seocnd generation with a low density.Exploring the mechanisms responsible for diapause induction, maintainence and termination in L. oryzophilus would provide a basis for the analysis of population dynamcis in this insect. To date, relations of its diapause induction and termination with ecological and physiological factors including host-plant, temperature, juvenile hormone esterase, and the post-emergence period experienced by adults have been reported. In this study, diapause-associated genes were isolated and identified from summer diapausing rice water weevils using suppression subtractive hybridization (SSH).A total of 206 clones expressed specifically during diapause were sequenced, their average length was approximately 470 nucleotides. 72 clones showed high sequence similarity to known genes deposited in GenBank, 55 clones had non-significance to database groups, and 31 clones were not matched. In this study, the highly expressed gene in diapausing adult rice water weevils was ribosomal protein (32 clones, 15.5%), cytochrome c oxidase (24 clones, 11.7%), ATP/ADP carrier protein (16 clones, 7.8%), cytoplasmic phosphatidylinositol transfer protein (12 clones, 5.8%), and adenylate kinase (9 clones, 4.3%). Actin and juvenile hormone esterase were also expressed in diapausing weevils. The key factors influencing SSH results, functions of the genes described above, and the issues needed to be further studied were discussed.The results we have got can enrich our knowledge on the molecular mechanisms regulating summer diapause in insects, and can also serve as a basis for further studies in this field in rice water weevil.