Trehalose, a Major Sugar Cryoprotectant of the Overwintering Rice Water Weevil, Lissorhoptrus oryzophilus (Coleoptera: Curculionidae)

Rice water weevil, Lissorhoptrus oryzophilus Kuschel, overwinters as an adult in reproductive diapause. We compared the cold tolerance between diapausing and reproductive adults, and analyzed their polyol contents. Diapausing adults showed significantly higher survival rates in response to −10°C than did reproductive adults. Reproductive adults acclimated to low temperature in the laboratory also showed enhanced cold tolerance, but were not as cold-hardy as the diapausing adults. Mean supercooling points were not significantly different between diapausing and reproductive adults with a range between −15°C and −18°C. Seven polyols consisting of four sugars (glucose, trehalose, fructose, and sucrose) and three sugar alcohols (glycerol, sorbitol, and mannitol) were identified from field and laboratory adults and quantified by an ionexchange HPLC with an electrochemical detector. Glucose and trehalose were the major sugar polyols and showed the greatest change in autumn field populations. Reproductive populations kept high glucose contents during summer, while diapausing populations had high trehalose contents during winter. Coldacelimated weevils also elevated trehalose contents. Most sugar alcohols, however, were relatively low except in May when the sorbitol content of the weevils increased significantly. These results indicate that the diapausing rice water weevil, a freeze-susceptible species, is cold-tolerant with elevated trehalose content.