Abstract: Numerical dynamics of adult rice water weevils, Lissorhoptrus oryzophilus Kuschel, during harvesting and subsequent storage of the first season rice crop, as well as relationships between adult survival duration, temperature and humidity, were examined. During harvesting, only 3%-13% of weevil adults were transferred to stored grain, and less than 1% of these could survive 2 days exposure to the sun; however, the number of adults transferred to rice straw was 5.1-12.3 times more than that transferred to grain. One month after harvesting, no adult weevils survived in stored grain, compared to 250 and 17 adults per 50 kg surviving in stored shrunken grain and straw, respectively. Survival duration of adults at ≥90% RH and in glass tubes was significantly longer than those at 35%-75% RH and in rice grain. Survival duration was not evidently affected by temperature for adults in stored grain; however, survival duration at 20℃ (constant temperature) was significantly longer than at 27.0-33.2℃ (room temperature) for adults in glass tubes. Analyses of relationships between survival and humidity, temperature and substrate using the exponential model of survival analysis revealed that the risk of death increased significantly as humidity decreased in the range 75%-98% RH, and that the risk of mortality was also higher under high temperatures (27.0-33.2℃) and in stored grain. These results provide a basis for the quarantine of L. oryzophilus in stored rice grain.

Key words: Lissorhoptrus oryzophilus, rice, environmental factor, survival dynamics, death risk