Abstract: In order to explore the roles of temperature and relative humidity in population development of the rice leaf folder, Cnaphalocrocis medinalis (Guenée), the duration, embryo development, hatchability and weight loss of eggs of this moth under different temperature and relative humidity were investigated in the laboratory experiments. The results showed that egg duration significantly shortened and egg hatchability significantly increased as relative humidity increased. Egg hatchability significantly reduced when relative humidity was less than 46% and 66% at 22℃ and 25-34℃, respectively, and no eggs were hatched at 37℃ under any relative humidity (46%-100%). Under the conditions of relative humidity less than 50% and temperature higher than 28℃, all eggs could not be hatched either. The optimal temperature and relative humidity ranges for rice leaf folder eggs were 22-31℃ and 77%-100%, respectively. The lower threshold temperature for development and effective accumulated temperature of eggs were 10.1±0.6℃ and 63.7±3.5 day degrees, respectively. The relationship between egg hatchability (Y) and the ratio of relative humidity to temperature (RH/T) fitted the logistic model very well, Y=0.8662/［1+exp(17.4084-7.5714×RH/T)］. When the RH/T value was less than 2.34, egg hatchability would be less than 50%. The optimal RH/T was about 3.0 for eggs. It is concluded that the higher weight loss of eggs, egg wizening and an arrested development of embryo resulted from lower humidity are the main lethal factors of eggs.

Key words: Cnaphalocrocis medinalis, egg, temperature, relative humidity, developmental duration, egg hatchability, embryonic development