Adaptability Of Rice Leaf Folder Reared On Maize Seedlings To Rice And The Effects Of Temperature And Humidity On The Eggs And Larvae

Rice leaf folder Cnaphalocrocis medinalis (Guenee)(RLF) broke out more and more frequently in the recent years and caused a destructive yield loss of rice. Because of lack of a good artificial diet to rear RLF in the laboratory now, it is a prefect method to rear RLF using maize seedlings. However, this method has just been used in recent years in China, so the studies on the capacity of RLF reared on maize seedlings to use rice are absent. At the same time the effects of association of temperature and humidity on eggs and larvae were still unclear. In this paper, the comparative study on biological characters of RLF on rice and maize which were reared different generations on maize seedlings were carried out, and the effects of different temperature and humidity combinations on the egg’s development, survival and weight were studied too. At last, the humidity stress on the survival of eggs and the hatch of larvae was checked. The results would be useful for forecasting the outbreak of RLF. The main results were list as following:The RLF larvae reared on maize seedlings for17,24,27, and29generations were transferred onto rice plants at tillering stage and maize seedlings to check their fitness. The results showed that larvae survial, pupation rate, number of eggs and egg hatchability of RLF on rice plants and maize seedling were not significant difference. The RLF reared on the maize seedlings still had a stronger ability to use rice, and the method using maize seedlings was an effective method to rear RLF in laboratory.The duration, embryo development, hatchability and weight loss of eggs under different temperature and relative humidity were studied. The results showed that the eggs duration significantly shortened and the hatchability significantly increased as the relative humidity increased. The hatchability significantly reduced when the relative humidity was less than46%and66%at22℃and25-34℃, respectively, and no eggs hatched at37℃under any relative humidity (46-100%). Under the conditions, relative humidity less than50%and temperature more than28℃, all the eggs could not hatch too. The optimum temperature and relative humidity regions for rice leaf folder eggs were the22-31℃temperature and77%-100%relative humidity. The lower threshold temperature for development and effective accumulated temperature of eggs were10.1±0.6℃and63.7±3.5day degree, respectively. The relationship between the hatchability (Y) and the ratio of relative humidity to temperature (Rh/T) fit the logistic model very well, Y=0.8662/(1+exp(17.4084-7.5714×Rh/T)). When the Rh/T value was less than2.34, the hatchability would be less than50%, and the optimum Rh/T was about3.0for eggs. The lower humidity resulted in the higher weight loss and wizened form of eggs, and inhibited the embryo development.The short-term low humidity stress,45%Rh for1-4day and6-12h per day on the survival of RLF eggs was studied in25℃. The results indicated that only the10h per day and last4days stress brought about the significant decrease of eggs survival, and the others had no significant impact on egg.The effects of humidity on the hatch of larvae in25℃were studied. The results showed that the45-80%Rh which lasted1h,2h, and3h on the hatch of larvae, the larvae survival had no significant impact, even if these larvae were reared six days on maize seedlings. Therefore, at optimum temperature (25℃), the low humidity of45%for3h could not influence the new-born larvae. Of course, the effect of other temperature and low humidity associations on larvae needed study in the future.