Interrelationship Between Migration And Reproduction Of The Rice Leafroller, Cnaphalocrocis Medinalis (Guenée) (Lepidoptera: Pyralidae)

The rice leafroller, Cnaphalocrocis medinalis (Guenee) is one of the most important migratory pests of rice in China and other Asian countries. Because of its long-distance migration, the C. medinalis took pace and made great harm to rice in burst up. In order to explain migratory laws and improve prediction and pest control, it is necessarily to study more on its population dynamics, migratory behavior, physiological characteristics and relationship between flight and reproduction. The research adopted the basic theory of pest migration, the integrated methods of field investigations and laboratory examinations. The systematical investigation of the C. medinalis of field population dynamics, behavioral and physiological characteristics between the emigrant and immigrant populations, influence of temperature on flight capacity, relationship between flight and reproduction were studied in this paper. The results were summarized as follows:Field population dynamics of C. medinalis. The dynamics and population characteristics of C. medinalis in four different areas, Xingan (25°36'N,110°40'E), Longyou (29°01'N,119°10'E), Xiantao (30°21'N,113°27'E) and Yizheng (32°16'N, 119°11'E) in Jun.-Sep.2010 were studied by systematic investigation. The results indicated that the number of moths suddenly jumped in the emigrant happenings and the number of moths suddenly declined in the immigrant happenings. Wind field direction at 850hPa air pressure level was analyzed. It indicated that slanting south wind benefited the C. medinalis immigration from the southern and slanting north wind profited the C. medinalis emigration from this area. And there exists positive correlation between the number of moth and rainfall, but it is not significantly different (P>0.05). There exists negative correction between the number of moths and daily mean temperature, but only the correction is significant in Yizheng population. Futhermore, the dynamics of rainfall, daily mean temperature and relative humidity during peak days of the 3rd generation of Yizhang population were analyzed. It was found that a highly significant positive correlation existed between the amount of immigrant moths and the occurrence of amount of eggs (based on the population size rice paddy) of C. medinalis.Comparison of behavioral and physiological characteristics of the emigrant and immigrant populations. Behavioral and physiological characteristics of the emigrant and immigrant populations of the C. medinalis moths trapped in field in Hepu County, Guangxi Zhuang Autonomous Region, Xingan County, Guangxi Zhuang Autonomous Region, Longyou County, Zhejiang Province, Xiantao, Hubei Province, Yizheng, Jiangsu Province were examined. The results showed that when the number of moths suddenly jumped, ovary of developmental grade and mating percentage are much higher. And when the number of moths suddenly declined, ovary of developmental grade and mating percentage are much lower. The population whose moths amount suddenly jumped and suddenly declined are immigrant and emigrant populations respectively. Most females in the emigrant population exhibited little or no ovarian development and were seldom mated and mean ovarian width, length, mating rate and frequency were significantly lower than those of the immigrant population. In addition, the ovarian developmental grade and mating rate in the immigrant females earlily trapped were lower than those of later trapped ones and increased as trapping time incresed. The moths of the emigrant population exhibited stronger flight potential than that of the immigrant population. The flight distance, total flight duration and average flight speed in the immigrant population were significantly less than those in the emigrant population. Dry weight of the flight muscle and content of triglyceride in female of the emigrant population was significantly higher than that of the immigrant population. Comparison of all these factors between the emigrant and immigrant populations suggest that there are obviously trade-off between flight and reproduction. The migrants have strong flight potential and reproduction activity are depressed before migration, while mating and oviposition begin rapidly after they arrive in new habitats. This model fits the eoogenesis-flight syndrome hypothesis well.Influence of temperature on flight capacity of the rice leaf roller C. medinalis. Flight capacity and triglyceride utilization of the rice leaf roller C. medinalis adults during flight at temperatures from 16℃to 32℃were investigated. The male and female moths flying at 24℃showed the greatest flight capacity, Adult flight capacity significantly declined at temperatures below 20℃or above 28℃. Suppression of high temperature on flight capacity of the female are more obvious than that of the male, but flight capacity of the female is stronger than the male in the low temperature condition and flight capacity of the male is stronger than the female in the high temperature condition. These results suggested that the most suitable temperature for their flight was about 24℃. With temperature increasing, adult mortality rate and biomass loss is much higher after tethered flight.Utilization of triglyceride by the moths during flight was greatly affected by ambient temperature. Variation in flight capacity of adults at different temperatures were primarily caused by differences in triglyceride utilization efficiency of the moths. The triglyceride used for a given flight distance at lower temperature was much less than those of the higher temperature in the female. The triglyceride utilized for a given flight distance was the highest efficiency at 24℃in the male. It showed that temperature might be one of the main reasons for difference in triglyceride utilization efficiency of the moths.Relationship between flight and reproduction of C. medinalis. Flight capacity of day-1-3 after emergence and day-1-3 after oviposition of C. medinalis were investigated by tethered flight. Flight capacity of day-2 after emergence is strongest, and there are significant difference in flight time of moths between day-2 age and day-3 age. But, there are no significant differences in flight distance and flight speed of moths among day-1-3 age. Flight capacity decreased as ovipositing time prolonged in day 1-3 after oviposition and the weakest in day-3 after oviposition. Effects of tethered flight on preoviposition period, fecundity, copulation and longevity of C. medinalis were investigated in the laboratory. The moths flown for 12 hours at day-1-2 after emergence began to oviposit significant earlier than the unflown ones. Life time fecundity, fecundity and mating percentage of the moths flown at day-1-2 age were also greater than that of the control. Longevity of moths day-1-2 age after tethered flight were investigated, and the results indicated that longevity of the day-1-2 age female moths were significant shorter than that of the controls. But, there are no significant differences between the day-2 age male moths and the controls about longevity. The results indicated that flight (day-1-2 age) can enhance the reproduction capacity of the moth.