The Relationship Between Flight And Reproduction In Cnaphalocrocis Medinalis (Guenée) And Its Physiological Mechanism

Rice leaffolder (RLF), Cnaphalocrocis medinalis (Guenée), is a destructive rice pest distributing inthe main rice growing areas of Asia. Its consecutive and serious outbreaks have caused great threats tothe rice production in China. The long distance migration of C. medinalis has been proved based onsome evidences. However, our understandings on the relationship between flight and reproduction andphysiological bases for the migration of C. medinalis are still very poor. In this paper, light trap, fieldtrap, ovary dissection, tethered flight test, flight energy utilities and enzyme activities of flight musclewere conducted to determine the population dynamics and status, flight-reproduction relationship, andphysiological mechanism of flight behavior. Our findings could provide the scientific bases forpopulation forecasting and integrated management of C. medinalis. The results were summarized asfollows:（1）The preoviposition and oviposition stages were4.0±0.5d and4.95±0.26d, respectively, based onthe observation of ovary development and eggs lying day by day. The number of eggs laid reached thepeak stage when the proportion of grade Ⅳ stage ovary was the highest (60.0%). Flight capacity of the3-d-old mated and virgin adults was the highest, and declined with the increasing ages of C. medinalis.Mating could significantly stimulate the ovary development, and decrease the flight capacity, but flightcould not influence the ovary development obviously. Moreover, flight tethered test showed that flightcould prolong preoviposition stages and longevity of female adult, decreased mating rate and fecundity,and shorten oviposition stage. Negative correlations were shown between the number of eggs laid andflight capacity in C. medinalis. All these showed that oogenesis-flight syndrome occurred in C.medinalis.（2）Analysis of light trap and field investigation data from May to October,2011, in Xing’an County,Guangxi Province, demonstrated that C. medinalis moths first occurred on May8, reached peak stagefrom late June to early August, and disappeared in late October. Moth peaks from black light lamp trapwere consistent with those from the high altitude light trap. A moth peak occurred on two light trapsfrom June28to July1. There’re4peaks in total from early July to early August. Hereafter, no obviouspeaks appeared. First moth peak emerged in field on June12, and the number of moths amounts to thehighest on June29. Adults keep high and stable quantity (beyond1,000/667m2) in the whole July, anddecrease gradually from late August to October.（3）Population status of per generation of C. medinalis in Xing’an region were determined by ovariandissection. Mating rates and the proportion of matured ovaries in the2nd and3rd generation were morethan90.0%, so the two generations were predominant immigrants. The4th generation was regarded aspart immigrant and a few individuals resident natively, because the proportion of female grade Ⅲovaries was88.1%and mating rate was88.3%in this generation. Population status of the5th generationwere very complicated, and most of them were native. Moths occurred in late July were immigrant due to females with high proportion of grade Ⅲ ovaries and more than80%mating rate. Moths occurred inearly August were typical emmigrant due to females with55.4%grade Ⅰovaries and20.1%matingrate. Less than30.0%non-mated females and below30.0%gradeⅠovaries, so population in the6thgeneration were native. Ovaries of94.3%females only developed into grade ⅠorⅡ and2.9%femalesmated in the7th generation, so population status of this generation were main emigrant.（4）Flight capacities and physiological characteristics in Xing’an rice region were compared betweenimmigrant and emigrant population. The results showed that flight capacity, fight muscle dry weight,triglyceride content and flight muscle enzymes of emigrant were higher than those of immigrant. Theseresults also revealed the physiological mechanism of migration in C. medinalis.