Effects Of Adult Nutrition On Migration And Reproduction Of Cnaphalocrocis Medinalis(Guenée)

The rice leaf folder,Cnaphalocrocis medinalis(Guenee),is a very important agricultural pest in rice production in Asian.The damage of C.medinalis is particularly serious especially in China,and has increased and the outbreak has been frequented in recent decades.C.medinalis has a seasonal long-distance migration habit,and their migratory type is known as multi-stop migration,and their migration process is extremely complicated.Researchers had made unremitting efforts for many years,the seasonal migration of C.medinalis in the east of China and the regulation mechanism of the environment for migration have been basically understood.However,due to the limitations of early research conditions and the complexity of the migration pattern of C.medinalis,there are still many unresolved issues and many controversies in the study of migration laws and environmental regulation mechanisms.There is still a lack of systematic and in-depth research on migratory behavior and the regulation mechanisms of migration and reproduction.At present,the studies were restricted to the effect of continuous starvation on reproduction in adult C.medinalis.Most studies have only used the preoviposition period to indirectly reflect migratory propensity,but the behavioral and physiological effects of adult nutrition on the flight and reproduction of C.medinalis are not yet clear,and further analysis is needed.In addition,there are obvious migratory characteristics and interesting migratory phenomena in C.medinalis,but little is known about its causes.Therefore,it is of great significance for further to improve the understanding of the occurrence and regulation mechanism of C.medinalis to study the effects of adult nutrition on the migration and reproduction,and to analyze the characteristics of migration from the perspective of adult nutrition,which can provide theoretical basis and scientific basis for forecasting and comprehensive prevention and control in C.medinalis.This paper systematically analyzes the effects of adult nutrition on the flight and reproduction of C.medinalis from both ecological and physiological aspects.Through the gender difference of the nutritional stress in adults,the reason of sex ratio bias in the immigratory population of C.medinalis was studied.The trajectory analysis and anatomy of the ovary in migratory population were used to analyze the migratory characteristics of C.medinalis,and the benefits of mating to migratory flight were analyzed from the perspective of the effect of mating on adult tolerance to nutritional stress.Some new research progress was made.The main findings are as follows:1.Ecological and physiological regulation mechanism of adult nutrition on the flight and reproductionIn order to clarify whether the adult nutrition has the migration-inducing effect,the physiological and ecological regulation mechanism of migration and reproduction,the effects of starvation in different durations or at different starting ages on the reproductive parameters,migratory parameters and energy allocation of newly emerged C.medinalis and to identify the stage at which adult insects are sensitive to a lack of nectar.(1)Effects of adult nutrition on reproduction and longevityC.medinalis moths have the ability to endure short-term starvation because of the sufficient energy stored during the larval stage,but the tolerance for starvation is only one day,the reproduction of the adult moths is strongly dependent on supplemental nutrition.The preoviposition period was prolonged by starvation on the first day after adult emergence,and the starvation on the first day after emergence the onset of migration.(2)Effects of adult nutrition on take-off behavior and flight capabilitystarvation in the early stage of adults increased the take-off percentage,and the longer the starvation duration was,the higher the take-off percentage.Starvation on the first day after emergence increased the take-off frequency of three-day-old adults.Adults starving during the first two days after emergence did not alter flight capacity,and there was no significant difference in flight duration.(3)Effects of adult nutrition on gonad development and mating behaviorAdult starvation slowed ovarian development but did not affect testicle development.The ovary development of female moths that provide nutritional supplements after starvation was still slow and took 1-2 days to develop to the same level as the control group.Adult starvation delayed the mating age,but did not affect the mating duration.(4)Effects of adult nutrition on migration and reproductive energy allocationStarvation cause an increase in thoracic triglyceride accumulation in C.medinalis,especially the accumulation of triglycerides is more conducive to the occurrence of migration.The above results indicate that adult nutrition is one of the environmental factors affecting the first migration of C.medinalis.C.medinalis moths have low starvation tolerance and that adult nutrition is essential for reproduction and flight.One day after emergence is a critical period for responding to starvation.Starvation in the critical period promotes migratory traits and leads to the occurrence of migration in C.medinalis.2.Adult nutrition and sex ratio bias in immigratory population of C.medinalis(1)Gender differences in the migratory population of C.medinalisThe population dynamics of C.medinalis in 2015-2018 were monitored by searchlight traps in Jiangyan area.Based on the field searchlight monitoring data,the rhythm of the lamp behavior of the migratory populations was analyzed.The results showed that there were differences in the population dynamics of C.medinalis during the interannual period,and there were significant differences between female and male.There was a significant difference in the number of trapped insects per year,but the time to trap C.medinalis was mainly from June to September.The peak period of the female and male was basically the same,and the peak period was also regular,and the maximum amount of trapping insects per year was mainly between late August and early September.According to the distribution results of the lamp period,the flight duration of most moths could reach 8-10 hours,but the females were mostly in the first half of the night,and the males were mostly in the latter half of the night.More females were trapped by searchlight traps than males in the immigration of C.medinalis.(2)The causes of sex ratio bias in immigratory populationThe phenomenon was analyzed from the behavioral and physiological mechanisms by laboratory experiments to understand the gender differences in the emergence time,phototaxis,take-off behavior,flight capability,starvation response and tolerance of C.medinalis.The results showed that the female bias in the immigratory population of C.medinalis was not caused by the difference in phototaxis between female and male,which was caused by protogyny,a stronger flight capability,migratory propensity and starvation tolerance in females than in males,and an earlier response to starvation in females than in males.3.Nutrition and trade-off between oogenesis and flight of adult C.medinalis(1)Number of nights flownTaking Jiangyan as the starting point,the trajectory analysis method was used to make the trajectory analysis,combined with the national field moth data.It is determined that the source area can be provided,the migration process is simulated,and the number of nights flown is initially determined.The results of the backward trajectory analysis showed that C.medinalis could migrate for 1-4 nights,and the effective endpoint after 4 nights flown was significantly reduced,up to 6 nights.Therefore,it is preliminarily believed that most of C.medinalis migrate 3-4nights and can migrate up to 6 nights.(2)Characteristics of ovarian development in the migratory populationThe female C.medinalis were trapped by searchlight traps in 2018,their ovaries were dissected to analyze for ovarian development.The relationship between migration and reproduction of the migratory population were determined.The results showed that the female moths were mostly sexually mature,and most of them were ovarian development Level-? that had already laid eggs,and the mating percentage was extremely high.Among them,most female moths mated once and twice,and mating three and four times also occupied a certain proportion.These results indicate that most female can migrate for 3-4 nights,and the ovary development of female moths during the migration is a gradual process,oviposition does not inhibit migration.Ovarian development and migration are carried out simultaneously,and C.medinalis can still migrate long distance after oviposition.(3)Effects of mating on the tolerance of adult nutritional stressIn order to clarify whether the mating is beneficial or not for female C.medinalis to deal with adult nutritional stress,we investigated the tolerance of adult nutritional stress of mated and virgin C.medinalis.The effects of different gender starvation on longevity and the effects of mating on ovarian development and fecundity were studied to further analyze whether mating is beneficial to females.In order to explore the reasons why C.medinalis can still migrate after mating,we study the response of mating to nutritional stress.We studied the effects of adult nutritional stress on the reproduction and longevity of different sexes,the effects of mating on ovarian development,and the effect of mating frequency on fecundity to clarified the benefits of mating on female moths.The results showed that mating enhanced tolerance of adult nutritional stress of female moths,but did not affect that of male moths;starvation male moths mated with non-starved female moths reduced the number of eggs laid and longevity of female;starvation female moths mated with non-starved male moths increase the longevity of them,but do not affect egg production;mating promoted ovarian development;mating can increase fecundity,and the more mating times,the more eggs are laid.These results suggest that there is a gender difference in the starvation tolerance of C.medinalis,and the reason for this difference may be that mating can bring benefits to females.