Flight Capacity Along With Its Physiological Mechanism In Bactrocera Dorsalis(Hendel)

Bactrocera dorsalis(Hendel)(Tephritidae,Bactrocera)is widely distributed in tropical and subtropical regions.It is an important fruit and vegetable pest,which is harmful to cirus,guava,mango and other 250 kinds of fruits with high economic value.Long distance dispersal is not only an important reason for B.dorsalis to realize regional expansion and form a wide range of hazards,but also is an important characteristic that is different from other fruit flies.The aim of this study is to confirm the autonomous flight capability of this pest under controlled laboratory conditions and to reveal the underling physiological mechanism,which will provide insights into its large range of regional distribution.By using the automatic recording and analysis system,and the methods of insect anatomy,physiology and molecular biology,the following aspects were carried out:the daily activities of B.dorsalis,and its ability to fly,characteristics of the flight muscle,expression of flightin protein in flight,internal relationship between flight muscle structure,ovary development,juvenile hormone titer of the flight muscle juvenile hormone.Here,the main research results and conclusions are summarized.1.B.dorsalis has strong ability to fly.Hanging fly experiments for13 h revealed that the sustainable flight time of 15-day-old male and female adults were 1.3 Oh and 1.1 8h with disposable maximum distance of 3.57 km and 2.96 km and average flight speed of 0.98 m/s and 0.95 m/s.The flight ability of B.dorsalis is closely related to age,gender,food and nutrition.B.dorsalis adult of15-day-old has the strongest flight ability,while 5-day-old and 25-day-old adults have the weakest flight ability.The flight ability of yeast syrup feeding group has significantly higher than that of water and sugar feeding ones.Flight capacity of female was significantly higher than male.B.dorsalis can fly several times after nutritional supplements,indicating that nutritional supplements can greatly extend the flight distance and flight time.During six days of continuous hanging fly,the total flight duration of male and female adults were 4.21 h and 3.74 h after nutritional supplements,and the farthest flight distance were 5.74 km and 5.24 km,respectivelyof which the average flight speed were 1.10 m/s and 1.21 m/s.The flight activity of B.dorsalis presented the daily rhythm.There were two flight hours during the day,which were from 7:00 to 15:00 and 17:00 to 21:00,respectively.It suggests that B.dorsalis flight activities are affected by light.The finding shows that B.dorsalis has strong autonomous flight capability,providing important biological data forthe interpretation of long distance migration dispersal of B.dorsalis.2.Flight muscle cells of B.dorsalis are composed by myofibril that filled with a large number of mitochondria.It has a bright and dark band structure,and the part between the adjacent dark band called sarcomeres;Myofibrils of B.dorsalis has unique spatial configuration.Each thick filament consists of six thin filaments arranged around the hexagonal structure with equal distance.The ratio of thick and thin filaments is 1:3.The contents of flight muscle weight,myofibril diameter,sarcomere length and mitochondrial are closely related to adult age.Flight capacities of both sexes were positively related to myofibril diameter and mitochondrial content in the flight muscle(P<0.01).But they were negatively correlated to sarcomere length(P<0.01).The results showed that flight muscle composition and structure reflected the characteristics of strong flight capacity,which is an important reason for eaxplanation of why B.dorsalis has strong ability to fly.3.B.dorsalis females have two groups of ovaries.Each ovary contains 28 ovarioles.The ovary development is related to growth,maturation and digestion process.It can be divided into five developmental satges including early development(grade I),yolk deposition period(grade ?),mature until birth(grade III),spawning period(grade IV)and end of spawning(grade V).Vitellogenin is synchronized with ovarian development.It reaches the peak in ovarian mature period,and decreases with the digestion of ovary.Vitellogenin showed a significant positive correlation with female flight ability(p<0.01).Theresults showed that there were mutually promote interaction between ovarian development,muscle development and flight ability.The flight muscle development was synchronized with reproductive system.When ovarian reached to grade ?,B.dorsalis had the strongest ability to fly.The microstructure of flight muscles could support the best flight capacity.Especifically,there were the longest flight duration,the farthest flight distance,the fastest average flight speed,and the flight muscle had the maximum diameter of myofibrils,the shortest sarcomere,and the highest content of mitochondria.The results showed thatB.dorsalis do not have the characteristics of‘oogenesis and flight conjugated',confirmed that B.dorsalis does not belong to long-distance migratory insects in terms of reproductive biology.4.B.dorsalis juvenile hormone titer in flight muscle is closely related to its age and gender.It reaches the highest at fully grown mature adult satge(15 days old),while the lowest level was detected in the initial stage of eclosion(5 days old)and at the end of the adult life(25 days old).Juvenile hormone titer of female flight muscle is higher than that of male.Its titer in flight muscle is synchronized with the development of the reproductive system.It reaches the highest when ovarian development to grade III,but the lowest level was observed when in the early ovary development and at the end of ovarian development.The results showed that there were significantly positive correlation between juvenile hormone titer in flight muscle and flight ability of B.dorsalis(P<0.01).These are helpful for us to undstande the relationship between B.dorsalis juvenile hormone in flight muscle and its flight ability,and the physiological role of juvenile hormone in B.dorsalis flight activities.5.In this section,we conducted a correlation analysis on the relative expression of flight protein of flightin to flight ability and flight muscle microstructure.There was a close genetic relationship between B.dorsalis and Tephritidae,Diptera,and B.dorsalis clustered together with melon fruit fly of the same family and Mediterranean fruit flies.The expression of flightin varied with insect developmental stage.Its expression level was lowest in egg.It reached the highest in pupae,of which were 8.7 folds to that in eggs.Also,its expression was closely related to its age and gender.It reached the highest when fully grown mature adult(15 days old),and the lowest level was detected when in the initial stage of eclosion(5 days old)and at the end of the adult life(25 days old).The relative expression of flightin in female adult was higher than that of male adults.The relative expressions of flightin in both sexes were related to the flight activities and microstructure of flight muscle fiber.They were significantly positive related to flight time,flight distance,average flight speed(P<0.01),muscle fiber diameter,mitochondrial content of flight muscle(P<0.01),while they were significantly negatively correlated to sarcomere length(P<0.01).The findings provide molecular basis to reveal the ability of B.dorsalis to fly,and an important clue for further investigation on molecular mechanism of its flying ability.The above researches provided key scientific data for well understanding of B.dorsalis field migration dispersal,and provided the physiology basis to explain the B.dorsalis autonomous flight and dispersal ability.The results important for deep analysis of long-distance migration and dispersal characteristic,and helpful for developing a sustainable strategy of the control of B.dorsalis.