Study On Moth Migratory Principle Across The Bohai Strait And Flight Capacity In Agrotis Segetum(Lepidoptera: Noctuidae)

The turnip moth,Agrotis segetum Denis and Schiffermaller(Lepidoptera:Noctuidae),is one of the most important crop pests which distributed widely in Europe,Asia and Africa.So far it is still unclear(1)whether the migration of this species is a regular ecological behavior,and if so,(2)what factors affecting its flight capacity.Insect migration is an evolved adaptation to resources that fluctuate spatiotemporally either seasonally or less predictably,which plays an important role in their life history.However,migration might be a key reason for the outbreaks of many agricultural pests.Bohai Strait is the major pathway for the seasonal northward and backward migration of many insect species in northern China.To clarify the annually and seasonal fluctuations of population size and flight capacity of A.segetum,the combination of searchlight trapping and ovarian dissection was carried out on an isolated small island in the center of the Bohai Strait during 2003-2015.Meanwhile,the flight performances of A.segetum were tested by tethering individuals to computerized flight mills for a 24 h trial period.Our work will provide effective information for the forecasting and management of A.segetum.The main results obtained are summarized as follows:(1)During 2003-2015,no A.segetum larvae were found on BH.However A.segetum moths were regularly captured in the searchlight trap,with 21242(the total number of captured A.segetum individuals during the 13-year period)and 156.23 ±4.66 d(the mean time from the earliest trapping to the latest trapping within a year).The vast majority of catches was trapped in summer(64.29 ± 4.21%),followed by autumn(24.68 ± 4.54%)and spring(11.03 ± 1.95).From May to September 2010-2014,the vast majority of trapped A.segetum were females,and there was no significant inter-month difference in the mean proportion of females.(2)From May to June during 2010-2014,the average mating rate of A.segetum females was significantly higher than that in August and September,76.74 ± 10.42%?71.91 ± 10.17% respectively,and the mean proportion of sexually mature females reached 78.37 ± 6.19% and 73.77 ± 7.35%.However,the average mating rate and proportion of sexually mature females in August and September were significantly lower than that in other months,and most of the trapped A.segetum females have little or no ovarian development.(3)The flight performances of A.segetum were tested by tethering individuals to computerized flight mills for a 24 h trial period.The results indicated that the laboratory population of 1-d-old A.segetum showed a weak flight capacity,but the 3-d-old moths took the strongest flight ability.The mean flight duration,mean flight distance and mean flight velocity for 3-d-old moths reached 12.16 ± 0.74 h,48.94 ± 3.40 km and3.76 ± 0.12 km/h,respectively.There were no significant differences of flight ability between female and male moths.The mean flight distance and velocity of the virgin moths were significantly higher than that of mated individuals.Both wild populations captured from early-middle and late seasons at Beihuang Island presented similar flight activity,which were significantly weaker than that of the laboratory population.Overall these results showed the population dynamics,migratory physiology,the flight capacity of A.segeum.During 13 years of searchlifght trapping study on BH provided direct evidence that A.segetum is a long-distance migrant(which flight at least40-60 km across the Bohai Strait),and the over-sea migration of this species is a regular ecological behavior rather than an accidental incident.There are significant inter-month differences in the reproductive status of migratory females of A.segetum.It might be due to the northward population emigrating from sites far away from the trapping site and therefore having several successive nights of migratory flight,which suggest that the migration of this species is not inhibited by the developed ovary and mating.However,the migratory of the backward population have little or no ovarian development,supporting the idea that the onset of migration is initiated by sexually immature individuals.A.segetum possessed a strong flight capacity,and both age and mating status were the key factors affecting its flight.These findings is helpful for us to develop more effective management strategies against this pest species.