Study On The Wingbeat Frequency Of Migratory Insects Across The Bohai Strait In China

Insect migration,a seasonal movement carried out by insects for coping with envioronment changes,is an important reason of pest sudden outbreaks and plant disease epidemic.Wing-beat is a biological behavior which determines a successful migration.In addition,many other important life activities of insects(e.g.,feeding on nectar,finding a spouse and mating)need to be achieved by vibrating wings.Wingbeat frequency(WBF)is an important characteristic parameter of flight.Therefore,study on WBF of insects is of great scientific significance for illuminating their flight activities.Bohai Strait,located in the adjoint area between Northeast China and Northern China,is an important insect migration passageway.In this study,we measured WBF of migratory insects across Bohai Strait,and assessed inter-specific and seasonal variablity in WBF for these species,we also assessed the influencing factors(e.g.,insect size,temperature and supplementary feedings)of WBF,and the main findings are listed as follows.1.Measurements of WBF were made on a total of 90 main migratory insect species representing 3 orders and 14 families in 2018-2019.Overall,WBF of test individuals ranged from 6.71 to 84.45 Hz,with significant differences between families and species.Members of the Bombycidae exhibited the highest mean wingbeat frequencies(i.e.,55.08 ± 0.97 Hz)and Saturniidae the lowest(8.53 ± 0.21 Hz).WBF of Ctenoplusia agnata and Helicoverpa armigera was sinificant higher than that of Agrotis ipsilon,Agrotis segetum,Athetis lepigone,Schinia scutosa,Mythimna separata,Scotogramma trifolii,Spodoptera litura and Spodoptera exigua.Aside from the above family-or species-level patterns,seasonal dofferences were also recorded,with spring migrants of three species(Mythimna separata,Scotogramma trifolii and Helicoverpa armigera)exhibited significantly higher WBF than those caught during autumn.2.Insect's WBF was correlated with their body mass and wing morphology.WBF of lepidopterans,neuropterans and dragonflies is moderately or lowly correlated to their body mass,thoracic mass and abdominal mass,with neuropterans' WBF had mid-negative correlation with their body mass and thoracic mass(-0.7 < R<-0.4).Among insect families,there are 6,8 and 7 insect families whose WBFs are negatively correlated with body mass,thoracic mass and abdominal mass,respectively.Among the insect species,WBF of C.agnata and Chrysopa sinica increased with the increase of their body mass,thoracic mass and abdominal mass;WBF of Anax parthenope decreased with the increase of their thoracic mass.WBF was highly negatively correlated with forewing length among insects whose mass ranges from 0.15~0.60g(R<-0.8),WBF was also highly negatively correlated with wing area among insects weighted more than 0.3g(R<-0.8).3.Ambient temperature,humidity and wind speed significantly affected WBF of insects.WBF of 6 noctuids with large biomass migration was tested,results showed WBF of these 6 species has a negative binomial regression relationship with temperature.The optimal temperature for highest WBF varied among species,A.ipsilon,A.segetum beat their wings faster at 20-35?,C.agnata,S.litura and S.exigua beat their wings faster at 25-35?,S.illoba beat their wings faster at 20-30?.Ambient humidity significantly affected the WBF of A.ipsilon especially for females.WBF of both females and males at 30% relative humidity was significantly lower than that of 75% and 90%.When A.ipsilon flying against the wind,WBF of females decreased with the increase of wind speed,WBF of males showed no significant difference when wind speed is 1~5m/s,but lower than that at no wind.Air pressure had no significant effect on WBF of both females and males in A.iplison.4.Supplementary feeding can enhance WBF of insects significantly.WBF of insects(A.ipsilon,H.armigera,M.separata and S.scutosa)which feeding on 10% honey solution was significantly higher than that of being fed with clean water or being fed with nothing.WBF showed no significant differences among 4 species that were fed with nothing.Among those species feeding on clean water,WBF of H.armigera was significantly higher than WBF of M.separata and S.scutosa.Among those species feeding on 10% honey solution,WBF of H.armigera was significantly higher than that of other 3 species.In this study,WBF and its influencing factors of main migratory insects has been clarified and determined.Our findings provide basic information for constructing the database of migratory insects biological parameters,add to the scientific knowledge on flight biology of migratory insects,and can have broader implications for(automatic)monitoring and population forecasting.