Fig. 4

Daily trajectory simulations for the southward migration of the northern population of M. separata at Luanxian (LX) and Ningjin (NJ) during G4 periods (16 August–30 September) from 2014 to 2017. Each solid circle represents the whereabouts of a migrating population and contains two pieces of information: the size of the emigrating population and the endpoint of the migrating trajectory. After five nights of trajectory simulation, A, B Most simulated trajectories (LX: 52.05%; NJ: 66.67%) originating from North China finally moved towards the north. C, D Most of these simulated trajectories (LX: 66.67%; NJ: 58.82%) had southernmost endpoints located to the south of their origins, and a few of them (LX: 3.52%; NJ: 5.03%) reached south of latitude 33° N, but none of them reached south of 30° N. Taking the size of emigration populations as a weighting factor, the success rates of the southward migration from LX and NJ were 1.17% and 7.84%, respectively