Fig. 5

The location of the center of the high-pressure system (CHP) at 925 hPa drives the interannual variation in M. separata population dynamics. A The CHPs in the previous September of the year when armyworm larval outbreaks occurred (dark blue solid circles) mostly were located to the west of the mean position of CHPs in September from 1959 to 2017 (red solid circle). On the contrary, most CHPs in the previous September of the year with a light occurrence level of M. separata (light colored solid circle) were located to the east of the mean CHP. B Distribution of the Pearson’s correlation coefficients between the longitude of the CHPs and u/v component of winds at 925 hPa in September during 1959–2017. Dark and light shadings indicate regions where the Pearson’s correlation coefficients of the meridional component of wind pass the t-test at 0.01 and 0.05 levels, respectively. The blue area represents the significantly negative correlative region, while the red one represents the significantly positive correlative region