Development of a numerical simulation model for long-range migration of rice planthoppers

Transoceanic migration of rice planthoppers was simulated by incorporating several parameters related to the flight behavior with a high performance atmospheric dispersion model. The model consists of an atmospheric dynamic submodel for calculating meteorological fields and a particle random-walk submodel for atmospheric dispersion. The model also functions in specifying the release area and take-off time of the migration of planthoppers. Using this model, we carried out a case study simulating the migration of planthoppers to western Japan with net-trap catches at 10 locations in mid-June 1998. In the simulation, 56 areas each with a width of 2° of latitude and longitude were set as tentative take-off areas. The take-off duration was assumed to be 1 h at dawn and dusk. To find the migration source areas, the relative density of immigrants originating from each take-off area was compared with each observed density by rank correlation coefficients. Possible migration release areas, which showed a high correlation to observations, were distributed around 23-27°N, including Fujian and Taiwan. An air temperature that allowed the planthoppers to fly continuously and flight duration were critical parameters for the simulation results.