Migration analyses and predictions for migratory insect pests toward Japan

Abstract

The oriental fruit fly, Bactrocera dorsalis (Hendel), complex was eradicated in 1986 in Japan, and the state of eradication has been maintained until present. However, male adults of B. dorsalis complex were occasionally caught in the surveillance network in southwestern islands of Okinawa and Kagoshima Prefectures. Assuming if these catches were wind-borne migrations, possible source could be estimated with trajectory analysis. The results indicated one third of all the catches from 1986 to 2012 in Okinawa were found to be due to possible wind-borne migration. In 72 percent of those cases, Taiwan was estimated as possible source. In Taiwan, southeastern part was often estimated as source area. On the other hand, several catch cases occurred in 2015, 2017 and 2018 in Kagoshima Prefecture, northwestern part of Taiwan was estimated as source area. Southwesterly winds in the Bai-u rainy season were key factor for these estimated migrations. The migration prediction model for the white-backed planthopper, Sogatella furcifera (Horváth), was modified by both fining horizontal resolution and implementing assumed landing processes. The prediction was evaluated with net trap data at five sites in three years in Miyazaki Prefecture. The results indicated the prediction hitting ratio has been improved to be 83.8%, demonstrating that the simulation method is one possible approach to unknown landing process. The common cutworm, Spodoptera litura, is highly dispersible insect pest and attacks soybean leaves in summer in western Japan. Its dispersion was monitored with searchlight trap and entomological radar. At the same time, soybean leaf damages were investigated. The two-year survey results indicated that the catch peak of the searchlight trap preceded the leaf damage caused by S. litura larvae by 3-7 days, potentially suggesting that a short-term forecasting of soybean damage based on the monitoring with the searchlight trap might be feasible. To get firm conclusions, repetition of the survey for one more year will be necessary.