Range Expansion of an Invasive Pest Spider Mite, Tetranychus evansi (Acari: Tetranychidae), in Okinawa, Southwestern Japan, and the Acaricidal Effect of Several Agrochemicals on an Okinawan Population of the Species

Abstract

To determine the current status of the southward range expansion of Tetranychus evansi, a recent invader of Japan, we surveyed occurrence of this species on solanaceous plants throughout Okinawa, a southwestern part of Japan. T. evansi was first detected on Okinawa Island where this species has not been found until 2009, suggesting recent range expansion. The occurrence of T. evansi on a commercially-grown eggplant in Japan was first confirmed, alerting us to the further expansion of damage by this pest. Besides the crop plants, T. evansi was frequently found on a weed, Solanum americanum, which is considered a major source plant. When the acaricidal effect of 22 agrochemicals on T. evansi was examined under laboratory conditions, all the tested chemicals except four spiracle-blocking insecticides were highly effective.