Laboratory Selections of Populations in the Citrus Red Mite, <i>Panonychus citri</i> (MCGREGOR), with Hexythiazox and Their Cross Resistance Spectrum

Abstract

Laboratory selection experiments for resistance and for susceptibility with hexythiazox were conducted using Haibara strain of citrus red mite, Panonychus citri MCGREGOR collected from a citrus orchard at Haibara Agricultural Research Station (Nippon Soda Co., Ltd.) in Shizuoka Prefecture, Japan. The mites had been selected with hexythiazox 17 times in the orchard. A high level of hexythiazox resistance developed with 6 successive laboratory selections for resistance, and the resistance ratios at LC 50 were 23,000 and 4450 compared with the unselected strain and parental generation for laboratory selection, respectively. After 5 selections for susceptibility, the strain became more susceptible to hexythiazox, and the susceptibility ratio at LC 50 was 0.59. In the resistant strain, the levels of the resistance were high at all developmental stages including eggs laid by treated adult females. No synergistic effects of piperonyl butoxide with hexythiazox were observed on the activity against eggs and eggs laid by treated females in the resistant strain. Among 20 miticides investigated about their efficacies against the hexythiazox resistant strain, clofentezine, flufenoxuron and flucycroxuron showed low activities to the resistant strain.