LABORATORY SELECTIONS OF POPULATIONS IN THE CITRUS RED MITE, PANONYCHUS-CITRI (MCGREGOR), WITH HEXYTHIAZOX AND THEIR CROSS-RESISTANCE SPECTRUM

Laboratory selection experiments for resistance and for susceptibility with hexythiazox were conducted using Haibara strain of citrus red mi te, Panonychus citri MCGREGOR collected from a citrus orchard at Haiba ra Agricultural Research Station (Nippon Soda Co., Ltd.) in Shizuoka P refecture, Japan. The mites had been selected with hexythiazox 17 time s in the orchard. A high level oi hexythiazox resistance developed wit h 6 successive laboratory selections for resistance, and the resistanc e ratios at LC(50) were 23,000 and 4450 compared with the unselected s train and parental generation for laboratory selection, respectively. After 5 selections for susceptibility, the strain became more suscepti ble to hexythiazox, and the susceptibility ratio at LC(50) was 0.59. I n the resistant strain, the levels of the resistance were high at ail developmental stages including eggs laid by treated adult females. No synergistic effects of piperonyl butoxide with hexythiazox were observ ed on the activity against eggs and eggs laid by treated females in th e resistant strain. Among 20 miticides investigated about their effica cies against the hexythiazox resistant strain, clofentezine, flufenoxu ron and flucycroxuron showed low activities to the resistant strain.