Effects of avermectin B1 and fenvalerate on the survival, reproduction, and egg viability of the twospotted spider mite tetranychus urticae koch (Acari: Tetranychidae)
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The effects of avermectin B1 (AVMB1) and fenvalerate on the survival, reproduction, and egg viability of the twospotted spider mite, Tetranychus urticae Koch, was assessed in laboratory tests at 16°, 24°, and 34°C. AVMB1 was as much as 1000 x more effective than fenvalerate in producing adult mortality. The efficacy of AVMB1 increased at 34°C, whereas fenvalerate was slightly less effective at this high temperature. The 10-day residual activity of AVMB1 (1 ppm) increased with increasing temperature. Adult mortality was 4, 65, 94% at 16°, 24°, and 34°C, respectively. Fenvalerate (200 ppm) displayed a lower residual activity, producing little adult mortality at any temperature after 5 days. At concentrations as high as 50 ppm, AVMB1 showed little toxic effect ( <18% mortality) on newly laid eggs at 16° and 24°C. At 34°C, AVMB1 caused 100% egg mortality at rates as low as 12.5 ppm. The ovicidal effect of fenvalerate did not increase with temperature. At 400 ppm, fenvalerate produced 69, 56, 65% egg mortality at 16°, 24°, 34°C, respectively. AVMB1 significantly accelerated egg development at 16°C, where mean days to hatch was 14.32 for the control treatment, but ≤ 11.98 for treated eggs. AVMB1 was significantly potentiated by emulsifiable oil. At 24°C, AVMB1 (0.78 ppm):oil (0.125%) combinations produced 100% egg mortality. Egg age also significantly influenced susceptibility to AVMB1, eggs being most susceptible ca. 10 h before hatching.