Effects of avermectin B1and fenvalerate on the survival, reproduction, and egg viability of the twospotted spider mitetetranychus urticaekoch (Acari: Tetranychidae)

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Abstract
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 ( 1 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.