Pesticidi i Fitomedicina (Jan 2006)
Sublethal Effects of Spirodiclofen on Tetranychus urticae Koch_Pre-Ovipositional Females After Different Exposure Times
Abstract
Sublethal effect of spirodiclofen on Tetranychus urticae females that survived different exposure times in the pre-ovipositional period was evaluated calculating two parameters - instantaneous rate of increase and net fertility - after six days of reproduction. The females were exposed to four concentrations/doses of the acaricide: 96 mg /L (0.24 μg/cm2), 48 mg/L(0.12 μg/cm2), 24 mg/L (0.06 μg/cm2) and 12 mg./L (0.03 μg/cm2) for 2, 6 and 24h in a leaf disc bioassay. After 24h exposure to 12 mg/L, instantaneous rate of increase was significantlyreduced (0.545; 0.634 in control), while significant reduction in net fertility (20.61; 28.57 in the control) was recorded even after 2h exposure to the same concentration. The effect of all tested concentrations of spirodiclofen on both parameters increased with exposure time. The lowest values of instantaneous rate of increase (0.268) and net fertility (2.58) were recorded after 24h exposure to 96 mg/L. After 24h exposure, the concentration increase from 12 to 24 mg/L significantly reduced both parameters, while a further increase from 24 to 96 mg/L significantly reduced instantaneous rate of increase, but not net-fertility. The results regarding T. urticae population management are discussed.
