Acaricidal and sublethal effects of a Chenopodium-based biopesticide on the two-spotted spider mite (Acari: Tetranychidae).

Abstract

Acaricidal and sublethal effects of the biopesticide Requiem®EC (containing an essential oil extract of Chenopodium ambrosioides near ambrosioides) on the two-spotted spider mite, Tetranychus urticae Koch, were evaluated in laboratory bioassays. The biopesticide was applied to bean leaves or leaf discs using a Potter spray tower. Acaricidal activity against eggs and immatures was evaluated in successive acute toxicity bioassays. Concentration-mortality data were subjected to probit analysis and the following LC50 values (ml/l) were calculated: 2.47 (eggs), 0.71 (larvae), 1.13 (protonymphs), 2.23 (female deutonymphs), and 6.02 (female teleiochrysalises). In adult bioassay, in which pre-ovipositional females were treated with a series of concentrations (0.31-10ml/l), a run-off effect ranging 4-80% (after 24h) and 8-93% (after 72h) was observed. In two-choice bioassay, T. urticae females preferred the untreated halves of leaves over the halves treated with 1.25-10ml/l biopesticide and they laid significantly more eggs on the untreated halves in the first 24h and summed over 72h. The indices of repellency and oviposition deterence ranged 11.2-77.3 and 14.8-87.9%, respectively. In age-stage two-sex life table bioassay, the females that hatched from eggs treated with 2.5ml/l biopesticide and reached adulthood on treated leaf surface showed a significantly reduced the intrinsic rate of increase (r=0.222), compared to the control (r=0.317). The reduction of population growth was mainly due to a reduced preadult survival rate (0.42±0.04) and extended juvenile developmental time (9.27±0.11days), compared to the control (0.93±0.03 and 7.70±0.06days, respectively).