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 significantly reduced (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.

Subletalni efekti spirodiklofena na ženke Tetranychus urticae koje su preživele različito vreme ekspozicije u pre-ovipozicionom periodu ocenjivani su izračunavanjem dva parametra - trenutne stope rasta i neto-fertiliteta - nakon šest dana reprodukcije. U biotestu na lisnim isečcima ženke su bile izložene 2, 6 i 24h delovanju četiri koncentracije/doze akaricida: 96 mg/L (0.24 μg/cm2), 48 mg/L (0.12 μg/cm2), 24 mg/L (0.06 μg/cm2) i 12 mg/L (0.03 μg/cm2). Nakon 24-časovne koncentraciji 12 mg/L trenutna stopa rasta bila je značajno redukovana (0.545; 0.634 u kontroli), dok je značajna redukcija neto-fertiliteta (20.61; 28.57 u kontroli) zabeležena već posle 2-časovne ekspozicije istoj koncentraciji. Efekat sve četiri testirane koncentracije spirodiklofena na oba parametra povećavao se produžavanjem ekspozicije. Najniže vrednosti trenutne stope rasta (0.268) i neto-fertiliteta (2.58) zabeležene su posle 24-časovne ekspozicije koncentraciji 96 mg/L. Pove.žćanje koncentracije sa 12 na 24 mg/L značajno je redukovalo oba parametra; dalje povećanje koncentracije sa 24 na 96 mg/L značajno je redukovalo trenutnu stopu rasta, ali ne i neto-fertilitet. Dobijeni rezultati razmatrani su u kontekstu upravljanja populacijama T. urticae.