Acaricidal activity and chemical characterization of Helichrysum bracteatum ‎and Salvia officinalis leaf extracts against Tetranychus urticae and its ‎predator, Stethorus gilvifrons (Coccinellidae)‎

Abstract

This study presents an attempt to evaluate the acaricidal activity of two ‎medicinal plants,Helichrysum bracteatum(Asteraceae) and Salvia officinalis(Lamiaceae) against Tetranychus urticae Koch and for the first ‎time to its predator, Stethorus gilvifrons adult females under laboratory conditions.The ethanolic leaf extracts of H. bracteatum [HbLEEtOH70%] and S.officinalis [SoLEEtOH70%] ‎were assessed for their direct toxicity against T.urticae and S.gilvifrons adult females. Then ‎both extracts were assessed for their effects on the egg-laying capacity, repellent and ‎oviposition deterrent effects of T.urticae adult females, as well as their direct effects on ‎T.urticae eggs. The chemical characterization of both extracts was conducted to investigate ‎their bioactive components by gas chromatography (GC-MS). Based on acute toxicity, ‎results showed that HbLEEtOH70% displayed the highest acaricidal activity (LC50=1.27%) ‎followed by SoLEEtOH70%(3.39%) against T.urticae adult females. Whereas, against S. ‎gilvifrons adult females, SoLEEtOH70% was less toxic (LC50=37.06%) than HbLEEtOH70% ‎‎(LC50=0.76%).Our results revealed that only HbLEEtOH70% had a significant effect on the ‎egg-laying capacity of T.urticae adult females. According to the repellent index (RI), the ‎HbLEEtOH70% and SoLEEtOH70% were classified as repellent.Both extracts revealed a potent ‎ovicidal effect, where the egg hatching percentage was 48.75±15.38 and 45.34±11.73% ‎for HbLEEtOH70% and SoLEEtOH70%, as compared to their control groups 98.81±0.7%,‎respectively. GC-MSanalysis showed that phytol was the major component of HbLEEtOH70% ‎and SoLEEtOH70%. The current study confirmed the potent acaricidal effect of H.bracteatum ‎and S.officinalis leaf extract against T.urticae. Thus, the S.officinalis leaf extract was the ‎safe acaricidal product suitable for use in integrated pest management strategies as it was ‎safe for S.gilvifrons.‎