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 the two medicinal plants, Helichrysum bracteatum L. (Asteraceae) and Salvia officinalis L. (Lamiaceae) against Tetranychus urticae Koch and its predator, Stethorus gilvifrons Muls. 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. Both extracts were assessed for their effects on the egg-laying capacity, repellent and oviposition deterrent effects of the 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 HbLEEtOH70% and SoLEEtOH70% 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-MS analysis 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.