Acaricidal Properties of Billygoat Weed Ageratum conyzoides L. Essential Oil on Polyphagous Two-Spotted Spider Mite, Tetranychus urticae Koch.

Abstract

Tetranychus urticae Koch (Acari: Tetranychidae), commonly known as the two-spotted spider mite, is a major polyphagous pest that affects a wide range of vegetable crops. Infestation of T. urticae is more prominent on eggplant which causes 50-80% yield loss if no control measures initiated. The economic threat posed by T. urticae is constantly increasing because of the development of pesticide resistance and resurgence. One of best alternative management strategies is use of plant-based pesticides like secondary metabolites and essential oils (EOs) which provides sustainable and long-term protection. In the present study, EO extracted from a billygoat weed, Ageratum conyzoides L. (Asterales: Asteraceae), and its binary compounds were evaluated against T. urticae. The A. conyzoides EOs showed highest mortality (97.5% with the LC₅₀ 10.61 µL/mL), due to the presence of Precocene I (32.32%), Geraniol (1.23%), and Neral (0.55%). Among the binary compounds, Geraniol (95%) showed highest mortality having LC₅₀ (95%) of 9.59 µL/mL followed by Citronellol (77.5%) and Alpha-pipene (75%). Significant increase in the activity of esterases, glutathione S-transferase, and acetylcholine esterases contributed for the toxicity in T. urticae following exposure to essential oils (EO) and their binary compounds. SEM images revealed shrinking of the bodies of treated T. urticae along with reduced body measurements compared to the untreated individuals. The present study indicates that A. conyzoides EO could be used for development of new acaricides for sustainable management of T. urticae.