Unveiling toxicological, microanatomical and in-silico assessment of beta-carboline alkaloids as potential acaricide against Haemaphysalis darjeeling

Beta-carboline alkaloids have been reported to show insecticidal and acaricidal activities. In the present study, Haemaphysalis darjeeling ticks were exposed to beta-carboline alkaloids, Harmaline, Harmalol, Harmine and Harmane, at concentrations of 10, 20, 30, and 40 mg/ml for 6, 12, 18, and 24 hours to evaluate their potential acaricidal effect and mode of action. Although all four alkaloids induced substantial mortality in both larvae and adults, Harmaline followed by Harmalol showed a tendency to achieve higher toxicity specifically than Harmine and Harmane with prolonged exposure times. Microanatomical study revealed severe body surface damage in Harmaline and Harmalol-exposed adults. Further exploration with molecular docking, molecular dynamics simulations and MM/GBSA free-energy calculations confirmed that the interaction of Harmaline–Chitin Synthase showed higher structural stability and persistent active-site interactions relative to Harmalol, in adults. This study suggests that all the beta carboline compounds, especially Harmaline, showed potential acaricidal efficacy, and thus can be used as potential alternatives and eco-friendly acaricides to eradicate tick infestation.