Acaricidal potential and mechanistic insights of Melinis minutiflora P. Beauv. grass extracts from different cutting...

Cattle tick (Rhipicephalus microplus) is a major vector of hemoparasitic diseases and causes significant economic losses in livestock. Control efforts face challenges, including the scarcity of environmentally and human health-friendly methods. This study evaluated the acaricidal activity of ethanolic extracts from Melinis minutiflora harvested at 60, 90, and 120 days. Extract composition was characterized by gas chromatography-mass spectrometry (GC-MS); extractable biomass per hectare was estimated, and potential mechanisms of action were explored via molecular docking. Leaves, stems, and, for 90- and 120-day plants, inflorescences, were extracted using Soxhlet, and acaricidal efficacy was assessed through adult immersion and larval packet tests; reproductive parameters were used to calculate extract effectiveness (PE). Docking targeted eight tick proteins, including GABA receptor, acetylcholinesterase (AChE), triosephosphate isomerase (TIM), glutathione S-transferase (GST), and four mitochondrial electron transport complex subunits. Multivariate analysis summarized metabolite-target interactions. Adult mortality ranged from 37% to 70%, the highest for the 120-day extract, whereas larval mortality approached 100% across all treatments. Reproductive indices were significantly inhibited, yielding PE values between 51% and 91%, the latter for the 120-day extract. GC-MS revealed predominant tocopherol derivatives, pentacyclic triterpenes, and sterols. Docking indicated that metabolites enriched in the 120-day extract, α-tocospiro A, γ-tocopherol, α-tocopherol, and 2-stearoylglycerol, exhibited strong predicted interactions, mainly with mitochondrial complexes, while compounds unique to the 90-day extract showed higher affinity for GABA. Estimated extract production suggests significant biomass bioprospecting potential. These findings highlight the acaricidal potential of M. minutiflora, especially at 120 days, and identify candidate metabolites for sustainable tick control in low-input systems.