Bioactivity of Essential Oils from Patagonian Wild Plants: Acaricidal and Insecticidal Effects on Varroa destructor and Apis mellifera

<i>Varroa destructor</i> represents a major threat to honeybee colonies worldwide, prompting the search for alternative organic acaricides. This study evaluated the biological activity of essential oils extracted from three Patagonian wild plants-<i>Adesmia boronioides</i>, <i>Dysphania multifida</i>, and <i>Senecio filaginoides</i>-on both <i>V. destructor</i> and <i>Apis mellifera</i>. Chemical analysis revealed that <i>A. boronioides</i> oil was dominated by esquelenone (34.49%), <i>D. multifida</i> by ascaridole (34.87%), and <i>S. filaginoides</i> by <i>α</i>-pinene (40.87%). All essential oils exhibited acaricidal activity, with <i>D. multifida</i> showing the lowest LC₅₀ against <i>V. destructor</i> (1.1 µL/mL at 24 h). Toxicity assays on adult bees indicated that <i>A. boronioides</i> and <i>D. multifida</i> significantly reduced bee survival, whereas <i>S. filaginoides</i> did not appear to cause significant mortality (LC₅₀ = 139.5 µL/mL). Repellency tests for <i>A. boronioides</i> and <i>D. multifida</i> showed significant mite repellence. Larval assays revealed a high survival rate under <i>S. filaginoides</i> treatment (survival rate > 80.24%), in contrast to the reduced viability observed with the other oils. The high selectivity index of <i>S. filaginoides</i> underscores its potential as a selective and safe botanical acaricide. Moreover, its LC₅₀ decreased over time, suggesting a residual acaricidal effect. These findings support <i>S. filaginoides</i> as a promising candidate for sustainable <i>V. destructor</i> control.