Carlina oxide from Carlina acaulis root essential oil acts as a potent mosquito larvicide

Developing effective larvicides for mosquito control is being challenging due to the quick development of resistance in targeted vectors. Botanical products can help, due to their multiple mechanisms of action coupled with eco-friendly features. Carlina acaulis (Asteraceae) is an Alpine perennial herb used as a traditional remedy and food. Its root essential oil (EO) has antimicrobial and antitrypanosomal properties, and is currently listed among botanicals employable in food supplements. Its insecticidal activity has not been explored so far. Here, after analysing the C. acaulis EO chemical composition by GC–MS and NMR, we detected extremely high larvicidal activity of this EO and its main constituent, carlina oxide, against Culex quinquefasciatus larvae by using the standard WHO protocol. LC50 were 1.31 and 1.39 μg mL-1, respectively. 24-h exposure to both products triggered significant mortality rates for five days post-treatment. Larvicidal tests on a wider scale confirmed >95% larvicidal effectiveness of the EO and carlina oxide tested at 1.25 μg L-1. Their non-target impact was evaluated through experiments on Daphnia magna adults. Both showed significantly lower toxicity if compared to cypermethrin. To shed light on the modes of action, carlina oxide was tested for anti-acetylcholinesterase activity by the Ellman method, with lower performances over galantamine. A moderate antioxidant potential was observed using DPPH and ABTS assays, since it has a role for preserving the shelf-life of herbal-based insecticides. Finally, cytotoxicity on vertebrate cells was noted, testing carlina oxide on human dermis, HCT116 and MDA-MB231 cell lines by MTT assay. Overall, the outstanding toxicity of the tested products make them excellent candidates to develop novel mosquito larvicides for real-world applications