Synergized mixtures of Apiaceae essential oils and related plant-borne compounds: Larvicidal effectiveness on the filariasis vector Culex quinquefasciatus Say

•Mosquito control is challenging, due to resistance development to synthetic pesticides.•We studied synergistic binary mixtures of Apiaceae oils on Culex quinquefasciatus larvae.•Trachyspermum ammi + Pimpinella anisum (1:2) and Smyrnium olusatrum + P. anisum (1:1) LC50 were 15.2 and 16.9 μl L−1.•Exposure to binary mixtures reduced Culex quinquefasciatus fertility and natality.•Germacrone, isofuranodiene and (E)-anethole LC50 were 18.6 mg L−1, 33.7 mg L−1 and 24.8 μl L−1, respectively.

The recent outbreaks of mosquito-borne diseases, such as chikungunya and Zika virus, highlighted the pivotal importance of effective mosquito control programs. Nowadays, Culicidae management is being challenging, due to the rapid development of resistance to synthetic pesticides and the spread of highly invasive mosquito vectors worldwide. This research explored the chemical composition of four Apiaceae essential oils (EOs) from Trachyspermum ammi, Smyrnium olusatrum, Pimpinella anisum and Helosciadium nodiflorum and their potential as sources of synergistic binary mixtures with high effectiveness against larvae of the filariasis vector Culex quinquefasciatus. The essential oils were all highly toxic to the larvae, showing LC50 of 17.6, 17.5, 25.9 and 20.6 μl L−1, respectively. GC-MS analysis put in evidence thymol, (E)-anethole, myristicin and (Z)-β-ocimene, and isofuranodiene and germacrone as the main essential oil components, respectively. Three effective EOs were selected to prepare binary mixtures. T. ammi + P. anisum (ratio 1:2) and S. olusatrum + P. anisum (ratio 1:1) were the most toxic larvicidal blends, showing LC50 of 15.2 and 16.9, μl L−1, respectively. LT50 values were 45 and 30 min, respectively. Notably, short time exposure to both binary mixtures strongly reduced emergence rates, fertility and natality of C. quinquefasciatus that survived after the treatment at the larval stage. Larvicidal assays assessing the acute toxicity of EO main constituents, i.e. germacrone, isofuranodiene and (E)-anethole, were carried out. LC50 were 18.6 mg L−1, 33.7 mg L−1 and 24.8 μl L−1. Overall, our results pointed out the promising potential of these EOs to develop cheap and effective mosquito larvicides, as well as the importance to consider the synergistic effects among the tested botanicals during the design of novel mosquito larvicides.

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