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

tThe recent outbreaks of mosquito-borne diseases, such as chikungunya and Zika virus, highlighted thepivotal importance of effective mosquito control programs. Nowadays, Culicidae management is beingchallenging, due to the rapid development of resistance to synthetic pesticides and the spread of highlyinvasive mosquito vectors worldwide. This research explored the chemical composition of four Apiaceaeessential oils (EOs) from Trachyspermum ammi, Smyrnium olusatrum, Pimpinella anisum and Helosciadiumnodiflorum and their potential as sources of synergistic binary mixtures with high effectiveness againstlarvae of the filariasis vector Culex quinquefasciatus. The essential oils were all highly toxic to the larvae,showing LC50of 17.6, 17.5, 25.9 and 20.6 l L−1, respectively. GC–MS analysis put in evidence thymol,(E)-anethole, myristicin and (Z)--ocimene, and isofuranodiene and germacrone as the main essentialoil 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, showingLC50of 15.2 and 16.9, l L−1, respectively. LT50values were 45 and 30 min, respectively. Notably, shorttime 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 acutetoxicity of EO main constituents, i.e. germacrone, isofuranodiene and (E)-anethole, were carried out. LC50were 18.6 mg L−1, 33.7 mg L−1and 24.8 l L−1. Overall, our results pointed out the promising potential ofthese EOs to develop cheap and effective mosquito larvicides, as well as the importance to consider thesynergistic effects among the tested botanicals during the design of novel mosquito larvicides.