Efficacy of sea fennel (Crithmum maritimum L., Apiaceae) essential oils against Culex quinquefasciatus Say and Spodoptera littoralis (Boisd.)

The effective management of insect pests and vectors still represents a major challenge in current entomology. Culex quinquefasciatus Say is a key vector of lymphatic filariasis, Rift Valley fever, West Nile, St. Louis encephalitis and Western equine encephalitis virus. Recently, the importance of the eco-friendly control of C. quinquefasciatus larval population using plant-borne biopesticides, including essential oils (EOs), has been stressed. Spodoptera littoralis (Boisd.) also known as tobacco cutworm, is one of the most destructive moth agricultural pests in tropic and sub-tropic regions. Despite the fact that sea fennel (Crithmum maritimum L., Apiaceae) is considered as a promising biosaline crop, its potential for commercial cultivation has not yet been exploited. Notably, it has been reported that in coastal marine environments insects stay away from sea fennel. This aromatic plant is endowed with secretory structures as ducts and vittae storing volatile compounds. In this study, the chemical composition of sea fennel essential oils from three different EO accessions, namely France (Brittany), Central and South Italy (Marche and Sicily regions) have been analysed by gas chromatography-mass spectrometry (GC-MS), and their toxicity against larvae of C. quinquefasciatus and S. littoralis evaluated. Selected pure compounds from the essential oils mentioned above have also been tested. The essential oils showed notable variability in chemical composition, being dominated by dillapiole and -terpinene (French EO), limonene and -terpinene (central Italy EO) and thymol methyl ether and-terpinene (Sicilian EO). As found out, the significantly most efficient essential oils were obtained from the seeds and aerial parts of plants of the French region. For these EOs, LD50 values were estimated as 62.3 and 71.7 μg/larva for S. littoralis, respectively, and LC50 as 13.7 and 15.6 μl/L for C. quinquefasciatus larvae, respectively. gamma-Terpinene and myristicin were the most effective on C. quinquefasciatus larvae showing LC50 values < 17 μl/L. Overall, these findings shed light on the insecticidal potential of C. maritimum EO against mosquitoes and agricultural pests, allowing to identify the most effective chemotype, and to stimulate cultivation of this species as a source of botanical insecticides.