Ascaridole-rich essential oil from marsh rosemary (Ledum palustre) growing in Poland exerts insecticidal activity on mosquitoes, moths and flies without serious effects on non-target organisms and human cells

Abstract Marsh rosemary (Ledum palustre, Ericaceae) has been widely used in the traditional medicine of various regions worldwide, and as insect repellent. Little is known on its essential oil (EO) insecticidal potential. This study explores the insecticidal effects of the EO obtained from L. palustre growing in Poland on selected insect pests and vectors. EO GC-MS analysis evidenced an uncommon chemotype characterized by ascaridole (35.3% as sum of cis-ascaridole and isoascaridole) and p-cymene (25.5%). The EO was effective against Culex quinquefasciatus, Spodoptera littoralis and Musca domestica, showing LC50/LD50 of 66.6 mg L−1, 61.4 μg larva−1 and 117.2 μg adult−1, respectively. It was not toxic to non-target Eisenia fetida earthworms and moderately toxic to Daphnia magna microcrustaceans, over the positive control α-cypermethrin. The EO cytotoxicity on human keratinocytes and fibroblasts showed high IC50 values (71.3 and 84.4 μg mL−1, respectively). Comet assay data highlighted no DNA damages. Based on our findings, this EO characterized by the ascaridole/p-cymene chemotype could be a candidate for the formulation of botanical insecticides; large-scale production of green insecticides by this rare species may be assured by ex situ cultivation and biotechnological techniques.