Green purification of Acmella oleracea extract by wiped-film short path molecular distillation boosts the insecticidal activity on mosquito larvae

The development of insecticide resistance by mosquito vectors highlighted an urgent need for effective and sustainable botanical insecticides. Acmella oleracea R.K. Jansen (Asteraceae)-derived extracts and the major constituents N-alkylamides have already demonstrated their potential as insecticidal and acaricidal agents. Nowadays, the development of scalable green extraction and purification processes in the manufacture of biopesticides is a topic of great interest. In this context, supercritical fluid extraction and wiped-film short path molecular (WSM) distillation techniques were combined for the first time to obtain an eco-friendly N-alkylamides-enriched fraction (AEF) from A. oleracea. This was characterized by a notably higher content of spilanthol and N-alkylamides than the supercritical fluid extract (SFE), as determined by HPLC-DAD-MS analysis. The AEF also contained free fatty acids (e.g., palmitic, linoleic, and linolenic acids) as revealed by GC-FID analysis. The mosquito larvicidal activity of SFE, AEF, and pure spilanthol was assessed against 3rd instar larvae of Aedes albopictus Skuse, Anopheles stephensi Liston, and An. gambiae Giles. Results showed that AEF exhibited an insecticidal efficacy comparable with that of spilanthol, and higher than that of SFE. These products were tested against human keratinocytes (HaCaT) confirming their dermal safety. The present study paves the way for the utilization of WSM distillation in the agrochemical industry for the manufacture of botanical insecticides. Indeed, this technique allows to avoid the use of organic solvents related to conventional extraction and spilanthol isolation procedures and gives a product devoid of undesired pigments appealing to other industrial application as well.