Rationale for developing novel mosquito larvicides based on isofuranodiene microemulsions

Isofuranodiene is a bioactive furanosesquiterpene occurring as the major volatile compound in the essential oil from Smyrnium olusatrum (Apiaceae). It has a notable potentiality to be used as a botanical insecticide. However, its low solubility together with susceptibility to oxidation and thermal degradation limit its application on a wide scale. To face these challenges, isofuranodiene was encapsulated in stable microemulsions (MEs) at two concentrations (ME 750: 0.75%, ME 375: 0.375%). We assessed the larvicidal activity in the short term and after several days of exposure of pure isofuranodiene and its MEs against the filariasis vector Culex quinquefasciatus. The impact of ME-based larvicidal treatment at sub-lethal concentrations on adult emergence was also evaluated. Finally, to shed light on potential ecotoxicology risks for non-target invertebrates, the MEs developed here were tested on the aquatic microcrustacean Daphnia magna and on the earthworm Eisenia fetida. Pure isofuranodiene and S. olusatrum leaf essential oil, used as controls, showed their potential as mosquito larvicidal agents (LC50 of 29.2 and 18.6 l.L-1, respectively). Isofuranodiene formulated in ME 750 was effective against Cx. quinquefasciatus larvae, leading to significant larval mortality over time and a marked decrease of adult emergence. Both isofuranodiene MEs showed little impact on the non-target aquatic microcrustacean Daphnia magna (ME 750 and ME 375: mortality <19% after 48 h of exposure to 32 ml.L-1 and 20 ml.L-1, respectively) as well as on earthworms (ME 750 and ME 375: no mortality and mortality <7% after 14 days of exposure to 1000 mg.kg-1, respectively), outlining their potential employ in vector control operations.