Isofuranodiene and germacrone from Smyrnium olusatrum essential oil as acaricides and oviposition inhibitors against Tetranychus urticae: impact of chemical stabilization of isofuranodiene by interaction with silver triflate

In this research, we isolated the sesquiterpenoids isofuranodiene and germacrone from the essential oil of Smyrnium olusatrum (Apiaceae), and evaluated their potential against Tetranychus urticae (Tetranychidae), an important agricultural pest, which attacks over two hundred species of plants. We evaluated both compounds for their acute and chronic toxicity via tarsal toxicity assays, and for oviposition inhibitory effects. Since isofuranodiene is a thermosensitive molecule undergoing Cope rearrangement at high temperature giving the less active isomer curzerene, we achieved its chemical stabilization by interaction with a silver(I) ion (Ag triflate, AgCF3SO3) and the isofuranodiene adduct was tested for acaricidal activity and oviposition inhibitory potential. Results showed that isofuranodiene showed the lowest LD50 values, both in acute (15.8 µg.cm-2) and chronic toxicity assays (11.9 µg.cm-3). The three tested products also led to significant oviposition inhibition, with IC50 of 4.1 (isofuranodiene), 17.8 (germacrone) and 19.3 µg.cm-3 (isofuranodiene+AgCF3SO3). Overall, the results from this study allowed us to candidate the two oxygenated sesquiterpenes isofuranodiene and germacrone isolated from the S. olusatrum essential oil as novel molecules to develop effective acaricides. In addition, we pointed out the potential value of chemical stabilization by interaction with a silver(I) ion (Ag triflate, AgCF3SO3) for the production of mite oviposition inhibitors.