Insect growth regulator and insecticidal activity of beta-dihydroagarofurans from Maytenus spp. (Celastraceae)

From the aerial parts of Maytenus disticha, we have isolated 9beta-benzoyloxy-1alpha,2alpha,6beta,8alpha,15penta-acetoxy-dihydro-beta-agarofuran (1) and from seeds of Maytenus boaria 9beta-furoyloxy-1alpha,6beta,8alpha-triacetoxy-dihydro-beta-agarofuran (2). These compounds and their MeOH and hexane/ethyl acetate (1:1 v/v) extracts were evaluated for their effects on the fall armyworm (Spodoptera frugiperda). Toosendanin, a commercial insecticide derived from Melia azedarach was used as a positive control. When tested for activity using neonate larvae in a nochoice artificial diet bioassays, the agarofurans 1, 2 and toosendanin as well as the MeOH and hexane/EtOAc extracts caused significant growth inhibitory effects with GC50 of 7.55; 3.84; 1.75; 14.0 and 7.3 ppm at 7 days, respectively. Compounds 1 and 2 caused 100% larval mortality at 25 and 15 ppm, respectively. MeOH and hexane/EtOAc extracts caused 100% larval mortality at 25.0 ppm, respectively, they also increased the development time of surviving larvae and a significant delay for the time of pupation and adult emergence. These compounds showed comparable potency of activity with toosendanin. Acute toxicity against adults of S. frugiperda was also found, for hexane/EtOAc extract and 2 had the most potent activity with LD50 value of 4.7 and 1.9 ppm, respectively. MeOH extract, hexane/EtOAc extract, 1 and 2 caused acetylcholinesterase inhibition with 78.0, 89.2, 79.3 and 100% inhibition at 15.0 ppm, respectively. Therefore, the furoyloxy agarofuran may be responsible for the insecticidal activity of these plants.