From a bioactive methanolic extract of Senecio fistulosus, the antifeedant effects of the alkaloidal and non-alkaloidal fractions were tested against the insects Spodoptera littoralis, Myzus persicae and Rhopalosiphum padi, with the non-alkaloidal fraction being antifeedant. The phytochemical study of the non-alkaloidal fraction of S. fistulosus, resulted in the isolation of four compounds, two 9-oxo-furanoeremophilanes (1, 2), an eremophilanolide, 1β,10β-epoxy-6-acetoxy-8α-hydroxy-eremofil-7(11)-en-8β,12-olide (3) and a maaliol derivative (4). The alkaloidal fraction yielded two known pyrrolizidine alkaloids (5, 6). Compounds 1, 3 and 4 are new natural products. Furanoeremophilane 2 was a strong antifeedant against S. littoralis and maaliane 4 inhibited the settling of M. persicae.