BACKGROUND: The cotton aphid (Aphis gossypii Glover) is one of the most invasive pests of cotton. Many botanical phytochemicals have a long history as a source of insecticides, and as templates for new insecticides. This study was undertaken to isolate aphicidal compounds from the seeds of Erythrina crista-galli L. using the bioassay-guided isolation method. RESULTS: Three novel and 11 known Erythrina alkaloids were isolated. Erysodine (9), erysovine (10), erysotrine (8) and erythraline (11) showed moderate to excellent aphicidal activity with LD(50) values of 7.48, 6.68, 5.13 and 4.67 ng aphid(-1) , respectively. The Potter spray tower bioassay gave corresponding LC(50) values of 186.81, 165.35, 163.74 and 112.78 microg ml(-1) . A unique substructure, which presents an sp(3) methylene at C-8, a non-oxygenated site at N-9 and a conjugated dienes group (Delta(1,2) and Delta(6,7) ), plays a crucial role in the aphicidal activity. Application of erythraline (11) led to different increases in the activities of superoxide dismutase, catalase and glutathione S-transferase. CONCLUSION: The study demonstrated that the Erythrina alkaloids erysodine (9), erysovine (10), erysotrine (8) and erythraline (11) have potential use as botanical aphicides for commercial application, or as templates for the development of new insecticides. (c) 2017 Society of Chemical Industry. CI - (c) 2017 Society of Chemical Industry.