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The fall armyworm (Spodoptera frugiperda), sweet potato weevil (Cylas puncticollis) and red flour beetle (Tribolium castaneum) are insect pests of economic importance that negatively impact production of maize, sweet potato and stored grain, respectively. The continued use of synthetic insecticides to control these insect pests can cause undesirable effects to the environment, human, and other non-target organisms, leading to renewed interest in botanical pesticides as a safer alternative. In this study, bioactivity-guided strategy was applied to isolate insect antifeedants from Melia volkensii, a native tree species to the drylands of East Africa. Initial laboratory screening of M. volkensii nut and pulp crude extracts showed antifeedant activity against S. frugiperda, C. puncticollis and T. castaneum in our previous publication. Fractionation of the nut and pulp crude extracts using various solvents of increasing polarity showed that the antifeedant activity was retained in the dichloromethane fraction, which was subsequently purified by column chromatography. The resultant bioactive fractions were further purified by preparative-HPLC, preparative-TLC and recrystallization, which yielded two pure bioactive compounds characterized as toosendanin and salanninolide using NMR and LC-MS. Toosendanin and salanninolide showed strong activity against T. castaneum and S. frugiperda , with EC 50 values of 0.11% and 0.14%, and 0.15% and 0.10%, respectively. In contrast, there was no antifeedant activity by both isolated compounds against C. puncticollis. This study provides new leads for development of insect control products from M. volkensii. • Antifeedant activity of M. volkensii was reported against S. frugiperda, C. puncticollis and T. castaneum. • Two bioactive principles, toosendanin and salanninolide, were isolated from M. volkensii nut and pulp. • Toosendanin showed antifeedant activity against T. castaneum and S. frugiperda with EC 50 of 0.11% and 0.14% respectively. • Salanninolide showed antifeedant activity against T. castaneum and S. frugiperda with EC 50 of 0.15% and 0.10% respectively. • First report of isolation of salanninolide from M. volkensii and of toosendanin from M. volkensii nuts. [ABSTRACT FROM AUTHOR]

The African sweet potato weevil, Cylas puncticollis, and fall armyworm, Spodoptera frugiperda, are insect pests of economic importance that have a negative impact on sweet potato and maize production, respectively. In this study, we aimed to evaluate the potential of Melia volkensii extracts to protect sweet potato and maize plants against damage by both insect pests. We evaluated extracts from the bark, leaves, pulp and nuts of Melia volkensii for antifeedant activity against C. puncticollis and S. exigua (used as a substitute for S. frugiperda), under laboratory conditions. Interestingly, extracts of all plant parts showed antifeedant activity. These results led us to investigate the effectiveness of nut and pulp extracts to protect sweet potato and maize crops in greenhouse conditions. Against C. puncticollis, the sweet potato plants treated with nut extracts showed the lowest tuber damage (18%) when compared to pulp extracts (30%), positive control (33%) and negative control (76%). Nut extracts, pulp extracts and positive control reduced maize leaf and whorl damage by S. frugiperda compared to the negative control. Altogether, this study highlights the potential of M. volkensii extracts and their application in integrated insect pest management [ABSTRACT FROM AUTHOR]