Amide alkaloids from Piper guineense and its crude extract as protectants against Sitophilus zeamais

The edible plant, Piper guineense Schum and Thonn, belongs to the family Piperaceae and possesses insecticidal properties against stored product insects, but information on isolation and use of its amide alkaloids for the control of insect pests is scanty. Therefore, amide alkaloids from P. guineense fruits as well as its crude extract were investigated as protectant against Sitophilus zeamais Motschulschy (Coleoptera: Curculionidae), a cosmopolitan insect pest. Chemical analysis of P. guineense was done using chromatographic techniques and amide alkaloids were identified using liquid chromatography–quadrupole time of flight-mass spectrometry (LC-QToF-MS). The compounds were assayed on five pairs of two-day-old S. zeamais, feeding with the maize variety, TZPB-SR-W. All parameters, including mortality and oviposition by female S. zeamais, repellent effect of the compounds and their effects on maize seed germination, were evaluated relative to the synthetic chemical, pirimiphos-methyl and ethanol, as positive and negative controls, respectively. The six compounds identified were dihydrowisanine (1.01%), guineensine (0.22%), piperine (6.64%), piperlonguminine (0.25%), propiverine (0.16%) and trichostachine (3.80%). Guineensine and piperine caused the highest mortalities (97.5% and 82.5%, respectively) of S. zeamais, which were not significantly different from the mortality (100%) caused by pirimiphos-methyl. In addition, piperine treatment significantly reduced oviposition (0.75 per grain) when compared to ethanol-treated grains (5.00 per grain). There were no significant differences in per cent germination between maize seeds treated with the amide compounds and those included in the control groups (positive and negative controls). Amide alkaloids from P. guineense offer a useful source of biopesticide material for controlling S. zeamais.