Efficacy of Piper guineense Schumach. seed powder in the control of Callosobruchus maculatus (Fabricius, 1775) (Coleoptera: Chrysomelidae: Bruchinae) and on the nutritional and organoleptic characteristics of stored cowpea Vigna unguiculata (L.) Walp

Brown pepper (Piper guineense) seed powder, used for culinary and medicinal purposes, was evaluated in the laboratory with a conventional storage chemical, actellic 2% dust (Pirimiphos-methyl), as standard, to protect stored cowpea against the cowpea bruchid, Callosobruchus maculatus. Four rates of the seed powder were used (2.5, 5.0 and 10.0 g/100 g seed with a control, 0.0 g) while actellic dust was applied at 1.0, 2.0, 3.0 g/100 g seed and 0.0 g/100 g seed as control. Data on percentage mortality, oviposition, adult emergence and seed damage were collected over a six-month period. Weevil perforation indexes (WPI) were estimated with the seed damage data. All data were analysed for variance at P≤0.05. Actellic dust at the lowest dose inflicted adult mortality (90 – 100%) in the first 48 h after treatment and prevented oviposition (95 – 100%) in the first five months of storage compared to the control. The highest rate of Piper guineense application caused mortality of up to 90.0% in 48 h, reduced oviposition (70 – 80%), decreased adult emergence (15.90 to 28.40 insects) as against the control (104.7 – 272.7 insects) and reduced seed damage by 80 % with a WPI of between 33.3 and 10.0 %. Proximate analysis and germination tests indicated that the treatment materials increased the moisture and crude fibre content, decreased crude protein content but had no significant effect on the viability of stored seeds. Organoleptic tests demonstrated that treatment materials had no significant negative effect on taste, odour, texture, appearance and overall acceptability of cooked cowpea seeds after six months of storage. It can be safely concluded that the powdered form of P. guineense seed at the highest doses (5.0 and 10.0 g) gave significant protection of cowpea seeds against the cowpea bruchid, which compared favourably with actellic dust when applied topically.