Abstract
BackgroundPowders and extracts of Piper guineense seeds and leaves were assessed for insecticidal activities against Callosobruchus maculatus in the laboratory at temperature and relative humidity of 29.6 °C and 75.9%, respectively. Bioactive compounds in P. guineense leaves and seeds were also investigated. The powders were tested at rates 1.0, 2.0 and 4.0 g/20 g cowpea seeds while extracts were tested at 1.0, 2.0 and 3.0%.ResultsResults of contact toxicity assay of the seed powder caused 100% adult mortality at 96 h post-treatment period whereas leaf powder evoked 90% adult mortality within the same period at concentration of 1.0 g/20 g cowpea seeds. Low adult emergence was observed on cowpea seeds treated with 1 g of seed powder with percentage adult emergence of 10.0% and inhibition rate (IR) of 97.5%. Beetle Perforation Index (BPI) obtained from treated cowpea seeds was significantly different (P < 0.05) from BPI of untreated seeds. Extracts of P. guineense seed were more toxic than seed powder. Piper guineense seed extract caused 87.5% adult mortality of C. maculatus while leaf extract caused 70.0% adult mortality within 24 h of infestation at concentration of 1%. Progeny development of C. maculatus was completely inhibited in cowpea treated with 2% and 3% leaf and seed extracts of P. guineense. β-Pinene was the most abundant active compound in P. guineense seed (55.6%) and leaf (48.4%). β-Phellandrene occurred 38.2% in seeds while Ocimene had the least value of 0.2% in seed and 0.5% in leaf.ConclusionThe study showed that P. guineense seed powder and extracts were more effective than leaf powder and extract. Utilization of plant products as alternative to synthetic insecticides in protecting cowpea seeds against C. maculatus should be encouraged for enhanced food safety and security. Piper guineense is used as spice and medicine and interestingly safe for human use.
Highlights
Powders and extracts of Piper guineense seeds and leaves were assessed for insecticidal activities against Callosobruchus maculatus in the laboratory at temperature and relative humidity of 29.6 °C and 75.9%, respectively
Beetle perforation index caused by C. maculatus in cowpea seeds treated with P. guineense powders Piper guineense seed powder completely protected cowpea seeds from being damaged by C. maculatus concentrations 2 g and 3 g/20 g (Table 3)
Beetle Perforation Index (BPI) was zero in cowpea seed treated with seed powder at rate 2 g and 3 g/20 g of cowpea seeds, leaf powder recorded 10% and 2.5% at rate 1 g and 2 g/20 g of cowpea seeds, while untreated seed recorded > 50.00% perforation index
Summary
Powders and extracts of Piper guineense seeds and leaves were assessed for insecticidal activities against Callosobruchus maculatus in the laboratory at temperature and relative humidity of 29.6 °C and 75.9%, respectively. Economic and agronomic reasons, cowpea seeds must be stored after harvest and in storage, the product is greatly damaged by Callosobruchus maculatus (Fab.) (Coleoptera: Bruchidae) insect pest (Casswell, 1981). Qualitative and quantitative depletions adversely affect available dietary protein level, market value and specimens for planting during cropping season, and these are obstacles to achieving food security in many developing countries (IITA, 1995; Rouanet, 1992). The control of C. maculatus has relied on the use of synthetic insecticide, which has caused problems such as development of resistance, pest resurgence, food poisoning and environmental contamination (Idoko and Adesina, 2012). The ecological and health problems associated with use of chemical insecticides justify the search for alternative methods of controlling C. maculatus such as the use of plant materials which are unquestionably safer
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