ABSTRACT

Laboratory experiments to evaluate the insecticidal activity of five plant extracts, clay and permethrin against bean beetle Callosobruchus maculatus (F.) on mung bean (Vigna radiata (L.) Wilczek) were carried out in the Teaching and Research Laboratory of the College of Crop and Soil Sciences, Michael Okpara University of Agriculture, Umudike. Five plant extracts: Tephrosia vogelii leaves, Tephrosia vogelii stem, Piper guineense fruits, Xylopia aethiopica fruits, and Carica papaya seeds were applied at four levels: 0.0 g, 1.0 g, 2.0 g and 3.0 g per 20 g of mung bean (w/w). Clay and permethrin dusts were equally applied at the above rates. The experiment was laid out in a 7 x 4 factorial fitted into a completely randomized design (CRD) with three replications. The effects of these plant extracts, clay and permethrin on mortality of adult Callosobruchus maculatus were evaluated at 7, 14, 21 and 28 days after treatment. Also the effect of these treatments on oviposition was determined and recorded at 7 days after treatment. Adult emergence from the treated mung bean and control was evaluated. Germination test for viability, weight loss, percentage damage were carried out at the end of the experiment. Phytochemical analysis of the plant extracts was carried out to identify the active principles responsible for their insecticidal activities. Proximate composition of mung bean was determined to evaluate the effect of the treatments on the basic food components. Results indicated that plant extracts controlled the bean beetle especially when applied at appropriate dosage of 3.0 g/20 g. Mortality increased significantly (P<0.05) in all the plant extracts with increase in dosage and length of exposure. Oviposition and adult emergence counts were significantly (P<0.05) suppressed. Percentage seed weight loss and damage were also suppressed. The viability and proximate composition of seeds tested with plant extracts, clay and permethrin were not adversely affected when compared with the untreated seeds. Permethrin was significantly (P<0.01) superior to the test plant extracts in all the parameters followed by clay though not different from Tephrosia vogelii leaves and Piper guineense fruits. Tephrosia vogelii leaves recorded the best protection followed by Piper guineense fruits at 3.0 g/ 20 g than other extracts. Phytochemical analysis revealed that plant extracts posses high values of alkaloids, flavonoids and saponins. Gas chromatograph mass spectometry (GC-MS) analysis revealed the presence of a wide array of bioactive volatile fatty acids in the extracts of the test plants. The major and highest dominant bioactive fatty acids present in the extracts were;  Oleic acid (19.90 - 60.79 %), Hexadecanoic acds (26.28 %), Benzene, 1,3-bis (2-2-dimethylpropyl)-2,4,5,6-tetramethyl (19.79 %), 7H-Pyrazolo(4,3-d)pyrimidin-7-one,1,4-dihydro-3-beta-D-ribofuranosyl (14.60 %), Benzene (1-methoxy-1-methylethyl) (9.64 %), Benzene (isothiocyanatomethyl) (8.93 %) Eicosane (6.30 %), 7-Oxabicyclo (4.1.0) heptanes, 3-oxiranyl (6.10 %) and these may be responsible for the observed insecticidal activity of the plant extracts against Callosobruchus maculatus.