Abstract
BackgroundCallosobruchus maculatus is an important insect pest of cowpea. The inhibitory effects of oil extract of Acalypha wilkesiana (Muell Arg.) leaves on antioxidant, neurotransmitter, and detoxifying enzyme in adult Callosobruchus maculatus (Fabricius) were evaluated under laboratory condition. The leaves of the plant were collected fresh and air-dried before the oil was extracted from them through cold extraction method while ethanol was used as solvent. Adult C. maculatus were exposed to 0.2, 0.4, 0.6, 0.8, and 1.0 ml of 0.5% concentration of the oil extract and were homogenized separately. The supernatants gotten from them were used as enzyme sources. The activities of SOD, CAT, GPx, AChE, CarEST and GST were observed with photospectrometer. GC-MS analysis was done to evaluate the active compounds present in the oil extract.ResultsThe activities of the enzymes increased at lower dosages of the oil extract (0.2 and 0.4 ml) and reduced drastically at higher dosages of the oil (0.6, 0.8, and 1.0 ml). However, AChE activity was more affected by the oil extract as it was almost inhibited by the oil extract. The GC-MS showed that 114 compounds were present in the oil extract of the plant while acetaldehyde had the highest percentage (46.07%) of the total compounds.ConclusionBased on these findings, the oil extract of A. wilkesiana could be a good biopesticide for the control of adult C. maculatus instead of synthetic chemical insecticides.
Highlights
Callosobruchus maculatus is an important insect pest of cowpea
The highest Superoxide dismutase (SOD) activity was recorded at 0.3 ml (14.64 μmol/min/ml) of the extract while the lowest activity of 3.71 μmol/min/ml was recorded at 1.0 ml dosage of the oil extract and they were significantly (p < 0.05) different from all other treatments
Tukey multiple comparison showed that for acetylcholine esterase (AChE), significant differences existed between all the treatments while for CarEST significant difference did not existed between 0.2 ml of the oil extract and the control at p = 0.223
Summary
Callosobruchus maculatus is an important insect pest of cowpea. The inhibitory effects of oil extract of Acalypha wilkesiana (Muell Arg.) leaves on antioxidant, neurotransmitter, and detoxifying enzyme in adult Callosobruchus maculatus (Fabricius) were evaluated under laboratory condition. Considering the importance of cowpea as main source of protein in the diet of families that cannot afford animal proteins, researchers have been combating the insect and other stored product insect pests with the use of synthetic chemical insecticides which were discovered in the late 1930s (Begum, Shaarma, & Pandey, 2013; Forim, Da-silva, & Fernandes, 2012; Isman, 2000, 2006). Martins, Freire, Parra, and Macedo (2012), Rattan and Sharma (2011), and Zibaee and Bandani (2010) suggested that once the insecticidal potential of a botanical has been discovered, its effects on antioxidant, digestive, and detoxifying enzymes in insects should be evaluated and active compounds present in it should be determined as this will ensure the protection of non-target organisms
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