Background: Many plants have been identified for their insecticidal properties as alternatives to synthetic ones, which are toxic to untargeted organisms and environment. Ricinus communis (Castor) has been re-ported to exhibit insecticidal properties against insect pests. Zonocerus variegatus (Grasshopper) is a notable pest of several crops, and has been linked with great economic losses to farmers. The present study investigates the in-vitro toxicity of R. communis seed kernel extract (RCSKE) on the activities of selected antioxidant and hydrolytic enzymes in nymph and adult Zonocerus variegatus (Grasshopper), using cypermethrin (CYPER-M) and chlorpyrifos (CPF) as standard conventional pesticides.
Methods: Seed kernel of Ricinus communis (Castor) was subjected to acidified aqueous extraction to obtain the extract (RCSKE). Crude enzyme preparations were obtained from nymph and adult Z. variegatus grass-hoppers. The in-vitro effects of different concentrations (15, 30, 45, 60, 75, 90 and 105μg/ml) each of RCSKE, CYPER-M and CPF on the activities of superoxide dismutase (SOD), catalase (CAT), acetylcholinesterase (AChE) and carboxylesterase (CES) in crude enzyme preparations were estimated spectrophotometrically. The level of statistical significance was 0.05.
Results: The RCSKE significantly reduced the in-vitro SOD activity (p < 0.05) in nymph Z. variegatus at all the concentrations, whereas both CYPER-M and CPF significantly reduced the activity only at certain concentrations. The CAT activity in the nymph was significantly decreased by RCSKE and CPF at all the concentrations, but CYPER-M decreased it only at certain concentrations. In adult Z. variegatus, SOD activity was not significantly affected (p > 0.05), while CAT activity was significantly increased (p < 0.05) by the three agents at all the concentrations. The AChE and CES activities in the nymph were significantly reduced by RCSKE, CYPER-M and CPF at all the concentrations. The RCSKE and CPF significantly increased the CES activity, while CYPER-M caused a significant decrease in the activity in adult Z. variegatus.
Conclusion: The seed kernel extract of Ricinus communis is an effective pesticidal agent and hence, it could be a source of biopesticide alternative with greater potential than cypermethrin and chlorpyrifos. In addition, the antioxidant, acetylcholinesterase and carboxylesterase enzymes in the nymphs of Z. variegatus grasshoppers are more susceptible to the effect of the extract than in the adult grasshoppers.
Sexual Variations in Nutritive Value of Adult Variegated Grasshopper, Zonocerus variegatus (Linnaeus, 1758)