Anti-acetylcholinesterase activities of leaf extracts of carphalea glaucescens and gnidia glauca from Mbeere North Subcounty, Kenya on chilo partellus larvae

Abstract

The stem borer (Chilo partellus) is one of the major constraints in maize and sorghum production worldwide. Control of Chilo partellus is mainly done through synthetic insecticides which are very expensive and have negative effects to environment and non-target organisms. Farmers in Mbeere use Carphalea glaucescens and Gnidia glauca in control of Chilo partellus because of the high cost of conventional insecticides. However, there is lack of scientific information on the their mode of action is not known. This study was designed to gather preliminary data that can be used to develop a bio-insecticide to control the Chilo partellus. Aqueous and dichloromethane leaf extracts from Carphalea glaucescens and Gnidia glauca were assayed in vitro for their activities against Chilo partellus anti-acetylcholinesterase activity. Acetylcholinesterase is one of the most efficient enzymes of nervous system which is concentrated at the cholinergic synapses and at neuromuscular synapses where it rapidly hydrolyses the neurotransmitter acetylcholine. Acetylcholinesterase plays a critical role in terminating synaptic transmission so that the next nerve impulse can be transmitted across the synapse. Plants were collected from Siakago, Mbeere North sub-county in Embu County, Kenya. Chilo partellus were obtained from KALRO (Katumani) and the crude enzyme acetlycholinesterase extracted through homogenizination. Activity of the isolated crude enzyme was determined as described by Ellman et al. (1961). Acetylthiocholine iodide was used as a substrate in the assay. The optical density (OD) was measured at 412 nm by spectrophotometer. The experiments were done in triplicates. This study bioassay six extracts concentrations for both aqueous and DCM extracts of C. glaucescens and G. glauca. Cyclone was used as the standard drug and normal control lacked the inhibitor. This design was followed for aqueous and dichloromethane of the two plants. The aqueous leaf extracts of C. glaucescens percent enzyme inhibition was between 86.67% – 47.57% while DCM extracts of C. glaucescens percent inhibition was between 73.64% - 34.54%. Aqueous extracts of G. glauca percent inhibition was between 90.00% - 33.63% and DCM extracts of G. glauca percent inhibition was between 96.97% - 35.09%. Cyclone percent inhibition was 96.97%. Results also showed that the extracts had tannins, phenols, flavonoids, terpenoids, saponins, alkaloids, cardiac glycosides and steroids which have been associated with AChE inhibition activity. Therefore, the study has revealed that aqueous and DCM leaf extracts from C. glaucescens and G. glauca have the potential of anti- acetlycholinesterase activity. Hence the studied extracts can further be purified and developed into plant- derived biopesticides.