TOXICITY OF FRESH AND CRUDE EXTRACTS OF PETIVERIA ALLIACEA (LINNAEUS) LEAF AND ROOT BARK AS FUMIGANTS AGAINST CULEX PIPIENS (LINNAEUS)

Abstract

Mosquitoes are vectors of parasitic diseases such as malaria, lymphatic filariasis, Japanese encephalitis and West Nile Virus. In particular, Culex mosquitoes have been implicated for the transmission of lymphatic filariasis, Brancroftian encephalitis and West Nile Virus. Culex mosquitoes as a major vector of public health importance have been implicated to cause several problems which include resistance to synthetic insecticides. This, then necessitate the search for insecticides of plant origin which are bio-degradable, non-toxic and readily available for man use. This study evaluated the efficacy of fumigants from the oil, powder and freshly harvested parts of Petiveria alliacea against Culex pipiens adult in the laboratory. Powder of P.alliacea leaf and root bark were administered at different doses of 1g, 2g, 3g, 4g and 5g. The oil of P.alliacea leaf and root bark was extracted with absolute ethanol using Soxhlet extractor and redistilled using Rotary evaporator (Rosena, Germany) and tested as fumigant insecticide against adult mosquitoes at 1%, 2%, 3%, 4% and 5% concentration. Mortality was used as indices of insecticidal activities at 30min, 1hr, 1hr30min, 2hrs, 2hrs30min and 3hrs post treatment period. The fumigant effect of the freshly harvested parts was carried out in a 2mx3m room while a white linen was placed on the floor for easy detection of the mosquitoes. The freshly harvested parts were distributed randomly within the room to avoid bias after which the mosquitoes were then introduced. The mortality was recorded at intervals of 30min for3hours. The oil extracts obtained from the leaf and root bark of Petiveria alliacea was analysed using Gas chromatography-Mass spectrometer (GC-MS). All data were subjected to one-way analysis of variance (ANOVA) to check for significance using Duncan’s New Multiple Range Test at P < 0.05 using Statistical Package for Social Sciences (SPSS) version 20.0. The mortality of each bioassay was subjected to Probit analysis to determine 50% lethal concentration (LC50) and the 90% lethal concentration (LC90). Result obtained shows that the oil extracts of P. alliacea leaf and root bark at all concentrations had significant toxic effect as fumigants on the adult mosquitoes with percentage mortality ranging from 75.00%-100% within 2hrs of exposure period (P<0.05) for the leaf extract and 81.67%-100% mortality for the root bark extract. However, the powder was also effective but less efficient than the oil extract and freshly harvested leaf and root bark of P.alliacea with percentage mortality range of 18.33%-60.00% for the leaf powder and 23.30%-71.60% for the root powder within 2hrs post treatment period (P<0.05). The freshly harvested leaf and root bark were also significant showing adult mortality of 55.00%-98.30% after 3hrs exposure period for the leaf and 65.00-100% for the root after 3hours post treatment period. The combined effect of the oil, powder, and freshly harvested parts were also investigated. Results from the phytochemical analysis of the oil showed the presence of phenols, flavanoids, tannins, alkaloids, steroids, glycosides, triterpenoids and saponins. A total of 29 organic compounds were isolated from leaf and root bark oil of the plant. These compounds are responsible for the insecticidal effect on the mosquitoes. These finding suggested P. alliacea extract and freshly harvested parts could be a good source of insecticidal material which may be used for the production of biopesticides.