Mosquitoes are implicated as ‘Public Enemy No. 1’ (World Health Organization, 1996). Over 4500 species of mosquitoes have been recorded to be distributed throughout the world in about 34 genera; most of which belongs to the Anophelinae and Culicidae family (Ghosh, Mukherjee, Dutta, Roy, & Mondal, 2013). Malaria is transmitted by female Anopheles mosquito; Aedes aegypti and some other mosquito species are responsible for the transmission of Dengue and Chikungunya while Culex mosquito specifically have been implicated in the transmission of Lymphatic Filariasis, Bancroftian encephalitis, and West Nile Virus (Yerpude, Jogdand, & Jogdand, 2013) These diseases not only cause mortality or morbidity among humans but also cause social, cultural, environmental, and economic loss of the society (Ghosh et al., 2013). Culex pipiens and Culex quinquefasciatus are the two Culex species with the most important public health importance capable of transmitting bancroftian encephalitis caused by West Nile virus and Japanese encephalitis. However, there are several other species of Culex that are of public health importance. The approach to combat this disease largely relied on interruption of the disease transmission cycle by either targeting the mosquito larvae through spraying of stagnant waters that serve as breeding sites or by killing the adult mosquitoes using insecticides. The vector borne control strategies in Nigeria include the effective combination of insecticide treated nets and indoor residual spraying which has been an adequate control measure. Mosquito resistance to the currently used insecticides, the emergence of multi drug resistant strains of parasites has escalated the malaria problem in the affected countries (Oduola, Obansa, Ashiegbu, Otubanjo, & Awolola, 2010).
Vector control is a major component of the World Health Organisation (WHO) global mosquito-borne diseases intervention strategy, and it aimed primarily at the indoor residual spraying and the use of insecticide-treated nets. Recently, these control measures have limitations, which include insecticide resistance as well as encumbrance in achieving high scope (Luz, Pinheiro, Silva, Monteiro, & Prediger, 2016). Organochlorines, Carbamates, Organophosphates, and Pyrethroids have been recorded by WHO to all have been resisted by Culex quinquefasciatus. In Nigeria, the susceptibility status of many mosquitoes in to Dichlorodiphenyltrichloroethane (DDT) and other classes of insecticides including organochlorine, organophosphate, carbamates, and recently pyrethroid in different zones has been well documented (Awolola et al., 2007). Thus, synthetic insecticides have caused several problems including the development of resistant insect strains, ecological imbalance, harm to mammals, and non-target arthropods. These setbacks of the hitherto developed insecticides have made researchers in these areas to effortlessly find and produce environmentally safe alternatives. As part of traditional healthcare, medicinal plants have been used in most parts of the world for thousands of years (Ajayi & Ojelere, 2010). The use of these plants by man in the treatment of ailments and diseases is a common practice in the developing countries. However, botanical insecticides may serve as suitable alternatives to synthetic insecticides in the future, as they are relatively safe, bio-degradable, and readily available in many parts of the world. Researchers have resorted to plant extracts as potent sources of natural bio-insecticides (Bekele, Petros, Tekie, & Asfaw, 2014). Although insecticides of plant origin have been broadly used in the control of agricultural pests, a very limited extent has been used against insect vectors of public health importance. Although various compounds of plant sources have been documented as insecticides and larvicides, there is still a vast scope for the discovery of more effective plant products particularly in the indigenous flora of lesser studied countries like Nigeria.
Petiveria alliacea L. belongs to the family Phytolaccaceae and is considered to be the most primitive family of the Caryophyllales (Cronquist, 2002). There are over 17 genera and 120 pan-tropical species in this group which are mostly found in North and South America (Barroso, 2004). Petiveria alliacea commonly known as guinea henweed (Tarzon plant) is known for its strong acrid and pungent smell, in the rural areas where these plants are found, it has been said that its pungent smell are very toxic to mosquitoes, and mosquitoes are less seen in the same areas where this plant are found. All parts of the P. alliacea plant are useful and to date several biologically active compounds have been secluded. Most eminent among these constituents are sulfur compounds (similar to allicin, found in garlic and onion), flavonoids, triterpenes, steroids, saponins, polyphenols, fredelinol, pinitol, and allantoin (De Andrade et al., 2012). Crude extracts of P. alliacea have been shown to exhibit diverse neuropharmacological benefits including cognitive enhancing activity, as well as antinociceptive, antidepressant, anxiolytic, and anti-seizure properties (Luz et al., 2016). Pentane extracts of the roots have revealed the presence of several volatile constituents such as benzaldehyde (48.3%), dibenzyl-disulfide (23.3%), dibenzyl-trisulfide (9.4%), and stilbene (8.1%). Whereas, benzaldehyde (54.8%), benzyl-thiol (20.3%), and dibenzyl-disulfide (18.0%) have been detected in the inflorescences. Compounds isolated from extracts (water, methanol, ethanol) of the entire plant include dibenzl-trisulfide, benzyldehyde, benzopyran astilbin, and coumarin which, based on in vitro studies, have inhibited the growth of leukemia cells and several other strains of cancerous tumor cells (Alegre & Clavo, 2007). Dibenzyl-trisulfide has also been reported to have a toxic effect on the adult sweet potato weevil (Cylas formicarius) and adult coffee borer beetle (Hypothenemus hampei) (Schmelzer & Gurib-Fakim, 2008). Antifeedant activity of leaf extracts was recorded against the grasshopper Zonocerus variegatus, and an allelopathic effect on germinating seeds was also noticed. Dibenzyl-trisulfide was not active on Bacillus subtilis and had little inhibitory effect on Cladosporium cucumerinum (Schmelzer & Gurib-Fakim, 2008). However, when dibenzyl trisulphide was transformed to methyl-benzyl-sulfonic anhydride it was found to be effective in preventing the growth of Bacillus subtilis, Pseudomonas fluorescens, and Cladosporium cucumerinum. In vitro studies of the growth of seeds of several crops revealed that methanol and dichloromethanol leaf extracts had an allelopathic effect (Schmelzer & Gurib-Fakim, 2008). Seeds sown in the soil were not affected. Furthermore, Petiveria alliacea has been shown to accumulate nitrates and has caused nitrate poisoning in cattle (Schmelzer & Gurib-Fakim, 2008). Therefore, these plants can be grown in the rural communities as well in the urban community to mitigate the incidence of mosquitoes in the environments. Scientifically, there is paucity of literature on these plants to control mosquitoes. This opened an insight of studying these plants as bio-pesticide against mosquito population. This present research focuses on the fumigant toxicity of Petiveria alliacea leaf and root bark powder on the mortality of adult Culex quinquefasciatus, these plants has been said to possess various medicinal properties including antibacterial, antifungal, and anticancer constituents. The effectiveness of this plant powder against mosquito can determine how important it might be in our environments.