Effect of Petroleum Products on the Larvicidal Activity of Aedes Mosquitoes in Ika North-East LGA, Delta State, Nigeria

Mosquitoes are among the most important medical vectors transmitting diseases worldwide. This being that they drive pathogens responsible for disease organisms in prey co-existence. According to Powell (2018), a number of diseases are transmitted by mosquito species causing severe burdens in human and veterinary concerns. Mosquito-borne diseases such as those transmitted by the Aedes species include yellow fever, dengue fever, chikungunya fever, and Zika virus. The reported cases and mortality records as a result of Aedes mosquitoes attack are immeasurable. However, valid records of reported cases and mortalities are described in the bulletin of the World Health Organization (WHO, 2009). The WHO has in 2007, 2010 and recently marked Nigeria as a country with the highest risk of yellow fever in Africa with a greater percentage of non-immune human population been reported to be at high risk of outbreaks caused by mosquitoes in Africa (WHO, 2015; WHO, 2016b; NCDC, 2019). This is occurring in eleven countries in Africa with the exception of Nigeria where the implementation of routine immunization as well as frequent vaccination is on the rise (WHO, 2017).

Mosquito transmitted viruses are not only known to cause mortalities but also affect the economic standards of any nation. In 2013, the infection rate of yellow fever in Africa was over 380,000 cases, with death estimated at 80,000 (Garske et al., 2014). The cost of attending to these viruses is expensive compared to the cost of living of an average African. This calls for immediate intervention not only on the use of vaccines targeting the infected individuals but also the vector causing the diseases. Aedes aegypti and Aedes albopictus include the prominent vectors species causing the spread of viruses in the world. The WHO has in 2009 pointed out the first occurrence of Ae. albopictus in Nigeria in 1991, after the outbreak of sylvatic (jungle) fever in several rural villages in Delta state. There has been a major epidemic threat in Lagos, one of which is the major cities in Nigeria, where about one-third of the population is at risk as a result of species development due to the availability of suitable breeding sites (WHO, 2009). Re-emergence of yellow fever occurred in Nigeria after the last case in Kano State, in 2000. In 2017, the yellow fever virus resurfaced with 341 suspected cases reported from 16 states (Abia, Anambra, Borno, Edo, Enugu, Kano, Katsina, Kogi, Kwara, Kebbi, Lagos, Nasarawa, Niger, Oyo, Plateau, and Zamfara states). Of these states, 6 states (Kano, Kebbi, Kogi, Kwara, Nasarawa and Zamfara) reported confirmed cases of the disease (WHO, 2017). Presently, Delta State was included due to the outbreaks of the yellow fever virus and this calls for swift intervention on the vectors while other intervention is targeted on the disease.

Aedes mosquito species can breed in various habitats, including puddles, ditches, tree holes in forests, and other habitats associated with human dwelling, as reported by McBride et al. (2014). They normally breed in transient water-contained habitats. These include collections in tree cavities, leaf axils, bamboo stumps, rock pools and artificial containers (including tin cans, coconut shells, water storage containers, discarded vehicle tires, broken earthen and ceramic wares). These breeding habits keep them in close proximity with man, facilitating disease transmission. They lay their eggs just above the water level. As a result, water waves/ripples or increases in water volume led to the hatching of viable eggs. Aedes mosquitoes are characteristically dark black in color, with patches of white or silver markings on their bodies. They previously dominated the tropical and sub-tropical regions, but have over time spread to all continents, excluding Antarctica (Bonizzoni et al., 2013). According to Ezihe and Chukwuekezie (2018), the spread of the mosquito was aided by an unhealthy environment due to anthropogenic activities. Unlike other mosquitoes, the Aedes mosquitoes are diurnal, functioning at special hours of the daytime. Studies also revealed that with the extended urbanization around the world, the preference of mosquitoes for artificial containers for breeding has increased to a large extent, which implies that the distribution of larval mosquitoes is greatly influenced by human ecology (Chen et al., 2009; Li et al., 2014). Thus, many of the studies have been carried out to examine the mosquito larval diversity in artificial breeding sites. Studies have reported that the species of mosquitoes such as Aedes aegypti and Aedes albopictus generally breed in artificial containers (Chen et al., 2009; Adeleke et al., 2008; Suganthi et al., 2014). It has also been contemplated that in the urban areas, the environment has a major effect on the incidence of Aedes albopictus larvae (Li et al., 2014). In addition, studies have also observed the existing and disappearing species of mosquitoes along with their pattern of distribution (Asha et al., 2014). It has been reported that artificial containers provide a good habitat for the vector of Dengue (Rajesh et al., 2013).

Aedes mosquitoes are more adapted to urban environments, especially to human habitation. The control of vectors has been the recommended approach to combating disease spread which could come in several perspectives, including intervention targeting the immature stages (larvicides) and likewise from the adults (adulticides) as the case may be. The control has involved the use of chemical compounds to prevent the development of adult mosquitoes in aquatic environments (Yang et al., 2017). Vector control is the primary form of prevention of these frequently occurring diseases since this vector reproduces easily, where there are small collections of water at home and peri-domestic habitats of urban areas. Thus, the participation of the population in the daily care with stagnant water around or inside their houses is of fundamental importance to avoid the biological cycle of this vector (Savage et al., 1992; Trillia et al., 2016). The most effective control strategy for mosquito-borne diseases is to control the mosquito at either the larval or adult life stages (Carvalho et al., 2017). Controlling them at the larvae stage is the best. Recently, studies on the control of mosquitoes have focused on their saliva as vaccine candidates (Jessica, 2018). It is well known that the saliva of mosquitoes houses various pathogens causing disease. Other control interventions targeting the larvae and pupa have focused on the use of industrialized insecticides, bacteria (Bacillus thuringiensis), understanding the biting cycle, the biological cycle, use of plants extracts, powders, and essential oils as viable control options of these vectors (Fillinger et al., 2009; Kandyata et al., 2012; Goellner et al., 2018; Mazigo et al., 2019).

The use of insecticides in the control of the vector that transmits these arboviruses is one of the preventive measures against the disease scourge (Jirakanjanakit et al., 2007). Four classes of insecticides which include organophosphates, carbamates, organochlorines, and pyrethroids are widely employed in these vector control programs (Marcombe et al., 2009; WHO, 2009). Resistance to multiple insecticides (pyrethroids and organophosphates) has been reported in Aedes aegypti in South-East Asia (Jirakanjanakit et al. 2005). This presents a serious problem that needs urgent attention on the next point of action. However, insecticide resistance to Aedes mosquitoes in Delta State has not been reported. The insecticide status of Aedes albopictus and Aedes aegypti is poorly documented in Nigeria (Ransom et al., 2010), especially Aedes albopictus, owing to its recent introduction in Africa. There is also a dearth of information on the insecticide susceptibility status of yellow fever virus in Awka South area of Anambra State, Nigeria, despite the dense population of monkeys in this area as reported by Savage et al. (1992). In their study, Aedes aegypti and Aedes albopictus showed high strength of insecticide resistance, this presenting a major problem to the control of yellow fever and other arboviral diseases in Nigeria (Savage et al. 1992).

The control of mosquito larvae has commonly relied on the use of synthetic insecticides and repellents, but treatments with such chemicals are expensive, show scarce efficacy and have a strong environmental impact associated to relevant human health risks (Nkya et al., 2013). For these reasons, alternative controls using petroleum products, oils and repellents are now being appreciated. Although, the use of petroleum products in the control of Anopheles mosquitoes has been reported (Ekedo et al., 2019). But information on the use of essential control agents such as petroleum products in the control of Aedes mosquito larvae is lacking. Thus, the need for this study to determine the efficacy of the use of petroleum products in the control of Aedes mosquitoes. This enhances the relevance of mosquito vector control, especially in areas where the outbreak of diseases is occurring and on the rise, and helping policy makers in predicting the best control options for diseases caused by Aedes.

The outbreak of arboviral diseases including Zika, Dengue, Yellow Fever, Chikungunya, among others, have always been associated with the Aedes mosquito species. The recent yellow fever outbreak in Delta State, Ika North East local government to be precise, has triggered the effort on controlling Aedes mosquitoes not only in the affected local government but in other areas where the mosquito exists. Despite the ongoing vaccination programme, the report of diseases is still on the rise. Thus, studies on the efficacy of using petroleum products as larvicides were conducted to add up to the existing treatments. A high mortality record was observed in all the highest concentrations of treatments. Although, 0.005% of kerosene and petrol recorded lowest mortality. The difference in the mortality recorded in the highest concentrations was not significant. Similarly, no significant difference was observed in. 0.005% of kerosene exposed to pupa and larva of Aedes The mortality recorded in this study is in agreement with those reported by Lee et al. (2006) where complete mortality was recorded in Aedes mosquitoes exposed to various concentrations of Citrus bergamia, Cuminum myrrha, and Pimenta racemose. The mortality recorded could be due to the petroleum products that block the respiratory tract of larvae and pupae. Residual effects of treatments may have led to the death of the resting stage, causing elongation of the pupae body.

The use of imidazolium salts was effective in causing mortality until the 15th day after larvae exposure (Goellner et al., 2018). But in this, high mortality was recorded from 30 to 80 minutes. This predicts effective vector control of the disease that may likely result from Aedes. Efforts on integrating adult control intervention on the species could be diverted to the immature stages (Fillinger et al., 2009). The time mortality recorded in this study is in agreement with those recorded in the study of Ekedo et al. (2019) where petroleum products caused complete mortality. The highest concentration in this present caused complete mortality compared to the lower concentrations, but the studies of Ekedo et al. (2019) observed that highest concentration of petrol had no larvicidal activity on Anopheles gambiae s.l. mosquito larvae at 20 mL within 5 minutes of treatment, while the lowest concentration of premium motor spirit yielding 100% mortality was recorded at 20 mL within 20 minutes. The differences in mortality may be ascribed to differences in mosquito species used. It may equally be due to that species of mosquitoes in their location were exposed to oil spilled habitats. Similarly, the studies of Ekedo et al. (2019) observed that the highest concentration of kerosene did not produce larval mortality at 60mL within 15 minutes of treatment, but the lowest concentration caused complete mortality at 20 mL within 30 minutes.

The Aedes Mosquito larvae and pupae exposed to the petroleum products were all susceptible. It is not certain if resistance may arise as a result of misapplication of the products if approved as a larvicidal agent. Over the years, the use of insecticides has recorded high resistance in adult Aedes mosquitoes (Moyes et al., 2017; Demok et al., 2019). Due to the high rate of resistance of the Aedes larvae and pupa, there has been a great increase in the infection and death rate of humans in Africa and all over the world. Potential breeding sites could be treated with petroleum products such as kerosene, petrol, kerosene and petrol to reduce larvae and pupae abundance. According to Snr et al. (2011) abandoned and disposed tires can stay for a very long time in harboring the larvae and pupa of Aedes mosquito. Moreover, Bi et al. (2007) and Sripugdee et al. (2011) also stated that the weather conditions inside discarded tires and containers, such as cool temperature, humidity, and reduced light, create a suitable environment for Aedes larvae mosquito breeding. One of the best methods suitable for the control of the diseases caused by the Aedes mosquito is to control the immature stages of the Aedes mosquito through the introduction of larvicides to terminate the eggs, larva and pupa before their development to adults. Controlling the life stages of these species will lessen the distribution and abundance of the Aedes population. Hence, the reduction of the diseases they cause. Projecting the highest treatments 0.02% with high records of mortality in this study shows that for 1000L of water twenty times the one milliliter of kerosene alone, and kerosene and petrol used in this study will cause larvae and pupae mortality. Similarly, time mortality may fluctuate by 5 minutes in larger scale of treatment.

The LC₅₀ of kerosene alone, kerosene and petrol mixture on larvae was lower at 0.0021 mL and LC₉₅ was estimated to be 0.0088 mL, respectively. Kerosene alone and kerosene and petrol mixture were effective on Aedes mosquito larvae at concentrations ranging from 0.005 ml to 0.02 ml within 80 minutes of exposure. The lethal concentrations (LC₅₀ and LC₉₅) recorded in this study were lower than those reported by Ekedo et al. (2019) for Anopheles gambiae with similar treatments. In the pupae group, The LC₅₀ and LC₉₅ of kerosene and petrol mixture were lower at 0.0037 mL and 0.0050 mL, respectively. This present study shows that the larvae and pupa of the Aedes mosquito were susceptible when introduced into various concentrations of petroleum products. Kerosene and petrol are locally available products affordable by any household in Nigeria and effectively adopting these products for Aedes population control in their potential habitats such as plastic containers, abandoned tires, pots, gutters, ditches amongst others, would go a long way to lessen the threat posed by the vector and disease burdens.

This study has shown that the highest concentrations of kerosene and petrol in single and mixed forms caused complete mortality in Aedes mosquito larva and pupae. Mortality of larvae and pupae was recorded within 30 to 80 minutes of exposure irrespective of concentration. Higher concentrations of kerosene alone, and kerosene and petrol were best at controlling larvae of Aedes while higher concentrations of kerosene and petrol mixture were best at controlling pupae. Therefore, adopting the treatment of potential habitats with these products and implementing house to house campaigns on their use to eliminate the immature stages of Aedes mosquitoes would reduce outbreaks of disease to a considerable limit.