Abundance of Mosquito Species Within Sokoto Metropolis
Chapter One
Objectives
General objective
To determine the Culicine mosquito species diversity in Sokoto Metropolis, Nigeria.
Specific objectives
- To determine the Culicine species composition in Sokoto Metropolis.
- To determine the blood meal sources of Culicine mosquitoes in Sokoto Metropolis LGA.
- To determine the human vector contact/human Blood Index (HBI) for Culicine mosquitoes in Sokoto Metropolis.
CHAPTER TWO
LITERATURE REVIEW
Biology and life cycle of Culicine mosquitoes
Culicine mosquito just like other insects consists of head, thorax, and abdomen. They have long, slender, legs and proboscis-style mouthparts for feeding on vertebrate blood or plant fluids. Female mosquitoes have maxillary palpi that are shorter than the proboscis and short hairs on the antennae. The males have long palpi with numerous long setae, but not swollen apically like those of Anophelines and long hairs on the antennae giving these appendages a feathery appearance.
The scutellum has three lobes with setae confined to each lobe (Becker et al., 2010). The wing veins are usually entirely dark-scaled, but speckles or patches of white or yellow scales are present in some species. The abdominal terga and sterna are thickly covered with scales, which distinguishes them immediately from almost all Anophelines. Adults stand with the body parallel to the surface on which they are resting. All Culicine larvae have a respiratory siphon, the dorsal and ventral abdominal setae arise separately and usually without basal sclerites, and the mouth brushes are composed of numerous, usually slender filaments. The Mosquito’s slender legs are attached to the triangular thorax. The abdomen is long and narrow (Becker et al., 2010). Only the female mosquitoes are blood feeders, requiring a high quality protein meal before they oviposit/breed. Since the mosquitoes are well adapted for finding hosts, the females can move quickly from one blood meal to another, and when injecting their saliva, can inject pathogens picked up from other hosts and thus efficiently transmitting disease.
Culicine mosquitoes are holometabolous insects. They complete their life cycle through the four stages including; egg, larva, pupa, and adult (figure 2.1). The mating of most mosquitoes takes place when females enter swarms of flying males. It usually occurs at low light intensities especially in the evening and morning (Becker et al., 2010). The swarm consist of only few or up to several thousands of male mosquitoes (Howell & Knols, 2009; Becker et al., 2010). Copulation requires a complex merging of the male and female reproductive structures. It usually takes less than half a minute for the male to deposit the spermatozoa in the bursa copulatrix of the (Clements, 1992). After copulation, the females have to take a blood meal to complete the egg development. They lay between 50 and 500 eggs in 2–4 days (or longer in cool temperate climates) after taking a sufficient blood meal (Becker et al., 2010). Females deposit their eggs onto the water surface in batches (Culex). All mosquitoes need aquatic habitats for their development, although Aedes and Ochlerotatus species can lay their eggs in moist soil. Water temperature plays a fundamental role in the hatching process of the floodwater mosquito. Premature hatching during cold weather would greatly delay the development of the larvae, since the process is very temperature dependent (Becker et al., 2010). After hatching, they pass through four larval instars, pupal stage then transformation into an adult.
The larval body is divided into three distinct parts; the head with mouthparts, eyes and antennae, the broader thorax and the abdomen, which is, composed of seven almost identical segments and three modified posterior segments. The larvae of mosquito are an aquatic stage feed on bacteria, yeasts, protozoa and particulate organic matter in the water. It has four instars, which takes 7-15 days to pupate in tropical areas. These period depends mainly on the temperature (Bayoh & Lindsay, 2004; White et al., 2011). The pupa stage usually lasts for about 2 days, though this period can be reduced or extended depending on the water temperatures at the breeding site. During the pupa stage, the process of metamorphosis takes place. Some larval organs are histolysis, whilst the body of the adults is formed through the development of imaginable disks. At high temperatures, most of fourth instars larvae die during pupation, or pupae simply fail to emerge into adults (Bayoh & Lindsay, 2004; White et al., 2011). Pupa is non-feeder stage. The adult emergence occurs when gas is forced between the pupal and the pharate adult cuticle, and into its midgut (Becker et al., 2010). Within a few minutes, it is able to fly when the soft cuticle has sclerotized. However, 1–1.5 days or more is required for males and females to adjust their metabolism (Gillett, 1983). The adult stage is responsible for the great impact on human and animal (Borkent & Grimaldi, 2004).
CHAPTER THREE
MATERIALS AND METHODS
The study area
A cross-sectional research was conducted in Sokoto Metropolis Area, Sokoto State, Nigeria, within the period of January–December 2020. Sokoto Metropolis. The local government area has a land mass of 331 km2 and comprises of a total of 360,268 people at the 2006 census. The area thus encompasses various sectors of the work force: the government house, various manufacturing companies, educational institutions, small firms etc. The climate in the study area is tropical with two distinct seasons, the rainy season (April–October) and dry season (November–March) with slight variations from year to year. The annual rainfall varies from 1150 mm in the northern parts to 2000 mm in the southern area; the state generally enjoys luxuriant vegetation. The vegetation consists of coastal forest and mangrove swamp forest in the south, moist lowland forest, and the forest savannah in the north.
CHAPTER FOUR
DATA ANALYSIS AND RESULTS
The anthropogenic activities of the study area as presented in Table 1 show that these activities vary significantly across the locations. Oja-Oba a predominant market in the study area is filled with carelessly disposed water-holding materials, puddles, gutters, and runoffs, and FUTA which is predominantly academic environment consists of various classrooms, administrative buildings, student hostels, and small businesses. This location (FUTA) contains lots of peridomestic containers such as can, plastic, Styrofoam, bottles, gutters with stagnant water, puddles, and runoff which encourage massive populations of mosquito developing stages. Sokoto road and Seebi on the other hand are considered semi-urban area comprising of small businesses along the road, supermarkets, and hotels with runoffs, gutters, and puddles. On the contrary, Alagbaka is an urban area that comprises of industrial buildings, government houses, hotels, event centers, restaurants, estate housing, and other various infrastructures.
CHAPTER FIVE
DISCUSSION OF FINDINGS AND CONCLUSION
Discussion
Generally, it was observed from this study that locations such as FUTA and Oja-Oba that correspond with high relative abundance of mosquito larvae are areas with high anthropogenic activities such as school and market where there is high density of peridomestic containers such as plastics, cans, and Styrofoam. These peridomestic containers serve as habitats for mosquito breeding especially during the raining season. In contrary, locations such as Alagbaka and Seebi where low relative abundance was recorded are noted for good drainage system, good sanitation, and well-organized structures. These factors might contribute to low density of mosquito obtained in these areas. In addition, the significant difference of mosquito density across the locations may have been as a result of the disparity in social and economic activities within the locations that would encourage or discourage mosquito breeding. Hence, areas with high anthropogenic activities may have high population density of mosquitoes while areas with low anthropogenic activities may have low population density of mosquitoes.
It was further observed that physico-chemical parameters of the mosquito habitat determine mosquito oviposition and abundance. The physico-chemical parameters where optimal breeding were noted in Sokoto Metropolis Area include pH 7.16, temperature 28.6 °C, dissolved oxygen 3.84 mg/l, and conductivity 68.6 μs. The optimal pH recorded in this study has also been reported by other authors (Adebote, Oniye, Ndams, & Nache, 2006; Afolabi, Ndams, Mbah, & Sokoto, 2010; Okogun, Anosike, Okere, & Nwoke, 2005). The authors reported that pH range of 6.8–7.2 and 7.0–7.4 were suitable for the weakening of the mosquito egg shells for the emergence of its first instar larvae and that pH less than 5.0 and higher than 7.4 have fatal effects on survival of mosquito species. Optimal temperature suitable for breeding (28.6 °C) in Sokoto Metropolis Area also concurred with the reports of Clement (1992). The author reported that temperature and precipitation are keen factors which affect the abundance and distribution of mosquito in various habitats. A recent study conducted by Afolabi and Aladesanmi (2018) also shows that the optimal temperature that favored breeding in Sokoto Metropolis North is 28 °C while mosquito breeding is not likely to be found in temperature below 25 °C.
Of the 11 species of mosquito species observed in this study, Cx. andersoni and Ae. aegypti had the highest abundance and distribution in all locations. This suggests that these two species are cosmopolitan and breed indiscriminately in all habitats. The dominance of Aedes and Culex mosquitoes had also been reported by Simon-Oke, Afolabi, and Olofintoye (2012) in Ekiti State, Nigeria. Likewise, Adeleke (2010) had earlier reported that Aedes mosquitoes prefer man-made larva habitats such as old tyres, clogged gutters, and animal pet bowls as breeding sites. These man-made habitats were abundant in the Sokoto Metropolis Area. In contrary, Anopheles gambiae was observed to be sparsely distributed and with relatively low abundance in FUTA and Sokoto road. This low abundance of Anopheles might be due to their innate characteristics of endophagy (indoor feeding) and endophilic (indoor resting). Their association with human dwellings might suggest that Anopheles mosquitoes are selective breeders that breed in containers with clean water within and around human houses, for easy accessibility to host.
Conclusions
The four mosquito genera (Aedes, Anopheles, Culex, and Toxorhynchites) with the exception of Toxorhynchites encountered in Sokoto Metropolis Area are well-known vectors of parasites and help in transmission of diseases such as yellow fever, malaria, and filariasis. All these diseases are associated with high morbidity and mortality. Recently, resurgence of yellow fever has been reported in some part of Nigeria. This suggests that a sustainable public health campaign on vector management and control should be intensified in Nigeria.
References
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