STUDIES ON SOME BIOLOGICAL AND PHYSICOCHEMICAL PARAMETERS OF ROCK POOL HABITATS OF MOSQUITOES (DIPTERA: CULICIDAE)
Entomological surveys were conducted to determine the biological and physicochemical parameters influencing mosquito breeding in rock pools on inselbergs in Kaduna State. Available rock pools were searched on the inselbergs fortnightly between June and October, 2013 in 21 settlements distributed in 7 Local Government Areas.This covered theState vegetation from the Guinea Savanna to SudanSavanna.A total of 368 rock pools were sampled for mosquito larvaeusing soup ladle dipper (0.105L) from 269 (69.7%) rock pools harbouring mosquito larvae. Biological (microinvertebrates, macroinvertebrates, macrophytes, algae and vertebrates) and physicochemical (depth, surface area, distances to adjoining pools, temperature, pH, total dissolve solid, electrical conductivity, total suspended solid, turbidity, hardness, dissolve oxygen, biochemical oxygen demand, chemical oxygen demand, phosphate, nitrate and alkalinity) parameters of the pools were determined. Polymerase Chain Reaction was used for the identification of mosquito species of Anopheles gambiaes.s. Of the 31,726 mosquito larvae collected, thirteen species in three mosquito genera(Aedes, Anopheles and Culex) including Ae. vittatus (95.71%),An. arabiensis (0.01%), An. gambiae s.s. (0.1%), An. longipalpis (0.0%), An. pretoriensis (0.0%), An. rufipes (0.02%), Cx. albiventris (0.84%), Cx. horridus (0.33%)Cx. macfiei (0.76%), Cx. perfidiosus (1.65%), Cx. pipiens pipiens (0.44%), Cx. simpsoni (0.0%) and Cx. tigripes (0.0%) bred in rock pools. Aedes vittatuswas the most dominant mosquito encountered in all the 21 sampling locations. PCR–based assay revealed 41.6% amplification of the An. gambiaecomplex sample with 38.9% populations belonging to An.gambiae s.s. whilst the remaining 2.6% were An. arabiensis. Up to 58.4% of the An. gambiae complex could not be identified through PCR even after three runs. ANOVA showed that the abundance of mosquito larvaediffered significantlywith pH of the rock pools (p<0.05). Highly significant difference existed between the abundance of mosquito larvae and total dissolve solid, electrical conductivity and alkalinity of the rock pools (p<0.001). The abundance of mosquito larvae did not differ significantly with depth, surface area, total suspended solid, hardness and turbidity of the rock pools (p>0.05).Principal Component Analysis showed that temperature, electrical conductivity and total dissolve solids were paramount for mosquito breeding in rock pool habitats. Low positive correlation (r = 0.394) existed between dissolve oxygen and abundance of mosquito larvae (p<0.001). Strong positive correlation (r = 1.000) exist between biochemical oxygen demand and the abundance of mosquito larvae (p<0.005). Nitrate (r=0.047) and chemical oxygen demand had low positive correlation (r=0.029) with mosquito abundance. Strong positive correlation (r) existed between macroinvertebrate and mosquito abundance(p<0.001) while microinvertebrates correlated negatively (r) with the abundance of mosquito larvae (p<0.05) in rock pools.Chlorophytes had widespread occurrence while Microcystis spp. had the highest percentage positivity, being the only cyanophyte associated with mosquito larvae (p<0.05) in rock pools. Chlorophytum laxumwas predominant amongst other aquatic macrophytes found with mosquito larvae in rock pools. Epidemiologically, the mosquito species encountered are potential vectors of human and animal diseases, hence rock pools should be inspected to incriminate vectors and be incorporated in mosquito control strategies.
Mosquitoes are probably the most notoriously undesirable arthropods with respect to their ability to transmit pathogens that cause human disesases such as malaria, dengue, yellow fever, filariasis, viral encephalitides and other deadly diseases. In several parts of the world, the indirect effect of malaria and other mosquito-borne diseases accounted for more deaths as well as reduced production following work losses (Rueda, 2008). Emergence of new vector-borne disease entities and the resurgence of old ones are caused by several factors, which are ecological changes that increase vector densities, such as climate, immunity status of humans, human and potential vector population densities and the presence of suitable reservoir amongst others (Adebote et al., 2006). The increase in economic activities, tourism and human migration have led to more cases of the movement of both disease vectors and the pathogens they carry thereby increasing the biodiversity of mosquitoes around the world (Manguin and Boete, 2010). Diversity of mosquito breeding environment stems from innate preferences shown by different taxa to the locations and conditions of various aquatic habitats (Adebote et al.,2008). Oviposition preferences of adult females and the ability of immature stages of mosquitoes to adapt to both biotic and abiotic environmental conditions of a given aquatic habitat determine the abundance and distribution of immature mosquitoes (Dejenie et al., 2002). Mosquitoes have diverse habits that allow them to colonize different kinds of environments. The immature stages of mosquito are thus found in a variety of aquatic habitats including ponds, streams, ditches, swamps, marshes, temporary and permanent pools, rock holes, tree holes, crab holes, lake margins, plant containers (leaves, fruits, husks, tree holes, bamboo internodes), artificial containers (tyres, tin cans, flower vases, bird feeders), and other habitats (Rueda, 2008). They can thrive in a variety of water conditions such as freshwater, brackish water and or any water quality (clear, turbid or polluted), except in marine habitats with high-salt concentration. Part of the problems militating against effective and sustained control of mosquitoes and the diseases transmitted by them is the overt advantages available to mosquitoes to breed in diverse aquatic media that are naturally occurring and or the creation of human activities.