MORPHOMETRIC AND MOLECULAR VARIATIONS AMONG MALARIA VECTORS IN AKURE NORTH LOCAL GOVERNMENT AREA OF ONDO STATE, NIGERIA.

Abstract

Anopheles gambiae s. l. and Anopheles funestus are very important vectors of the malaria parasite; Plasmodium species in the Afro – tropical region of the world. Morphometric study was carried out to determine the morphology of the adult female of An. gambiae s. l. and An. funestus and to investigate morphological variations among local populations of these Anopheles mosquitoes found in five different locations in Akure North Local Government Area of Ondo State (Oba – Ile, Igoba, Isinigbo, Ita – Ogbolu and Iju). More than thirty important morpho – taxonomic characters from the head, wing and leg were considered. Variation in morphometrics was combined with molecular identification of the malaria vectors in order to reveal important body parts in identification process and to understand the population structure in the study area. The physicochemical factors associated with the breeding of malaria vector was observed for the period of twelve (12) months (Oct. 2018 – Sept. 2019) to understand the relationship between some selected factors and breeding of malaria vector in the study area. The five selected physicochemical factors include electrical conductivity, pH. total dissolved solid, temperature, and dissolved oxygen. One-way ANOVA test was used to test the significant differences between each of this physicochemical parameter across the study area, while Pearson correlation analysis (r) was use to study the relationship between these parameters and the distribution of malaria vectors. Regression analysis was use to check the linear regression (R2 linear) value between the study parameters and abundance of Anopheles mosquitoes in the study areas. Two species of malaria vectors were morphological identified from the study area, these two species belong to the complex of Anopheles gambiae s. l. and An. funestus group. The electrical conductivity of the immature stages habitats of Anopheles mosquitoes was not significantly different across the study areas (p>0.05). The highest mean of electrical conductivity was recorded from Ita – Ogbolu (263.25± 36.9), while the lowest was recorded from Isinigbo (254.67±37.89). Electrical conductivity was significantly correlated with the abundance of An. gambiae s. l. and An. funestus group larvae in the area, r = 0.840 and 0.843 respectively (p = 0.001; R2 linear = 0.691). The pH of Anopheles mosquitoes’ habitats was not significantly different in all the selected study sites (p>0.05). The highest pH was found in Igoba (7.09±0.18) and the lowest was recorded at Ita – Ogbolu (6.68±0.09). The pH was found to be negatively correlated with the abundance of An. gambiae s. l. and An. funestus larvae with correlation coefficient value (r) of – 0.530 and – 0.470 respectively (R2 linear = 0.552). Total dissolved solid was positively correlated with the abundance of Anopheles larval. The correlation coefficient (r) value of total dissolved solid was weak (r = 0.219). The highest mean was recorded in Igoba (17.50±1.46). There is slightly increase in Anopheles mosquitoes larval has total dissolved solid increases (R2 linear = 0.048). The abundance of Anopheles mosquito’s larval increases while the dissolved oxygen (DO) decreases in the larval habitats, the linear regression square value (R2) = 0.552. Dissolved oxygen was not significantly correlated with An. gambiae s. l. and An. funestus larvae abundance, correlation coefficient (r) value = – 0734 and – 0789 respectively, there was no significant difference across the study area (p>0.05). The range of temperature recorded was 23.1 – 28.7°C. The temperature was found to be significantly correlated with An. gambiae s. l. and An. funestus larvae from the study sites, r = 0.74 and 0.76 respectively. Anopheles larvae increase has temperature increases (R2 linear = 0.582). The study of morphometric was significant difference in most of the measured characters on females An. gambiae s. l and An. funestus based on their localities. Statistically, the body length of mosquitoes from these locations showed no significant different (p>0.05). The palp length and broadness of the pale band on palp varies among the species of An. gambiae s. l. and An. funsetus. An. gambiae s. l. was found to have broader pale bands and within these species the degree of broadness varies across the five locations with the species from Isinigbo (0.27mm) appearing to have the broadest apical pale band. The wing characters vary across the five locations with An. gambiae species from Isinigbo having more broad wings (length = 4.04mm and width = 1.17mm) compared to the same species from Ita – ogbolu (length = 2.70mm and width = 0.69mm). Among the An. funestus, the wing of the species collected from Igoba was found with broader wings (length = 3.03mm and width = 0.71mm). Among 750 individual Anopheles gambiae s. l. identified using Polymerase Chain Reaction (PCR method), 433 samples which represent 57.73% were Anopheles gambiae s. s. while 97 (12.93%) samples were Anopheles arabiensis. Anopheles leesoni was the only member of Anopheles funestus group identified in the study area. Anopheles leesoni mosquito identified in the study location were 182 which represent 24.27% of the total Anopheles mosquito species identified using molecular method. The study of physicochemical parameters and its association with immature stages of Anopheles mosquitoes’ habitats have revealed different levels at which aquatic stage of this vector prefer and survive in their habitat. Manipulation of these ecological factors can help in managing these vectors of parasitic diseases. Morphometric analysis confirmed the existence of some variations in the morphological characters among local populations of malaria vector (An. gambiae s. s., An. arabiensis and An. leesoni) in the five selected locations in Akure North. This shows that some of these morpho – taxonomic characters used in species identification keys are sometimes unreliable and could result in species discrimination problems most especially among species complex or group that share closely related morphological characters. The report of this research study is very important in identification and controlling malaria vectors in the study area.