ECOLOGICAL NICHE MODELLING OF ANOPHELES GAMBIAE (GILES) IN SOUTHWEST NIGERIA AND EFFICACY OF TWO BOTANICALS IN VECTOR CONTROL

Abstract

Mosquitoes are key vectors notable for the transmission of several diseases with species such as Anopheles gambiae is a species known to transmit the pathogens that causes malaria and filariasis respectively. This project was carried out to estimate the overall present-day (2019) and year 2050 distribution of An. gambiae across South-west Nigeria using Ecological Niche Modeling (ENM). The project also determined the potency of the ethanolic leaf extracts of Clerodendrum volubile and Petivera alliacea on the different life stages of An. gambiae.The data for ENM were sourced from literatures that have reported the presence of the above-named mosquitoes species in locations within the study area. Fresh leaves of the two plants (C. volubile and P. alliacea) were obtained from Ondo Town, air dried in the laboratory, pulverized, soaked in ethanol and then extracted using rotary evaporator. Each plant extract was formulated into concentrations of 50, 100, 200, 400 and 800 mg/l of water or ethanol depending on the bioassay. Various life stages of the mosquitoes were exposed to the different concentrations of the plant extracts to determine their oviposition deterrent activities, larvicidal, pupicidal, adulticidal, and repellency effects on the insect stages. Ecological niche modelling data were processed and analysed using Aeronautical Reconnaissance Coverage Geographic Information System (ArcGIS), ENM tools and Maximum Entropy (MaxEnt). The results from the bioassays were subjected to one-way analysis of variance (ANOVA) to check for significance in their mortality rate and Probit analysis to get their respective lethal concentrations using Statistical Package for the Social Sciences (SPSS) version 20. Level of significance was established between all the concentrations of the plant extracts used (p<0.05). More than two-third of the study area was observed to be favourable for An. gambiae population. This favourability ranged from very low to very high. The land use land cover (Sw_lulc) proved to be a key contributor to the habitat suitability of An. gambiae. Increased favourability of the 3 study area is predicted for future scenarios. The highest concentration of C. volubile and P. alliacea had oviposition active index of -0.60 and -0.76 respectively. Larval mortality of 58.33 and 100% were recorded for 800mg/l concentration of C. volubile and P. alliacea after 24 h of exposure. However, the same concentration for both plant extracts caused 100% mortality after 48 and 72 h of exposure. The pupicidal activity of 800mg/l of C. volubile and P. alliacea were 51.67 and 85% after 24 h but the same concentration caused 100% moratlity after 72 h of exposure. The adult mortality for both plant extracts were 16.67% at the highest used concentration after 30 minutes of exposure. Nevertheless, after 120 minutes of application the same concentration of C. volubile and P. alliacea extracts caused mortalities of 75 and 100% respectively. Clerodendrum volubile extract provided 100 % protection of against An. gambiae bites for 90 minutes while P. alliacea lasted for about 120 minutes Petivera alliacea recorded the lowest LC50 and LC90 values for all the various life stages. This study revealed that the study area is a favourable habitat for An. gambiae and will even be more favourable in the future. The plant extracts used in this study have proven to be effective in controlling different life stages of An. gambiae. Hence, they can be incorporated into integrated management of mosquitoes.