Background
Mosquitoes are key vectors for the transmission of several diseases. Anopheles gambiae is known to transmit pathogens of malaria and filariasis. Due to several anthropogenic factors such as climate change and population growth leading to diverse land use, their distribution and disease spreading pattern may change. This study estimated the potential distribution and climatic suitability of An. gambiae under the present-day and future conditions across Southwest Nigeria using Ecological Niche Modelling (ENM). The future scenarios assessed were based on two general circulation models (GCMs), namely community climate system model 4 (CCSM4) and geophysical fluid dynamics laboratory-climate model 3 (GFDL-CM3), in two representative concentration pathways (RCP 2.6 and RCP 8.5).
Methodology
The occurrence data were obtained from literatures that have reported the presence of An. gambiae mosquito species in locations within the study area. Ecological niche modelling data were processed and analysed using maximum entropy algorithm implemented in MaxEnt.
Result
Fifty-five (55) unique occurrences of An. gambiae were used in the model calibration after data cleaning. Data analysis for the present-day habitat suitability shows that more than two-thirds (81.71%) of the study area was observed to be suitable for An. gambiae population. However, the two future GCMs showed contrasting results. The CCSM4 models indicated a slight increase in both RCPs with 2.5 and 8.5 having 81.77 and 82.34% suitability, respectively. The reverse was the case for the GFDL-CM3 models as RCPs 2.5 and 8.5 had 78.86 and 76.86%.
Conclusion
This study revealed that the study area is climatically suitable for An. gambiae and will continue to be so in the future irrespective of the contrasting results from the GCMs used. Since vector population is often linked with their disease transmission capacity, proper measures must be put in place to mitigate disease incidences associated with the activities of An. gambiae.
Female Anopheles mosquitoes are the vectors of human malaria. The use of chemical insecticides for vector control has hampered with environmental pollution and insect. This suggests the need for the development of more potent and environment-friendly insecticides for effective control of malaria.This research investigated the larvicidal, pupicidal and adulticidal activities of Chromolaena odorata and Vernonia amygdalina leaf extracts against, An. gambiae in the laboratory at ambient temperature of 28 ± 2 °C and 75 ± 5% relative humidity. Different concentrations of 20 mg/L, 40 mg/L, 80 mg/L, 120 mg/L and 160 mg/L were prepared and these aqueous solutions were used for the experiments. Larval, pupal and adult mortality of An. gambiae were tested after 24 hours of exposure. Results showed that there were significant differences (P < 0.05) in toxicity level of the two plant extracts on An. gambiae larvae, pupae and adults. Vernonia amygdalina extract was the most toxic to An. gambiae larvae at all tested concentrations of 20 mg/L, 40 mg/L, 80 mg/L, 120 mg/L and 160 mg/L causing 47.5%, 82.5%, 100%, 100% and 100% mortality after 24 hours of treatment, respectively. Chromolaena odorata extract caused 32.5%, 60%, 82.5%, 92.5% and 100% mortality of An. gambiae larvae after 24 hours of treatment at concentrations 20 mg/L, 40 mg/L, 80 mg/L, 120 mg/L and 160 mg/L, respectively. Vernonia amygdalina extract was the most lethal to An. gambiae pupae and adults which caused 55% mortality of adult An. gambiae at concentration 160 ml/L. The concentration of C. odorata and V. amygdalina leaves extracts required to evoke 50% death of An. gambiae adult were 296.20 mg/L and 147.98 mg/L respectively. The LC 90 of C. odorata extract was 3107.55 mg/L while V. amygdalina extract was 2221.05 mg/L for mosquito adults. The plant extracts were not as effective against adults compared to larva and pupa of An. gambiae. This study showed that C. odorata and V. amygdalina were toxic to malaria vector with V. amygdalina being more potent. This suggest that V. amygdalina extracts could serve as an alternative method to synthetic chemical control of malaria vectors.
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