BackgroundUnderstanding the ecology of exophilic anophelines is a key step toward developing outdoor control strategies to complement existing indoor control tools against malaria vectors. This study was conducted to assess the movement pattern of exophilic Anopheles mosquitoes between blood meal sources and resting habitats, and the landscape factors dictating their resting habitat choice.ResultsResting clay pots were placed at 5 m, 25 m, 50 m, 75 m and 100 m away from isolated focal houses, radiating from them in four directions. The locations of the clay pots represent heterogeneous land cover types at a relatively fine spatial scale in the landscape. The effect of the landscape characters on the number of both female and male anophelines caught was modelled using zero-inflated negative binomial regression with a log link function. A total of 420 Anopheles mosquitoes (353 females and 67 males) belonging to three species; Anopheles arabiensis, Anopheles pharoensis, and Anopheles tenebrosus were caught in the resting clay pots, with An. arabiensis being the dominant species. Canopy cover, distance from the house, and land cover type were the significant landscape characters influencing the aggregation of resting mosquitoes. Both the count and binary models showed that canopy cover was the strongest predictor variable on the counts and the presence of Anopheles mosquitoes in the clay pots. Female Anopheles were most frequently found resting in the pots placed in banana plantations, and at sampling points that were at the greater distances (75 m and 100 m) from the focal house.ConclusionsThis study showed that exophilic Anopheles mosquitoes tend to rest in shaded areas some distance away from human habitation. These findings are important when targeting mosquitoes outdoors, complementing the existing effort being made to control malaria vectors indoors.Electronic supplementary materialThe online version of this article (10.1186/s12936-018-2499-7) contains supplementary material, which is available to authorized users.
Hotspots constitute the major reservoir for residual malaria transmission, with higher malaria incidence than neighbouring areas, and therefore, have the potential to form the cornerstone for successful intervention strategies. Detection of malaria hotspots is hampered by their heterogenous spatial distribution, and the laborious nature and low sensitivity of the current methods used to assess transmission intensity. We adopt ecological theory underlying foraging in herbivorous insects to vector mosquito host seeking and modelling of fine-scale landscape features at the village level. The overall effect of environmental variables on the density of indoor mosquitoes, sporozoite infected mosquitoes, and malaria incidence, was determined using generalized linear models. Spatial analyses were used to identify hotspots for malaria incidence, as well as malaria vector density and associated sporozoite prevalence. We identify household occupancy and location as the main predictors of vector density, entomological inoculation rate and malaria incidence. We propose that the use of conventional vector control and malaria interventions, integrated with their intensified application targeting predicted hotspots, can be used to reduce malaria incidence in endemic and residual malaria settings.
Background: Plasmodium parasites manipulate the interaction between their mosquito and human hosts. Patients infected with gametocytes attract anopheline mosquitoes differentially compared to healthy individuals, an effect associated with an increased release of attractive volatile cues. This odour-driven manipulation is partly mediated by the gametocyte-specific metabolite, (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), which induces increased release of select aldehydes and terpenes from red blood cells and results in the enhanced attraction of host-seeking mosquitoes, which are vectors of malaria. This study investigates the effect of the HMBPP-induced volatiles on the attraction of wild Anopheles mosquitoes to humans under field conditions. Methods: The efficacy of the HMBPP-induced odour blend to attract Anopheles was evaluated in a 4 × 6 Latin rectangular study design indoors using baited Suna traps. Furthermore, to assess the efficacy of the HMBPP-induced odour blend in (1) augmenting the attractiveness of human odour, and (2) attracting Anopheles mosquitoes in the absence of human odour, a two-choice assay using host decoy traps (HDTs) was used and evaluated using binomial generalized regression. Results: Traps baited with the HMBPP-induced odour blend attracted and caught both Anopheles arabiensis and Anopheles pharoensis females in a dose-dependent manner in the presence of background human odour, up to 2.5 times that of an unbaited trap. Given a choice between human odour and human odour laden with the HMBPPinduced odour blend, mosquitoes differentially preferred traps augmented with the HMBPP-induced odour blend, which caught twice as many female An. arabiensis. Traps baited with the HMBPP-induced odour blend but lacking the background of human odour were not effective in attracting and catching mosquitoes. Conclusion: The findings of the present study revealed that the HMBPP-induced odour blend, when augmented with human body odour, is attractive to anopheline mosquitoes and could be used as a complementary vector control tool along with existing strategies.
Background Odour-based tools targeting gravid malaria vectors may complement existing intervention strategies. Anopheles arabiensis are attracted to, and stimulated to oviposit by, natural and synthetic odours of wild and domesticated grasses associated with mosquito breeding sites. While such synthetic odour lures may be used for vector control, these may have limited efficacy when placed in direct competition with the natural source. In this study, workflows developed for plant-feeding pests was used to design and evaluate a chimeric odour blend based on shared attractive compounds found in domesticated grass odours. Methods Variants of a synthetic odour blend, composed of shared bioactive compounds previously identified in domesticated grasses, was evaluated sequentially in a two-choice olfactometer to identify a ratio-optimized attractive blend for malaria vectors. During this process, blends with ratios that were significantly more attractive than the previously identified synthetic rice blend were compared to determine which was most attractive in the two-choice olfactometer. To determine whether all volatile components of the most attractive blend were necessary for maximal attraction, subtractive assays were then conducted, in which individual components were removed for the most attractive blend, to define the final composition of the chimeric blend. Binary logistic regression models were used to determine significance in all two-choice assays. The chimeric blend was then assessed under field conditions in malaria endemic villages in Ethiopia, to assess the effect of dose, trap type, and placement relative to ground level. Field data were analyzed both descriptively and using a Welch-corrected t-test. Results A ratio-optimized chimeric blend was identified that significantly attracted gravid An. arabiensis under laboratory conditions. In the field, trap captures of An. arabiensis and Anopheles pharoensis were dependent on the presence of the lure, trap type (CDC, BG Sentinel and Suna traps), placement relevant to ground level, with low release rates generally luring more mosquitoes. Conclusions The workflow designed for the development of chimeric lures provides an innovative strategy to target odour-mediated behaviours. The chimeric lure identified here can be used in existing trapping systems, and be customized to increase sustainability, in line with goals of the Global Vector Control Response Group.
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