Preferred resting surfaces of dominant malaria vectors inside different house types in rural south-eastern Tanzania

et al. 2021

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Background: Wild populations of Anopheles mosquitoes are generally thought to mate outdoors in swarms, though once colonized, they also mate readily inside laboratory cages. This study investigated whether malaria vectors, Anopheles funestus and Anopheles arabiensis can naturally mate both inside and outside human dwellings. Method: Mosquitoes were sampled from three volunteer-occupied experimental huts in a rural Tanzanian village at 6 pm each evening, after which the huts were completely sealed and sampling repeated at 11 pm and 6 am the next morning to compare proportions of inseminated females. Similarly-timed collections were done inside local unsealed village houses. Lastly, wild-caught larvae and pupae were introduced inside or outside experimental huts constructed within two semi-field screen house chambers. The huts were then sealed and fitted with exit traps, allowing mosquito egress but not entry. Mating was assessed in subsequent days by sampling and dissecting emergent adults caught indoors, outdoors and in the exit traps.Results: Proportions of inseminated females inside the experimental huts in the village increased from ~60% at 6 pm to ~90% the following morning despite no new mosquitoes entering after 6 pm. Insemination in the local homes increased from ~78% to ~93% over the same time points. In the semi-field observations of wild-caught captive mosquitoes, proportions of inseminated An. funestus were 20.9% (95% CI: ± 2.8) outdoors, 25.2% (± 3.4) indoors and 16.8% (± 8.3) in exit traps, while proportions of inseminated An. arabiensis were 42.3% (± 5.5) outdoors, 47.4% (± 4.7) indoors and 37.1% (± 6.8) in exit traps.Conclusion: This study demonstrates that wild populations of An. funestus and An. arabiensis in Tanzania can mate both inside and outside human dwellings. Most mating likely happens outdoors before the mosquitoes enter houses, but significant additional mating happens indoors. The evidence of insemination inside experimental huts fitted with exit traps and in the unsealed village houses suggests that the mosquitoes can voluntarily mate indoors even when there is unrestricted egress. These findings could enable improved vector control, e.g., by targeting males, and potentially inform alternative methods for colonizing eurygamic Anopheles species (e.g. An. funestus) inside laboratories or semi-field chambers.

Section: Discussionsupporting

confidence: 65%

Section: Observations Of Male Mosquitoes Resting Inside Different Types Of Housesmentioning

confidence: 99%

Wild Populations of Malaria Vectors Can Mate Both Inside and Outside Human Dwellings

Nambunga

Msugupakulya

et al. 2021

Preprint

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“…, of which > 93% are known to be An. funestus s.s. [ 47 ]. Wild-caught females were transported to the Ifakara Health Institute and used in experiments at the vector biology & control laboratory, the VectorSphere at Ifakara (Fig.…”

Section: Methodsmentioning

confidence: 99%

Fitness characteristics of the malaria vector Anopheles funestus during an attempted laboratory colonization

Ngowo

Matthiopoulos

et al. 2021

Malar J

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Background The malaria vector Anopheles funestus is increasingly recognized as a dominant vector of residual transmission in many African settings. Efforts to better understand its biology and control are significantly impeded by the difficulties of colonizing it under laboratory conditions. To identify key bottlenecks in colonization, this study compared the development and fitness characteristics of wild An. funestus from Tanzania (FUTAZ) and their F1 offspring during colonization attempts. The demography and reproductive success of wild FUTAZ offspring were compared to that of individuals from one of the only An. funestus strains that has been successfully colonized (FUMOZ, from Mozambique) under similar laboratory conditions. Methods Wild An. funestus (FUTAZ) were collected from three Tanzanian villages and maintained inside an insectary at 70–85% RH, 25–27 °C and 12 h:12 h photoperiod. Eggs from these females were used to establish three replicate F1 laboratory generations. Larval development, survival, fecundity, mating success, percentage pupation and wing length were measured in the F1 -FUTAZ offspring and compared with wild FUTAZ and FUMOZ mosquitoes. Results Wild FUTAZ laid fewer eggs (64.1; 95% CI [63.2, 65.0]) than FUMOZ females (76.1; 95% CI [73.3, 79.1]). Survival of F1-FUTAZ larvae under laboratory conditions was low, with an egg-to-pupae conversion rate of only 5.9% compared to 27.4% in FUMOZ. The median lifespan of F1-FUTAZ females (32 days) and males (33 days) was lower than FUMOZ (52 and 49 for females and males respectively). The proportion of female F1-FUTAZ inseminated under laboratory conditions (9%) was considerably lower than either FUMOZ (72%) or wild-caught FUTAZ females (92%). This resulted in nearly zero viable F2-FUTAZ eggs produced. Wild FUTAZ wings appear to be larger compared to the lab reared F1-FUTAZ and FUMOZ. Conclusions This study indicates that poor larval survival, mating success, low fecundity and shorter survival under laboratory conditions all contribute to difficulties in colonizing of An. funestus. Future studies should focus on enhancing these aspects of An. funestus fitness in the laboratory, with the biggest barrier likely to be poor mating.

“…To account for these biases in sampling, a new parameter of “trap-biasness” was added in the observation model for both precision and varying daily means . The prior values for were estimated from independent studies from the same locations [ 6 , 58 ], and ranged from 0.05–0.15 (Table 1 ), with variations between the two life stages . Therefore, the observation model for blood-fed and gravid ( was rewritten by modifying Eq.…”

Section: Methodsmentioning

confidence: 99%

Using Bayesian state-space models to understand the population dynamics of the dominant malaria vector, Anopheles funestus in rural Tanzania

Ngowo

Okumu

et al. 2022

Malar J

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Background It is often assumed that the population dynamics of the malaria vector Anopheles funestus, its role in malaria transmission and the way it responds to interventions are similar to the more elaborately characterized Anopheles gambiae. However, An. funestus has several unique ecological features that could generate distinct transmission dynamics and responsiveness to interventions. The objectives of this work were to develop a model which will: (1) reconstruct the population dynamics, survival, and fecundity of wild An. funestus populations in southern Tanzania, (2) quantify impacts of density dependence on the dynamics, and (3) assess seasonal fluctuations in An. funestus demography. Through quantifying the population dynamics of An. funestus, this model will enable analysis of how their stability and response to interventions may differ from that of An. gambiae sensu lato. Methods A Bayesian State Space Model (SSM) based on mosquito life history was fit to time series data on the abundance of female An. funestus sensu stricto collected over 2 years in southern Tanzania. Prior values of fitness and demography were incorporated from empirical data on larval development, adult survival and fecundity from laboratory-reared first generation progeny of wild caught An. funestus. The model was structured to allow larval and adult fitness traits to vary seasonally in response to environmental covariates (i.e. temperature and rainfall), and for density dependency in larvae. The effects of density dependence and seasonality were measured through counterfactual examination of model fit with or without these covariates. Results The model accurately reconstructed the seasonal population dynamics of An. funestus and generated biologically-plausible values of their survival larval, development and fecundity in the wild. This model suggests that An. funestus survival and fecundity annual pattern was highly variable across the year, but did not show consistent seasonal trends either rainfall or temperature. While the model fit was somewhat improved by inclusion of density dependence, this was a relatively minor effect and suggests that this process is not as important for An. funestus as it is for An. gambiae populations. Conclusion The model's ability to accurately reconstruct the dynamics and demography of An. funestus could potentially be useful in simulating the response of these populations to vector control techniques deployed separately or in combination. The observed and simulated dynamics also suggests that An. funestus could be playing a role in year-round malaria transmission, with any apparent seasonality attributed to other vector species.