Biology subjects

Samake, D.

Publications and source records attributed to Samake, D..

7 recordsLinked to original sources

bioRxiv2026

Continuous mark-release recapture to improve estimates of movement and survival of the African malaria mosquitoes

Despite extensive efforts to understand the population biology and ecology of the African malaria mosquitoes questions regarding their movement pattern, survival, and population size persist, reflecting methodological limitations. Site fidelity, in which mosquitoes return to feeding sites, resting sites, or oviposition sites remain debated. Mark release recapture (MRR) studies are vital to address such questions. Using locality- and date-specific DNA tags in fluorescent spray, we carried out a continuous MRR in a Malian village from September to December 2019 with three days interval between capture and release across seven zones. A total of 12,937 Anopheles gambiae s.l. (7,455 females) were captured during 35 indoor collections. Handling related mortality was 3.4%., A. coluzzii predominated (89.7%), followed by A. gambiae (9.4%), and A. arabiensis (0.9%). Overall recapture rate was 1.05% (N=129). Contrary to the site-fidelity hypothesis, the distribution of recaptured mosquitoes across zones (regardless of their zone of release) was similar to the distribution of the captured mosquitoes (r=0.97, P<0.001), with 70% recaptured in a different zone. There was no difference in distance moved between sexes, but males average distance increased over time since release, whereas females distance remained unchanged. Simulated movements (across released points), with equal probability to reach any of the village houses predicted actual distance moved by mosquitoes. The regression of observed distance from each zone over predicted had a slope of 1 (r2=94%, P=0.006), suggesting that the layout of the capture area greatly affected the results. The average days post release (minimum age of wild captured mosquitoes) for recaptures was 6.4 d with the longest being 30 d. No seasonal and sex related difference in minimum age were detected. The corrected probability of daily survival (PDS) was 94% and the daily increase in sporozoite rate was 4.9%. Limiting the recapture duration period showed that PDS increased with recapture duration from 74% to 86% (12 to 30 d, uncorrected). Thus, larger recapture area and longer recapture duration are needed to obtain accurate estimates of movement range and of daily survival.

ecology↗

bioRxiv2022

Diversity, composition, altitude, and seasonality of high-altitude windborne migrating mosquitoes in the Sahel: Implications for disease transmission

Recent studies have reported Anopheles mosquitoes captured at high-altitude (40-290 m above ground) in the Sahel. Here, we describe this migration modality across genera and species of African Culicidae and examine its implications for disease transmission and control. As well as Anopheles, six other genera--Culex, Aedes, Mansonia, Mimomyia, Lutzia, and Eretmapodites comprised 90% of the 2,340 mosquitoes captured at altitude. Of the 50 molecularly confirmed species (N=2,107), 33 species represented by multiple specimens were conservatively considered high-altitude windborne migrants, suggesting it is a common migration modality in mosquitoes (31-47% of the known species in Mali), and especially in Culex (45-59%). Overall species abundance varied between 2 and 710 specimens/species (in Ae. vittatus and Cx. perexiguus, respectively). At altitude, females outnumbered males 6:1, and 93% of the females have taken at least one blood meal on a vertebrate host prior to their departure. Most taxa were more common at higher sampling altitudes, indicating that total abundance and diversity are underestimated. High-altitude flight activity was concentrated between June and November coinciding with availability of surface waters and peak disease transmission by mosquitoes. These hallmarks of windborne mosquito migration bolster their role as carriers of mosquito-borne pathogens (MBPs). Screening 921 mosquitoes using pan-Plasmodium assays revealed that thoracic infection rate in these high-altitude migrants was 2.4%, providing a proof of concept that vertebrate pathogens are transported by windborne mosquitoes at altitude. Fourteen of the 33 windborne mosquito species had been reported as vectors to 25 MBPs in West Africa, which represent 32% of the MBPs known in that region and include those that inflict the heaviest burden on human and animal health, such as malaria, yellow fever, dengue, and Rift Valley fever. We highlight five arboviruses that are most likely affected by windborne mosquitoes in West Africa: Rift Valley fever, Onyongnyong, Ngari, Pangola, and Ndumu. We conclude that the study of windborne spread of diseases by migrating insects and the development of surveillance to map the sources, routes, and destinations of vectors and pathogens is key to understand, predict, and mitigate existing and new threats of public health.

ecology↗

bioRxiv2021

Evaluating the contribution of aestivation to the persistence of malaria mosquitoes through the Sahelian dry season using stable isotopes

Data suggests the malaria vector Anopheles coluzzii persists in the Sahel by dry-season aestivation though evidence is scant. We have marked Anopheles mosquitoes using deuterium (2H) to assess the contribution of aestivation to persistence of mosquitoes through the seven-month dry season. If local aestivation is the only way A. coluzzii persists, the frequency of marked mosquitoes should remain stable throughout, whereas finding no marked mosquitoes would be evidence against aestivation. Larval sites were spiked with 2H at the end of the 2017 wet season in two Sahelian villages in Mali. We monitored 2H-enriched populations until the onset of rains. By the end of the enrichment period, 33% of A. coluzzii mosquitoes were clearly marked. Expectedly, 2H levels in marked mosquitoes degraded over time, resulting in a partial overlap of the marked and non-marked 2H distributions. We utilized three methods to estimate the fraction of marked mosquitoes in the population. Seven months after enrichment, 7% of the population had 2H values above the highest pre-enrichment value. An excess of 21% exceeded the 3rd quartile of the pre-enrichment population. A finite mixed population model showed 2.5% represented a subpopulation of marked mosquitoes with elevated 2H, compatible with our predictions. We provide evidence that aestivation is a major persistence mechanism of A. coluzzii in the Sahel, contributing at least 20% of the adults at the onset of rains, suggesting A. coluzzii utilizes multiple persistence strategies enabling its populations rapid buildup, facilitating subsequent malaria resurgence. These may complicate vector control and malaria elimination campaigns. Significance statementHere we estimated the contribution of aestivation to the persistence of mosquitoes through the seven-month long dry season, by marking a known fraction of the adult population through larval site 2H-spiking by the end of the wet season and assessing the change in this fraction through the dry season, until after the onset of the first rain of the subsequent wet season. In a mark-release-recapture study using stable isotopes, we provide compelling evidence that the primary Sahelian malaria vector Anopheles coluzzii aestivates on a population-scale, contributing at least 20% of the adults which reestablish the population of the subsequent wet season. The capacity to use multiple strategies of persistence in time and space might complicate vector control and elimination campaigns.

ecology↗

bioRxiv2020

A novel fluorescence and DNA combination for complex, long-term marking of mosquitoes

BackgroundCurrent mark release recapture methodologies are limited in their ability to address complex problems in vector biology, such as studying multiple groups overlapping in space and time. Additionally, limited mark retention, reduced post-marking survival, and the large effort in marking, collection and recapture, all complicate effective insect tracking. MethodWe have developed and evaluated a marking method using a fluorescent dye (Smartwater(R)) combined with synthetic DNA tags to informatively and efficiently mark adult mosquitoes using an airbrush pump and nebulizer. Using handheld UV flashlights, the fluorescent marking enabled quick and simple initial detection of recaptures in a simple, field-ready, and non-destructive approach that when combined with a simple, extraction-free PCR on individual mosquito legs provides potentially unlimited marking information. ResultsThis marking, first tested in the laboratory with Anopheles gambiae s.l. mosquitoes, did not affect survival (median ages 24-28 days, p-adj > 0.25), oviposition (median eggs/female of 28.8, 32.5, 33.3 for water, green, red dyes, respectively, p-adj > 0.44), or Plasmodium competence (mean oocysts 5.56 to 10.6, p-adj > 0.95). DNA and fluorescence had 100% retention up to 3 weeks (longest time point tested) with high intensity, indicating marks would persist longer. ConclusionsWe describe a novel, simple, no/low-impact, and long-lasting marking method that allows separation of multiple insect subpopulations by combining unlimited length and sequence variation in the synthetic DNA tags. This method can be readily deployed in the field for marking multiple groups of mosquitoes or other insects.

ecology↗

bioRxiv2020

The effects of high-altitude windborne migration on survival, oviposition and blood-feeding of the African malaria mosquito, Anopheles gambiae s.l.

Recent results of high-altitude windborne mosquito migration raised questions about the viability of these mosquitoes despite ample evidence that many insect species, including other dipterans have been known to migrate regularly over tens or hundreds of kilometers on high-altitude winds and retain their viability. To address these concerns, we subjected wild An. gambiae s.l. mosquitoes to a high-altitude survival assay, followed by oviposition (egg laying) and blood feeding assays. Despite carrying out the survival assay under exceptionally harsh conditions that probably provide the lowest survival potential following high altitude flight, a high proportion of the mosquitoes survived for six and even eleven hours assay durations at 120-250m altitudes. Minimal differences in egg laying success were noted between mosquitoes exposed to high altitude survival assay and those kept near the ground. Similarly, minimal differences were found in the female’s ability to take an additional blood meal after oviposition between these groups. We conclude that similar to other high-altitude migrating insects, mosquitoes are able to withstand extended high-altitude flight and subsequently reproduce and transmit pathogens by blood feeding on new hosts.Competing Interest StatementThe authors have declared no competing interest.View Full Text

zoology↗

bioRxiv2020

Quantifying flight aptitude variation in wild A. gambiae s.l. in order to identify long-distance migrants

BackgroundIn the West African Sahel, during the 5-7 month-long dry season mosquito reproduction is halted due to the absence of surface waters required for larval development. Recent studies have suggested that both Anopheles gambiae s.s and A. arabiensis persist in this region by migration from distant locations where larval sites are perennial, and A. coluzzii engages in long-distance migration, presumably within the Sahel, following shifting resources due to the ever-changing patterns of Sahelian rainfall. Understanding mosquito migration is key to malaria control, a disease that still kills >400,000 people, mostly children in Africa. MethodsWe used a new tethered-flight assay to characterize flight in the three primary malaria vectors mentioned above and evaluated seasonal differences in their flight activity. The flight of tethered wild mosquitoes was audio-recorded from 21:00h to 05:00h in the following morning and three flight aptitude indices were examined: total flight duration, longest flight bout, and the number of flight bouts during the assay. Based on recent studies, we predicted that (i) the distribution of the flight aptitude indices would exhibit bi-modality and/or marked skewness, indicating a subpopulation of high flight activity (HFA) associated with long-distance migrants, in contrast to low flight activity (LFA) in appetitive flyers. Additionally, flight aptitude would (ii) increase in the wet season, (iii) increase in gravid females, and (iv) vary among the vector species. ResultsThe distributions of all flight indices departed sharply from a normal curve, and were strongly skewed to the right, consistent with the division of the population into a majority of LFAs and a minority of HFAs, e.g., the median total flight was 586 seconds, and its maximum value was 16,110 seconds (~4.5 h). As predicted, flight aptitude peaked in the wet season and was higher in gravid females than in non-bloodfed females. Flight aptitude was higher in A. coluzzii than in A. arabiensis, but A. gambiae s.s. was not statistically different from either. We evaluated differences in wing size and shape between LFAs and HFAs. During the wet season, wing size of HFA A. coluzzii was larger than that of LFAs; it was wider than predicted by its length, indicating a shape change. However, no statistically significant differences were found in wings of A. gambiae s.s. or A. arabiensis. ConclusionsThe partial agreement between the assay results and predictions suggest a degree of discrimination between appetitive flyers and long-distance migrants. Wing size and shape seems to indicate higher flight activity in A. coluzzii during the wet season.

ecology↗

bioRxiv2020

Massive windborne migration of Sahelian insects: Diversity, seasonality, altitude, and direction

Knowledge on long-distance migration of insects is especially important for food security, public health, and conservation-issues that are especially significant in Africa. During the wet season, the Sahel nourishes diverse life forms which are soon purged by the long dry season. Windborne migration is a key strategy enabling exploitation of such ephemeral havens. However, our knowledge of these large-scale movements remains sparse due to the virtual invisibility of insects flying at altitude. In this first cross-season investigation (3 years) of the aerial insect fauna over Africa, we sampled crepuscular and nocturnal insects flying 40-290 m above ground in four Sahelian villages in Mali, using sticky nets mounted on tethered helium-filled balloons. Nearly half a million insects were caught, representing at least thirteen insect orders following preliminary sorting of the collections. At least 100 insect families were determined to have been captured at altitude in samples collected on 222 nets, obtained in 125 collections over 96 nights. Control nets (raised momentarily to >40 m during system launch and retrieval) confirmed that the insects were captured at altitude, not near the ground. Thirteen ecologically and phylogenetically diverse species were studied in detail. The flight activity of all species peaked during the wet season every year across localities up to ~100 km apart, and occurred over multiple nights, suggesting regular migrations. Species differed in flight altitude, seasonality, and correlations with aerial temperatures, humidity, and wind speed. All taxa exhibited frequent migrations on southerly winds, accounting for the recolonization of the Sahel from southern source populations. "Return" southward movement at the end of the wet season occurred in most taxa but no selectivity for such winds was detected. Extrapolation of aerial density to estimate the seasonal number of migrants crossing Mali at latitude 14{degrees}N suggested numbers in the trillions, even for the modestly abundant taxa. Assuming 2-10 hours of flight, the nightly distances traversed exceed tens and even hundreds of kilometers. Two migration strategies were proposed: "residential Sahelian migration" and "round trip migration". The unprecedented magnitude and diversity of long-range windborne insect migrations highlight the importance of this life strategy in their impact on Sahelian and neighboring ecosystems.

ecology↗