Occurrence of natural Anopheles arabiensis swarms in an urban area of Bobo-Dioulasso city, Burkina Faso, West Africa
Graphical abstract
Anopheles arabiensis swarming system was described at the first time in Burkina Faso (West Africa) surprisingly in a central urban area crossed by a River.
Introduction
In the less humid countries of tropical Africa, Anopheles arabiensis Patton, a member of the Anopheles gambiae Giles species complex, is a major malaria vector, particularly in southern Africa, Madagascar and along a wide East–West belt fringing the Sahel (Della Torre et al., 2005). Generally, An. arabiensis is regarded as being more exophilic, exophagic and zoophilic than An. gambiae Giles sensu stricto, but even so it remains a highly efficient vector of malaria (White, 1974). This species is thus an important subject of research, with a particular need for a greater understanding of its biological, genetic and ecological characteristics as they relate to malaria control (Petrarca et al., 2000, Costantini et al., 2005, Tirado et al., 2006, Taye et al., 2006). The release of sterile male mosquitoes into malaria and dengue endemic regions is proposed as a technique to control mosquitoes and reduce incidence of disease, and known as the Sterile Insect Technique, or SIT (Benedict and Robinson, 2003). This might be an effective means to reduce malaria cases in this region of Burkina Faso, but this approach relies on an appropriate knowledge of mosquito mating biology (Ferguson et al., 2005). In the past ten years the swarming and mating characteristics of natural populations of An. gambiae s.s. have been relatively well studied, especially in West Africa (Tripet et al., 2005, Diabaté et al., 2006, Diabaté et al., 2009, Diabaté et al., 2011, Dabiré et al., 2013). However, despite its medical and epidemiological importance, little is known about An. arabiensis natural swarming and mating patterns in the field (Marchand, 1984, Charlwood et al., 2002). In particular, there is currently very little basic information about An. arabiensis swarming behaviour, including swarm location and composition, factors influencing mating success, and the relative competitiveness of laboratory grown and wild male mosquitoes following release of the former into the field. The availability and diversity of plant nectar, as well as factors such as the nature of ground cover and climatic conditions are all likely to impact male dispersal patterns, which in turn are likely to affect the nature and locations of swarms. Before basic knowledge is gained about these and other elements of the mating behaviour of disease vectors it will be difficult to achieve successful population control using SIT.
Recent studies have shown that An. coluzzii and An. gambiae (formerly An. gambiae M and S molecular forms, respectively, (Coetzee et al., 2013), mainly have distinct, separate swarm sites (though shared sites have been reported, REFs), suggesting that the environmental and endogenous cues that determine the nature of swarming/mating sites must be under strong genetic control (Diabaté et al., 2009, Diabaté et al., 2011, Dabiré et al., 2013). There is concern therefore, that the mating competitiveness of released sterile males may be compromised by selection pressures during laboratory rearing, that alter their responsiveness to swarming cues under natural conditions (Bartlett, 1984, Peloquin and Asman, 1988, Howell and Benedict, 2009). These observations about the selection of swarm sites also indicate that males consistently arrive at predictable sites every day, and local knowledge of these sites may be of great use when monitoring overall population densities during mosquito control campaigns. As part of a series of several studies into the adaptation of An. arabiensis to an urban setting, the goal of the current study was to gather data on the locations and characteristics of swarms of mosquitoes in an urban setting within the city of Bobo-Dioulasso, Burkina Faso. Previous work has shown that An. gambiae s.s. and An. arabiensis are sympatric in Dioulassoba, with the proportion of An. arabiensis increasing over the last decade (Dabiré et al., 2012). Particular emphasis was placed on investigating species composition and the visual cues used by males to select a swarm site. Selected houses were sampled for resting adult mosquitoes and larval breeding sites were also sampled; collected individuals were identified by species.
Section snippets
Study area
Dioulassoba (11°10′42″ N; 4°17′35″ W) is a longstanding residential district in the centre of Bobo-Dioulasso, the second largest city in Burkina Faso located in the Southwest of the country. This district is crossed by a permanent stream along which are dotted small plots of vegetables and herb plants grown by the residents, and which is polluted with domestic waste litter and waste water (including sewage). Small puddles along the banks of the stream and the surrounding borders constitute
Physical and visual markers for swarm formation
All swarm sites and breeding sites where larvae were sampled were geo-referenced, which allowed a map of swarms and the dispersal of breeding sites across the district to be produced both from dry and wet season surveys (Fig. 1). During both the dry and the rainy seasons swarms were observed along the length of the transect and fairly evenly distributed, though concentrated slightly more on the edges of blocks of residences and along the banks of the Houet river. Larval breeding sites were
Discussion
The desire to investigate mating and swarming behaviour in wild populations of anopheline mosquitoes is not new. In fact the state-of-the-art research began early (Downes, 1969) and since these first observations several types of insects whose mating systems require swarms have been closely studied (e.g. Sullivan, 1981, Cooter, 1989) and with more relevance to this current study by Yuval et al. (1993), who provided a thorough description of swarming and mating behaviour within natural swarms of
Conflict of interest
Authors declare no conflict of interests.
Authors’ contributions
SPS conducted fieldwork and contributed to data analyses. HDF and BSNS conducted fieldwork and contributed to molecular analysis in the lab. SDD conducted the PCR analysis. MA drew the swarm map. BT, GLC, SF, TL, DA and LRS, contributed to drafting and revising the manuscript. GJ and DKR designed the study and wrote the manuscript.
Acknowledgments
Authors are grateful to the people of Dioulassoba who were very cooperative and allowed this work to be carried out in a very good working ambiance. Authors thank Ouari Ali, field technician of IRSS/Centre Muraz who initiated the fieldwork and geo-referenced the swarm's sites. This work was supported by an IAEA grant, contract no 16190/R0, accorded to Dabiré K. Roch under CRP G34002.
References (29)
- et al.
The first releases of transgenic mosquitoes: an argument for the sterile insect technique
Trends Parasitol.
(2003) - et al.
Natural swarming behaviour in the molecular M form of Anopheles gambiae
Trans. R. Soc. Trop. Med. Hyg.
(2003) - et al.
Redressing the sex imbalance in knowledge of vector biology
Trends Ecol. Evol.
(2005) - et al.
Biting behaviour and Plasmodium infection rates of Anopheles arabiensis from Sille, Ethiopia
Acta Trop.
(2006) - et al.
Spatial and temporal distribution of the malaria mosquito Anopheles arabiensis in northern Sudan: influence of environmental factors and implications for vector control
Malar. J.
(2009) Genetic changes during insect domestication
- et al.
The swarming and mating behaviour of Anopheles gambiae s.s (Diptera: Culicidae) from Sao Tome Island
J. Vector Ecol.
(2002) - et al.
Anopheles coluzzii and Anopheles amharicus, new members of the Anopheles gambiae complex
Zootaxa
(2013) Swarm flight behavior in flies and locusts
- et al.
Intrinsic host odor preferences of Anopheles arabiensis and An. quadriannulatus from a remote game area of Zimbabwe
Am. J. Trop. Med. Hyg.
(2005)