Studies on the bionomics of male Anopheles gambiae Giles and male Anopheles funestus Giles from southern Mozambique

Little is known about the fitness of wild male mosquitoes, the females of which are vectors of malaria. The problem of studying male biology has been exacerbated by difficulties associated with catching them. In southern Mozambique, however, almost the entire adult population of An. funestus and An. gambiae s.l. rest inside houses. They leave in a dusk exodus, which makes them easy to collect. In 8,348 exit collections from a village from 2003 to 2009, 567,195 male An. funestus and 34,591 male An. gambiae s.l. were collected. During the study, numbers of An. funestus increased but numbers of An. gambiae s.l. declined to the point of extinction. Overall numbers of An. gambiae s.l. were positively correlated with temperature, whilst the relationship between temperature and numbers of An. funestus changed from an initially positive one in the first three years of the study to a negative one in the last three years. Marked males were recaptured up to 300 m from the release site, with most recaptures occurring within 150 m. Estimated mean daily survival of male An. funestus was 0.86 (95% C.I. 0.869-0.850). For the years 2003-2007, estimated mean daily survival of male An gambiae s.l. was 0.660 (95% C.I. 0.682-0.638). For either species, there was no relationship between mean weekly temperature and estimated daily survival. These results imply that males of An. funestus live as long as females but have a relatively short flight range. They are discussed in the light of possible release strategies of sterile or genetically modified mosquitoes.     

Interspecific variation in diving activity among Anopheles gambiae Giles, An. arabiensis Patton, and An. funestus Giles (Diptera: Culicidae) larvae.

Anopheline larvae generally inhabit the near-surface of aquatic habitats, but they dive and remain at the bottom of these habitats for some time. This study examined forced and voluntary diving behavior and submergence tolerance in the three major African malaria vectors, Anopheles gambiae Giles, An. arabiensis Patton, and An. funestus Giles. The former two species occur sympatrically in temporal and shallow water bodies, while the latter occurs in permanent deeper water bodies. Anopheles funestus was the most tolerant of submergence, but the larvae tended to halt their descent before reaching the bottom by attaching onto a wall. The difference in diving behavior between An. funestus and the two species in the An. gambiae complex may be an adaptation to their contrasting breeding sites, because the former species must spend considerable energy to surface in its typical breeding sites. Both An. gambiae and An. arabiensis reached the bottom and crawled along the substrate, but An. gambiae voluntarily crawled more often than An. arabiensis. The possible importance of asymmetric bottom-feeding between these two sympatric species is discussed.     

Influence of soil quality in the larval habitat on development of Anopheles gambiae Giles.

Larval ecology is an important aspect of the population dynamics of anopheline mosquitoes (Diptera: Culicidae), the vectors of malaria. Anopheles larvae live in pools of stagnant water and adult fitness may be correlated with the nutritional conditions under which larvae develop. A study was conducted in Mbita, Western Kenya, to investigate how properties of the soil substrate of Anopheles gambiae breeding pools can influence development of this mosquito species. An. gambiae eggs from an established colony were dispensed into experimental plastic troughs containing soil samples from a range of natural Anopheles larval habitats and filtered Lake Victoria water. The duration of larval development (8-15 days), pupation rate (0-79%), and adult body size (20.28-26.91 mm3) varied among different soil types. The total organic matter (3.61-21.25%), organic carbon (0.63-7.18%), and total nitrogen (0.06-0.58%) levels of the soils were positively correlated with pupation rate and negatively correlated with development time and adult body size.     

Mating affects egg maturation in Anopheles gambiae Giles (Diptera: Culicidae).

The effect of mating on egg development and the size of the female accessory glands during the gonotrophic cycle of Anopheles gambiae was investigated. Although females that received a measured meal of blood were more likely to produce an egg batch when they were mated, the increased reproduction was not the result of male accessory gland substances. Changes in the size of the female accessory gland were not observed after mating nor at any time during the gonotrophic cycle, but there was a more rapid increase in its size following emergence in mated females.     

Genomic characterization of mycobacteriophage Giles: evidence for phage acquisition of host DNA by illegitimate recombination

A characteristic feature of bacteriophage genomes is that they are architecturally mosaic, with each individual genome representing a unique assemblage of individual exchangeable modules. Plausible mechanisms for generating mosaicism include homologous recombination at shared boundary sequences of module junctions, illegitimate recombination in a non-sequence-directed process, and site-specific recombination. Analysis of the novel mycobacteriophage Giles genome not only extends our current perspective on bacteriophage genetic diversity, with more than 60% of the genes unrelated to other mycobacteriophages, but offers novel insights into how mosaic genomes are created. In one example, the integration/excision cassette is atypically situated within the structural gene operon and could have moved there either by illegitimate recombination or more plausibly via integrase-mediated site-specific recombination. In a second example, a DNA segment has been recently acquired from the host bacterial chromosome by illegitimate recombination, providing further evidence that phage genomic mosaicism is generated by nontargeted recombination processes.     

A Microsporidan Infection of Anopheles gambiae Giles, from Tanzania, Interpretation of Its Mode of Transmission and Notes on Nosema Infections in Mosquitoes

SYNOPSIS A microsporidan found parasitic in Anopheles gambiae in Tanzania was identified as Nosema algerae Vavra & Undeen, 1970. Its development was traced in laboratory-bred Anopheles stephensi. Spores were oval, 3.0-4.3 μ× 1.8-2.5 μ and had filaments 40-60 μ long; schizonts were uni-, bi- or tetranucleate; elongate sporonts gave rise to 2 sporoblasts. The parasite attacked almost every tissue of the body of the larvae, pupae and adults including the ova, but transovarial transmission was thought to be unimportant as infected ova did not develop into viable larvae. Hosts reacted to the presence of the parasite by encapsulating some spores in a coat of melanin.
The parasite was lightly infective to several species of culicine mosquitoes, but the infection was limited mainly to the nervous system, mid-gut epithelium and Malpighian tubules.
The species of Nosema parasitizing mosquitoes are reviewed.     

Relationship of larval desiccation to Anopheles gambiae Giles and An. arabiensis Patton survival

The relationship between mosquito 4^th instar larval desiccation and survival to adulthood was explored by three methods in the laboratory. Two colonies of Anopheles arabiensis and one of Anopheles gambiae were studied. We found significant differences in tolerance to desiccation among all three stocks suggesting an intra‐ and interspecific genetic component to desiccation tolerance. An. arabiensis KGB, originating from Zimbabwe about 1975, had a much‐reduced desiccation tolerance compared to An. gambiae G3, colonized in the Gambia in 1975, and An. arabiensis DONGOLA which originated in Sudan in 2004. Individuals of the G3 stock survived desiccation of times up to 40 min with survival of 0.52. The degree of difference in tolerance between G3 and DONGOLA was smallest and was detected by one of three experimental methods. Mass losses of individuals that were weighed individually and survived to adulthood averaged 27% and 29% for G3 and DONGOLA and 20% for the less tolerant KGB stock, respectively. Such differences in survival in transiently dry larval habitats may account in part for differences in the distribution of these species and karyotypes.     

Seasonal climate effects anemotaxis in newly emerged adult Anopheles gambiae Giles in Mali, West Africa

The direction and magnitude of movement by the malaria vector Anopheles gambiae Giles has been of great interest to medical entomologists for over 70 years. This direction of movement is likely to be affected by many factors, from environmental conditions and stage of life history of the mosquito to the existence of attractants in the vicinity. We report here the direction of movement of newly emerged An. gambiae in nature, around the village of Donéguébougou, Mali. We assessed the direction of movement for individual mosquitoes by placing them in a novel enclosure with exit traps oriented in the direction of the cardinal and intermediate points of the compass. We consistently found predominantly Southward directions of movement during 2009 and 2010, with an additional Eastward component during the dry season and a Westward one during the wet season. Our data indicate that wind has an important effect on the direction of movement, but that this effect varied by season: Average directions of movement were downwind during the dry season and upwind during the wet season. A switch in anemotactic response suggests that the direction of movement of An. gambiae relative to the wind immediately after emergence under varying conditions of humidity should be further investigated under controlled conditions.