Browsing by Author "Davies, Craig"

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    Influence of environmental characteristics on the habitat of and behavioural interactions between anopheles species in South Africa
    (2016) Davies, Craig
    This project explored the ecological conditions of aquatic breeding sites of Anopheles gambiae sensu lato immatures in the Lowveld region of eastern Mpumalanga Province, South Africa. The aim was to determine the environmental conditions influencing anopheline abundance as well as abiotic parameters which associated with vector productivity. In addition to this, the levels of insecticide resistance to the three dominant compounds used in vector control in the region were assessed. Taking into account the sympatric occurrence of the major malaria vector in South Africa (An. arabiensis Patton) and its sibling, non-vector species (An. quadriannulatus Theobald), a laboratory study was devised which investigated the outcome of intra- and inter-specific competition under constant and fluctuating temperature regimes. There was a heterogenous distribution of anophelines across aquatic habitats in Mpumalanga with small-scale variation in salinity and Total Dissolved Solids (TDS) influencing species composition and Anopheles arabiensis was found in all sites surveyed with low numbers occurring where salinity levels were elevated. Anopheles merus associated with high salinity and TDS (Pearson’s Product Moment, r = 0.922, p < 0.05) whilst An. quadriannulatus dominated in breeding sites within 50m of a building or road. Anopheles gambiae complex members were susceptible to the insecticides tested with possible resistance (97%) to DDT in An. merus. Under laboratory conditions, temperature and competitive scenarios affected the life-history traits of both species studied here. The treatment 18 - 35°C generally reduced survivorship except for An. arabiensis in mixed, larval species treatments where it was similar to values reported for 25°C. Survivorship of both species at 20 - 30°C was not significantly impacted and the adult production was high across species treatments. The development rates at 25°C and 20 - 30°C were significantly different between species when reared alone and in mixed species treatments from larvae and from eggs. The effect of temperature was more pronounced at 18 - 35°C with An. arabiensis developing faster under both competitive scenarios and An. quadriannulatus slower, notably when in the presence of its competitor (p < 0.05). In the field component of this study, Anopheles arabiensis exploited all the habitats surveyed. It is therefore recommended that larval control operations should include all available breeding sites, focusing efforts during the dry season when these sites are limited and discreet within the landscape. In the laboratory component, it was possible to test whether or not community composition of anophelines at the adult stage was regulated by different temperature and competitive conditions at the larval stage to better understand the ecological conditions that determine anopheline composition and relative abundance. Taken together, the results of each component emphasize the need for local scale studies, especially under conditions of changing temperatures and rainfall patterns. The results of responses to temperatures and biotic interactions are necessary data for use in models predicting the impact of climate change on malaria vector mosquitoes.
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    Molecular and physiological analysis of Anopheles funestus swarms in Nchelenge, Zambia
    (BMC, 2018-01) Zawada, Jacek W.; Dahan‑Moss, Yael L.; Muleba, Mbanga; Dabire, Roch K.; Maïga, Hamid; Venter, Nelius; Davies, Craig; Hunt, Richard H.; Coetzee, Maureen; Koekemoer, Lizette L.
    Background: Anopheles funestus has been recognized as a major malaria vector in Africa for over 100 years, but knowledge on many aspects of the biology of this species is still lacking. Anopheles funestus, as with most other anophelines, mate through swarming. A key event that is crucial for the An. funestus male to mate is genitalia rotation. This involves the 135° to 180° rotation of claspers, which are tipped with claws. This physical change then enables the male to grasp the female during copulation. The aim of this investigation was to molecularly characterize wild An. funestus swarms from Zambia and examine the degree of genitalia rotation within the swarm. Methods: Anopheles funestus swarms were collected from Nchelenge, northern Zambia, during dusk periods in May 2016. All the adults from the swarm were analysed morphologically and identified to species level using a multiplex PCR assay. Anopheles funestus s.s. specimens were molecularly characterized by restriction fragment length polymorphism type and Clade type assays. The different stages of genitalia rotation were examined in the adult males. Results: A total of six swarms were observed during the study period and between 6 and 26 mosquitoes were caught from each swarm. Species analysis revealed that 90% of the males from the swarms were An. funestus s.s. MWtype, with 84% belonging to clade I compared to 14% clade II and 2% failed to amplify. Very few specimens (3.4%) were identified as Anopheles gambiae s.s. Eighty percent of the males from the swarm had complete genitalia rotation. Conclusions: This is the first time that An. funestus swarms have been molecularly identified to species level. Anopheles funestus swarms appear to be species-specific with no evidence of clade-type differentiation within these swarms. The An. funestus swarms consist mainly of males with fully rotated genitalia, which strongly suggests that swarming behaviour is triggered primarily when males have matured.