A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand,
South Africa in fulfilment of the requirements for the degree of Master of Science.
2016 / 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. / MT2016
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/21417 |
| Date | January 2016 |
| Creators | Davies, Craig |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf |
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