Genetically modified (GM) crops were introduced in South Africa in 1989 and commercially
available by 1998. Legislation to control the use of GM crops was only implemented in 1999,
with the genetically modified organisms (GMO) act (15 of 1999). In 2012 2.9 million ha of
GM crops were planted in South Africa alone. GM Crops, such as Bt maize, are promoted as
safer for the environment since no chemical pesticides are needed. However, recently GM
crops have been making headlines as more and more studies find adverse effects of these
crops on non-target organisms. The effects on aquatic environments have not yet been fully
determined, even though traces of Bt residue have been found in water systems surrounding
agricultural lands. The aim of this study was to establish the effects of the Bt toxin on
fecundity, development and growth of Bulinus tropicus, a freshwater snail.
The experiment made use of a static renewal tests to expose B. tropicus to 50 cm2 Bt maize
and cotton leaves in 900 ml of synthetic freshwater. The snails were exposed for the
duration of one full life cycle (embryo to adult). Endpoints measured included the
development, growth, fecundity, and deformities of the reproductive organs.
The results obtained showed retarded development and low embryo survival when the snails
were exposed to cotton leaves, irrespective of the presence or absence of Bt, indicating to
the possibility of trace residues of chemical pesticides may have been present on the leaves.
Initial stimulated growth of hatchlings was observed for both Bt cotton and maize exposures,
but after sexual maturity has been reached, ‘surplus’ energy was probably shared between
growth and fecundity, resulting in a reduction of growth rate. Energy is gained from their diet,
thus a sub-optimal diet would result in less energy available to functions such as growth and
fecundity. Signs of developmental instability were found in the formation of the shell opening
of the snails exposed to Bt. Fecundity decreased significantly after snails had been exposed
to Bt maize / cotton leaves. No differences were found in the penis sheath-preputium length
ratio, indicating that Bt had no deleterious effects on the reproductive organs. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/13394 |
| Date | January 2014 |
| Creators | Minnaar, Karin |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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