The evolution of pest resistance to Cry proteins threatens the long-term use of Bt crops.
Busseola fusca developed resistance to Bt maize in South Africa but the mechanism of
resistance is not well understood. According to the gut microbiota theory, extensive cell lysis
caused by Cry proteins provide gut microbes access to the more favourable environment of
the hemocoel where they germinate and reproduce, causing septicemia and death of the
host. This theory brought on questions about the role of gut microbes in the efficacy of Bt
maize against target lepidopteran pests. The aim of this study was to determine whether
microbes present in the mid-gut of B. fusca influence the efficacy of Cry 1Ab proteins.
Larvae were collected from 30 different geographical locations, dissected to excise the midgut
and mid-gut content which was separated according to morphological types. The
morphological types were used to test the antibiotic susceptibility of the bacteria and proved
that ciprofloxacin, ampicillin and doxycycline were the most effective bacteriostatic and
bactericidal antibiotics. These three antibiotics were exposed to the morphological types at
different concentrations to visualise the possible deleterious effects of the antibiotics on the
bacteria. This visualisation was performed by observing the growth curve of the bacteria in
the presence of the combination of antibiotics. The antibiotics concentration of 500 μg/ml
showed the highest efficacy compared to the other concentrations tested. An antibiotic
concentration of 500 μg/ml of ciprofloxacin, ampicillin and doxycycline was incorporated into
an artificial diet for the larvae to feed on for 7 days. This method was used to rid the larvae of
gut microbes before allowing them to feed on Bt maize (MON810) plant material expressing
Cry proteins. The results suggests that by placing antibiotic reared larvae on a Bt plant, the
absence of the mid-gut microbes contributed to larvae survival on Bt maize. This observation
will contribute to understanding the role of gut microbes on the efficacy of Cry proteins. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/15722 |
| Date | January 2015 |
| Creators | Van Staden, Megan |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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