Resistance development and possible non–target effects have been of
concern since the first deployment of genetically modified crops with
insecticidal properties. It is especially at the third trophic level and with
important predators such as lacewings (Chrysoperla spp.) (Neuroptera:
Chrysopidae) where negative effects of Cry 1Ab protein could have adverse
effects in agro–ecosystems. Monitoring of the effect of genetically modified Bt
maize on non–target organisms is required by law in South–Africa. Neuroptera
are excellent indicators of environmental and habitat transformation, and also
include key species for signifying areas and faunas that require priority
protection. Monitoring techniques, especially for insect eggs, are often labour
intensive and time consuming. A study was conducted to determine the
preferred oviposition site of Chrysoperla spp. on maize plants to facilitate
time–effective searching for eggs of these beneficial insects. Furthermore we
determined if the presence of aphids on plants influenced Chrysoperla spp.
oviposition preference. Another study was conducted to evaluate the effect of
indirect exposure of C. pudica to Cry 1Ab protein, through healthy Bt–maize
feeding prey, on its biology. Daily flight activity patterns and the height at
which chrysopid adults fly above the crop canopy were also determined, as
well as the movement of adult Chrysoperla spp. between maize fields and
adjacent headlands. A clear spatial oviposition pattern was observed on
maize plants and oviposition was not random as reported in earlier studies.
This data facilitates rapid monitoring of the presence of eggs in maize
cropping systems and is also of use in general pest management. Choicetest
data showed that females responded positively to host plants that were
infested with aphids. Feeding studies in which C. pudica larvae were
indirectly exposed to Bt–toxin at the 3rd trophic level, showed a limited effect
of Bt–toxin on only a few of the parameters that were evaluated. The pupal
period and percentage adult emergence of larvae exposed to an unusually
high amount of Bt–toxin was significantly shorter and lower respectively than
that of the control group. The overall result of this study, in which the possible
effect of food quality (prey) was excluded, showed that Cry 1Ab protein had an adverse affect only on certain fitness components during the life cycle of
C. pudica. However, since this study represented a worst–case scenario
where diverse prey was not available to C. pudica, negligible effects is
expected under field conditions where prey is more diverse. It was
determined that chrysopids was most active between 16:00 – 23:00 and that
they fly largely between 0.5 m – 2.5 m above ground level. An attempt was
also made to quantify migration between different vegetations types. This part
was terminated because of bad weather conditions at several occasions
when the experiment was attempted. Chrysopids were never present in
grassland vegetation, but an adjacent lucerne field maintained a large
population. As the maize crop developed chrysopid population numbers
increased inside the field, presumably originating from the lucerne field. / Thesis (M.Sc (Environmental Science))--North-West University, Potchefstroom Campus, 2011.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/4469 |
| Date | January 2010 |
| Creators | Keulder, Rozelle |
| Publisher | North-West University |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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