1 |
An investigation into the development and status of resistance of Busseola fusca (Lepidoptera: Noctuidae) to Bt maize / Marlene KrugerKruger, Marlene January 2010 (has links)
Based on surface area, South Africa is currently ranked 8th in planting genetically
modified (GM) crops in the world. The stem borer, Busseola fusca (Fuller) (Lepidoptera:
Noctuidae) is of economic importance throughout sub–Saharan Africa. Bt maize
(MON810) has been grown to control lepidopterous stem borers in South Africa since its
first release in 1998. The first report of resistance to Bt maize was made in the
Christiana area of South Africa in 2007. The objectives of this study were to evaluate
the status of resistance of populations of B. fusca to Bt maize; to evaluate farmers'
perceptions of the regulatory aspects guiding the planting of Bt maize and refugia and
how the field situation developed between 1998 and 2010; to compare the fitness of the
fertility, fecundity and longevity of Bt–resistant and susceptible B. fusca populations and
to determine if there are fitness costs associated with resistance of B. fusca to Bt maize.
Questionnaire surveys were conducted amongst 185 farmers in seven districts
throughout the maize production region. The questionnaire addressed signing of
contracts upon purchasing GM seed, refuge compliance, pest management practices,
perceived benefits and risks relating to Bt maize. In order to study fitness and fitness
costs that may be associated with resistance development, the life history parameters of
known Bt–resistant and susceptible populations were compared in the laboratory using a
diapauses–as well as second–generation populations collected in maize fields. The
following parameters were compared between different stem borers populations and
treatments: pupal mass, moth longevity, fecundity, fertility, larval mass and survival, and
sex ratio. This study confirmed resistance of B. fusca to the Cry1Ab toxin (MON810)
and that larvae collected from refugia at Vaalharts were resistant and survived on Bt
maize. Compliance to refugia requirements was low especially during the initial 5 – 7
years after release. An alarmingly high number of farmers applied insecticides as
preventative sprays on Bt maize and refugia. Except for moth longevity and LT50–
values, no other fitness costs were observed to be associated with the resistance trait in
the highly resistant B. fusca population used in this study. The LT50 may indicate some
degree of fitness cost but does not translate into observable costs in terms of fecundity,
larval mass and survival. The absence of fitness costs may promote the use of
alternative Bt–resistance management strategies, such as the introduction of a multigene strategy. The introduction of a stacked event such as MON89034 which produces
more than one protein with activity active against the resistant target pest, together with
compliance to the refuge strategy, is most likely the only solution to managing Btresistant
stem borer populations in South Africa. / Thesis (Ph.D. (Environmental Science))--North-West University, Potchefstroom Campus, 2011.
|
2 |
An investigation into the development and status of resistance of Busseola fusca (Lepidoptera: Noctuidae) to Bt maize / Marlene KrugerKruger, Marlene January 2010 (has links)
Based on surface area, South Africa is currently ranked 8th in planting genetically
modified (GM) crops in the world. The stem borer, Busseola fusca (Fuller) (Lepidoptera:
Noctuidae) is of economic importance throughout sub–Saharan Africa. Bt maize
(MON810) has been grown to control lepidopterous stem borers in South Africa since its
first release in 1998. The first report of resistance to Bt maize was made in the
Christiana area of South Africa in 2007. The objectives of this study were to evaluate
the status of resistance of populations of B. fusca to Bt maize; to evaluate farmers'
perceptions of the regulatory aspects guiding the planting of Bt maize and refugia and
how the field situation developed between 1998 and 2010; to compare the fitness of the
fertility, fecundity and longevity of Bt–resistant and susceptible B. fusca populations and
to determine if there are fitness costs associated with resistance of B. fusca to Bt maize.
Questionnaire surveys were conducted amongst 185 farmers in seven districts
throughout the maize production region. The questionnaire addressed signing of
contracts upon purchasing GM seed, refuge compliance, pest management practices,
perceived benefits and risks relating to Bt maize. In order to study fitness and fitness
costs that may be associated with resistance development, the life history parameters of
known Bt–resistant and susceptible populations were compared in the laboratory using a
diapauses–as well as second–generation populations collected in maize fields. The
following parameters were compared between different stem borers populations and
treatments: pupal mass, moth longevity, fecundity, fertility, larval mass and survival, and
sex ratio. This study confirmed resistance of B. fusca to the Cry1Ab toxin (MON810)
and that larvae collected from refugia at Vaalharts were resistant and survived on Bt
maize. Compliance to refugia requirements was low especially during the initial 5 – 7
years after release. An alarmingly high number of farmers applied insecticides as
preventative sprays on Bt maize and refugia. Except for moth longevity and LT50–
values, no other fitness costs were observed to be associated with the resistance trait in
the highly resistant B. fusca population used in this study. The LT50 may indicate some
degree of fitness cost but does not translate into observable costs in terms of fecundity,
larval mass and survival. The absence of fitness costs may promote the use of
alternative Bt–resistance management strategies, such as the introduction of a multigene strategy. The introduction of a stacked event such as MON89034 which produces
more than one protein with activity active against the resistant target pest, together with
compliance to the refuge strategy, is most likely the only solution to managing Btresistant
stem borer populations in South Africa. / Thesis (Ph.D. (Environmental Science))--North-West University, Potchefstroom Campus, 2011.
|
3 |
The indirect effect of Cry 1Ab protein expressed in Bt maize, on the biology of Chrysoperla pudica (Neuroptera: Chrysopidae) / Jo-Ann Francis WarrenWarren, Jo-Ann Francis January 2014 (has links)
Genetically modified (GM) maize was developed mainly to control lepidopteran pests
such as the maize stem borer (Busseola fusca) (Lepidoptera: Noctuidae). Since the
first commercialization of GM crops with insecticidal properties, possible non-target
effects such as the effect at the third trophic level on important predators for example
lacewing species (Chrysoperla spp.) have been of concern. Contradicting results
were reported in previous studies with regard to the effect of Cry 1Ab protein
produced by Bt maize on the performance of lacewings. Some studies found that Bt
proteins had no effect while others reported that C. carnea performed poorly if they
consumed prey that consumed Cry 1Ab protein. In South Africa one of the most
common chrysopid species in maize ecosystems is Chrysoperla pudica (Navás)
(Neuroptera: Chrysopidae). Evolution of Bt resistant pests, such as B. fusca in
South Africa facilitates a new pathway for exposure of predators to healthy prey that
consumes Cry 1Ab proteins. The aims of this study was to determine the effect of
the Cry 1Ab protein expressed in Bt maize on a non-target organism‟s (C. pudica)
biology via indirect exposure, and to determine the concentration of Cry 1Ab protein
in the plant, prey and predator. Chrysoperla pudica larvae were indirectly exposed
to the Bt-toxin through healthy Bt-maize feeding prey (B. fusca larvae) in two feeding
experiments and lacewing survival and life history parameters recorded. Bt had a
limited effect on some parameters that were evaluated. The larval and pupal periods
of C. pudica larvae that were exposed to the Bt-toxin had a significant difference
from that of the control treatment. The Bt-toxin had a significant effect on fecundity,
fertility and malformation after emergence of C. pudica adults of which larvae fed
only on Bt resistant B. fusca larvae, but not on the mortality rate. Cry 1Ab
concentration was the highest in the plant, followed by the prey and lacewing larvae.
This study showed that the Cry 1Ab protein had a slight adverse effect only on
certain life parameters of C. pudica, and that Cry 1Ab protein was hardly detectable
in C. pudica larvae. However, since this study represented a worst-case scenario
where diverse prey was not available, insignificant effects is expected under field
conditions where prey is diverse. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014
|
4 |
Bt maize and frogs : an investigation into possible adverse effects of Bt toxin exposure to amphibian larvae / J.L. Zaayman.Zaayman, Jazel Larissa January 2012 (has links)
Genetically modified maize expressing the Bt-protein Cry1Ab (Bt maize) is planted widely in South Africa. Crop residues of Bt maize often end up in aquatic ecosystems where aquatic organisms are exposed to Cry1Ab protein. The effect of this protein on non-target aquatic organisms has not yet been studied in South Africa. The aim of this study was to evaluate the possible effect of exposure to Bt maize on morphological development of Xenopus laevis and Amietophrynus gutturalis tadpoles. Three experiments were conducted with each of X. laevis and A. gutturalis. Five of these were conducted in the bio-secure Amphibian Biology laboratory and one with A. gutturalis in a shade-house facility where microcosms were exposed to natural conditions. In the first experiment of X. laevis and A. gutturalis, which was replicated three times, large portions of maize leaves were placed in the bottoms of microcosms. X. laevis received supplementary pulverised leaves in suspension while A. gutturalis tadpoles fed on provided leaves. For both control and experimental groups microcosms were divided in three groups receiving respectively 15, 30 and 45 g of maize leaves. In the second and third experiment tadpoles only received pulverised Bt maize leaves in suspension. Each replicate (microcosm) contained 50 one-day old tadpoles. Experiment two was conducted to determine whether the Bt-protein has adverse effects on A. gutturalis tadpoles when tadpoles are exposed to the protein in the water but not feeding on the plant material. A total of 100 tadpoles were used during the experiment and tadpoles were placed individually in 250 ml plastic cups that were filled with 100 ml water witch contained an extract of either Bt and non-Bt maize leaves. Tadpoles were fed twice a week with TetraTabimin bottom-feeding fish pellets in suspension. Experiment three was conducted to determine whether the Bt-protein will have adverse effects on A. gutturalis tadpoles when tadpoles feed on Bt maize leaves. Tadpoles were divided into a treatment in which 50 tadpoles were fed Bt maize leaves and a control treatment in which 50 tadpoles were fed non-Bt maize leaves. Tadpoles were placed individually in 250 ml plastic cups that were each filled with 100 ml borehole water. On a weekly basis 10 randomly selected tadpoles were collected, measured and staged for morphological development, using the Nieuwkoop and Faber Normal Table for X. laevis and Gosner stages for A. gutturalis tadpoles. The significant effects observed in some life history parameters of tadpoles exposed to Cry1Ab protein cannot be ascribed to the effect of the protein. Poor husbandry turned out to be the single most important confounding factor. Before follow-up studies are conducted husbandry practices should be optimized. / Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2013.
|
5 |
The indirect effect of Cry 1Ab protein expressed in Bt maize, on the biology of Chrysoperla pudica (Neuroptera: Chrysopidae) / Jo-Ann Francis WarrenWarren, Jo-Ann Francis January 2014 (has links)
Genetically modified (GM) maize was developed mainly to control lepidopteran pests
such as the maize stem borer (Busseola fusca) (Lepidoptera: Noctuidae). Since the
first commercialization of GM crops with insecticidal properties, possible non-target
effects such as the effect at the third trophic level on important predators for example
lacewing species (Chrysoperla spp.) have been of concern. Contradicting results
were reported in previous studies with regard to the effect of Cry 1Ab protein
produced by Bt maize on the performance of lacewings. Some studies found that Bt
proteins had no effect while others reported that C. carnea performed poorly if they
consumed prey that consumed Cry 1Ab protein. In South Africa one of the most
common chrysopid species in maize ecosystems is Chrysoperla pudica (Navás)
(Neuroptera: Chrysopidae). Evolution of Bt resistant pests, such as B. fusca in
South Africa facilitates a new pathway for exposure of predators to healthy prey that
consumes Cry 1Ab proteins. The aims of this study was to determine the effect of
the Cry 1Ab protein expressed in Bt maize on a non-target organism‟s (C. pudica)
biology via indirect exposure, and to determine the concentration of Cry 1Ab protein
in the plant, prey and predator. Chrysoperla pudica larvae were indirectly exposed
to the Bt-toxin through healthy Bt-maize feeding prey (B. fusca larvae) in two feeding
experiments and lacewing survival and life history parameters recorded. Bt had a
limited effect on some parameters that were evaluated. The larval and pupal periods
of C. pudica larvae that were exposed to the Bt-toxin had a significant difference
from that of the control treatment. The Bt-toxin had a significant effect on fecundity,
fertility and malformation after emergence of C. pudica adults of which larvae fed
only on Bt resistant B. fusca larvae, but not on the mortality rate. Cry 1Ab
concentration was the highest in the plant, followed by the prey and lacewing larvae.
This study showed that the Cry 1Ab protein had a slight adverse effect only on
certain life parameters of C. pudica, and that Cry 1Ab protein was hardly detectable
in C. pudica larvae. However, since this study represented a worst-case scenario
where diverse prey was not available, insignificant effects is expected under field
conditions where prey is diverse. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014
|
6 |
Bt maize and frogs : an investigation into possible adverse effects of Bt toxin exposure to amphibian larvae / J.L. Zaayman.Zaayman, Jazel Larissa January 2012 (has links)
Genetically modified maize expressing the Bt-protein Cry1Ab (Bt maize) is planted widely in South Africa. Crop residues of Bt maize often end up in aquatic ecosystems where aquatic organisms are exposed to Cry1Ab protein. The effect of this protein on non-target aquatic organisms has not yet been studied in South Africa. The aim of this study was to evaluate the possible effect of exposure to Bt maize on morphological development of Xenopus laevis and Amietophrynus gutturalis tadpoles. Three experiments were conducted with each of X. laevis and A. gutturalis. Five of these were conducted in the bio-secure Amphibian Biology laboratory and one with A. gutturalis in a shade-house facility where microcosms were exposed to natural conditions. In the first experiment of X. laevis and A. gutturalis, which was replicated three times, large portions of maize leaves were placed in the bottoms of microcosms. X. laevis received supplementary pulverised leaves in suspension while A. gutturalis tadpoles fed on provided leaves. For both control and experimental groups microcosms were divided in three groups receiving respectively 15, 30 and 45 g of maize leaves. In the second and third experiment tadpoles only received pulverised Bt maize leaves in suspension. Each replicate (microcosm) contained 50 one-day old tadpoles. Experiment two was conducted to determine whether the Bt-protein has adverse effects on A. gutturalis tadpoles when tadpoles are exposed to the protein in the water but not feeding on the plant material. A total of 100 tadpoles were used during the experiment and tadpoles were placed individually in 250 ml plastic cups that were filled with 100 ml water witch contained an extract of either Bt and non-Bt maize leaves. Tadpoles were fed twice a week with TetraTabimin bottom-feeding fish pellets in suspension. Experiment three was conducted to determine whether the Bt-protein will have adverse effects on A. gutturalis tadpoles when tadpoles feed on Bt maize leaves. Tadpoles were divided into a treatment in which 50 tadpoles were fed Bt maize leaves and a control treatment in which 50 tadpoles were fed non-Bt maize leaves. Tadpoles were placed individually in 250 ml plastic cups that were each filled with 100 ml borehole water. On a weekly basis 10 randomly selected tadpoles were collected, measured and staged for morphological development, using the Nieuwkoop and Faber Normal Table for X. laevis and Gosner stages for A. gutturalis tadpoles. The significant effects observed in some life history parameters of tadpoles exposed to Cry1Ab protein cannot be ascribed to the effect of the protein. Poor husbandry turned out to be the single most important confounding factor. Before follow-up studies are conducted husbandry practices should be optimized. / Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2013.
|
Page generated in 0.0471 seconds