Maize, a genetically diverse crop, is the third largest cereal crop in the world and the most important staple cereal in sub-Saharan Africa, supplying 50% of the calorie intake in this region. The stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) is a key constraint to cereal production in most resource-poor smallholder farming systems in sub-Saharan Africa causing crop losses accruing up to 88%. Previous studies have shown that feeding by herbivorous insects induces maize to emit volatiles attractive to natural enemies. However, these antagonists are recruited when damage has already been inflicted on the plant. Recent investigations revealed that egg deposition can induce maize landraces of Mesoamerican origin to emit volatiles attractive to C. partellus parasitoids, a trait previously reported to be absent in maize hybrids. However, genotypic variation in this indirect defence trait within maize varieties adapted to local agroclimatic conditions and the effect of processes such as domestication and breeding on this trait are not known. Moreover, it is not known whether maize varieties possessing this indirect defence trait can directly deter further herbivore colonization and constitutively suppress the herbivore‟s larval development or whether they can induce the same defence trait in neighbouring unattacked plants. This study sought to fill these knowledge gaps with the aim of exploiting these plant defence traits in the development of ecologically sound crop protection strategies. Experiments were conducted in which headspace volatile samples were collected from plants of wild, landrace and hybrid maize with and without C. partellus eggs. Chemical analyses were done using gas chromatography (GC), coupled GC-mass spectrometry (GC-MS) and coupled GC-Electroantenography (GC-EAG). Behavioural bioassays were done using egg (Trichogramma bournieri Pintureau (Hymenoptera: Trichogrammatidae)) and larval (Cotesia sesamiae Cameron (Hymenoptera: Braconidae)) parasitoids in a 4-arm olfactometer using volatiles collected from the plants. Moreover, C. partellus larval preference, growth and development as well as subsequent oviposition behaviour of gravid C. partellus moths on these plants were determined. Behavioural assays showed that both T. bournieri and C. sesamiae preferred volatiles from four of the five wild teosinte species, five landraces and one of two maize hybrids exposed to egg deposition. Similarly, volatiles collected from unoviposited maize landrace plants exposed to oviposited landrace maize plants emitting oviposition-induced volatiles, were attractive to both egg and larval parasitoids. Moreover, maize varieties emitting these oviposition-induced volatiles deterred further herbivore colonization and suppressed larval development. Volatile analysis by GC and GC-MS revealed marked increases in volatile emission as well as qualitative changes in the odour blends in four wild types, five landraces and one hybrid, following stemborer oviposition. Coupled GC-EAG analysis of attractive samples revealed that C. sesamiae was responsive to (E)-2- hexenal, (Z)-3-hexen-1-ol, nonane, 6-methyl-5-heptene-2-one, α-pinene, myrcene, limonene, (E)-4,8-dimethyl-1,3,7-nonatriene, decanal, 3,4-dimethylacetophenone and (E)-β-farnesene. Results from this study provide insights into tritrophic interactions thus paving the way for designing novel and ecologically sound pest management strategies through breeding crops with this novel oviposition-induced defence trait. / PhD (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Maize, a genetically diverse crop, is the third largest cereal crop in the world and the most important staple cereal in sub-Saharan Africa, supplying 50% of the calorie intake in this region. The stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) is a key constraint to cereal production in most resource-poor smallholder farming systems in sub-Saharan Africa causing crop losses accruing up to 88%. Previous studies have shown that feeding by herbivorous insects induces maize to emit volatiles attractive to natural enemies. However, these antagonists are recruited when damage has already been inflicted on the plant. Recent investigations revealed that egg deposition can induce maize landraces of Mesoamerican origin to emit volatiles attractive to C. partellus parasitoids, a trait previously reported to be absent in maize hybrids. However, genotypic variation in this indirect defence trait within maize varieties adapted to local agroclimatic conditions and the effect of processes such as domestication and breeding on this trait are not known. Moreover, it is not known whether maize varieties possessing this indirect defence trait can directly deter further herbivore colonization and constitutively suppress the herbivore‟s larval development or whether they can induce the same defence trait in neighbouring unattacked plants. This study sought to fill these knowledge gaps with the aim of exploiting these plant defence traits in the development of ecologically sound crop protection strategies. Experiments were conducted in which headspace volatile samples were collected from plants of wild, landrace and hybrid maize with and without C. partellus eggs. Chemical analyses were done using gas chromatography (GC), coupled GC-mass spectrometry (GC-MS) and coupled GC-Electroantenography (GC-EAG). Behavioural bioassays were done using egg (Trichogramma bournieri Pintureau (Hymenoptera: Trichogrammatidae)) and larval (Cotesia sesamiae Cameron (Hymenoptera: Braconidae)) parasitoids in a 4-arm olfactometer using volatiles collected from the plants. Moreover, C. partellus larval preference, growth and development as well as subsequent oviposition behaviour of gravid C. partellus moths on these plants were determined. Behavioural assays showed that both T. bournieri and C. sesamiae preferred volatiles from four of the five wild teosinte species, five landraces and one of two maize hybrids exposed to egg deposition. Similarly, volatiles collected from unoviposited maize landrace plants exposed to oviposited landrace maize plants emitting oviposition-induced volatiles, were attractive to both egg and larval parasitoids. Moreover, maize varieties emitting these oviposition-induced volatiles deterred further herbivore colonization and suppressed larval development. Volatile analysis by GC and GC-MS revealed marked increases in volatile emission as well as qualitative changes in the odour blends in four wild types, five landraces and one hybrid, following stemborer oviposition. Coupled GC-EAG analysis of attractive samples revealed that C. sesamiae was responsive to (E)-2- hexenal, (Z)-3-hexen-1-ol, nonane, 6-methyl-5-heptene-2-one, α-pinene, myrcene, limonene, (E)-4,8-dimethyl-1,3,7-nonatriene, decanal, 3,4-dimethylacetophenone and (E)-β-farnesene. Results from this study provide insights into tritrophic interactions thus paving the way for designing novel and ecologically sound pest management strategies through breeding crops with this novel oviposition-induced defence trait. / PhD (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Thesis (M.Sc. (Environmental Science and Management)--North-West University, Potchefstroom Campus, 2008

Thesis (M.Sc. (Environmental Science and Management)--North-West University, Potchefstroom Campus, 2008

Thesis (M.Sc. (Environmental Science and Management)--North-West University, Potchefstroom Campus, 2008

Host recognition behaviour of two braconid larval parasitoids Cotesia sesamiae and Cotesia flavipes was studied using suitable stemborer hosts [i.e. Busseola fusca for C. sesamiae, and Chilo partellus for C. flavipes] and one non-host [Eldana saccharina]. The wasps displayed similar sequences of behavioural steps when locating their hosts largely depending on their antennae for host recognition and both antennae and tarsi for final host acceptance and oviposition. Tactile and contact chemoreception stimuli from the hosts seem to play a major role in oviposition decision by the parasitoids. In addition, the external morphology and distribution pattern of sensilla present on antennae, tarsi and ovipositor of the parasitoids were examined by scanning electron and optic microscopy after staining with silver nitrate. Three sensillar types were identified on the distal antennomeres: (i) non-porous sensilla trichoidea most probably involved in mechanoreception, (ii) uniporous sensilla chaetica likely to be gustatory and, (iii) multiporous sensilla placodea likely to be olfactory. The tarsi possess a few sensilla chaetica which could be gustatory while the manubrium is likely to be used in detection of vibrations. The distal end of the ovipositor bears numerous multiporous dome-shaped sensilla. Additionally, the ability of the wasps to discriminate between contact cues was studied. When host larvae were washed in distilled water the wasps did not insert their ovipositors. However, ovipositor insertion resumed when washed host or non-host larvae were painted with water extracts of their respective host larvae. The water extracts of the suitable hosts were more attractive to the wasps than those of non-hosts. Similarly, the frass is important in host recognition during short-range examination as those of respective hosts are more intensely antennated than of non-hosts. The parasitoids were able to discriminate the regurgitant of E. saccharina by not antennating the cotton wool ball of this host; while the regurgitant of B. fusca and C. partellus appeared not useful in discriminating between the two species for both parasitoid species. Further analysis suggests the presence of a protein(s) component(s) in the regurgitant possibly responsible for host recognition and oviposition by C. flavipes. / Thesis (Ph.D. (Environmental Science))--North-West University, Potchefstroom Campus, 2009.

Host recognition behaviour of two braconid larval parasitoids Cotesia sesamiae and Cotesia flavipes was studied using suitable stemborer hosts [i.e. Busseola fusca for C. sesamiae, and Chilo partellus for C. flavipes] and one non-host [Eldana saccharina]. The wasps displayed similar sequences of behavioural steps when locating their hosts largely depending on their antennae for host recognition and both antennae and tarsi for final host acceptance and oviposition. Tactile and contact chemoreception stimuli from the hosts seem to play a major role in oviposition decision by the parasitoids. In addition, the external morphology and distribution pattern of sensilla present on antennae, tarsi and ovipositor of the parasitoids were examined by scanning electron and optic microscopy after staining with silver nitrate. Three sensillar types were identified on the distal antennomeres: (i) non-porous sensilla trichoidea most probably involved in mechanoreception, (ii) uniporous sensilla chaetica likely to be gustatory and, (iii) multiporous sensilla placodea likely to be olfactory. The tarsi possess a few sensilla chaetica which could be gustatory while the manubrium is likely to be used in detection of vibrations. The distal end of the ovipositor bears numerous multiporous dome-shaped sensilla. Additionally, the ability of the wasps to discriminate between contact cues was studied. When host larvae were washed in distilled water the wasps did not insert their ovipositors. However, ovipositor insertion resumed when washed host or non-host larvae were painted with water extracts of their respective host larvae. The water extracts of the suitable hosts were more attractive to the wasps than those of non-hosts. Similarly, the frass is important in host recognition during short-range examination as those of respective hosts are more intensely antennated than of non-hosts. The parasitoids were able to discriminate the regurgitant of E. saccharina by not antennating the cotton wool ball of this host; while the regurgitant of B. fusca and C. partellus appeared not useful in discriminating between the two species for both parasitoid species. Further analysis suggests the presence of a protein(s) component(s) in the regurgitant possibly responsible for host recognition and oviposition by C. flavipes. / Thesis (Ph.D. (Environmental Science))--North-West University, Potchefstroom Campus, 2009.

Organic insecticides play a big role in reducing the usage of chemical insecticides and their negative impact on the environment. Bacillus thuringiensis (Bt) spays are the only tool that organic farmers are allowed to use for the control of pests. Genetic engineering and modification of crops have been made possible with scientific advances in cell and molecular biology. These advances are used to transfer some of the Bt Cry toxins into crops for control of target species to reduce yield loss. Bt maize were commercialised for the first time in South Africa in 1998 and the economic important stem borers, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and Sesamia calamistis (Hampson) (Lepidoptera: Noctuidae) were exposed to the Cry1Ab toxin that is found in Bt maize. Busseola fusca developed resistance to Cry1Ab under field conditions within eight years after it had been released. Eldana saccharina (Walker) (Lepidoptera: Pyralidae) is a major pest on sugarcane in South Africa and although it has not been recorded on maize in this country, is it known as a major pest of maize in other African countries. African armyworm, Spodoptera exempta (Walker) (Lepidoptera: Noctuidae) has a very wide distribution in Africa and is known to be an occasional pest on maize. The aims of this dissertation were to determine the efficacy of Bt spray applications for control of four lepidopteran pests and whether development of Cry1Ab resistance by B. fusca caused a loss in susceptibility to other Bt toxins (i.e. cross-resistance). Susceptibility bioassays with 10 day old larvae were conducted under laboratory conditions. Treatments included application of various dosage rates of Dipel® and deltamethrin as well as exposure to MON810 (maize leaves). Stemborer populations of C. partellus, E. saccharina, and B. fusca (Venda) as well as the S. exempta were effectively controlled by the Bt spray, Dipel®. Care should be taken not be interpret the percentage C. partellus, E. saccharina and S. exempta larvae that survived after exposure to MON810 and Bt spray treatments as development of resistance without verification of these experiments with earlier instars that are known to be more susceptible. Spodoptera exempta is active throughout a year in temperate zones of Africa. If S. exempta develop resistance to Cry toxins and Bt maize events would be released for commercial planting in these areas, S. exempta pose a threat added to their injuriousness. Busseola fusca larvae were sampled from Venda (susceptible population), Ventersdorp and the Vaalharts Irrigation Scheme (resistant population). The Ventersdorp B. fusca population was controlled by MON810 and MON89034 and Bt sprays, but the percentage larvae that survived showed reduced susceptibility within the population. Dipel® treatments, MON810 and MON89034 did not provide effective control of the Vaalharts B. fusca population reported to be resistant to Cry1Ab, in two experiments. The high survival rates indicate a reduction in susceptibility to Cry toxins other than Cry1Ab and therefore development of cross resistance in the Vaalharts B. fusca population. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014

Organic insecticides play a big role in reducing the usage of chemical insecticides and their negative impact on the environment. Bacillus thuringiensis (Bt) spays are the only tool that organic farmers are allowed to use for the control of pests. Genetic engineering and modification of crops have been made possible with scientific advances in cell and molecular biology. These advances are used to transfer some of the Bt Cry toxins into crops for control of target species to reduce yield loss. Bt maize were commercialised for the first time in South Africa in 1998 and the economic important stem borers, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and Sesamia calamistis (Hampson) (Lepidoptera: Noctuidae) were exposed to the Cry1Ab toxin that is found in Bt maize. Busseola fusca developed resistance to Cry1Ab under field conditions within eight years after it had been released. Eldana saccharina (Walker) (Lepidoptera: Pyralidae) is a major pest on sugarcane in South Africa and although it has not been recorded on maize in this country, is it known as a major pest of maize in other African countries. African armyworm, Spodoptera exempta (Walker) (Lepidoptera: Noctuidae) has a very wide distribution in Africa and is known to be an occasional pest on maize. The aims of this dissertation were to determine the efficacy of Bt spray applications for control of four lepidopteran pests and whether development of Cry1Ab resistance by B. fusca caused a loss in susceptibility to other Bt toxins (i.e. cross-resistance). Susceptibility bioassays with 10 day old larvae were conducted under laboratory conditions. Treatments included application of various dosage rates of Dipel® and deltamethrin as well as exposure to MON810 (maize leaves). Stemborer populations of C. partellus, E. saccharina, and B. fusca (Venda) as well as the S. exempta were effectively controlled by the Bt spray, Dipel®. Care should be taken not be interpret the percentage C. partellus, E. saccharina and S. exempta larvae that survived after exposure to MON810 and Bt spray treatments as development of resistance without verification of these experiments with earlier instars that are known to be more susceptible. Spodoptera exempta is active throughout a year in temperate zones of Africa. If S. exempta develop resistance to Cry toxins and Bt maize events would be released for commercial planting in these areas, S. exempta pose a threat added to their injuriousness. Busseola fusca larvae were sampled from Venda (susceptible population), Ventersdorp and the Vaalharts Irrigation Scheme (resistant population). The Ventersdorp B. fusca population was controlled by MON810 and MON89034 and Bt sprays, but the percentage larvae that survived showed reduced susceptibility within the population. Dipel® treatments, MON810 and MON89034 did not provide effective control of the Vaalharts B. fusca population reported to be resistant to Cry1Ab, in two experiments. The high survival rates indicate a reduction in susceptibility to Cry toxins other than Cry1Ab and therefore development of cross resistance in the Vaalharts B. fusca population. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014