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Egg-laying decisions can have significant fitness consequences. In female Drosophila melanogaster, egg-laying involves foraging-like behaviour. Natural allelic variation in foraging (for) underlies the rover/sitter foraging behaviour polymorphism found in D. melanogaster. for encodes a cGMP-dependent protein kinase (PKG) where rovers have higher for-PKG transcript levels and PKG activity than sitters. Interestingly, the orthologue of for in nematodes (egl-4) affects both egg-laying and foraging behaviours. When given a choice between low- and high-nutrient patches, rovers preferentially lay more eggs on the low-nutrient patches while sitters and a sitter mutant prefer high-nutrient patches. Using the neuronal driver elav-GAL4, rover-like preferences were rescued in sitter flies. Compared to sitters, rovers have higher fitness on a sub-optimal substrate which may explain the observed egg-laying preferences. By studying the link from genes to behaviour, this study provides insight to the evolutionary basis and maintenance of behaviour.

Egg-laying decisions can have significant fitness consequences. In female Drosophila melanogaster, egg-laying involves foraging-like behaviour. Natural allelic variation in foraging (for) underlies the rover/sitter foraging behaviour polymorphism found in D. melanogaster. for encodes a cGMP-dependent protein kinase (PKG) where rovers have higher for-PKG transcript levels and PKG activity than sitters. Interestingly, the orthologue of for in nematodes (egl-4) affects both egg-laying and foraging behaviours. When given a choice between low- and high-nutrient patches, rovers preferentially lay more eggs on the low-nutrient patches while sitters and a sitter mutant prefer high-nutrient patches. Using the neuronal driver elav-GAL4, rover-like preferences were rescued in sitter flies. Compared to sitters, rovers have higher fitness on a sub-optimal substrate which may explain the observed egg-laying preferences. By studying the link from genes to behaviour, this study provides insight to the evolutionary basis and maintenance of behaviour.

1 v. (various paging) : ill. ; 27 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Dept. of Zoology, University of Adelaide, 1975

Thesis (Ph.D.) -- Dept. of Zoology, University of Adelaide, 1975.

This thesis focuses on the UK pond newts, the smaller bodied species known as Lissotriton newts and the larger Triturus. The primary aims were to identify and address gaps in the current Tritus/Lissotriton literature; to provide a more complete understanding of this group as many assumptions about morphology and physiology exist untested, for example that larger/fatter females will lay more eggs. Specifically for Lissotriton helveticus, many assumptions are based on the similarly sized Lissotriton vulgaris, potentially missing any species specific differences. A further focus of the work was to provide a clearer view over the whole breeding season; using measures of condition over a season and egg-laying.

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

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