No description available.

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

No description available.

No description available.

Bibliography: leaves 113-144. Investigates the functions of the maternal, protein secretions of the endoparasitoid wasps Venturia canescens Gravenhorst regarding their role in providing protection against the host's immune system. Also investigates mucinous protein secretions on the egg surface and coagulation reactions and their role in protecting eggs against host cellular attacks.

Bibliography: leaves 113-144. / ix, 144 leaves, [56] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates the functions of the maternal, protein secretions of the endoparasitoid wasps Venturia canescens Gravenhorst regarding their role in providing protection against the host's immune system. Also investigates mucinous protein secretions on the egg surface and coagulation reactions and their role in protecting eggs against host cellular attacks. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied & Molecular Ecology, 2002

Bibliography: leaves 175-191. Trissolcus basalis (Wollaston) is a solitary endoparasitoid of the eggs of many pentatomid bugs. It is a quasi-gregarious scelenoid and aggressively defends host patches. In the Adelaide (S. Aust.) region its most abundant host is the native horehound bug, Agonoscelis rutila (Fabricius). This study of patch defence draws together important areas of research in parasitoid behavioural ecology, including the theories of adaptive superparasitism, sex ratio decisions, foraging behaviour and contest resolution.

Bibliography: leaves 165-188. This research examines biological and behavioural interactions among the diamond-back moth, Plutella xylostella L. (Lepidoptera: Plutellidae), Cotesia plutellae Kurdjumov (Hymenoptera: Braconidae) and the microbial insecticide, Bacillus thuringiensis Berliner. A deterministic simulation model is developed describing the influence of C. plutellae on the evolution of resistance to Bt in a diamond-back moth poulation.

The biology of Euphranta connexa was investigated to assess its potential as a biological control agent for introduction in North America against the invasive weeds Vincetoxicum rossicum (Kleopow) and V. nigrum (L.) (Apocynaceae). A range of temperatures suitable for development was determined for the pupal and egg stages of E. connexa. The pupa is the overwintering stage of E. connexa and does not exhibit a diapause, but undergoes a cold induced quiescence. The relationship of temperature to pupal developmental was investigated and did not differ among insects from sites over a range of altitude of 1300 m, indicating E. connexa may not be locally adapted. When adult female E. connexa emerged from pupae they had not developed eggs but 10 to 15 days later they had a full complement of developed eggs. Mating of E. connexa did not affect the egg load of females but egg load was reduced in females that had spent longer as pupae in cold conditions. There was evidence that females could reabsorb previously developed eggs. In surveys for larval and larval-pupal parasitoids of E. connexa infested seedpods of V. hirundinaria from three countries, there were a total of 1599 parasitoids from eight Hymenoptera families,and most parasitoids were Braconidae. Prior to the survey, the fruit midge, Contarinia asclepiadis (Diptera: Cecidomyiidae) was considered rare, but it was found in seedpods from all collection sites in Switzerland and infested about 9.2% of seedpods at two localities in 2013. Of 13 parasitoid morphospecies found in the survey, two braconid and one ichneumonid morphospecies were frequent and were parasitoids of E. connexa, three platygastrid morphospecies were probably parasitoids of C. asclepiadis, and three morphospecies were probably hyperparasitoids. The thesis research will allow development of effective methods for studying impact and host range of E. connexa, studies that are required to assess the potential as a biological control agent against V. rossicum and V. nigrum.