Diversity, host plant range and ecology of Lepidoptera stem borers in South Africa
- Authors: Stemele, Mxolisi Arnold
- Date: 2019
- Subjects: Lepidoptera Host plants Stem borers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/15409 , vital:40405
- Description: The biology and ecology of Lepidopteran pests stem borers has been extensively studied because of the economic importance of pest species such as Busseola fusca (Fuller) (Noctuidae), Sesamia calamistis (Hampson) (Noctuidae), Chilo partellus (Swinhoe) (Crambidae), and Eldana saccharina (Walker) (Pyralidae). Knowledge relating to diversity, infestation dynamics, and host plant range is readily available. In natural vegetation, the variety of stem borers is higher than that found in agroecosystems. However, there is a paucity of South African studies that explain the observed differences in diversity between the two systems. Stem borers are also known to exhibit species-specific ecological requirements, which influence their distribution between African countries. South African biomes are classified based on vegetation structure and climate, which happens to be the most critical factors that affect the distribution of phytophagous insects. This makes biomes an excellent model to investigate diversity and distribution of stem borer species. In this study, we investigated diversity, distribution and species composition in four biomes. The results showed that diversity and distribution of the stem borers in natural vegetation was determined by host plant distribution. Stem borer diversity correlated with high diversity of host plants. Thirty-two stem borer species were collected from 27 host plants and another three from light traps. Widely distributed host plants supported a higher diversity of stem borers, which is consistent with the resource availability hypotheses. Non-metric dimensional scale unfolding revealed disparity in host plant preference and plant species composition between the various stem borer families (Kruskal’s Stress = 0.16). Tortricidae species and Sesamia typhae (Le rü) (Noctuidae) feed exclusively on hydrophytic Cyperaceae species. The majority of Noctuidae, Crambidae and Phycitidae species collected were oligophagous on terrestrial Poaceae, with a few polyphagous exceptions feeding on hydrophytic Cyperaceae and Typhaceae. Additionally, species composition of Poaceae host plants differed between 8 Crambidae and the Phycitidae species. Stem borer species composition between biomes revealed the presence of distinct host plants (2D stress = 0.09) and stem borer (2D stress = 0.13) communities. The stem borer abundance and diversity were strongly correlated (R2 = 0.64), but species diversity (R2 = - 0.95) and host plant diversity (R2 = - 0.85) were inversely correlated to altitude. Based on these results it was concluded that stem borer diversity and distribution in natural vegetation was influenced by host plant diversity and distribution as well as climate associated with altitudinal gradients. In the last two decades, four stem borer species previously known on wild host plants; Busseola segeta (Bowden), Busseola phaia (Bowden), Pirateolea piscator (Fletcher) and Conicofrontia sesamoides (Hampson) have invaded cultivated crops. These invasions remained undetected because of a shortage of surveys, habitat transformation and misidentifications. Misidentifications are common among stem borers due to the considerable resemblance between morphospecies. In this study, we assessed the capacity of the mitochondrial gene Cytochrome c oxidase (COI) to delineate closely related species to develop monitoring and early detection of invasive species and to assess migration patterns and gene flow between the populations. The results demonstrated that COI is an effective DNA marker for species delineation and assessment of intra- and interspecific genetic relationship. The K2P distances and phylogenetic tree defined boundaries between Noctuidae species with high resolution. No divergence distance was detected between intraspecific species, but for the congener species, divergence distance was 0.044%-0.111% with an average of 0.076%. The average interspecies K2P distance (0.57%) was 5-15 times higher than the congener species distances. Phylogenetic analysis revealed the presence of two clades. Busseola and Sesamia species were connected in a monophyletic clade with a strong (93%) bootstrap. The second monophyletic clade comprised of a cluster of Pirateolea, Acrapex and Conicofrontia species, and this was also supported with 9 a strong bootstrap (100%). The gene flow study revealed low levels of genetic differentiation between the populations of B. fusca collected from different maize producing areas in South Africa. This low genetic differentiation was consistent with high gene flow. The number of effective migrants between the populations was between 8 and 99 individuals per generation. These results indicate high connectivity between the populations.
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- Date Issued: 2019
Extraction, isolation and characterization of oleanolic acid and its analogues from Syzygium aromaticum (cloves) and evaluation of their biological activities
- Authors: khwaza, Vuyolwethu
- Date: 2019
- Subjects: Antibacterial agents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/19076 , vital:39882
- Description: Pathogenic microorganisms have serious impact on people's lives. Every year, millions of people around the world die of bacterial infections. Resistance to common antibacterial drugs has proven to be a challenging problem in control of bacterial infections. In an attempt to develop an effective and affordable treatment for bacterial infections, oleanolic acid isolated from syzygium aromaticum conjugates incorporating other pharmaceutical scaffolds such as chloroquine derivatives, curcumin, and ergocalciferol etc have been developed. Based on the previous successes of testing combination of antimicrobial drugs and pharmaceutical drugs which appeared to be the promising strategy to overcome treatment failure; a series of hybrid compounds containing oleanolic acid and other pharmaceutical scaffolds were synthesized. 4- Aminoquinoline derivatives were first hybridized with selected organic compounds to form a class of hybrid compounds containing either amide bond or ester bond as a linker between the precursor molecules. Analogues/hybrid compounds can overcome the disadvantages of combination therapy such as drug-drug interaction. The structural effects of this type of conjugation of oleanolic acid and other pharmaceutical scaffolds were characterised by FTIR, Mass Spec and NMR spectroscopy. These compounds were studied along with the monosubstituted oleanolic acid analogues and the organic components in order to compare the effects of the substitution on their biological response.‖ All the synthesized analogues were tested against 11 bacterial strains on both Gram-positive and Gram-negative bacteria. The synthesized compounds showed selectivity and higher activity against Enterococcus faecalis (EF), Klebsiella oxytoca (KO), Escherischia coli (EC), Staphylococcus aureous (SA), Proteus vulgaris (PV) and Bacillus subtilis (BS) with MIC values; ranging between of 1.25 mg/mL to 0.072 mg/mL
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- Date Issued: 2019