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Aspects of the biology, thermal physiology and nutritional ecology of Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae), a specialist herbivore introduced into South Africa for the biological control of Chromolaena odorata (L.) King and Robinson (Asteraceae)
No full textChromolaena odorata (L.) King and Robinson (Asteraceae) is an invasive weedy shrub
native to the Americas that has proven to be a significant economic and ecological burden to
many tropical and sub-tropical regions of the world where it impacts negatively on
agriculture, biodiversity and livelihoods. A distinct biotype of C. odorata was first recognised
as naturalized in KwaZulu-Natal (KZN) province, South Africa, in the 1940s and has since
spread to other climatically suitable provinces. Pareuchaetes insulata (Walker) (Lepidoptera:
Erebidae: Arctiinae) was released in KZN, South Africa, as a biological control agent against
the weed between 2001 and 2009. Although the moth did establish at one out of some 30
release sites, its population level is generally low in the field. This thesis attempts to unravel
the reasons for the poor performance of P. insulata in South Africa.Studies of life history traits of P. insulata in the laboratory indicated that the moth possess
good biological attributes such as low mortality, high fecundity, egg hatchability and high
female mating success. Overall, adult female moths eclosed before their male counterparts
suggesting the presence of protogyny. Beyond the contribution of this study to our
understanding of the life history traits of erebid moths, it hypothesized that the absence of
protandry might have contributed to the low population levels of the moth in the field.
To determine if a degree of agent-host plant incompatibility is culpable for the poor
performance of P. insulata, insect performance metrics were compared on two distinct C.
odorata plants (one from Florida and another from South Africa) in laboratory experiments.
Pareuchaetes insulata performance metrics were similar on both plant forms; there were no
significant differences in total leaf area consumed, egg and larval development, immature
survival rates, feeding index (FI), host suitability index (HSI), growth index (GI), and
fecundity between the Floridian and southern African C. odorata plants. In sum, there was no
evidence to demonstrate that differences in plant forms in C. odorata are culpable for the
poor performance of P. insulata in South Africa.The effects of temperature on the developmental and reproductive life history traits,
locomotion performance and thermal tolerance range of P. insulata were studied in order to
elucidate the possible role of temperature on the poor performance of the moth. The results
showed that at temperatures below 25 °C, mortality increased and development time was
prolonged. Fecundity and egg hatchability were negatively affected at a constant temperature
of 15 °C. Results futher showed that third instar larvae were unable to initiate movement at 6
°C and locomotor abilities were significantly reduced at 11 °C. In sum, it is hypothesized
that both direct and indirect negative impacts of low temperature may partly explain the poor
performance of P. insulata in South Africa.
Theeffects of seasonal and spatial variations in the leaf characteristics of C. odorata on the
performance of P. insulata were investigated. Foliar nitrogen and magnesium concentrations
were higher in shaded plants during winter due to low temperatures. Leaves of C. odorata
plants growing in the shaded habitat (relative to full sun) and leaves of plants during autumn
(relative to winter) were more nutritionally balanced and suitable for herbivore performance.
Consequently, P. insulata developed faster, had heavier pupal mass and increased fecundity
when reared on shaded leaves (relative to full sun) or when reared on autumn leaves
compared to leaves growing in winter. This study demonstrates that low winter temperatures
can indirectly affect insect herbivore performance by changing the phytochemistry of host
plant and hypothesized that excess nitrogen and possibly magnesium may have detrimental
effects on the insect herbivore performance.A cross-feeding experiment was conducted to determine P. insulata response to a change in
the diet of offspring due to a shift in plant quality in shaded versus full sun habitats. The
results showed that a ‘negative switch’ in herbivore diet (i.e. when progeny from parents
reared on shaded leaves were fed on full sun leaves) resulted in high (40%) mortality,
prolonged development time and reduced fecundity. Thus full sun foliage is an inferior diet
for P. insulata offspring. In laboratory experiments, foliar nitrogen was positively correlated
with the performance of P. insulata.
From this study, it is demonstrably evident that the poor performance of P. insulata on C.
odorata in South Africa is caused by multiple factors such as low temperatures as well as
spatio-temporal variations in the leaf characteristic of C. odorata leaves. This study shows
the complexity of determining the causes of low populations and apparent low impact of
biological control agents and herbivorous insects generally, in the field. The implications of
this research to the biological control programme against C. odorata and the direction of
future research for the control of C. odorata are discussed
Towards an evaluation and protection strategy for critical infrastructure
No full textCritical Infrastructure is often overlooked from an Information Security perspective as being of high importance to protect which may result in Critical Infrastructure being at risk to Cyber related attacks with potential dire consequences. Furthermore, what is considered Critical Infrastructure is often a complex discussion, with varying opinions across audiences.
Traditional Critical Infrastructure included power stations, water, sewage pump stations, gas pipe lines, power grids and a new entrant, the “internet of things”. This list is not complete and a constant challenge exists in identifying Critical Infrastructure and its interdependencies.
The purpose of this research is to highlight the importance of protecting Critical Infrastructure as well as proposing a high level framework aiding in the identification and securing of Critical Infrastructure. To achieve this, key case studies involving Cyber crime and Cyber warfare, as well as the identification of attack vectors and impact on against Critical Infrastructure (as applicable to Critical Infrastructure where possible), were identified and discussed. Furthermore industry related material was researched as to identify key controls that would aid in protecting Critical Infrastructure.
The identification of initiatives that countries were pursuing, that would aid in the protection of Critical Infrastructure, were identified and discussed. Research was conducted into the various standards, frameworks and methodologies available to aid in the identification, remediation and ultimately the protection of Critical Infrastructure. A key output of the research was the development of a hybrid approach to identifying Critical Infrastructure, associated vulnerabilities and an approach for remediation with specific metrics (based on the research performed).
The conclusion based on the research is that there is often a need and a requirement to identify and protect Critical Infrastructure however this is usually initiated or driven by non-owners of Critical Infrastructure (Governments, governing bodies, standards bodies and security consultants). Furthermore where there are active initiative by owners very often the suggested approaches are very high level in nature with little direct guidance available for very immature environments
Development of high performance computing cluster for evaluation of sequence alignment algorithms.
No full textAs the biological databases are increasing rapidly, there is a challenge for both Biologists and Computer Scientists to develop algorithms and databases to manage the increasing data. There are many algorithms developed to align the sequences stored in biological databases - some take time to process the data while others are inefficient to produce reasonable results.
As more data is generated, and time consuming algorithms are developed to handle them, there is a need for specialized computers to handle the computations. Researchers are typically limited by the computational power of their computers. High Performance Computing (HPC) field addresses this challenge and can be used in a cost-effective manner where there is no need for expensive equipment, instead old computers can be used together to form a powerful system. This is the premise of this research, wherein the setup of a low-cost Beowulf cluster is explored, with the subsequent evaluation of its performance for processing sequent alignment algorithms.
A mixed method methodology is used in this dissertation, which consists of literature study, theoretical and practise based system. This mixed method methodology also have a proof and concept where the Beowulf cluster is designed and implemented to perform the sequence alignment algorithms and also the performance test.
This dissertation firstly gives an overview of sequence alignment algorithms that are already developed and also highlights their timeline. A presentation of the design and implementation of the Beowulf Cluster is highlighted and this is followed by the experiments on the baseline performance of the cluster. A detailed timeline of the sequence alignment algorithms is given and also the comparison between ClustalW-MPI and T-Coffee (Tree-based Consistency Objective Function For alignment Evaluation) algorithm is presented as part of the findings in the research study. The efficiency of the cluster was observed to be 19.8%, this percentage is unexpected because the predicted efficiency is 83.3%, which is found in the theoretical cluster calculator. The theoretical performance of the cluster showed a high performance as compared with the experimental performance, this is attributable to the slow network, which was 100Mbps, low processor speed of 2.50 GHz, and low memory of 2 Gigabytes
Corrole–BODIPY conjugates: enhancing the fluorescence and phosphorescence of the corrole complex via efficient through bond energy transfer
Get PDFNew corrole–BODIPY conjugates have been synthesized in high yield under mild conditions. Upon excitation at the absorption maximum of the BODIPY antenna chromophore, the fluorescence intensity of the free base corrole–BODIPY conjugate increases by ca. 300%, and significant phosphorescence intensity is observed for the iridium(III) complex of the conjugate, while almost no phosphorescence is observed for the parent iridium(III) corrole, due to through-bond energy transfer from the BODIPY antenna-chromophore to the corrole core.Original publication is available at http://dx.doi.org/10.1039/c5ra07250
Photophysical studies of newly derivatized mono substituted phthalocyanines grafted onto silica nanoparticles via click chemistry
No full textThis work reports on the synthesis, characterization and photophysical studies of newly derived phthalocyanine complexes and the phthalocyanine–silica nanoparticles conjugates. The derived phthalocyanine complexes have one terminal alkyne group. The derived phthalocyanine complexes showed improved photophysical properties (ФF, ФT, ΦΔ and τT) compared to the respective phthalocyanine complexes from which they were derived. The derived phthalocyanine complexes were conjugated to the surface of an azide functionalized silica nanoparticles via copper (1) catalyzed cyclo-addition reaction. All the conjugates showed lower triplet quantum yields ranging from 0.37 to 0.44 compared to the free phthalocyanine complexes. The triplet lifetimes ranged from 352 to 484 μs for the conjugates and from 341 to 366 μs for the free phthalocyanine complexes.Original publication is available at http://dx.doi.org/10.1016/j.saa.2014.12.07
Nonlinear optical response of tetra and mono substituted zinc phthalocyanine complexes
No full textThe nonlinear absorption properties of 6 mono-substituted and 3 symmetric zinc phthalocyanine complexes have been studied in dimethylsulfoxide (DMSO) using 10 ns pulses at 532 nm. The non linear absorption of the complexes has been studied using the Z-scan technique. The study showed that both the singlet and triplet excited states contribute to the non linear absorption behavior. The nonlinear third-order susceptibility and second-order hyperpolarizability values of the complexes are reported. It was observed that two of the symmetric phthalocyanine complexes (5-α substituted with aminophenoxy and 9-β substituted with carboxyphenoxy) showed better and promising optical nonlinearity when compared to the other complexes studied.Original publication is available at http://dx.doi.org/10.1016/j.jlumin.2015.06.00
Comparative electrocatalytic studies of nanocomposites of mixed and covalently linked multiwalled carbon nanotubes and 4-(4,6-diaminopyrimidin-2-ylthio) phthalocyaninato cobalt(II)
No full textElectrocatalytic behavior of 4-(4,6-diaminopyrimidin-2-ylthio) phthalocyaninato cobalt(II) (CoPyPc) when mixed or covalently mixed to multiwalled carbon nanotubes (MWCNTs) is reported. Infra-red spectroscopy was used to confirm amide linkage of the covalently linked nanocomposite. Rotating disk electrode (RDE) and cyclic (CV) voltammetry studies were used for the electrochemical characterization of the prepared phthalocyanine and MWCNT nanocomposite. The electrocatalytic effects of the nanocomposites of the cobalt phthalocyanine derivative were then investigated towards l-cysteine oxidation using both RDE and CV experiments, and the electrocatalytic performance of the covalently linked cobalt phthalocyanine-MWCNT was found to be superior over the mixed nanocomposite.Original publication is available at http://dx.doi.org/10.1016/j.poly.2015.05.03
Comparative photophysicochemical behavior of nanoconjugates of indium tetracarboxyphenoxy phthalocyanines covalently linked to CdTe/ZnSe/ZnO quantum dots
No full textThis work reports on the photophysicochemical behavior of different nanoconjugates of core/shell/shell (GSH-CdTe/ZnSe/ZnO), core/shell (GSH-CdTe/ZnSe) and core (GSH-CdTe) (quantum dots QDs) with indium tetracarboxyphenoxy phthalocyanines ((OH)InTCPPc) in dimethylsulfoxide. The fluorescence quantum yields (Φf) and lifetimes (τf, in brackets) of QDs ranged from 0.20 (13.9 ns) to 0.42 (25.6 ns). The highest Φf value was obtained for GSH-CdTe/ZnSe/ZnO (4.5) while the least was observed in GSH-CdTe/ZnSe/ZnO (7.6), the numbers in brackets refer to the sizes. For (OH)InTCPPc alone a Φf and τf values of 0.02 and 2.43 ns, respectively were obtained. In the nanoconjugates, pivotal decrease in the Φf and τf of the QDs were observed with increase in the triplet and singlet oxygen quantum yields of (OH)InTCPPc.Original publication is available at http://dx.doi.org/10.1016/j.jphotochem.2015.07.00
"Blade where's the money?"
No full textOn Wednesday, 21 October 2015, Rhodes University closed in solidarity with the higher education sector as students and staff embarked on nationwide protest action against the shortage of funding in the South African higher education sector. #FeesMustFall is a national student led protest movement that began in mid-October 2015 in response to proposed increases in fees at South African universities. These images depict the peaceful march and illustrate the extent of solidarity among staff, students and community members who joined in support of the protest
"Paying 4 school 2 get a job, just 2 get a job 2 pay 4 school"
No full textOn Wednesday, 21 October 2015, Rhodes University closed in solidarity with the higher education sector as students and staff embarked on nationwide protest action against the shortage of funding in the South African higher education sector. #FeesMustFall is a national student led protest movement that began in mid-October 2015 in response to proposed increases in fees at South African universities. These images depict the peaceful march and illustrate the extent of solidarity among staff, students and community members who joined in support of the protest