Insecticide treated mosquito bed nets, insecticide aerosol sprays, repellent lotions and creams, repellent candles, vaporizable repellent essential oils, mosquito mats and coils are some of the many malaria personal protection tools that are in use. The latter of these measures are the most accessible and affordable options for the rural population in sub-Saharan Africa. It is therefore important to determine how effective these personal protection measures are by determining their ability to efficiently disperse an active ingredient when the protection measure is in use. In this study, a copper II oxide montmorillonite clay burner (CuOMontmorillonite clay burner) was created to vaporize repellent formulations containing various concentrations of p-menthane-3,8-diol (PMD) as the active ingredient with the aim of determining the percentage of the active ingredient that is released into the air and the rate of release. The performance of the CuO-Montmorillonite clay burner was also compared to that of the Lampe Berger fragrance burner (LBFB). In addition to this, the percentage of PMD released from 6 percentage wt PMD candles of diameters 40mm, 69mm and 83mm was determined and compared to that released when the CuO-Montmorillonite clay burner and Lampe Berger Fragrance burner where used to vaporize PMD repellent formulations. It was found that the rate of vaporization of the various PMD repellent formulations vaporized using the Lampe Berger fragrance burner is affected by the mass of PMD present in the repellent formulations. The 6 percentage wt PMD repellent candles released the least percentage of PMD as compared to that released when the CuO-Montmorillonite clay burner and the Lampe Berger fragrance burner were used to vaporize the PMD repellent formulations.

The synthesis of para-menthane-3,8-diol in a batch reactor was investigated in some detail with the view to evaluate the potential of producing said p-menthane- 3,8-diol in a continuous-flow reactor from the results obtained from the batch process. The methodology used as base for this investigation was a published procedure by Takasago of Japan. The Takasago-method produced 92.3 percent Yield for the product para-menthane-3,8-diol, and 2.7 percent Yield of the by-product, acetal. The objective for this investigation was to produce a minimum p-menthane-3,8- diol content of 97.0 percent and a maximum content of 3.0 percent for the by-product acetal. The batch production process was evaluated in detail using statistical experimental design methodologies. Three process variables, namely catalyst loading, organic/aqueous phase ratio and reaction temperature were selected for the study. The experimental method was based on the Takasago procedure, however the substrate was added as a single slug as opposed to gradual addition method and the reaction period was reduced to 30 minutes. Apart from statistical analysis, mechanistic aspects were also used to interpret the following results. Using a central composite design, three response models (one for the conversion of citronellal, p-menthane-3,8-diol and acetal formation) were determined. An analysis of the response surfaces indicated that, to increase the citronellal conversion all three variables should be increased. To increase the amount of pmenthane- 3,8-diol, the reaction temperature and acid concentration should be increased, but the Aq/org ratio should be decreased as the acid catalyst concentration is increased. To minimize the amount of acetals formed during the reaction, the Aq/org ratio should be decreased; temperature and acid concentration can be decreased or increased. The reaction mechanism suggested that p-menthane-3,8-diol may be formed along two pathways: One pathway directly forms p-menthane-3,8-diol, whilst the second pathway forms the isopulegol first, then proceeds to form product by hydrolysis. The acetal is formed as result of the reaction between unreacted citronellal and p-menthane-3,8-diol. From the design experiments it was suggested that reaction time can be reduced to 8 minutes at reaction temperatures between, 80-85 0C The product and acetal were isolated by simple vacuum evaporation of the low boiling citronellal and isopulegol. Results from recycling the catalyst phase were similar to those of the initial process. The results of this investigation has clearly shown that with a proper understanding of the effect of process variables on the performance of the batch synthesis route, the conversion of this traditionally batch (actually semi-batch) process into a continuous process is quite feasible provided that suitable equipment is available. The most important features required for such equipment would be: Intense mixing throughout the reaction zone so as to maximise the surface area between the two immiscible phases, hence the rate of mass transfer between the two phases; and the ability to run reactions above the boiling point of water. Plans for the further study of the process are already well underway and sections of static mixing tubes have been acquired to build a continuous lab scale tubular reactor that would be capable of providing the level of mixing required.

Many animals are able to scale smooth surfaces using adhesive structures on their feet. These organs are either soft pads with a relatively smooth surface or dense arrays of microscopic adhesive hairs with both designs having independently evolved in diverse taxa of arthropods and vertebrates. Biological adhesive pads out-perform conventional adhesives in many respects, making them important models for biomimetics. Hairy pads have attracted particular attention, because it has become feasible to fabricate similar synthetic microstructures. Nevertheless, the detailed performance and functional properties have not been characterised for any natural fibrillar adhesive system, and many fundamental aspects are still not understood. The aim of this thesis was therefore to investigate the fibrillar adhesive system of leaf beetles as a model. To investigate the functional implications of hairy pad design, the attachment performance between hairy pads of the leaf beetle Gastrophysa viridula and smooth pads of stick insects (Carausius morosus) was compared. Adhesive and frictional stresses were found to be similar in smooth and hairy pads, inconsistent with contact splitting theory, which predicts higher adhesive stresses for fibrillar adhesives. Hairy pads showed a greater direction-dependence of friction forces than smooth pads, confirming the importance of the asymmetric design of individual setae for effortless detachment. Experiments with contaminating particles also showed that hairy pads removed contamination more rapidly and efficiently than smooth pads. Self-cleaning ability had not been previously documented for adhesive organs of insects. To investigate to what extent the hairy system is able to compensate for surface roughness, whole-body attachment forces were measured for varying roughness levels. Attachment was reduced for all length scales of surface roughness, but in particular for asperity sizes smaller than the diameter of individual seta tips. Leaf beetles possess adhesive pads on three tarsal segments, which vary in setal morphology. However, the functional implications of this variation are unknown. The mechanical and adhesive properties of individual pads were therefore tested and their use during climbing observed. Proximal pads were shown to be stiffer than distal pads, conferring stability during pushing. In contrast, the softer distal pads allowed better attachment to rough surfaces. Hence the morphological variation is explained by an effective division of labour between the pads. To investigate an extreme example of pushing in a hairy system, pad use was studied during jumping in flea beetles. The pushing forces needed during take-off were exclusively produced by the proximal pads, again confirming the division of labour. To characterise the effects of different hair morphologies and to understand how individual setae contribute to array and whole-animal performance, single hair forces were measured using a glass capillary cantilever. Male-specific discoidal hairs were shown to be both stiffer and more adhesive than pointed and spatula-tipped setae, likely affecting overall pad stability and attachment. This thesis has shown that hairy pads are similar to smooth pads in the magnitude of adhesive stress supported yet outperform them in detachability and self-cleaning. It was also demonstrated that there are considerable differences in design and performance even within setal arrays of the same insect, indicating the limitations of general models of fibrillar adhesion and underlining the importance of specialised adaptations.

No description available.

Rapeseed is grown from two closely related species of Brassica in many varieties. The behaviour of seven insects was studied to determine their responses to low erucic acid rapeseed, represented by a typical and a Canola variety of each species. The Canola varieties have a lower gluco-sinolate concentration in the seed coat than typical varieties. The insects were chosen because they were oligophagous or polyphagous. The actions of adults of two species of moths, Mamestra configurata Walker and Plutella maculipennis (Curtis), were studied by using an olfactometer; four species of aphids, Myzus persicae Sulzer, Macrosiphum euphorbiae (Ashmead), Brevicoryne brassicae (Linnaeus), and Acrythosiphon pisum (Harris), were studied when the adults were placed at the base of each type of plant. The insects responded in accordance with their normal associations with cruciferous plants as hosts. Their responses were not materially affected by genetic differences among the four varieties, even though these included distinct morphological and biochemical differences. Behavioural differences towards plant species were observed in the polyphagous aphids, which affected their distribution on the plants. These differences were not associated with varieties or glucosinolate contents. These results indicated that the differences between the two rapeseed species and typical and Canola varieties would neither materially affect the responses of attacking insects nor the resistance of the plants to insect attack in the field. / Land and Food Systems, Faculty of / Graduate

Treatment of cedar leaf oil with aqueous potassium permanganate resulted in the oxidative ring opening of thujone (XXIV) to yield the crystalline α-thujaketonic acid (XXV).⁷⁰ This material, because of its availability and interesting structure, represented an attractive starting material for the synthesis of analogues of insect juvenile hormone. Therefore, to achieve this aim, α-thujaketonic acid (XXV) was converted to form two products (or 'half-molecules') which were then coupled together and transformed to the analogues. In the initial study Grignard treatment of (XXV) produced an intermediate tertiary alcohol (LVIII) which cyclized spontaneously to a lactone (XXVI). The latter compound resisted further transformation and this approach was abandoned. On the other hand, (XXV) was refluxed in water to give β-thujaketonic acid (XXIX). This ring-opened acid was hydrogenated to give the ketoacid (XXX) which reacted with excess methylmagnesiurn iodide to yield the alcohol acid (XXXI). In the last reaction of this sequence some carboxylic acid was found to be converted to an alcohol ketone. This product (XXXII) was apparently formed via attack of the excess Grignard reagent (on to the salt of the acid) to yield the ketone from the acid. This alcohol ketone (XXXII) was reduced to a diol (XXXIII) and the latter converted to an acetate derivative (XXIV) 1n order to investigate its structure. Next, the desired alcohol acid (XXXI) was pyrolyzed to give the olefin acids (XXVII) and (XXVIII) which were separated via silver nitrate impregnated silica gel column chromatography. The required intermediate (XXVII) afforded one of the necessary products or 'half molecules'. In order to improve the overall yield of the required synthon (XXVII), α-thujaketonic acid was quantitatively converted to the methylene derivative (LIX) via reaction with two equivalents of methyl triphenyphosphorane.⁵⁹ Pyrolytic ring opening of the cyclopropane ring system in (LIX) afforded a good yield of the dienoic acid (XXXV). Reduction of the desired acid (XXXV) with potassium in liquid ammonia gave an 85% yield of the key intermediate (XXVII). The second required intermediate was synthesized via the esterification of β-thujaketonic acid (XXIX) with diazomethane in ether. This yielded the ketoester (XXXVII) which was used in the following coupling reaction sequence. Thus the key intermediate (XXVII) was treated with lithium diisopropylamide (LDA) in tetrahydrofuran (THF) to form the carboxylic acid dianion which was reacted with the keto ester (XXXVII) in THF to give a mixture of β-hydroxy carboxylic acids (XXXIX) and (XL). This product mixture was dissolved in dry pyridine and excess benzene-sulfonyl chloride was added 1n order to achieve the required cyclization to the expected olefinic β-lactones (XLI) and (XLII). Epoxidation of this mixture with metachloroperbenzoic acid (MCPBA) in methylene chloride yielded the corresponding epoxy β-lactones (XLIII) and (XLIV). The final step in the synthetic strategy was to utilize the pyrolytic decomposition of the intermediate β-lactone function to the central double bond inherent in the juvenile hormone systems. Therefore, the epoxy lactones (XLIII) and (XLIV) were subjected to such pyrolytic conditions but only decomposition products resulted. For this reason further studies with (XLIII) and (XLIV) were abandoned. The olefin acid (XXVII) was reacted with mercuric acetate in dry alcohol and the mercury intermediate thus derived was converted with sodium borohydride in methanol or ethanol to yield respectively the methoxy (IL) or the ethoxy acids (XLVIII). The ethoxy acid (XLVIII) was reacted with LDA in THF to give the expected carboxylic acid dianion, the latter upon addition of the ketoester (XXXVII) yielded a mixture of the β-hydroxycarboxylic acids (L) and (LI). This mixture was lactonized with benzenesulfonyl chloride in pyridine as described above to yield the ethoxy β-lactones (L11) and (LI 11). These were pyrolyzed and separated to give the juvenile hormone analogues (LIV) and (LV). Analogous investigations on the methoxy acid (IL) yielded the analogous β-hydroxy carboxylic acids (LVI) and (LVII). Time constraints precluded the conversion of these to the hormone analogues. / Science, Faculty of / Chemistry, Department of / Graduate

The occurrence and biological activity of ecdysterone (insect moulting hormone) was examined in a number of plant species. A simple method was developed for the semiquantitative analysis of ecdysterone in plant extracts. The procedure consists of repeated washing of an aqueous methanolic extract of the plant with petroleum ether, followed by gradient elution of the freeze-dried aqueous extract on a SepPak (CIS reverse-phase cartridge), and high-performance liquid chromatography. Crude extract was purified on Sephadex LH20 for spectral analysis. Twelve species of ferns, three species of gymnosperms, and five species of angiosperms were examined for the presence of ecdysterone. Ecdysterone was found in a number of plant species, the chemistry of which has not previously been examined with respect to phytoecdysteroids. These include four species of ferns (Aspidotis densa (Brackenr.) Lellinger., Cryptogramma crispa (L.) R.Br., Blechnum spicant (L.) Roth, Polypodium glycyrrhiza D.C. Eat); two species of gymnosperms {Taxus brevifolia Nutt., Taxus canadensis Marsh.); and two species of angiosperms (Trillium cernuum L, Trillium ovatum Pursh.). Applied ecdysterone had no effect in a cytokinin bioassay, but elicited a slight increase in elongation of mung bean epicotyls (GA₃ bioassay) and elongation of excised dwarf pea hypocotyl hooks (auxin bioassay). / Science, Faculty of / Botany, Department of / Graduate

Because of recent advances in genotic insect control theory, it has become important to investigate the fitness effects of, and isolation procedures for, homozygous autosomal translocations. I isolated 57 autosomal translocations in Drosophila melanoqaster. Of these 21 were homozygous viable. From data obtained during the isolation of these trunslocations and from fitness tests and competition cage experiments, rhe following points can be made; (1) Between one in ten and one in one hundred homozygous viable laboratory produced translocations are likely to be of value in field tests of genetic insect control procedures. (2) Translocations which produce high levels of unbalanced gametes when heterozygous do not tend to be lass fit in the homozygous state than others. Therefore screening procedures dependent only on reduced progeny production from translocation heterozygote parents should be satisfactory for the isolation of useable stocks. (3) Translocations whose breakpoints are vary near the center of chromosomes tend to produce small progeny reduction in the heterozygous state, making these translocations useless as negative heterotic carriers of useful genes. (4) Those translocations which are the result of multiple break events tend to be less fit than simple double-break translocations and therefore should be discarded. / Science, Faculty of / Zoology, Department of / Graduate

This study is an investigation into entomophagy (insect eating by humans) as a practice that could enrich a culinary experience and thereby create a sense of ‘place’ in the urban context of Pretoria. Entomophagy is as old as man itself, but has suffered under globalised trends in food production and consumption. Humans are furthest removed from the origins and growth medium of the food they consume as food has become merely a commodity. The investigation entails exploring how architecture can be a cognitive tool and mediating device between food production processes and the public consumer. By bringing awareness and value to insects as food, the study hopes to redirect prejudices and open up new thoughts and behaviours in the food industry. / Dissertation MArch(Prof)--University of Pretoria, 2012. / Architecture / MArch(Prof) / Unrestricted

Soybean, Glycine max (L.) Merr., is planted across a vast amount of land in the Mid-Southern U.S. (Arkansas, Louisiana, Mississippi, and Tennessee), and yield responses to defoliation can vary. Experiments were conducted during 2015-2017 evaluating how soybean yield responds to multiple and continuous defoliation, as well as planting date and plant population. Multiple defoliation events were evaluated by defoliating soybean at varying levels at V3, V6, and both growth stages. There was no interaction between defoliation occurring at V3 and V6 growth stages, indicating that the impact of each defoliation event was independent of the other. The effect of continuous defoliation was evaluated by defoliating soybean weekly, beginning at V2. Defoliation continued throughout the vegetative growth stages or throughout the entire growing season, and was compared to the same defoliation level occurring one time at R3. Continuous defoliation during vegetative growth stages only, did not reduce yield at any of the levels tested. Defoliation occurring throughout the growing season reduced yields more than a one-time defoliation event at R3, but only when defoliation levels exceeded the 20% defoliation threshold. This indicates that thresholds do not need to be modified to account for multiple or continuous defoliation. To evaluate the effect of planting date on yield loss from defoliation, soybean was planted at six planting dates beginning in early-April and continuing through mid-June. Each planting date included a defoliated treatment and an undefoliated control. It was determined that later planted soybean lose a greater amount of yield than earlier planted. Higher yielding soybean also lost more yield than lower yielding soybean at every planting date until Mid-June. It was concluded that late planted soybeans could benefit from a lower treatment threshold. The effect of plant population on yield loss from defoliation was evaluated by planting soybean at five populations ranging from 123,500 seeds/ha to 420,070 seeds/ha. A undefoliated control and a defoliated treatment was included for each plant population. Defoliation significantly reduced yields only where final plant populations were lower than 192,800 plants/ha. This indicates that fields with substandard plant populations are more susceptible to yield loss from defoliating pests.