Doctoral Degrees (Zoology and Entomology)

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Open Access
Ecological analysis of Afromontane grasslands in the Eastern Free State using the biotope quality index
(University of the Free State, 2023) Modise, Serero Abiot; Bredenhand, Emile; Stander, Marga; Rakotoarivelo, Andrinajoro
Environmental disturbance poses threats to conservation efforts in highland montane grassland in temperate regions prone to land transformation, overgrazing, habitat fragmentation, soil erosion, uncontrolled fires and plant invasion. In this study, the Biotope Quality Index (𝘉𝘘𝘐) was adopted and applied as a species surrogate to evaluate impact of disturbance on the Afromontane grassland vegetation types namely Sandy Eastern Free State, Basotho Montane Shrubland and North Drakensberg Highlands Drakensberg Grasslands in the Golden Gate Highlands National Park. In addition, the Biotope Conservation Status (𝘉𝘊𝘚) was developed as an additional to 𝘉𝘘𝘐 to indicate the impact of environmental disturbance on conservation efforts in protected areas. Chapter 1 begins with a brief history that highlights the importance of temperate grasslands and the role that protected areas play in the conservation of sensitive biomes. In Chapter 2, the most regularly used environmental quality indices, their application domain (air, water and terrestrial), arithmetic formulation, development and application process as well as suggestions into continuous usage and nomenclature of those environmental indices were reviewed. Chapter 3 indicates how the 𝘉𝘘𝘐 was adopted into the 𝘉𝘘𝘐veg for vegetation ecology analysis, using three common plant species abundance-cover scales (Domin, Braun-Blanquet and percentage density), and results suggested that, for 𝘉𝘘𝘐, species list must include most plants present in the vegetation type to allow variation within data points. Furthermore, 𝘉𝘘𝘐veg was able to indicate variation in sites which were affected by relatively high degree of soil erosion, plant invasion / encroachment and long-term effects of historical agricultural practices. Moreover, the application of the 𝘉𝘘𝘐 as a species surrogate was demonstrated, with inclusion of the 𝘉𝘊𝘚 add-on as well as a ArcGIS Feature Analysis parameter, to illustrate the conservation status of the Sandy Eastern Free State in Chapter 4 and the Basotho Montane Shrubland grassland vegetation type in Chapter 5 using arthropod assemblages to evaluate as a unit of measure. Furthermore, the inclusion of the 𝘉𝘘𝘐 as a species surrogate for rapid bioassessments and biomonitoring was supported using both plant communities and arthropod assemblages to highlight the impact of environmental disturbances in the Highlands Drakensberg Grassland vegetation unit in Chapter 6. In conclusion, 𝘉𝘘𝘐 indicated the ability to use plants as a unit of measure and its flexibility for common vegetation abundance-cover scales. Again, 𝘉𝘘𝘐 was able to highlight the impacts of environmental disturbances on plant communities and arthropod assemblages. Therefore, it is recommended that 𝘉𝘘𝘐 and 𝘉𝘊𝘚 be used as a surrogate for bioassessment and biomonitoring to assess impacts of disturbance toward and to indicate the conservation status of important ecosystems, bioregions, or biotopes.
Open Access
Evolutionary, physiological and phenological responses of Spodoptera frugiperda to climate change
(University of the Free State, 2023) Mbande, Abongile; Chidawanyika, F.; Mutamiswa, R.
The threat of biological invasions due to global climate change and anthropogenic activities is growing globally. Environmental changes, such as increasing mean temperatures due to global climate warming, may exacerbate the spread of invasive insect species by improving their voltinism, survival, reproductive success and geographic range expansion. The fall armyworm (FAW) Spodoptera frugiperda is one of the most economically important invasive insect pests attacking sub-Saharan Africa (SSA) staple crops, such as maize and sorghum. First reported in West Africa in 2016, FAW has spread to the rest of SSA. Key questions arising from this rapid geographic expansion is how climate and its physiological attributes aid its invasion potential. This is particularly important in this era of global climate change where phenological mismatches are known to also influence their host utilization and survival across different life-stages and physiological status such as mating or feeding. Evolutionary responses at individual and population also play a pivotal role in survival and population persistence across various temporal scales. This study explored the evolutionary, physiological and phenological responses of S. frugiperda to climate change. First, I measured the effects of short-term exposure to heat shock on physiological responses vis critical thermal limits (critical thermal minima [CTmin] and critical thermal maxima [CT max]), and ecological traits vis reproductive success (fecundity [number of eggs per female] and hatching success) and longevity using virgin adults following heat shock at 32, 35, and 38 °C for 2 hours. Second, I assessed the effects of repeatable exposure to cold (CTmin) and chill coma recovery time (CCRT) for 0; 24; 48 and 72 hours and the body lipid content (BLC) and body water content (BWC) on adult fall armyworm (24 h old). Last, I investigated the thermal tolerance of S. frugiperda at 3, 6 and 9 days old adults heat shocked at adult, pupal and larval stages, at 40℃ for 2 hours. Heat shock improved tolerance to heat (measured as CTmax) but negatively affected cold tolerance (measured as CTmin). Males were more vulnerable to heat stress than females. Interestingly, heat shock also reduced fecundity, hatching success and adult longevity. Cold tolerance measured as CTmin improved with repeated exposure in 5th instar larvae, virgin males, and females while CCRT improved in 4th, 5th and 6th instar larvae following repeated cold exposure. Heat tolerance in virgin females showed highest CTmax in 6 day olds while it fluctuated in males. Mated males had higher CTmax than mated females across all heat shocked developmental stages. This study shows that, under heat stress, reproductive fitness in FAW is largely compromised due to low fecundity and stress resistance that is dependent on mating status, age and life-stage. Taken together, the results show that thermal variation has fitness consequences for FAW at both individual and population level. These results provide valuable data that inform mechanistic models for the geographic distribution of FAW under variable climate scenarios. This will especially be critical in developing early warning systems and area-wide strategies for FAW control.
Metadata only
Assessing small-scale fisheries potential of Gariep Dam, South Africa's largest impoundment
(University of the Free State, 2022-07) Swanepoel, Pieter Johannes; Van As, L. L.; Ellender, B. R.; Barkhuizen, L. M.
South African inland fisheries are considered poorly developed and fish resources are mainly utilised by recreational and subsistence fishers. The South African government has identified inland fisheries as an opportunity to contribute to food security, job creation and economic development, and has established a mandate to develop this sector. The Gariep Dam is South Africa’s largest freshwater reservoir, and its fish resources can potentially be utilised by the small-scale fisheries sector. The objectives of this study were to assess the fisheries potential of Gariep Dam by determine the viability of small-scale fisheries development by establishing up-to-date utilisation rates, determining fish abundance and catch rates, and assessing the viability of various harvest strategies. To assess resource status, a fisheries-independent multi-method approach was applied using gillnets, fyke nets and longlines to determine relative abundance, population structure and harvest potential. Fisheries-dependent roving creel surveys and angler counts were conducted to assess the recent utilisation of fish resources. To complement previous biological assessments of other species, Clarias gariepinus was studied to understand the biology, ecology, and population dynamics of this species in Gariep Dam. To assess potential development, a fisheries management plan that determined harvest costs, fish prices and financial viability was included. Labeobarbus aeneus dominated gillnet catches, with an average catch per unit effort of 5.7 ± 4.1 kg.net-1.night-1, which comprised 63% of the species composition. The remainder of gillnet catches comprised C. gariepinus (16%), Labeo capensis (10%), Labeobarbus kimberleyensis (10%) and Labeo umbratus (1%). Longlines proved to be successful in harvesting C. gariepinus, with an average catch per unit effort of 35 ± 24 kg.20-hooks-1.night-1, with very low catch rates for fyke nets. The longline catches were dominated by C. gariepinus (99%) with low numbers of L. kimberleyensis (1%). Roving creel surveys revealed that the Covid-19 pandemic had a major effect on the current hook-and-line fishery that was dominated by subsistence anglers, while recreational fishing disappeared during this period. A large proportion of the subsistence fishing sector were found to be out of work with unemployment rates of 70.9% and 34.5% in the two angling areas. Angler catches were dominated by L. aeneus (37.3%), followed by Cyprinus carpio (32.7%), C. gariepinus (13.7%), L. capensis (14.1%) and L. kimberleyensis (1.4%). The angling effort was estimated at an average of 42 ± 1 anglers.day-1 for the Gariep Dam which harvested an estimated 27 tonnes.year-1 during the sampling period. Clarias gariepinus from the Gariep Dam represents a stable population that matures late (5.2 years for males and 3.3 years for females), is dominated by old fish (Amax = 32 years) and exhibits slow growth (Lt = 1 013.28 (1-e0.092(t+7.78)) and a low natural mortality rate (0.369 year-1). These characteristics point towards a species that is likely to be utilised by inland fishers; however, spawning stock should be protected through special refuge areas. e study has revealed that the existing hook-and-line fishery is very important to the local communities surrounding the Gariep Dam and should be recognised and protected from future inland fisheries development. Results of the study indicate that a sustainable small-scale fishery is possible in the form of a longline fishery harvesting 40 tonnes.year-1 of C. gariepinus and a gillnet fishery using a 100 mm mesh size to harvest L. aeneus if they are separated by area to protect the current fishery. The financial analysis, however, indicated that substantial fishing effort will be required to harvest the projected amount of fish. With the recent price of freshwater fish (ZAR 13.50–16.00), a longline fishery is likely to be feasible, but a gillnet fishery is unlikely to generate sufficient revenue based on catch rates for a small-scale sector. The results of this study have been used to inform specific recommendations to develop inland fisheries for Gariep Dam, which can be used by government for decision-making.
Open Access
Biological control pre-release studies on the ecological impacts and biotic interactions of Robinia pseudoacacia L. (Black locust) with indegenous fauna and flora in South Africa
(University of the Free State, 2021-05-28) Chikowore, Gerald; Chidawanyika, Frank; Martin, Grant D.
The growing invasion of Afromontane grassland ecosystems of South Africa by Robinia pseudoacacia, a tree from North America is threatening this fragile and fast disappearing biome. Despite numerous studies on the species in the northern hemisphere, a serious lack of information in the southern hemisphere was noted. With the species targeted for biological control in South Africa, there is a need to understand its impacts in a local context and set baseline indicators for future evaluation of management interventions. Thus, multi-scaled studies to determine and quantify the impacts of this IAP were undertaken in the eastern Free State Province of South Africa. These included interactions between the invasive alien tree, biotic and abiotic components of the ecosystem, and implications of control on human wellbeing. Robinia pseudoacacia functional traits such as phenology, canopy cover, tree diameter and population demographics such as population density were measured including how these influence abiotic components of the ecosystem such as temperature and light availability (microclimatic conditions). Furthermore, the cascading effects of environmental modification on native vegetation and grassland arthropods as well as interruption of key ecosystem services such as rangeland condition and pollination in agro-ecological ecosystems were evaluated. Contributions of the invasive alien tree to livelihoods of invaded communities were also assessed inorder to avoid any conflict of interest that may arise from its management. Results showed that invasion by R. pseudoacacia significantly transforms understory microclimatic conditions. Temperatures were at least 2ºC lower under R. pseudoacacia stands as compared to uninvaded grassland while light availability differed by at least 1200 lumens-ft2. Grass communities subsequently differed by 96% between invaded plots and adjacent uninvaded grassland. Species richness was significantly lower in the understory where there was a dominance of exotic grasses . Furthermore, these habitat conditions differentially affect grassland arthropod assemblages, with grasshoppers in the family Acrididae, the most common grassland taxa to be excluded from invaded sites. Apart from the absence of thier main host plants, invasion mediated differences in microenvironments appeared to be the main driver of this shift in arthropod assemblages. This study also provided evidence that important ecosystem services such as grazing and pollination, are affected by R.pseudoacacia invasion. Apart from the reduction in available rangeland, changes in grass communities also significantly lowers the grazing capacity of rangelands. Differences in grass species composition between invaded and uninvaded rangeland resulted in a reduction in range condition especially under smaller and dense R. pseudoacacia stands. Furthermore, results from paired flower visitation rates in an agro-ecological system showed that R. pseudoacacia shares pollinators with apples. Since the two plants develop flowers during the same period, there is competition for key pollinators such as Apis mellifera. Hence, successful pillonation of apples is compromised with a potential reduction in fruit yield and quality. A survey conducted in this study showed that while the tree is currently being utilised by peri-urban dwellers, it is not the preferred species for several functions. Several respondents cited harvesting difficulties (due to thorns) and poor firewood qualities (production of bad smoke) as the major reasons for the underutilisation of R. pseudoacacia. Moreover, its contribution to household incomes is very insignificant while several negative impacts such as reduction in building space and uncontrollable spreading were noted. Information generated from this study shows that R. pseudoacacia is negatively affecting grassland ecosystems and subsequent ecosystem services. Therefore, there is a need to find a sustainable management solution for the species. Considering the limited success achieved by current management efforts, biological control is expected to be the major technique implemented for the species. Several impacts quantified in this study can be used to prioritise the species for management as well as a baseline for evaluation of future management interventions.
Open Access
Studies on stalk borers of maize and sorghum in Lesotho
(University of the Free State, 1998-11) Ebenebe, Adama Audu; Van den Berg, Johnnie; Van der Linde, T. C de K.
English: Investigations on various aspects of stalk borers of maize and sorghum were conducted in Lesotho during the 1995/96, 1996/97 and 1997/98 growing seasons. Aspects investigated were their distribution and relative abundance on these two crops; seasonal moth flight pattern of Busseola fusca; impact of natural stalk borer populations on maize and sorghum; response of some maize and sorghum varieties/hybrids to artificial infestations with B.fusca and Chilo partellus respectively; farmers' perceptions and farm management practices with regard to the management of stalk borers; relative efficacy of insecticides used for C. partellus control in Lesotho; effect of planting date of maize on B.fusca infestations; effect of intereropping with beans on B. fusca infestations in maize, and relative abundance of natural enemies of B. fusca and C. partellus. These investigations provided the following results: B. fusca was distributed throughout Lesotho and was important on both maize and sorghum. C. partellus occurred only in the central lowlands where it attacked only sorghum. Seasonal B. fusca moth flight activity was characterised by distinct periods of high and low activity, with three and two to three generations of moths per season in the lowlands and mountains respectively. Infestations of B. fusca in Lesotho caused substantial yield losses in susceptible maize varieties and hybrids. Lesotho's maize varieties and hybrids were observed to be susceptible, with yield losses of up to 39.4% observed under field conditions. Their susceptibility was further demonstrated through artificial infestations in glasshouse and field studies. The glasshouse study showed that the levels of antibiosis and antixenosis resistance to B. fusca in these varieties and hybrids were low, while the field studies showed only moderate resistance to foliar damage. Lesotho's sorghum varieties exhibited susceptibility to stalk borer damage, both under field conditions and artificial infestations with C. partellus. A glasshouse study also found antibiosis to be the main resistance mechanism against C. partellus larvae in whorls of resistant sorghum genotypes. The variety Tenant White, exhibited tolerance to damage, both under natural and artificial infestations.Lesotho's farmers regarded stalk borers as important pests. The commonly employed control measure was insecticide application. Although the use of routine farm management practices has potential for suppressing borer populations, they were not utilised in this regard. Comparison of the efficacy of six insecticides used for stalk borer control in Lesotho indicated granular formulations beta-cyfluthrin 0.05 % and carbaryl 2.5 % to be more effective against C. partellus larvae in sorghum whorls than spray formulations. Early planting of maize (in November) substantially reduced damage and yield loss caused by B.fusca. Intereropping maize with beans reduced damage and yield loss caused by B. fusca in maize. Furthermore, alternating rows of maize with rows of beans was more effective than alternating maize with beans within a row. The braconids Bracon sesamiae, Cotesia sesamiae, Euvipio sp. and Habrobracon brevicornis parasitized B. fusca larvae. Only B. sesamiae and C. sesamiae were recorded on C. partellus larvae. An unidentified ichneumonid was reared from C. partellus pupae, while a red ant species Dory/us sp. (Formicidae) was recorded as a predator of both B. fusca and C. partellus larvae. However, the activity of these natural enemies was generally low, increasing only towards the end of the growing season. These investigations have shown that stalk borer infestations are economically important in Lesotho. However, adopting such cultural practices as planting date adjustment, intereropping and destruction of crop residues can limit infestations. These practices, together with limited insecticide use, should form components of an integrated stalk borer management system. Future research efforts in Lesotho need to include the identification and development of maize and sorghum varieties and hybrids with high yields even under stalk borer infestations. Where such varieties are open-pollinated, they will be of particular benefit to the resource-poor farmers, who may not be able to afford hybrid seeds.
Open Access
Aspekte van die ekologie van avifauna op 'n binnelandse lughawe
(University of the Free State, 1999-11) Kok, Alettta Catharina; Kok, O. B.; Van der Linde, T. C. de K.
English: Owing to the world-wide increase in air traffic the number and intensity of collisions between birds and aircraft have increased accordingly. Bird strikes are not only responsible for considerable physical damage and fmancial losses, but also endanger human lives unnecessarily. Aspects of the ecology of avifauna at the Bloemfontein airport were, therefore, investigated in order to reduce hazards posed by birds at inland airports. Plant surveys conducted during 1994 and 1995 confirm the classification of the study area as a chy Cymbopogon-Themeda veld type. Based on botanical composition and basal cover the veld is in a relatively good condition. Regularly mowed experimental plots were characterised by a greater variety of plant species consisting of a lower percentage of climax grasses and a larger component of pioneer grasses, forbs and dwarf shrubs compared to undisturbed tall grass areas. A total of 270 pitfall traps were used over a continuous period of 15 months to determine the diversity, relative abundance and seasonal variation of terrestrial invertebrates in the study area. Members of seven classes, 23 orders and 57 families were identified of which insects comprised the most important component by far. As .opposed to this, flying and plantliving invertebrates which were monitored on a monthly basis by means of sweep-nets were represented by only two classes, comprising 13 orders and 70 families. Mouse trapping and incidental catches of smaller vertebrates in pitfall traps suggest a limited presence of amphibia, reptiles and small mammals. Broadly speaking significantly more invertebrates were collected during the wet than during the dry season. Evidently, the opposite trend applies with regard to the sampling of reptiles and small mammals. Although no direct relationship between catches and rainfall as environmental factor could be demonstrated, a significant correlation with temperature was indicated. Over a period of eleven years approximately 5 000 individuals representing 51 bird species which, potentially, posed a threat to aviation were collected at the Bloemfontein airport. More than half of the species concerned can be considered as I medium-sized terrestrial birds of which the crowned plover (Vane/Ius coronatus) is by far the most important. A similar species composition occurred at the Kimberley airport, in contrast to the greater percentage of water associated birds at the Johannesburg airport. Indirectly, food availability appears to be one of the main environmental factors involved in the presence of, amongst others, the five dominant bird species at the Bloemfontein airport. Analyses of the stomach contents of 3 544 bird carcasses from the Bloemfontein airport, supplemented by 906 stomach contents from the Johannesburg and Kimberley airports, indicate that insects can generally be considered the main food source of the birds concerned. Based on dry mass composition the Isoptera, followed by the Coleoptera and Orthoptera, constitute the most important component in the diet. The Isoptera, more specifically the harvester telmite (Hodotermes mossambicusi), is, moreover, the only important prey taxon showing a conspicuous utilisation peak during the relative food shortage of the dry season. Evidently, temporary superabundant food sources which periodically come about in grassland habitats are opportunistically utilised by the birds. Indications are that habitat manipulation at airports can serve as an effective long-term bird control strategy. Based on the superabundant availability of invertebrate prey species in short grass areas compared to that in tall grass, a socalled tall grass policy would not only lead to the reduction of available food sources, but would also hamper the prey searching abilities of the largely insectivorous avifauna. According to results obtained, chemical manipulation can also be successfully employed to limit the presence of harvester termites, the staple food of the majority of terrestrial bird species in grassland habitat, thereby bringing about a reduction in bird numbers. At the same time, a five layered model is discussed setting out the responsibilities of all the role players associated with the implementation of a successful bird control programme. Key words: Airport, avifauna, bird hazard, feeding ecology, harvester termites, pitfall trapping, grassland, habitat manipulation, management.
Open Access
Molecular detection, genetic diversity and phylogenetic analysis of anaplasma marginale infecting cattle in South Africa
(University of the Free State, 2015-12) Mutshembele, Awelani Mirinda; Mtshali, M. S.; Thekisoe, O. M. M.
Bovine anaplasmosis caused by Anaplasma marginale is endemic in South Africa. This endemicity is due to presence of tick vectors that transmit A. marginale the causal agent of the disease and the high seroprevalence in Limpopo, Free State and North West provinces. To date, the genetic diversity of A. marginale isolates infecting cattle in all South African provinces, except Free State, are generally unknown. Recently, vaccines based on the A. marginale major surface protein 1 a (MSP1 a) has been proposed as a strategy for controlling bovine anaplasmosis. However, characterization of genetic diversities of the A. marginale isolates in these regions is still needed before this protein can be used for vaccine development. Therefore, the aim of this study was to determine the prevalence, genetic diversity and phylogenetic relationship of A. marginale infecting cattle in all South African provinces except the Free State. A total of 280 whole blood samples were collected from cattle in all provinces with exception of the Free State. Twenty six districts and municipalities were included in this sampling. Anaplasma marginale genomic DNA was then extracted from the blood sample using ZR Genomic DNA 1M Tissue Miniprep (Zymo Research, CA, USA). A polymerase chain reaction (PCR) was done with primers targeting msp1a and msp4 genes and the PCR products were sequenced using genetic analyser (ABI, Life technologies, CA, USA). The generated sequences were analysed by bioinformatics and their phylogeny as well as genetic diversity index (GDI) was determined based on the sequences of msp1a and msp4 genes. Overall, the prevalence of A. marginale infection in cattle was 76% in all provinces except for Northern Cape Province where the prevalence was zero. The prevalence per province was as follows: Eastern Cape 19.1 %, Gauteng 9.6%, KwaZulu-Natal 23.0%, Limpopo 15.3%, Mpumalanga 10.1%, North West 12.4% and Western Cape 10.5%. The msp1 a revealed genetic variability with regions of different types of tandem repeats. Some repeats were conserved amongst the A. marginale strains and revealed low variable peptides in the MSP1 a tandem repeats. A polynomial correlation (R2=0. 76) was observed between the GDI and anaplasmosis prevalence per province. Interestingly, provinces with the highest prevalence were not the ones with highest or lowest GDI. The analysis of msp4 gene sequences, which provided evolutionary information about geographically distinct A. marginale strains, was used in the present study for phylogenetic analysis of samples from Limpopo (LP), Mpumalanga (MP), North West (NW), Gauteng (GP), KwaZulu-Natal (KZN), Eastern Cape (EC) and Western Cape (WC) provinces of South Africa. Two clades were observed which consisted of first clade (LP, NW, GP, KZN and WC) and second clade (MP and EC) isolates. In addition when DNA sequence variation of msp4 gene was analysed in combination with isolates from other countries outside South Africa, important phylogeographic information was observed. The South African strains had 100% identity with isola tes from Kenya, Zimbabwe and Australia. Good representation of the Southern and Northern Hemispheres was observed and demonstrated that the msp4 gene was a good phylogeographic marker. These results indicated that A. marginale is widespread in South Africa, and suggested that the analysis of msp1a and msp4 gene sequences provided an understanding of the phylogeny and epidemiology of A. marginale in South Africa.
Open Access
Fish myxosporeans from the Okavango Delta, Botswana and the south coast of South Africa
(University of the Free State, 2003-12) Reed, Cecile Catharine; Basson, Linda; Van As, Liesl L.; Dykova, Iva
English: Myxozoans form a diverse and economically important group of endoparasites that have been intriguing researchers ever since the early1800's. These parasites are notorious, having been associated with the devastating effects many species have shown in aquaculture and fisheries industries throughout the world. Research on both freshwater and marine myxosporeans in Africa is limited to a few countries and has, until recently, been largely neglected in southern Africa. In recognition of the need to investigate the presence of fi sh-infecting myxosporeans in both the freshwater and marine environments of southern Africa, a study was initiated in 1997 investigating the biodiversity of myxosporeans infecting fi shes in two very unique southern African localities. Firstly, the Okavango River and Delta in Botswana contains one of the worlds largest inland deltas composed of about 18 000 km2 waterways. Situated in the middle of the Kalahari Desert, this pristine wetland is the only one of its kind that forms an inland delta and one of the few river systems in the world that is visible from space. The research on myxosporeans infecting marine fi shes was conducted along the Cape south coast of South Africa, which has one of the most diverse marine fauna and flora compositions in the world of which 13 % is endemic. This study aimed to review all existing literature concerning freshwater and marine fish-infecting myxosporeans in Africa, report on the biodiversity and prevalence of fi sh-infecting myxosporeans in the Okavango River and Delta, Botswana, investigate the pathogenic potential of myxosporeans infecting the Okavango fi shes, determine the taxonomic status, species biodiversity and prevalence of myxosporeans infecting fi shes along the Cape south coast, South Africa and investigate the pathogenic potential of myxosporeans infecting intertidal and surf zone fi shes along the Cape south coast of South Afri ca. The examination of 285 8 fi shes representing 14 families and 65 species on several field trips to the Okavango Ri ver and Delta from 1997 to 2001 revealed the presence of 29 different fish infecting myxosporeans representing the genera Henneguya Thelohan, 1892 and Myxobolus Btitschli, 1882. Six of these species have been described as new in three articles prior to this study. Another two new species have been recorded in this thesis, together with the records of 14 miscellaneous species that have never been described before, but require more materi al for the completion of species descriptions. During the course of nine surveys conducted along the Cape south coast of South Africa since March 1998, a total of 410 fishes representing 33 species were examined for parasitic infections. Results from these surveys revealed the presence of 15 different myxosporean species. Three species from the genus Ceratomyxa Thelohan, 1892, one species from the genus Henneguya, two from the genus Myxidium Biltschli, 1882, one species from the genus Myxobolus and one species from the genus Sphaeromyxa Thelohan, 1892 are described in this thesis. Two keys for the identification of both the freshwater, as well as marine and estuarine fish-infecting myxosporeans in Africa are presented as a conclusion to this study. The results obtained from this study have laid the foundation for the continuation of research on these parasites in southern Africa and has provided an insight into the great diversity of myxosporeans infecting southern African fishes.
Open Access
Mating behaviour and competitiveness of male Glossina brevipalpis and Glossina austeni in relation to biological and operational attributes for use in the Sterile Insect Technique
(University of the Free State, 2016) De Beer, Chantel Janet; Venter, G. J.; Vreysen, M. J. B.; Brink, S. L.
English: In South Africa, African Animal Trypanosomosis (AAT), caused by Trypanosomae parasites transmitted by Glossina brevipalpis and Glossina austeni (Diptera: Glossinidae), is restricted to the north east of KwaZulu-Natal Province with an estimated 250 000 cattle being at risk. For the control of these flies an area-wide integrated pest management (AW-IPM) strategy with a sterile insect technique (SIT) component has been proposed. Accurate knowledge of the distribution of target populations is fundamental to the success of any control programme. In the present study tsetse fly distribution was determined with odour baited H traps and cattle screened using the buffy coat analyses to produce updated tsetse fly distribution, abundance and trypanosome prevalence maps for north eastern KwaZulu-Natal. Glossina brevipalpis and G. austeni were collected in areas where they had previously not been captured. Vegetation and temperature was shown to influence their distribution and abundance. The fact that no significant correlation between tsetse fly abundance and nagana prevalence could be established underlines the complex interactions between these two entities. This was epitomised by the fact that despite large differences in the apparent densities of G. austeni and G. brevipalpis, overall trypanosome prevalence was similar in all districts in north eastern KwaZulu-Natal. This indicated that both species can play a role in transmission of AAT and need to be controlled. The G. brevipalpis and G. austeni populations of north eastern KwaZulu-Natal extends into southern Mozambique (both species) and Swaziland (G. austeni). Morphometrical analyses showed an absence of any significant barriers to gene flow between the various KwaZulu-Natal populations as well as between the South African populations and those of the two neighbouring countries. Tsetse fly control in a localised area will therefore be subjected to reinvasion from uncontrolled areas. An area-wide approach, i.e. against the entire tsetse fly population of South Africa, southern Mozambique and Swaziland will therefore be essential. The maintenance of colonised G. brevipalpis and G. austeni at the Agricultural Research Council-Onderstepoort Veterinary Institute (ARC-OVI), necessitate a high quality blood source. For the potential improvement of the current rearing diet various anticoagulants, phagostimulants and blood sources were evaluated and production assessed using standardised 30-day bioassays. Defibrinated bovine blood was found to be the most suitable. Anticoagulants such as sodium citrate, a combination of citrate and sodium acid, phosphate dextrose adenine and citric acid can be used to simplify blood collection. While G. brevipalpis preferred bovine to porcine blood, G. austeni preferred a mixture of equal parts bovine and porcine blood. The phagostimulants adenosine triphosphate, as well as tri-posphates of inosine, and the mono-posphates of guanosine and cytosine improved production in both species. Attempts to colonise the local KwaZulu-Natal strain of G. brevipalpis failed due to a reluctance of field flies to feed on the artificial feeding system. In preparation for the SIT component the irradiation sensitivity of colonised G. brevipalpis and G. austeni when treated as adults and late-stage pupa was determined. A dose of 40 Gy induced 97% sterility in G. brevipalpis males when irradiated as late-stage pupae and 80 Gy induced a 99% sterility in flies irradiated as adults. Higher doses were required for G. austeni, with 80 Gy and 100 Gy inducing higher than 97% sterility in females that mated with males treated as adults or late-stage pupae. As colonised and irradiated males must be able to compete with their wild counterparts the mating performance of the colonised G. brevipalpis and G. austeni was determined under near natural conditions in walk-in field cages. Although the mating latency for both species was shorter, their mating performance did not differ significantly between mornings and afternoons. For both species mating frequency was significantly higher in nine-day-old males compared to six- or three-day-old males. Age did not affect the males’ ability to transfer sperm, their mating duration or mating latency. There was no significant difference in mating performance of sterile and fertile males. This study indicated that AAT and tsetse flies are abundant in KwaZulu-Natal and tsetse fly presence seems to be a dynamic process that is influenced by a number of environmental factors. The earlier proposed AW-IPM strategy with a SIT component, although still applicable, will need to be adapted to incorporate the new distributions records. Initial results indicate that the colonies at the ARC-OVI will be suitable for programmes that have a SIT component.
Open Access
Mating behaviour and competitiveness of male Glossina brevipalpis and Glossina austeni in relation to biological and operational attributes for use in the sterile insect technique
(University of the Free State, 2016) De Beer, Chantel Janet; Venter, G. J.; Vreysen, M. J. B.; Brink, S. L.
English:In South Africa, African Animal Trypanosomosis (AAT), caused by Trypanosomae parasites transmitted by Glossina brevipalpis and Glossina austeni (Diptera: Glossinidae), is restricted to the north east of KwaZulu-Natal Province with an estimated 250 000 cattle being at risk. For the control of these flies an area-wide integrated pest management (AW-IPM) strategy with a sterile insect technique (SIT) component has been proposed. Accurate knowledge of the distribution of target populations is fundamental to the success of any control programme. In the present study tsetse fly distribution was determined with odour baited H traps and cattle screened using the buffy coat analyses to produce updated tsetse fly distribution, abundance and trypanosome prevalence maps for north eastern KwaZulu-Natal. Glossina brevipalpis and G. austeni were collected in areas where they had previously not been captured. Vegetation and temperature was shown to influence their distribution and abundance. The fact that no significant correlation between tsetse fly abundance and nagana prevalence could be established underlines the complex interactions between these two entities. This was epitomised by the fact that despite large differences in the apparent densities of G. austeni and G. brevipalpis, overall trypanosome prevalence was similar in all districts in north eastern KwaZulu-Natal. This indicated that both species can play a role in transmission of AAT and need to be controlled. The G. brevipalpis and G. austeni populations of north eastern KwaZulu-Natal extends into southern Mozambique (both species) and Swaziland (G. austeni). Morphometrical analyses showed an absence of any significant barriers to gene flow between the various KwaZulu-Natal populations as well as between the South African populations and those of the two neighbouring countries. Tsetse fly control in a localised area will therefore be subjected to reinvasion from uncontrolled areas. An area-wide approach, i.e. against the entire tsetse fly population of South Africa, southern Mozambique and Swaziland will therefore be essential. The maintenance of colonised G. brevipalpis and G. austeni at the Agricultural Research Council-Onderstepoort Veterinary Institute (ARC-OVI), necessitate a high quality blood source. For the potential improvement of the current rearing diet various anticoagulants, phagostimulants and blood sources were evaluated and production assessed using standardised 30-day bioassays. Defibrinated bovine blood was found to be the most suitable. Anticoagulants such as sodium citrate, a combination of citrate and sodium acid, phosphate dextrose adenine and citric acid can be used to simplify blood collection. While G. brevipalpis preferred bovine to porcine blood, G. austeni preferred a mixture of equal parts bovine and porcine blood. The phagostimulants adenosine triphosphate, as well as tri-posphates of inosine, and the mono-posphates of guanosine and cytosine improved production in both species. Attempts to colonise the local KwaZulu-Natal strain of G. brevipalpis failed due to a reluctance of field flies to feed on the artificial feeding system. In preparation for the SIT component the irradiation sensitivity of colonised G. brevipalpis and G. austeni when treated as adults and late-stage pupa was determined. A dose of 40 Gy induced 97% sterility in G. brevipalpis males when irradiated as late-stage pupae and 80 Gy induced a 99% sterility in flies irradiated as adults. Higher doses were required for G. austeni, with 80 Gy and 100 Gy inducing higher than 97% sterility in females that mated with males treated as adults or late-stage pupae. As colonised and irradiated males must be able to compete with their wild counterparts the mating performance of the colonised G. brevipalpis and G. austeni was determined under near natural conditions in walk-in field cages. Although the mating latency for both species was shorter, their mating performance did not differ significantly between mornings and afternoons. For both species mating frequency was significantly higher in nine-day-old males compared to six- or three-day-old males. Age did not affect the males’ ability to transfer sperm, their mating duration or mating latency. There was no significant difference in mating performance of sterile and fertile males. This study indicated that AAT and tsetse flies are abundant in KwaZulu-Natal and tsetse fly presence seems to be a dynamic process that is influenced by a number of environmental factors. The earlier proposed AW-IPM strategy with a SIT component, although still applicable, will need to be adapted to incorporate the new distributions records. Initial results indicate that the colonies at the ARC-OVI will be suitable for programmes that have a SIT component.
Open Access
The bio-ecology and control of Coproica vagans and Coproica hirtula (diptera: Sphaeroceridae) in cattle feedlots
(University of the Free State, 1998-12) Badenhorst, Daniel; Van der Linde, T. C. D. K.; Louw, S. V. D. M.
English: Sphaeroceridae are generally known as "lesser dung flies". These are small to medium sized dark-brown to blackish flies ranging from about 0.5 mm to 6 mm in length. They are saprophagous and occur throughout the tropical and subtropical regions of the world. A unique scenario involving Sphaeroceridae flies that constitute a serious problem at South African feedlots is discussed. Two species, namely Coproica vagans (Haliday) and Coproica hirtula (Rondani) are both associated with cattle dung at feedlots, with the former species reflecting dominance. The flies cause a nuisance to the cattle by forming black clouds of swarming flies. It therefore became imperative to find a way to control these flies. The establishment of separate sphaerocerid laboratory colonies from which experimental studies could be conducted was successful and is described. The seasonal occurrence and relative abundance of the Diptera fauna occurring within undisturbed cattle droppings exposed to shaded and sunny locations in the central Free State was investigated. The Sphaeroceridae was of particular interest, but only five presumably new species were discovered among the 21 fly species reared from these droppings. No C. vagans or C. hirtula specimens were encountered. The influence of physical parameters such as temperature and moisture content of the dung on the development and survival of immature stages and adult flies is described. Temperature had a major effect on all stages of both species, and both too low and too high temperatures led to severe mortality. Optimum developmental temperatures were between 24°C and 30°C. The development time of all stages also increased with a decrease in temperature. Moisture content of the dung had the same influence on all stages of the Sphaeroceridae, and optimum moisture content levels were at approximately 90%. Development times also increased somewhat with a decrease in moisture content levels of the dung. Oviposition by adult females of both sphaerocerid species and the influence of temperature and photo periodicy was determined and is described. Oviposition continued for more than 60 days at colder temperatures, although the number of eggs produced was often very low. Higher temperatures on the other hand resulted in large numbers of eggs produced by sphaerocerid females (up to 607 eggs per female) at 24°C, but the duration of oviposition dropped. Different photoperiods had no severe effect on oviposition or egg production. Development and survival of immature stages and adult Sphaeroceridae were also influenced by the type of dung which they were offered and the effect of this phenomenon on the flies is also described. Some dung types, e.g. horse, buffalo and rhino dung, had a negative influence on larval and adult survival most probably as a result of the higher fiber contents of these dung types. The other dung types such as cattle, sheep and elephant dung, led to successful development and survival of all stages. Biological control was attempted with several Coleoptera (a staphylinid, Philonthus caffer (Boheman) and scarabaeids Aphodius pseudolividus Balthasar and Harmogaster strydomi Endrëdi), Diptera (Musea xanthomelas Wiedemann and Coboldia fuscipes (Meigen)) and mite species. These biological control agents all failed to control Sphaeroceridae numbers mainly because of their inability to survive in wet feedlot dung. Chemical control on the other hand produced positive results and seemed like the only option available. Several insecticides and chemicals were tested but only two, namely Neporex (cyromazine) and Scatterkill (piperonyl butoxide), showed irradication potential. A further advantage of Scatterkill is its long residual effect in feedlot dung.
Open Access
Branchial monogenean parasites (Monogenea: Dactylogyridae) of fishes from the Okavango River and Delta, Botswana
(University of the Free State, 2002-06) Christison, Kevin William; Van As, J. G.; Basson, Linda
English: The Okavango Delta has received much popularity for the host of wildlife that it sustains. More recently it has gained increasing interest for the rich diversity of fish species that occur there. The fishes of the Okavango are also becoming increasingly important as a natural resource attracting revenue to Botswana in the forms of ecotourism and aquaculture and also as an important food source for the local community. The Okavango Delta is a flood driven system and much of the fish distribution throughout the Delta and the timing of certain behavioural activities are dependent on the timing and magnitude of the flood. For the purpose of determining the distribution of fish parasites throughout the system, the distribution of the fish hosts was determined and it was found that fish community structure could be used to distinguish different habitat types within the different ecological regions. Fifty-nine of the expected 68 fish species for the Delta have been collected. These species represent 12 families of which the families Cichlidae and the Cyprinidae are the most abundant, making up about 50 percent of the species collectively. Various parasites have been collected from these fishes of which the monogeneans seem to be the most prevalent and abundant and currently represent approximately 36% of the parasites collected. Most of the monogeneans recorded thus far were representatives of the subclass Polyonchoinea. Of these, all belonged to the families Dactylogyridae and Gyrodactylidae. Of the monogenean parasites infesting the Okavango fishes, the representatives of the family Dactylogyridae were the most diverse. Genera of African dactylogyrids are either endemic to Africa or belong to genera with wider geographical ranges. In general dactylogyrids are host specific and their zoo geographical affinities are therefore linked to the faunistic origin of their hosts. The distribution of dactylogyrid species within Africa is determined by the distribution pattern of their hosts. Twenty-two dactylogyrid species comprising seven genera were recorded, of these 10 species were previously undescribed. This study represents the first records of representatives of the class Monogenea from Botswana and hence the Okavango Delta.
Open Access
An integrated approach to pest management in field pea, Pisum sativum (L.), with emphasis on pea aphid, Acyrthosiphon pisum (Harris)
(University of the Free State, 2002-03) Ahmed, Kemal Ali; Louw, S. V. D. M.; Swart, W. J.
This study comprises investigations into pea aphid, Acyrthosiphon pisurn, and ascochyta blight damage on field pea, the evaluation of plant resistance levels in both breeding lines and cultivars, the identification of plant resistance and the underlying mechanisms, and cultural, chemical and biological control methods. Varietal resistance studies indicated that there were differences between the Ethiopian and the South African strains of pea aphid with regard to their survival and reproduction on the field pea genotypes evaluated. The field pea entries performed very well against the former strain compared with the latter. Three lines (Holetta Local-90, 305PS210687 and 061K-2P-2/9/2) performed well across both strains. Field pea lines exhibiting tolerance, antixenosis and antibiosis resistance to A. pisum were identified under greenhouse conditions. Some lines showing high levels of antibiosis to nymphal feeding were also found in both strains. This kind of resistance mechanism may promote insect biotype development through increased selection pressure on the pest population. Strain variation was also evident in tolerance, antixenosis and antibiosis resistance. The South African strain was the least aggressive across all entries. Of the 30 varietiesllines (including a local susceptible cultivar from Ethiopia) evaluated for resistance to isolates of Mycosphearella pinodes, Oregon Sugar Pod II had a 1.9 blight severity and was scored as resistant, three genotypes (Green Feast, Sugar Queen and line 304WAll01973) were scored as intermediate (2.1 - 3.0 severity factor) and the remaining 26 genotypes were scored as susceptible (3.1 - 4.0 severity factor) or highly susceptible (4.1 - 5.0 severity factor). In all scoring dates, significant differences occurred among genotypes, isolates and genotype x isolate interactions. However, the genotype x isolate interaction contribution to total variation was much lower than that of genotypes and isolates separately. The isolate of the Denbi site in Ethiopia was slightly more virulent than those of the Holetta and Kulumsa sites. Assessments regarding the potential of biological control of pea aphids using a predatory beetle (Hippodamia variegata) and entomopathogenic fungus (Beauveria bassiana) indicated that predator-treated plots supported significantly lower aphid numbers from the third week onwards, when compared to the fungus-treated and infested control plots. The degree of mycosis caused by Beauveria on pea aphids was 14.3% in week three after inoculation and the figure dropped to 2.5% in week 5. Percentage yield loss due to pea aphid in predator-treated plots was 8.3 % compared with 16.0 % in fungus-treated plots. Field pea intercropped with Ethiopian mustard sustained less pea aphid and ascochyta blight incidence, compared to faba bean, wheat and field pea mono crop at all locations studied. The land equivalent ratio for this particular mixed crop system exceeded 1.0, indicating that the mixed crops selected were efficient for yield and monetary outcome. The increase in efficiency was ascribed to the barrier effect of mustard plants in the intercrop set-up, which was significant in reducing pea aphid population size and disease severity. The effect of fertilizer application and sowing date on pea aphid and ascochyta blight severity was location specific. At the Holetta site in Ethiopia disease severity and pea aphid infestation were significantly reduced in fertilized plots compared with unfertilized plots, while it was only the disease that showed significant difference at the Denbi and Kulumsa sites. This indicates the importance of fertilizer application as a cultural control strategy for this disease. Neither early nor late sowing resulted in reduced aphid infestation and disease infection at any of the locations. Significant interactions between variety, sowing date and fertilizer for ascochyta blight was observed, indicating that the effect of one factor was influenced by the other two factors. For aphid population density and yield, the three factors had little or no effect on each other at the Denbi and Kulumsa sites. Cultivar Markos was moderately resistant to ascochyta blight and it gave higher yield compared to Mohanderfer and the varieties used by farmers. Neem seed kernel extract application was superior to Multineem", a commercial product, against pea aphid development and reproduction. The neem preparations significantly reduced the number of molts, longevity and fecundity of A. pisum in a concentration-dependent manner. The effect on young adults exposed to neem was not as drastic as in the case of immatures. Acute and chronic toxicity effects on pea aphid were noted showing that azadirachtin is an effective inhibitor of population growth of pea aphid both on treated plants and when topically applied to the insect. Host plant resistance and natural chemical (neem) pest control in large scale farming systems, or integrated with cultural and biological control in low-input subsistence farming systems provides effective management strategies for pea aphid and ascochyta blight in field pea. From this study, possible implementation of IPM in field pea is presented and includes aspects of varietal resistance and biological, cultural and chemical control.
Open Access
Alternative methods of controlling the brown locust, Locustana pardalina (Walker)
(University of the Free State, 2003-07) Price, Roger Edward; Van der Westhuizen, M. C.
Outbreaks of the brown locust, Locustana pardalina (Walker), occur almost annually in the semi-arid Karoo region of South Africa and southern Namibia. Current suppressive control strategy relies on the application of fast-acting, synthetic pyrethroid insecticides, applied as ultra low volume drift sprays, to control gregarious brown locust targets at source within the Karoo outbreak region. However, the negative impact that the repeated application of insecticides may have on the rich diversity of endemic invertebrates and reptiles found in the Nama-Karoo biome is of great concern to landholders and conservationists. How to reduce the insecticide load and minimise the environmental impact in the Karoo and yet at the same time control this serious agricultural pest has become a controversial issue. There is thus an urgent need for more environmentally benign methods of locust control, as an alternative to the current spraying of insecticide. As part of a locust research project initiated by the Plant Protection Research Institute, Pretoria, the potential of various alternative methods of controlling the brown locust were evaluated against gregarious hopper populations in the laboratory and in the field. It was first important to update the available information on the background level of control provided by natural enemies and diseases of the brown locust. Although a range of natural enemies were found to prey upon the various life stages, their impact on brown locust populations in the present study was negligible. Of particular interest was a study of the impact of the sarcophagid fly, Wohlfarhtia pachytyli, which is a well-known facultative parasite of late instar brown locust hoppers and fledglings. However, field data suggested that the potential of the fly as a biological control agent may have been over estimated in the past, as the fly failed to cause more than 6% mortality of fledgling swarms in the present study. Before the first insecticides became available at the turn of the zo" century, farmers had to resort to mechanical methods to protect their crops and pastures from the ravages of locusts. Turning back the clock, the destruction of locust egg beds and the harvesting of locusts were re-examined as control methods. Excavation of locust eggs gave effective control, but the disturbance of the friable soils in the Karoo would damage the vegetation cover and cause severe erosion problems and is therefore not advocated. Harvesting of live locusts using nets or vacuum machines was not practical due to the avoidance behaviour of locusts. However, the harvesting of locust cadavers lying on the soil surface following insecticide spraying, once they had dried out and insecticide residues had broken down, was possible. With their high protein and fat content, the processing of locust cadavers into animal feed may become economically viable in future. Before organo-chlorine insecticides became available in the 1940s, bran bait containing sodium arsenite was extensively used for brown locust control. The baiting technique was re-evaluated in the present study using minute dose rates of the phenyl-pyrazol insecticide, fipronil, dissolved in water and mixed into wheat bran as the edible carrier. Bran bait containing 0.02% fipronil 200Se (Regent®) was prepared on site and was broadcast by hand onto the soil surface around bushes occupied by hopper bands as overnight roosting sites. Excellent control (>95%) of small and medium sized hopper bands was achieved, as long as baiting was undertaken shortly after sunrise, before hoppers scattered from the baited area. Baiting large band targets, or baiting later in the day once hoppers became active, was not effective. Baiting with 0.02% Regent® proved very effective if applied to compact, roosting hopper bands. It was also inexpensive and was easy to prepare and apply, requiring basic equipment and limited training. However, the logistics of the bulk transport, preparation and application of locust baits under operational conditions appear daunting. Insecticide barrier treatments using fipronil (Adonis® 5UL), applied to 21m-wide strips of Karoo vegetation at a dose rate of 12.5g a.i./ha, were used to intercept gregarious brown locust hopper bands marching through the veld. Barriers of Adonis® proved very effective against mobile L2-L3 bands and against small L4-L5 bands, giving >90% control within 48 hours. However, barriers sometimes failed to adequately control large and mobile L5 bands that had sufficient momentum to march through barriers before the majority of hoppers acquired a lethal dose of Adonis®. Barriers also proved less effective where the vegetation density was sparse or where the vegetation was unacceptable to locusts. The size and density of the hopper bands and the time of day when bands made contact with the barriers also appeared to influence efficacy. Despite these factors, Adonis® barriers were still considered to have potential for the control of brown locust hopper bands in the more remote areas of the Karoo, especially during the early stages of an outbreak when hopper bands are still young. However, barriers would have to be judiciously applied to restrict the environmental impact of Adonis® against non-target organisms. Large-scale operational trials are recommended. Insect Growth Regulators (IGRs) have shown promise when applied as barrier treatments against various locust and grasshopper species. However, laboratory experiments with the IGRs, flufenoxuron and teflubenzuron, applied to leaf discs and fed to L5 brown locust hoppers at dose rates of 3-l5Ilglg, gave variable mortality of 30-70%, with most mortality occurring as the hoppers attempted to moult. In another experiment, diflubenzuron (Dimilin OF6®), was sprayed onto maize plants at volume rates of l-3.f;ha and subsequently fed to L2 brown locust hoppers in the laboratory. Dimilin OF6® produced 100% mortality of L2 hoppers within Il days at all application rates, as long as hoppers were continuously exposed to treated vegetation. However, irregular exposure to Dimilin® during the inter-moult period produced unsatisfactory mortality, as the product is evidently non-accumulative and is readily excreted. The fact that brown locust hoppers have to be regularly exposed to IGR-treated vegetation, combined with the sporadic feeding behaviour and high mobility of brown locust hopper bands in the Karoo, would probably make IGR barriers unsuitable for brown locust control operations. In collaboration with nBC and the LUBILOSA programme (CABI Bioscience, Ascot, UK), the locust-killing fungus, Metarhizium anisopliae var. acridum, was imported and evaluated by PPRI locust researchers as a myco-insecticide agent in laboratory and field trials against the brown locust. Under suitable application conditions the myco-insecticide, applied at a standard dose rate of lOOgconidia/ha, regularly produced >90% mortality of hoppers maintained in cages, although speed of kill was slow, with median lethal times of 10.3 and 13.4 days for the ground and aerial application trials respectively. In most cases, acceptable >90% mortality was not achieved for at least three weeks after application. Despite the slow speed of kill, the myco-insecticide agent was considered a significant advance in locust control and the product was subsequently registered as Green Muscle® in South Africa in 1998. However, the lack of a knock-down action and the slow kill currently makes Green Muscle® unsuitable for operational use in the Karoo. The thousands of individual hopper bands treated during control campaigns, and the high mobility of bands, would make the recognition of treated and untreated targets by locust officers impossible. The hot and dry Karoo climate is also usually detrimental for the survival and transmission of fungal conidia, while the thermoregulation behaviour of brown locust hoppers enables them to effectively delay the onset of Metarhizium mycosis. An alternative application strategy needs to be developed and tested before Green Muscle® can be recommended for brown locust control. Other pathogenic micro-organisms evaluated in the laboratory for brown locust control were certain acid-tolerant strains of Bacillus thuringiensis and an entomopoxvirus isolated from a West African grasshopper, Odaleus senegalensis (De Geer). Unfortunately, none of these microorganisms proved virulent to the brown locust. The alternative locust control methods evaluated against the brown locust were all ranked according to various performance criteria and compared with the conventional spraying of ULV insecticides. Of the alternative control methods, only Adonis® barrier treatments and Regent® bait showed sufficient promise for brown locust control. However, none of the alternatives were considered suitable under all locust control situations to entirely replace the spot spraying of conventional ULV insecticides, which will thus remain the backbone of brown locust control strategy. Recommendations on the development of an lPM strategy for brown locust control, to incorporate barrier treatments and baiting in certain areas of the Karoo in order to complement conventional insecticide spraying, are given.
Open Access
Aspekte van die algemene biologie van Culex (culex) theileri Theobald (Diptera: Culicidae)
(University of the Free State, 1984-01) Van der Linde, Theunis Christiaan De Klerk; Van Pletzen, R.; Hewitt, P. H.
English: Since little is known of the occurence, distribution and possible vector roles of mosquitoes in the western Orange Free State, a trapping survey was undertaken to determine the species richness, relative abundance and seasonal fluctuations of mosquitoes in this region. Trapping of mosquitoes was done at weekly intervals from 1976 to 1978 on the farm Daniëlskuil, 30 km west of Bloemfontein. Twentyfive species were found to be present, of which eight had not previously been recorded from the Orange Free State. Culex (Culex) theileri Theobald was the most abundant species, accounting for 55,44% of the total catch. The temporal distribution and abundance of the seven dominant species viz. Aedes caballus, Ae. juppi, Ae. lineatopennis, Ae. durbanensis-group, Anopheles squamosus, Cx. theileri and Cx. univittatus were analyzed in terms of meteorological parameters such as air temperature, water temperature, relative pumidity and rainfall, all of which were recorded continuously. From these it was concluded that temperature and saturation deficit proved to be the most important variables. A Cx. theileri colony was established in the laboratory. Field observations and laboratory experiments led to the following rearing procedure and environmental conditions: Adults were held at 27°C and 65% RH with a day-night cycle of 12 hours each, which included a dawn and a dusk of one hour each respectively. Adults were fed on 7,5% sugar water and pigeons were used for bloodmeals. Optimum oviposition occured when individual gravid females were placed in pill vials containing 10 ml of water in which larvae had developed. Larvae were held in 0,02 M NaCI in shallow pans at 27°C. They were fed a mixture of brewer's yeast and an infant cereal. An electronmicroscopic study of the surface structure of the eggs revealed that the exochorion of the egg can be divided into four main regions viz. an anterior pole, a transitional region, an attachment region and a posterior pole. A cup-shaped corolla filled with gelatine-like material is present on the anterior pole and a prominent oil droplet on the posterior pole. In the attachment area the exochorion bears knobs with gaps between them. The knobs of adjacent eggs are arranged in such a way that adjacent eggs are joined to one another in a similar way as a press-stud operates. The eggs are thus held together to form a raft. Mating before or after a bloodmeal had no significant effect on the number of eggs produced. Intake of sugar after a bloodmeal had a detrimental effect on the number of egg-rafts produced, but not on the number of eggs per raft. Females which fed on white rats produced significantly more eggs than those which had fed on pigeons. The females, however, which fed on male rats produced large numbers of nonviable eggs. Aging prior to a bloodmeal resulted in decreased egg production. Repeated bloodmeals and oviposition by young females did not cause a decline in egg production or viability. Females oviposited during late dusk. They preferred 0,01 - 0,08 M NaCl solutions with a dark background. Furthermore, solutions in which larvae or pupae were reared, or which contained bacteria, were even more attractive. If offered no choice females oviposted on the available aqueous solution. Although temperatures below 15°C and above 33°C had a detrimental effect on oögenesis, no effect on selection of a suitable oviposition site could be established. The eggs are not particularly temperature sensitive during embryogenesis, but hatching does not occur below 12°C or above 36°C. The optimum developmental temperature was 27°C. NaCI concentrations above 0,08 M led to a decrease in the hatching percentage, while above 0,16 M no hatching took place. The temperature extremes of 12°C and 36°C were lethal to the larvae. The optimum temperature was 27°C. Increases in NaCI concentration up to 0,06 M had only a slight effect of larval developmental time. Thereafter a rapid increase in mortality occured. A direct correlation between survival of adults, temperature and saturation deficit was established. Sugar and bloodfed females survived longer at temperatures 6°C - 24°C and saturation deficits of 0,4 and 0,8 kPa. The results obtained form both field and laboratory studies were used in an attempt to explain the occurrence, temporal distribution and abundance of Cx. theileri.
Open Access
Activity patterns of birds in the central Free State, South Africa
(University of the Free State, 2009-11) Van Niekerk, Daniël Johan; Kok, O. B.
Activity patterns of bird species were studied at Glen Agricultural College within the grassland area of the central Free State, South Africa, during a period of 11 years (July 1997 - July 2008). The study focused on a specific grassland locality where 5-minute checklists were compiled continuously from dawn to dusk at least once a week for a total of 656 days. Data were also collected each minute for selected species. Additional observations in an adjacent tree and shrub dominated drainage line included I-minute checklists compiled during transects over a two-year period (late autumn 2000/1 to mid-autumn 2002/3) as well as surveys from a fixed position from dawn to approximately 70 minutes after sunrise during 2007/8. The central aim of the study was to quantify and explain annual, seasonal and daily activity patterns of all bird species recorded in the study area. This data is summarised in separate species accounts where aspects of the annual cycle, particularly breeding and moulting, were also considered. In addition, the potential influence of rainfall was investigated. The study reveals, for the first time, how the activity patterns of a southern African bird community change through time, and how the amount and timing of rainfall can influence these patterns. In spite of similarities amongst species when daily, seasonal and annual patterns are considered separately, the study also shows that each species is unique when all its data is considered simultaneously. Because activity patterns can have a substantial influence on the detectability of a species, the accuracy and usefulness of surveys aimed at estimating bird numbers is consequently questioned. The study at Glen also shows how activity patterns can be used to help unravel the annual cycle of species in a time and cost effective way.
Open Access
Reproductive processes of scyphidiid peritrichs associated with limpet and haliotid hosts along the coast of South Africa
(University of the Free State, 2002-11) Peters, Helene; Basson, Linda; Van As, Liesl L.
English: During the early 19th century a lot of progress was made in clarifying reproduction patterns and cycles in the kingdom Protozoa Goldfuss, 1818. During the first half of the 20th century various scientists studied the reproductive processes of peritrichs and made valuable contributions. While thousands of recent papers exist on reproduction of ciliates, not much work has been done on epibiontic peritrichs. In this study the processes of binary fission, telotroch formation and conjugation are described for Mantoscyphidia branchi Van As, Basson & Van As, 1998, M. marioni Van As, Basson & Van As, 1998, M. midae Botes, Basson & Van As, 2001 and M. spadiceae Botes, Basson & Van As, 2001. It was also determined whether binary fission, telotroch formation and conjugation occur in a new species of Ellbiophrya Peters, Van As, Basson & Van As, in prep. Haliotids were collected from 1997 to 2002 at the De Hoop Nature Reserve on the south coast of South Africa and were also obtained from the Danger Point Abalone Farm near Gansbaai, and the Abagold Farm in Hermanus. Limpets were collected from 1993 to 2002 from the Goukamma Nature Reserve, De Hoop Nature Reserve and Keurboom Beach on the south coast; Mc Dougall's Bay and the Olifants River Mouth on the west coast; Bazley and at the rocky shores of Lake St. Lucia on the east coast of South Africa; and on the east coast of Marion Island at Boulder Beach which is situated in the southern Indian Ocean. Live symbiont specimens undergoing reproduction were observed with light microscopy and photomicrographs were taken of the various stages of binary fission, conjugation and telotroch formation. Mayer's, Harris' and Heidenhain's Iron Hematoxylin were used to stain the nuclear apparatus. The details of the infundibulum were studied by staining Bouin's fixed smears with protargol. Gills were also examined using scanning electron microscopy. Binary fission was mostly observed in M. spadiceae and also occurred earlier in M. spadiceae than in M. branchi and M. midae populations. The formation of telotrochs was mostly observed in populations of M. branchi and M. spadiceae. Throughout this study it was uncertain whether binary fission always has to occur before a telotroch can develop, or whether binary fission follows telotroch formation. Conjugation was mostly observed in populations of M. branchi and M. midae. In the Ellobiophrya species conjugation was also observed and this is the first record of conjugation in the genus Ellobiophrya (Chatton & Lwoff, 1923). It would be possible to study all these processes in detail if a suitable medium could be cultured in future.
Open Access
Zooplankton of the Okavango Delta and associated basins in Botswana
(University of the Free State, 2016-07) West, Deirdré Theresa; Van As, J. G.; Van As, L. L.; Rayner, N. A.
English: The Okavango Delta, one of the most iconic wetlands on the planet, is the third largest Ramsar site and in 2014 was listed as the 1000th UNESCO World Heritage Site. It is situated in the centre of the Kalahari Basin of southern Africa, which is a semi-desert and the largest continuous sea of sand on earth. The Okavango Delta, in northern Botswana, receives its waters from the Okavango River which originates as many tributaries in Angola and flows as a single river through Namibia’s Caprivi Strip before entering Botswana where it is met by a series of fault lines. These faults control the shape of the delta and result in its water spreading across the Kalahari Sands, forming the world’s largest alluvial fan. Most years there is little to no outflow from the Okavango Delta, but the system recently experienced consecutive years of record high floods from the catchment area in Angola, resulting in the basins associated with the delta being inundated for the first time in up to four decades. This provided the perfect opportunity to study the zooplankton of the Okavango Delta, from which only a few studies have been conducted, and it has allowed an insight into the zooplankton species diversity of the associated basins. The aims of the present study were to obtain specimens of aquatic micro-invertebrates, correctly identify Rotifera and micro-Crustacea material collected up to species level where possible, create a photographic data base of the organisms and to map the distribution of each species throughout the study area. Water bodies included in the study are the Okavango Panhandle, the Okavango Delta Fan, the Thamalakane River, Lake Ngami, the Boteti River and Lake Xau. A total of 33 rotifer species were identified, including three genera (Asplanchnopus de Guerne, 1888, Synchaeta Ehrenberg, 1832 and Sinantherina Bory de St. Vincent, 1826) and six species, i.e. Asplanchnopus multiceps (Schrank, 1793), Epiphanes senta (Müller, 1773), Synchaeta pectinata Ehrenberg, 1832, Conochilus dossuarius Hudson, 1875, Conochilus unicornis Rousselet, 1892 and Sinantherina sp., which have not been identified from the waterways of northern Botswana before. The cladoceran species diversity, excluding the family Chydoridae which was the most diverse, but lacks taxonomic review, totalled 12 species. Amongst these was the species Macrothrix propinqua Sars, 1909 which has not been recorded from the study area previously. The calanoid copepod Tropodiaptomus schmeili (Kiefer, 1926) was present in the Okavango Delta and its associated basins, except in Lake Xau where no calanoids were collected. Furthermore, a possibly undescribed species of Metadiaptomus Methuen, 1910 was found in the Okavango Panhandle and Lake Ngami. Eight species of the order Cyclopoida were collected from the Okavango Delta and its associated basins, five of which were recorded from the system for the first time. Zooplankton studies were also conducted in the Nata River during low flow and results indicated a total of 14 rotifer, cladoceran and copepod species. Unlike the Okavango System where the calanoid genus Tropodiaptomus thrives, Metadiaptomus transvaalensis Methuen, 1910 was found in the Nata River. Furthermore, this calanoid copepod was infested with the peritrich, Trichodina diaptomi Šrámek-Hušek, 1953, of the order Mobilida. Notes on the possible life-history of this trichodinid are provided. The results from the entire study have laid down the framework for future zooplankton research in the waterways of the semi-arid Botswana, where no baseline data exists for many of the life-sustaining water bodies.
Open Access
The biology of gnathiid isopod parasites and their role as vectors of fish blood parasites in South Africa
(University of the Free State, 2000-12) Smit, Nicholas Jacobus; Van As, J. G.; Basson, Linda; Russell, Angela Davies
English: Research on marine fish parasites has been largely neglected in South Africa. This is especially true for the temporary fish parasites of the isopod family Gnathiidae and fish blood parasites of the family Haemogregarinidae. In this study, surveys were carried out to determine the presence of gnathiid isopods and fish haemogregarines associated with different intertidal and sub-tidal fish hosts over a period of four years, at two different localities on the South African south coast. The study also focussed on the relationship between gnathiids and haemogregarines, specifically the possibility that the gnathiid Gnathia africana Barnard, 1914 might be a vector of the fish blood parasite Haemogregarina bigemina Laveran and Mesnil, 1901. Laboratory work was conducted to elucidate the life cycle of G. cfricana. It was found that G. cfricana has three larval stages, consisting of three unfed (zuphea) and three fed (praniza) stages, with the final stage praniza larvae moulting into either male or female adults. Forty days after their last feed as praniza 3 larvae, mature females release stage 1 zuphea larvae. Detailed information was also supplied on the feeding and digestion length for each larval stage. The females of G. africana were re-described from the material collected. Furthermore, other gnathiid larvae, not resembling any of the known species from South Africa, were collected from three species of elasmobranchs as well as the evileye pufferfish. Both groups of larvae were kept in the laboratory, where they moulted into adult males that did not conform to the description of any other gnathiid species in South Africa, or worldwide. These specimens were described as new species (Gnathia pantherinum sp. n. and G. pipindae sp. n.), using light and scanning electron microscope observations. Extensive information was also provided on the final life cycle stages of G panthertnum sp. n. Special attention was given to finding distinguishing characteristics to identify females and larvae of various species in the absence of males. Comparing material in this study with information from the literature showed that the morphology of the pleotelson and cephalosome appendages of females and larvae could be successfully used as differentiating characteristics. The research conducted on fish haemogregarines led to new distribution and host records for two known species, and the description of two new, but un-named species. Development stages of H. bigemina were found in the gut of G. africana larvae that had fed on H. bigemina-infected host fish. The data obtained from these results was used to compile a complete life cycle for H. bigemina in both the fish and the arthropod host.
Open Access
The ecology and ecophysiology of Marion Island house mice, Mus Musculus L.
(University of the Free State, 1999) Avanant, Nico Loubser; Kok, O. B.; Smith, V. R.
English: This thesis presents the results of a studv of the biotic and abiotic conditions experienced by house mice on Marion Island, their morphological and reproductional adaptations to island conditions, the seasonal changes in their diet. and of the densities and biomasses of their prey items. By establishing burrow systems and sheltered aboveground runways nuce experience a microelimate that is far less harsh than the macroelimatie regime. In terms of warmth, this extends the season of mouse activity significantly compared with what would be allowed by the macroclimate. House mice are opportunistic feeders and this plays a major role in their survival under the harsh conditions on Marion Island. The mice are primarily carnivores and impact severely on soil macroinvertebrate populations, annually removing up to several times the average instantaneous standing crop of some macroinvertebrate populations. Since macroinvertebrates are cardinal agents of ecosystem functioning by being the main mediators of nutrient cycling on the island, their predation by mice has severe ecological implications. Between 1979/80 and 1992/93 the densities and biomasses of the mouse's major invertebrate prey species have decreased. The percentage composition of the various prey types in the macroinvertebrate population has also changed. These changes have caused changes in the composition of the mouse's diet. Seasonal changes in reproductive status, sex ratio, age structure, body mass and length, kidney- and adrenal mass, and length and shape of intestines were determined, in order to provide information concerning the house mouse's response to fluctuating environmental parameters and to assess the levels of stress experienced by mice at different times of the year. Stress levels are influenced by population density, sex, reproductive status, temperature and availability of food. In 1992/93 mice had significantly larger body to tail length ratios than in 1979/80, despite the fact that the island warmed considerably in the interim. This warming has allowed a significantly longer breeding season, perhaps by as much as two months. It is suggested that this is the reason that end of season densities are now considerably higher than in 1979/80.

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