Zoology and Entomology

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Browsing Zoology and Entomology by Advisor "Chidawanyika, Frank"

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    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.
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    Distribution and acaricide resistance status of the theileriosis vector, 𝘙𝘩𝘪𝘱𝘪𝘤𝘦𝘱𝘩𝘢𝘭𝘶𝘴 𝘢𝘱𝘱𝘦𝘯𝘥𝘪𝘤𝘶𝘭𝘢𝘵𝘶𝘴 Neumann (Acarina:Ixodidae) in response to changing climate in Zimbabwe
    (University of the Free State, 2023) Nemaungwe, Tinotenda Mercy; van Dalen, Elsie Maria Susanna Petronella; Chidawanyika, Frank
    Tick control is a key aspect of managing Tick-Borne Diseases (TBDs) with chemical control being the widely applied method. However, continued application of chemicals can lead to the development of resistance. A recent increase in theileriosis in Zimbabwe coupled with indications of shifts in outbreaks from seasonal to spontaneous, raised possibilities of acaricide resistance by the vector, Rhipicephalus appendiculatus. Factors behind changes in the spatio-temporal distribution of the tick and the disease it transmits are poorly understood. This study evaluated the distribution of the theileriosis vector, R. appendiculatus, its response to frequently applied acaricides and the implications of current management practices on acaricide resistance development in Zimbabwe. Initially, the thermal tolerance of larvae, nymphs and adult R. appendiculatus ticks were assessed followed by modeling the current and future distribution of suitable habitats using MaxEnt. Bioassays were then conducted to determine the tick’s resistance status to frequently applied acaricides namely amitraz and deltamethrin. Furthermore, a survey was undertaken to understand the relation between tick management strategies and acaricide resistance development in ticks of economic importance.Results indicated that suitable habitats for R. appendiculatus may expand into previously non-endemic areas between 2040 and 2060 if temperatures rise by 2 °C. This expansion may be aided by the ability of the species to tolerate higher temperatures during assays than those recorded in the environment. Results further showed that R. appendiculatus populations are still highly susceptible to amitraz and deltamethrin (Resistance ratios<4). In contrast, the indicator species R. decoloratus which was used for comparison had 50% of populations moderately resistant to amitraz and two dip tanks resistant to deltamethrin (4