A contribution to the biology of warthog (Phacochoerus africanus, Gmelin) in the Sengwa region of Rhodesia
- Authors: Cumming, D H M
- Date: 1971
- Subjects: Warthog Warthog -- Physiology Warthog -- Ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5843 , http://hdl.handle.net/10962/d1010740
- Description: To the AmaZulu a warthog is "inhlovudawana" or "little elephant"; to arrogant hunters it is the "poor man's rhinoceros"; to some writers of encyclopaediae it is a "grotesque and hideous beast"; to stockmen it has long been a carrier of diseases. Injury was added to insult with the discovery that the blood of these self-assured, often comical and certainly engaging animals supports the greater proportion of tsetse flies in the African savannas. Their significance as the primary hosts of Glossina morsitans Westw., the vectors of tryanosomiasis, justified an extended field study of warthog biology. This thesis reports four years of field work on warthogs, together with complementary observations of hand-reared warthogs (and their offspring) which roamed freely in the vicinity of the remote field station on which I live. The Sengwa Research Project, of which this study forms a part, was initiated in 1965 to study relationships between game animals and tsetse flies. One of the main problems investigated in the Sengwa Project is that of "host encounter" (Glasgow, 1961, Bursell, 1970) and how the distribution, abundance and behaviour of game animals may affect their availability to hungry tsetse flies. I have, accordingly, been concerned with discovering how warthog are dispersed in the Sengwa area and have attempted to gain some understanding of the factors, both environmental and social, which may affect or govern their dispersion and possibly population number. Intro. p. 1.
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- Date Issued: 1971
Induced plant responses of different Lantana camara L. (Verbenaceae) varieties to herbivory by Falconia intermedia (distant) (Hemiptera: Miridae)
- Authors: Heshula, Unathi-Nkosi Lelethu Peter
- Date: 2010
- Subjects: Lantana camara -- South Africa -- Eastern Cape , Lantana camara -- Biological control -- South Africa -- Eastern Cape , Biological pest control agents -- South Africa -- Eastern Cape , Weeds -- Biological control -- South Africa -- Eastern Cape , Invasive plants -- Biological control -- South Africa -- Eastern Cape , Hemiptera -- South Africa -- Eastern Cape , Miridae -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5911 , http://hdl.handle.net/10962/d1015368
- Description: A highly variable invasive shrub, Lantana camara L. (Verbenaceae), has been notoriously difficult to control thus far despite a well established biological control programme in South Africa. A promising leaf-feeding biological control agent, Falconia intermedia (Distant) (Hemiptera: Miridae), released to control this invasive plant eventually crashed at three out of five sites in the Eastern Cape Province. In the Mpumalanga Province, after initially colonising and building up high numbers on the L. camara stands the agent populations crashed. Several reasons for these population crashes have been suggested, but induced plant defences have not been investigated. Although plants face the challenge of herbivory by various organisms while remaining immobile, some plants may possess the ability to induce physical and/or chemical defensive responses following feeding and thus prevent further plant tissue damage and loss. Laboratory trials were conducted to determine the existence, nature and effect of physical and chemical feeding-induced responses of L. camara on the performance of the leaf-feeding biological control agent, F. intermedia. Lantana camara plants used in the study were obtained from five localities in the Eastern Cape Province, South Africa, while the insect culture was established from field populations. Plants from all varieties on which F. intermedia was released significantly increased the toughness of their leaves compared to control treatment plants. In addition, plants from three localities: Lyndhurst Farm, East London and Port Alfred, significantly increased trichome density after prolonged feeding by F. intermedia. On the three varieties showing increases in these two factors (i.e. leaf toughness and trichome density), oviposition, survival and feeding damage by the mirid agent was significantly lower on previously damaged plants. A significant negative correlation between trichome density and population numbers was found (R²= 0.52, p < 0.0003), suggesting that an increase in trichome density strongly contributes to a reduction in F. intermedia's growth. The growth and reproduction of the resistant plants was not significantly impacted by F. intermedia feeding. The defensive responses were found to be plant systemic and rapidly induced as they were elicited and expressed throughout the plant in both damaged and undamaged leaves within five weeks after insect release. Leaf toughness and trichome density were not significantly increased after feeding on plants from Whitney Farm and Heather Glen Farm. On the contrary, mirid individuals performed significantly better on plants from Whitney Farm and Heather Glen Farm than on plants of other varieties, indicating their susceptibility and suitability to the agent and the lack of induced resistance against the agent. Plants from all localities besides East London showed some level of tolerance and overcompensated for feeding damage by increasing plant growth and reproductive factors on plants fed upon. This was however only significant in two variables of the more susceptible localities, Whitney Farm and Heather Glen Farm. This increase in plant fitness did however indicate an induced defence response by these plants to feeding, a response designed to lessen the effects of agent feeding. Headspace volatile analysis was used to investigate any volatile chemical responses by L. camara due to F. intermedia feeding at two of the five localities chosen: East London and Whitney Farm. There was no significant difference in headspace volatiles emitted by leaves of plants from the East London insect infested and control treatment plants. On the Whitney Farm damaged plants however there was a 2.5 fold increase in the emission intensity of one of the three main compounds, later identified as Beta-caryophyllene. Three major chemical constituents which were found to be common to leaf volatiles of the two varieties were identified through gas chromatography-mass spectrometry (GC-MS) from the damaged and undamaged leaves of these two varieties. The methods used in collecting leaf volatiles were shown to be significant in the strength of chromatogram peaks. Using general authentication methods and purified standards, one of these was identified as the sesquiterpene, Beta-caryophyllene (C₁₅H₂₄). This compound is one of the major constituents found in isolations of L. camara varieties worldwide. This is the first such work done on a variety of L. camara in South Africa, and hopefully the beginning of more in-depth studies of the volatile organic chemicals from the numerous naturalised varieties of L. camara. It is suggested that the sum of these responses may play a role bigger than is currently understood in this plant-insect relationship. It is also argued that feeding induced plant defences may play an important role in attempts to control alien plants using insect agents.
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- Date Issued: 2010
Impact of adoption of drought tolerant maize varieties on yield in the face of climate change: A case of Salima, Chikwawa and Karonga districts, Malawi
- Authors: Rukasha, Conscience Tanyaradzwa
- Date: 2019
- Subjects: Climatic changes Food security Dry farming
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/15628 , vital:40491
- Description: Drought is a huge limiting factor in maize production, mainly in the rain-fed agriculture of subSaharan Africa. In response to this threat, drought-tolerant (DT) maize varieties have been developed with an aim to ensure maize productivity under drought conditions. This study assessed the impact of smallholder farmers’ adoption of DT maize varieties on maize productivity. The first step into understanding the impact of adoption of these varieties on smallholder farmers’ productivity was to first identify the varieties that they were growing. To achieve this, data was collected through the means of a household survey of 600 farmers from Karonga, Chikwawa and Salima districts in Malawi. The major findings drawn were that though most of the farmers have adopted the use of hybrids, as they are fairly common among the varieties that are being grown, most of these hybrids were not drought tolerant varieties. Previous studies had concluded that most of the farmers in Malawi were still growing local varieties. Results from this study showed a major increase in the use of hybrids with SC403 being the most grown variety. The second step in the analysis of the impact of DT maize adoption was to analyse the level and intensity of adoption of these varieties among the smallholder farmers. This was done using a Double Hurdle Model. The results from the double hurdle showed that only 23% of the sampled farmers were growing one or more DT varieties on their plots. Generally, farmers’ decision to use improved agricultural technologies and the intensity of the use in a given period of time are hypothesized to be influenced by a combined effect of various factors such as household characteristics, socioeconomic and physical environments in which farmers operate. The results in this study have shown that the geographical location of farmers plays a significant role in the decision to adopt as well as off-farm income and input subsidies. In terms of intensity, the results revealed that the farmers allocated an average of 0.46 ha of their land under maize cultivation to DT varieties. The results also showed that the intensity of adoption was influenced by gender, household size, whether or not the farmer is recycling the seed and soil fertility. The next step in the study was analysing the impact that intra-seasonal weather variability had on maize productivity. This was done by using daily weather variables for the whole growing season so as to take into account evaporation, rain gaps and other intra seasonal weather limitations. The Just and Pope Production Function was used to analyse the impact of intra-seasonal weather vi variability on productivity. The results suggest that the amount and distribution of rainfall have a strong impact on the development of the maize crop and consequently the quantity harvested. From the results, there was evidence of high variability in rainfall characteristics in terms of the intraseasonal distribution which in turn translated into high variability in maize quantity harvested by the smallholder farmers in Malawi. Lastly, the Endogenous Switching Regression Model was used to analyse the impact of adoption of DT varieties on yield. The results showed that the adoption of DT varieties increases productivity. The use of counterfactual data from the Endogenous Switching Regression (ESR) allowed for an in-depth analysis of the productive implications. The results from the ESR model showed that the farm households that did not adopt, had they adopted, they would have increased their productivity. Furthermore, the results indicated that the use of DT maize varieties successfully delivered relatively less reliance on the total and net rainfall, that is, adopters managed to support their productivity in the face of changing climate while the non-adopters were adversely affected by an increase in temperature and decrease in total rainfall. Adoption of DT varieties increased output among smallholder farmers by 441.33 kg which translates to a 41% increase. Conclusively, the results from this study showed that smallholder farmers are adopting new and improved hybrids and improved OPVs and moving away from the use of local varieties. However the new varieties they are currently using are mostly not DT varieties. This is an interesting finding because the farmers when asked about their preferred traits in maize seed mentioned drought tolerance, therefore the low level of adoption points to numerous factors. These factors include lack of awareness of these varieties among smallholder farmers and unavailability of seed. The results also showed that the level of adoption was low among the farmers. With respect to productivity, this study has shown that adoption of DT varieties by smallholder farmers will increase their yield in the face of climate change
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- Date Issued: 2019