Fruit flies (Tephritidae) can enter and establish in new territories due to the movement of fruit from one area to another through trade or tourism, which can negatively impact on fruit production and market access. An invader fruit fly species (Bactrocera invadens) has established on the African continent and has spread throughout sub-Saharan Africa. This newly described polyphagous fruit fly species is a successful invader species which continues to distribute and establish in new habitats. The introduction and establishment of B. invadens in South Africa may have serious market access consequences with regard to fruit exports due to its absence in the territories of many trading partners. The Musina area was considered as the study area as it is the first entry point from Zimbabwe. The national highway (N1) which runs through the area is a major route from several B. invadens infested countries in the Southern Africa region. A species initiated pest risk assessment was conveyed to determine the risk potential of this pest. The pest risk assessment (PRA) identified several pathways with a high risk to the Musina area, that B. invadens can follow. A detection survey was carried out to determine the status of B. invadens in the Musina area as support to the PRA. The detection survey continued over three years and by the second year B. invadens was detected for the first time in the study area. The detection survey was followed by a delimiting survey and the pest was eradicated in the area. After several months of no detection, it was however detected again in the area. Risk management options were suggested for regulatory control as an outcome of the pest risk assessment. These measures can be utilised by the National Plant Protection Organisation of South Africa for the commercial importation of host material of B. invadens, control of fruit imported by travellers, informal traders and national control in the event of pest incursions in the area. Corrective actions as well as quarantine actions should be implemented in an integrated approach in the affected areas. / Thesis (Master of Environmental Sciences)--North-West University, Potchefstroom Campus, 2013.

Fruit flies (Tephritidae) can enter and establish in new territories due to the movement of fruit from one area to another through trade or tourism, which can negatively impact on fruit production and market access. An invader fruit fly species (Bactrocera invadens) has established on the African continent and has spread throughout sub-Saharan Africa. This newly described polyphagous fruit fly species is a successful invader species which continues to distribute and establish in new habitats. The introduction and establishment of B. invadens in South Africa may have serious market access consequences with regard to fruit exports due to its absence in the territories of many trading partners. The Musina area was considered as the study area as it is the first entry point from Zimbabwe. The national highway (N1) which runs through the area is a major route from several B. invadens infested countries in the Southern Africa region. A species initiated pest risk assessment was conveyed to determine the risk potential of this pest. The pest risk assessment (PRA) identified several pathways with a high risk to the Musina area, that B. invadens can follow. A detection survey was carried out to determine the status of B. invadens in the Musina area as support to the PRA. The detection survey continued over three years and by the second year B. invadens was detected for the first time in the study area. The detection survey was followed by a delimiting survey and the pest was eradicated in the area. After several months of no detection, it was however detected again in the area. Risk management options were suggested for regulatory control as an outcome of the pest risk assessment. These measures can be utilised by the National Plant Protection Organisation of South Africa for the commercial importation of host material of B. invadens, control of fruit imported by travellers, informal traders and national control in the event of pest incursions in the area. Corrective actions as well as quarantine actions should be implemented in an integrated approach in the affected areas. / Thesis (Master of Environmental Sciences)--North-West University, Potchefstroom Campus, 2013.

The main objective of this thesis is the development of a nonparametric sequential estimation technique for the off-pulse interval(s) of a source function originating from a pulsar. It is important to identify the off-pulse interval of each pulsar accurately, since the properties of the off-pulse emissions are further researched by astrophysicists in an attempt to detect potential emissions from the associated pulsar wind nebula (PWN). The identification technique currently used in the literature is subjective in nature, since it is based on the visual inspection of the histogram estimate of the pulsar light curve. The developed nonparametric estimation technique is not only objective in nature, but also accurate in the estimation of the off-pulse interval of a pulsar, as evident from the simulation study and the application of the developed technique to observed pulsar data. The first two chapters of this thesis are devoted to a literature study that provides background information on the pulsar environment and -ray astronomy, together with an explanation of the on-pulse and off-pulse interval of a pulsar and the importance thereof for the present study. This is followed by a discussion on some fundamental circular statistical ideas, as well as an overview of kernel density estimation techniques. These two statistical topics are then united in order to illustrate kernel density estimation techniques applied to circular data, since this concept is the starting point of the developed nonparametric sequential estimation technique. Once the basic theoretical background of the pulsar environment and circular kernel density estimation has been established, the new sequential off-pulse interval estimator is formulated. The estimation technique will be referred to as `SOPIE'. A number of tuning parameters form part of SOPIE, and therefore the performed simulation study not only serves as an evaluation of the performance of SOPIE, but also as a mechanism to establish which tuning parameter configurations consistently perform better than some other configurations. In conclusion, the optimal parameter configurations are utilised in the application of SOPIE to pulsar data. For several pulsars, the sequential off-pulse interval estimators are compared to the off-pulse intervals published in research papers, which were identified with the subjective \eye-ball" technique. It is found that the sequential off-pulse interval estimators are closely related to the off-pulse intervals identified with subjective visual inspection, with the benefit that the estimated intervals are objectively obtained with a nonparametric estimation technique. / PhD (Statistics), North-West University, Potchefstroom Campus, 2014

The main objective of this thesis is the development of a nonparametric sequential estimation technique for the off-pulse interval(s) of a source function originating from a pulsar. It is important to identify the off-pulse interval of each pulsar accurately, since the properties of the off-pulse emissions are further researched by astrophysicists in an attempt to detect potential emissions from the associated pulsar wind nebula (PWN). The identification technique currently used in the literature is subjective in nature, since it is based on the visual inspection of the histogram estimate of the pulsar light curve. The developed nonparametric estimation technique is not only objective in nature, but also accurate in the estimation of the off-pulse interval of a pulsar, as evident from the simulation study and the application of the developed technique to observed pulsar data. The first two chapters of this thesis are devoted to a literature study that provides background information on the pulsar environment and -ray astronomy, together with an explanation of the on-pulse and off-pulse interval of a pulsar and the importance thereof for the present study. This is followed by a discussion on some fundamental circular statistical ideas, as well as an overview of kernel density estimation techniques. These two statistical topics are then united in order to illustrate kernel density estimation techniques applied to circular data, since this concept is the starting point of the developed nonparametric sequential estimation technique. Once the basic theoretical background of the pulsar environment and circular kernel density estimation has been established, the new sequential off-pulse interval estimator is formulated. The estimation technique will be referred to as `SOPIE'. A number of tuning parameters form part of SOPIE, and therefore the performed simulation study not only serves as an evaluation of the performance of SOPIE, but also as a mechanism to establish which tuning parameter configurations consistently perform better than some other configurations. In conclusion, the optimal parameter configurations are utilised in the application of SOPIE to pulsar data. For several pulsars, the sequential off-pulse interval estimators are compared to the off-pulse intervals published in research papers, which were identified with the subjective \eye-ball" technique. It is found that the sequential off-pulse interval estimators are closely related to the off-pulse intervals identified with subjective visual inspection, with the benefit that the estimated intervals are objectively obtained with a nonparametric estimation technique. / PhD (Statistics), North-West University, Potchefstroom Campus, 2014