Browsing by Author "Karsten, Minette"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- ItemGeographic variation and plasticity in climate stress resistance among southern African populations of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae)(Nature Research, 2018-06-29) Weldon, Christopher W.; Nyamukondiwa, Casper; Karsten, Minette; Chown, Steven L.; Terblanche, John S.Traits of thermal sensitivity or performance are typically the focus of species distribution modelling. Among-population trait variation, trait plasticity, population connectedness and the possible climatic covariation thereof are seldom accounted for. Here, we examine multiple climate stress resistance traits, and the plasticity thereof, for a globally invasive agricultural pest insect, the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). We also accounted for body size and population genetic connectivity among distinct populations from diverse bioclimatic regions across southern Africa. Desiccation resistance, starvation resistance, and critical thermal minimum (CTmin) and maximum (CTmax) of C. capitata varied between populations. For thermal tolerance traits, patterns of flexibility in response to thermal acclimation were suggestive of beneficial acclimation, but this was not the case for desiccation or starvation resistance. Population differences in measured traits were larger than those associated with acclimation, even though gene flow was high. Desiccation resistance was weakly but positively affected by growing degree-days. There was also a weak positive relationship between CTmin and temperature seasonality, but CTmax was weakly but negatively affected by the same bioclimatic variable. Our results suggest that the invasive potential of C. capitata may be supported by adaptation of tolerance traits to local bioclimatic conditions.
- ItemPopulation genetic structure and abundance of two Ceratitis species (Tephritidae) of agricultural importance in South Africa(Stellenbosch : Stellenbosch University, 2014-12) Karsten, Minette; Addison, Pia; Terblanche, J. S.; Jansen van Vuuren, Bettine; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Research in the field of biological invasions has increased dramatically in the last two decades, especially due to the impact of human activity such as, transport, travel and international trade. Different stages of invasion have been proposed, each stage posing different barriers that must be overcome by the organism for it to become established. For the prevention of new invasions and the formulation of a successful integrated pest management program (IPM), knowledge of natural species community assemblage, as well as movement patterns, temporal distribution and invasion pathways are critical. In this dissertation I make use of two agricultural important fruit fly species, Ceratitis capitata amd C. rosa, in the Tephritidae family in different stages of the invasion process using different research methods to (i) investigate seasonal variation in fruit fly abundance in orchards and natural vegetation in the Western Cape to determine whether natural vegetation is used as possible refugia; (ii) to investigate maccrogeographic population structure of C. capitata with a focus on southern Africa to reconstruct and test C. capitata’s invasion pathway using a Bayesian framework; (iii) to investigate the population genetic structure, using molecular and morphological markers, to estimate gene flow and dispersal ability of C. rosa in South Africa. Results showed that C. capitata was the most abundant species captured and Biolure® the most effective lure. The largest number of individuals of either species (C. rosa and C. capitata) were captured in austral autumn (March-May) in both orchards and natural habitat with low capture rates throughout the rest of the year. Orchards and natural habitats were significantly different with higher trap catches always found in orchards. Based on microsatellite markers, C. capitata showed a decrease in genetic diversity moving away from the native range (Africa) into the introduced range (Australia, Greece, Guatemala, Madeira). Moreover, there was a clear pattern of differentiation between the African continent and the rest of the world indicating low levels of genetic connectivity. High connectivity throughout the African continent is problematic as this suggests that new invasions will move and colonize new areas unimpeded after first introduction. Lastly, my results indicate that there is no population structure in C. rosa within South Africa. This indicates that there are high levels of connectivity between different pest-occupied sites within the country and suggests that area-wide pest management should be undertaken on a much larger, preferably country-wide, scale. My results are discussed in the framework of invasion biology as well as integrated pest management. In conclusion, when investigating biological invasions, information from organismal biology and ecology as well as molecular biology can be valuable to inform decision-making regarding prevention and mitigation of pest species.
- ItemPopulation genetics of Ceratitis capitata in South Africa : implications for dispersal and pest management(Public Library of Science -- PLoS, 2013-01) Karsten, Minette; Jansen van Vuuren, Bettine; Barnaud, Adeline; Terblanche, J. S.The invasive Mediterranean fruit fly (medfly), Ceratitis capitata, is one of the major agricultural and economical pests globally. Understanding invasion risk and mitigation of medfly in agricultural landscapes requires knowledge of its population structure and dispersal patterns. Here, estimates of dispersal ability are provided in medfly from South Africa at three spatial scales using molecular approaches. Individuals were genotyped at 11 polymorphic microsatellite loci and a subset of individuals were also sequenced for the mitochondrial cytochrome oxidase subunit I gene. Our results show that South African medfly populations are generally characterized by high levels of genetic diversity and limited population differentiation at all spatial scales. This suggests high levels of gene flow among sampling locations. However, natural dispersal in C. capitata has been shown to rarely exceed 10 km. Therefore, documented levels of high gene flow in the present study, even between distant populations (.1600 km), are likely the result of human-mediated dispersal or at least some form of long-distance jump dispersal. These findings may have broad applicability to other global fruit production areas and have significant implications for ongoing pest management practices, such as the sterile insect technique.
- ItemPopulation genetics of the Mediterranean fruit fly Ceratitis capitata in the Western Cape Province, South Africa : invasion potential and dispersal ability(Stellenbosch : Stellenbosch University, 2011-12) Karsten, Minette; Terblanche, J. S.; Jansen van Vuuren, Bettine; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: The Mediterranean fruit fly (medfly), Ceratitis capitata, is a highly invasive species throughout the world and considered as one of the most successful agricultural and economical pests. The increase of global trade in fruit and human travel combined with the biology of the medfly has allowed the species to spread from its proposed Afrotropical origin, to a number of locations throughout the world. In the Western Cape various control strategies have been implemented to control medfly populations, including insecticides and more environmentally-friendly techniques such as the Sterile Insect Technique (SIT). In order to be effective, however, an SIT program requires some knowledge of the population structure and the movement of individuals between pest-occupied sites. The identification of sites from which re-invasion is most likely to occur and knowledge regarding the primary routes through which pests are likely to re-establish are critical to ensure successful SIT programmes. To provide this important information to SIT and area-wide pest control programs in South Africa, sampling at two different spatial scales (regional- and fine-scale) in South Africa was undertaken. Regional scale sampling was done at 13 locations in the Western Cape and fine scale sampling was done at 13 locations within the Ceres-valley. All individuals were genotyped at 11 polymorphic microsatellite markers and selected individuals from the regional scale were sequenced for the mitochondrial gene COI. Our results show that populations at regional- and fine-scale in the Western Cape are characterized by high levels of genetic diversity (HEregional = 0.805; HEfine = 0.803). Little or weak population differentiation was detected at the regional- and fine-scales, suggesting overall high levels of gene flow among sampling locations. These findings were supported by coalescent based methods indicating sufficient levels of gene flow to prevent population differentiation between neighbouring (200m) and distant (350km) populations. However, natural dispersal in C. capitata has been shown to rarely exceed 10 km. As such, high levels of gene flow between distant populations are more likely the result of humanmediated dispersal, linked to the movement of fresh produce within South Africa. This high level of gene flow has important implications for pest management practices, as my results suggests that area-wide pest management should be undertaken at a regional scale, rather than on a farm or valley scale. My results are placed within a management framework, and I argue for more stringent control when fruit are transported within South Africa. Of particular interest for future studies is the investigation of gene flow at broader spatial scales (i.e. the whole of South Africa) and a comparison of the genetic diversity, population differentiation and gene flow patterns of C. capitata with that of Ceratitis rosa will be important to establish a successful pest management strategy in South Africa.
- ItemThree new Drosophilidae species records for South Africa(AOSIS, 2019-06-26) De Araujo, Liana I.; Karsten, Minette; Terblanche, John S.Background: Data on the current species diversity from the Drosophilidae family in South Africa is limited or outdated. Objectives: Using haphazard, limited trapping for a different study, we serendipitously report on and document Drosophilidae species in two distinct regions (representing a sub-tropical and a Mediterranean climate region) of South Africa. Method: Drosophilidae were trapped using mixed fruit and mushroom traps around urban areas in two climatically distinct regions of South Africa. The flies were identified using standard barcoding ( Cytochrome c Oxidase Subunit I [COI] gene sequence) and, in some cases, additional identification from a taxonomical expert using morphological traits. Species were checked against literature, online resources and a previously compiled library of South African Drosophilidae to determine whether they were new records. Results: Thirteen species were readily collected and identified. Of these, three species (Drosophila ananassae, Drosophila nasuta and Zaprionus taronus) have not been reported previously in South Africa. One of the species (Z. taronus) was captured in a home garden, while the other two species were captured in an urban-agricultural region with a sub-tropical climate. Conclusions: From our limited serendipitous sampling, three new species records have been found in sub-tropical climates in South Africa. With more comprehensive, systematic sampling, a better understanding of the South African Drosophilidae composition, and thus the detection of alien or invasive species, can be pursued. Baseline data for understanding spatio-temporal patterns of native biodiversity, or for informing management actions in the case of alien or invasive species, are currently inadequate for this group in the region.