Browsing by Author "Geldenhuys, Marinus"

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    Fruit fly (Diptera : Tephritidae) ecology in the Western Cape, South Africa
    (2015-12) Geldenhuys, Marinus; Addison, Pia; Manrakhan, Aruna; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: The Mediterranean fruit fly (medfly) Ceratitis capitata (Wiedemann) and the Natal fly C. rosa Karsch are two important tephritid pest species of commercially grown deciduous fruit in the Western Cape. Detailed information on the status of these two fruit fly species in terms of the influence that different host fruits have on their development, abundance and distribution in this region is not known. This project investigated the status of the two fruit fly species in the Western Cape by a) determining the influence of different fruit types on life table parameters such as egg development, larval development, pupal success rate, adult emergence, fecundity and adult survival, b) assessing trapping data and fruit infestation from home gardens in or near areas where deciduous fruits are grown commercially, in order to determine relative abundances and distribution of C. capitata and C. rosa in the region, and c) using geometric morphometrics to assess variability in development associated with host type, by determining shape variation in the wings of C. capitata that were reared on different host fruits. Life table parameters of C. capitata and C. rosa were determined with a series of laboratory experiments on “Golden delicious” and “Granny smith” apples (Malus domestica L. Borkh.), “Crimson seedless” and “Dauphine” grapes (Vitis vinifera L.), “Excellence” peaches (Prunus persica Sieb. & Zucc.), “Packham‟s triumph” pears (Pyrus communis L.), “Angeleno” plums (Prunus japonica Thunb.), “Navel” oranges (Citrus sinensis Osbeck), clementine (Citrus unshiu Swingle) and “Fan Retief” guava (Psidium guajava Linn.). To gain a broader understanding of the population dynamics of fruit flies, on different commercial and non-commercial host plants in various fruit growing areas during different months of the year, baited traps were installed and fruit infestation of known and potential host fruits were assessed at selected sites. Geometric morphometrics were used to assess shape variation of wings of a F1 generation of C. capitata reared on different host fruits, namely plum, pear and clementine that were of the same varieties as mentioned above. No significant differences (p = 0.773) were found in egg hatch between fruit fly species on the different deciduous fruit types grown commercially in the Western Cape: grape, plum, pear, apple and peach. No positive puncture response was found on oranges, therefore this fruit type was excluded from further analyses. Ceratitis capitata and C. rosa favoured guavas and displayed significant preferences for this fruit in terms of field collected samples and developmental parameters. Developmental success was significantly higher on guavas compared to other fruit types tested, for males and females (p < 0.015), of both C. capitata and C. rosa. Piquanté peppers (Capsicum baccatum L.) and jambos (Syzygium jambos (L.) Alston) were also significant alternate host plants based on high fruit infestation rates in the field and they should be the focus of control actions in home gardens. Patterns of relative abundance of the two fruit fly species were found to adhere to seasonality in terms of host availability and certain abiotic factors such as annual rainfall and elevation. Ceratitis capitata was found to be the dominant species, as has been recorded previously in other studies. Significant differences were found in the wing shape of males and females of C. capitata only. Shape variation was significant for flies reared on different fruit types, more so for males. These results suggest developmental differences for flies reared on different hosts. Results of the present study can be used to gain a better understanding of factors that determine the relative distribution of these two species and which hosts they more readily infest in the Western Cape. Key words: Fruit flies, host, abundance, distribution, development
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    Viticultural effects on arthropod diversity in the Cape Winelands Biosphere Reserve
    (Stellenbosch : Stellenbosch University, 2021-03) Geldenhuys, Marinus; Gaigher, Rene; Pryke, James S.; Samways, Michael J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Agricultural land-use intensification negatively impacts biodiversity, ecosystem function, and ecosystem services at local and global scales. Biosphere reserves consist of interrelated and complementary zones of different land-use intensity, are important platforms for integrating human-environment interactions, and support effective conservation through bridging the gap between conservation science, practitioners, and other stakeholders. This study assesses the success status of arthropod conservation within the Cape Winelands Biosphere Reserve (CWBR), a biosphere reserve situated in a global biodiversity hotspot where viticulture is the dominant agricultural land use. The focus is on viticultural management practices and their interactions with the surrounding landscape at multiple spatial scales. Assessment of a wide range of viticultural management practices and environmental variables at the local scale, showed that arthropod species richness can be enhanced through maintaining herbaceous vegetation in vineyard inter-rows, and by leaving plant litter on the vineyard floor. The results were consistent across different management regimes and landscape contexts, emphasising the broad applicability of this agro-ecological approach at the local scale, which also aligns with global trends in plant diversification in perennial crops. At the larger, farm scale, there was limited spillover of stenotopic species associated with remnant fynbos vegetation into vineyards, and no variables were identified that could enhance their spillover. This suggests that proximity of remnant patches, stepping-stone habitats, and conservation corridors may be important for improving functional landscape connectivity for these stenotopic arthropods across this vineyard mosaic. Nonetheless, ubiquitous arthropods in vineyards benefited from increased herbaceous vegetation in the inter-rows. Conversely, there was some spillover of cultural species from vineyards into fynbos, and the ecosystem consequences of this requires further investigation. Furthermore, contrary to main trends in the literature, I found no mediating effects of landscape complexity on local-scale practices (increased vegetation cover and organic farming) with regard to arthropod species richness. However, there were strong interacting effects of organic farming and landscape complexity on arthropod assemblages within vineyards, with greater assemblage dissimilarity among organic farms along a landscape complexity gradient, than among integrated farms. Lastly, at a regional scale, vineyards were nearly equal to natural vegetation in terms of alpha and beta diversity, but vineyards had significantly lower functional diversity. There were significant differences in fynbos and vineyard assemblages. Additionally, there were strong trait associations of predatory beetles with vineyards, as well as smaller sized beetles and plant- dwelling spiders to natural vegetation, indicating a shift in assemblage trait composition between natural and cultivated areas. Deviations from main trends in the literature here highlight the natural variation among different regions, and the importance of site-specific studies for the assessment of arthropod responses to local conditions. Vineyards in the CWBR show great potential for supporting diverse and abundant arthropod assemblages that are functionally dissimilar from the surrounding natural species pool, in-turn contributing to heterogeneity across the landscape. Furthermore, there are opportunities for enhancing arthropod diversity within vineyards, benefitting wine production. The results also emphasise the value of biodiversity conservation in the buffer and transition zones of the CWBR, and in biosphere reserves in general.