Faculty of AgriSciences

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https://scholar.sun.ac.za/handle/10019.1/9

The Faculty of AgriSciences at Stellenbosch University (SU) is held in high esteem at national and international levels for the quality of its training and research and also as consultant in the agricultural and forestry industry.

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Browsing Faculty of AgriSciences by browse.metadata.advisor "Addison, Matthew"

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    Determining the quality of mass reared male codling moth, Cydia pomonella (Lepidoptera: Tortricidae), by assessing flight performance under laboratory, semi-field and field conditions.
    (Stellenbosch : Stellenbosch University, 2016-03) Visser, Andri; Addison, Matthew; Addison, Pia; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology
    ENGLISH ABSTRACT: The codling moth, Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae), is the insect pest that poses the greatest threat to the South African pome fruit industry. Traditionally, insecticides have been used to control this pest, but recently these chemicals have failed to adequately suppress codling moth due to the build-up of resistance in populations. Along with the added pressure from export markets to reduce insecticide residues, the need for feasible control alternatives has never been greater. The Sterile Insect Technique (SIT) is an environmentally friendly control method that has had great success with the control of a number of different insect pests, including codling moth. The technique involves the mass production and release of sterile insects with the goal of over-flooding the natural population, but it is also crucial that the mass reared insects can successfully compete for mating opportunities. However, no comprehensive quality control assessment method currently exists for mass reared codling moth. This study aimed to identify and develop laboratory, semi-field and field methods that can be used to assess the quality of mass reared codling moth. This would be accomplished by developing flight performance assessments that could be used to distinguish between mass reared moths of high and low quality. The experiments conducted for each assessment method compared the flight performance of moths subjected to different treatments of radiation dose, ageing and handling during transport. For the laboratory quality control assessment, a matrix of nine flight cylinders with combinations of three heights (2.5, 15 and 26.5 cm) and three diameters (10, 14 and 16 cm) was developed which compared the escape rate from these cylinders of moths subjected to different treatments. The semi-field assessment (conducted in a horticultural tunnel) measured the arrival time of the moths subjected to different treatments at a trap 12 m from the point of release. Field release/recapture assessments were conducted at two apple orchards in Elgin (one covered with netting and one uncovered), as well as an uncovered pear orchard in Stellenbosch. The flight performance of mass reared moths was determined by evaluating their dispersal rate from a central point of release with a trapping grid of eight pheromone baited delta traps. The efficacy of the three assessment methods was also evaluated for mass reared false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), in separate experiments. Results indicated that increasing radiation dose had a detrimental effect on moth quality, but no effect could be observed for the age treatments. The effect of bran handling on moth quality could be observed in the field only, suggesting that it is dependent on the time period the moths are transported in the bran. The flight cylinder method was able to accurately indicate of the quality of moths as it relates to flight performance, but that the field assessments were the best indication the overall competitiveness in the field. This was true for both codling moth and false codling moth. The semi-field assessment method was not successful at distinguishing between moths of different quality; the development of an effective semi-field quality test is therefore still on-going.
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    Diversity and ecology of phytophagous weevils in the deciduous fruit industry, South Africa
    (Stellenbosch : Stellenbosch University, 2019-03) Magagula, Mxolisi Meshack; Addison, Pia; Addison, Matthew; Haran, Julien; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: The banded fruit weevil, Phlyctinus callosus, Boheman, 1834 (Coleoptera: Curculionidae), is a serious and economically significant pest of apple orchards and vineyards in the Western Cape Province of South Africa. Adults can be accidentally packed with export fruit causing quarantine problems and is regarded as an international phytosanitary pest. A nine month population survey (during the fruiting season of September 2017 to May 2018) was conducted in three different fruit growing areas, namely; Stellenbosch, Ceres and Grabouw, Western Cape Province, South Africa, to determine the assemblage structure and an identification key was compiled for all weevils found in vineyards and apple orchards during this survey. Fortnightly monitoring using 15 cm cardboard bands (tied around the base of the trunk), has indicated that there were nine weevil species found to occur in apple orchards and vineyards, namely, Eremnus atratus (Sparrmann, 1785), Eremnus chevrolati Oberprieler, 1988, Eremnus occatus Boheman, 1843, Eremnus setifer Boheman, 1843, Naupactus leucoloma Boheman, 1840, Pantomorus cervinus (Boheman, 1840), Phlyctinus callosus Boheman, 1834, Sciobius tottus (Sparrmann, 1785) and Tanyrhynchus carinatus Boheman, 1836. Vineyards recorded the highest diversity with eight species recorded: T. carinatus, P. callosus, E. setifer, E. atratus, E. chevrolati, E. occatus, P. cervinus and N. leucoloma, whereas apple orchards recorded the lowest diversity with only four weevil species found: S. tottus, P. cervinus, E. atratus and P. callosus. E. occatus was collected for the first time in vineyards. All nine species belong to the sub-family Entiminae (root weevils). T. carinatus was found in low abundance and it is the only weevil species with a long rostrum and easier to distinguish from the rest of the weevils collected during the study. The rest of the weevils differ only slightly in morphology, especially the Eremnus. Based on collected species during the survey, an illustrated morphological key was produced with species identification information. DNA barcoding was supplied to provide a complementary diagnosis tool. Seasonal monitoring was undertaken to establish population peaks during the fruiting season, in relation to P. callosus, which was regarded as a key pest in apple orchards and vineyards. Furthermore, damage assessments were conducted by assessing fruit clusters or bunches and recording the percentage damage per block, first in early December (pre-thinning assessment) and later in early April (pre-harvest assessments). Weevils emerged in midOctober in vineyards and around late-October in apple orchards. A peak in adult populations were reached between November and December, after which the population dropped drastically from January up to May. P. callosus was the most abundant weevil species and it accounted for 82 % of all the weevils collected during the survey. Other weevils were found in lower abundance: E. occatus (5.9 %), E. setifer (5.8 %), E. chevrolati (2.1 %), P. cervinus (1.9 %), N. leucoloma (1.1 %), T. carinatus (0.4 %), S. tottus (0.3 %), and E .atratus (0.3 %). Most damage took place during the pre-thinning assessment and to a lesser extent in the preharvest assessment. Most of the damage in apple orchards and vineyards was attributed to P. callosus, based on Spearman’s rank correlations, with the remaining weevils contributing to some damage. As it is possible that certain soil physical parameters such as soil texture, soil chemistry and soil bulk density along with the presence of ground cover impact the population of weevils, soil samples were collected in early September, and analyzed for soil chemistry and soil texture. Groundcover surveys and identification took place every two weeks. The results indicated that there was no significant (P = 0.05) relationship between soil chemistry, soil bulk density, soil texture or ground cover percentage and weevil population. The association between adult P. callosus and groundcover was very weak. It is possible that other factors such as soil moisture, cultural practice within the ground cover, relative humidity and soil penetrability impact the weevil population in apple orchards and vineyards. This study identified and recognized nine weevil species causing damage in vineyards and apple orchards in the Western Cape Province, South Africa, of which one was recorded for the first time in vineyards, as well as assessing the effect of abiotic and biotic attributes towards the population of weevils on these crops. The findings of this study aimed towards supporting the development of ecologically-based control strategies; which enable further research into sustainable and integrated approaches to the management of these weevils.
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    Spatio-temporal analyses of fruit fly populations in selected areas of the Western Cape
    (Stellenbosch : Stellenbosch University, 2019-02) Bekker, Gerard Francois Hermanus van Ginkel; Addison, Pia; Addison, Matthew; Van Niekerk, Adriaan; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: The aim of this study was to investigate the spatio-temporal distribution of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) populations in heterogeneous fruit producing environments in Western Cape, South Africa, using geospatial analyses and machine learning (ML) techniques. A small scale study was conducted at orchard level on the Welgevallen experimental farm in Stellenbosch, South Africa, investigating the spatial patterns and associations of C. capitata and Ceratitis quilicii females, another important fruit fly pest in the Western Cape. The females of both species had aggregated spatial patterns, but their temporal patterns differed, with C. capitata aggregating significantly more towards the end of the season while C. quilicii aggregated significantly towards the beginning of the season. Ceratitis capitata and C. quilicii females were spatially associated, most prominently in home gardens, natural vegetation, citrus and nectarines. A geographical database was developed, incorporating existing area-wide trap monitoring data for C. capitata populations in the Elgin/Grabouw, Villiersdorp, Vyeboom (EGVV) region, Western Cape, an area currently under Sterile Insect Technique (SIT) management, was used to develop a geographical database with the aim to investigate the area-wide spatiotemporal distribution of C. capitata. There were no definitive spatial distribution pattern of C. capitata across all seasons. However, through visual analyses of spatial maps, a southeast/north-west split was observed where traps in the south-eastern parts of the study area showed higher catches and traps in the north-western parts showed lower catches. The results suggested a relationship between the geographic characteristics of EGVV and the abundance and distribution of C. capitata populations. The relationship between the geographic characteristics of the study area (EGVV) and the spatio-temporal distribution of C. capitata were further investigated using ML techniques. Monthly and seasonal long-term C. capitata spatio-temporal distributions were quantified into hot-and cold spots (HCSs), using spatial analyses tools. HCSs were then related to a set of geographic variables, using the random forest (RF) ML classification algorithm to determine the main drivers of the HCSs for C. capitata in the EGVV region. Spatial analyses showed that hot spots were concentrated in the hotter and drier areas, while cold spots were concentrated in the colder and wetter areas. The RF results indicated that rainfall was the most important driver of the HCSs in the EGVV region. To test the robustness of the RF algorithm for the purpose of explaining C. capitata HCSs in a heterogeneous fruit producing environment, the sample size and the variability in the geographic variables were increased by combining data from two regions: the EGVV and the Warmbokkeveld (WB), another fruit producing region under SIT. RF model accuracies from the combined dataset were not significantly lower than those of the individual regions. The drivers of C. capitata spatial distribution were different between regions, but distance to urban areas in the early fruiting season emerged as a strong driver in all scenarios. The findings showed that RF is a useful tool for investigating the spatio-temporal distribution of area-wide tephritid fruit fly trapping data, and that it can handle complex classification problems. It was evident from this study that the spatio-temporal distribution of C. capitata populations are driven by area-specific geographic variables. The area-specific RF models provided invaluable information, which could be used to improve the planning and implementation of area-wide C. capitata management programmes in heterogeneous agricultural landscapes. This study is relevant to the integrated management of fruit flies and potentially other insect pest species, on a local and regional scale. The framework which was developed will allow for the integration of a variety of data and the resultant analyses are relevant at an orchard and regional level. The information will assist efficient decision making by farmers and managers of area-wide integrated pest management programmes.