Masters Degrees (Conservation Ecology and Entomology)

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Browsing Masters Degrees (Conservation Ecology and Entomology) 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.