Doctoral Degrees (Conservation Ecology and Entomology)
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Browsing Doctoral Degrees (Conservation Ecology and Entomology) by browse.metadata.advisor "Addison, Pia"
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- ItemBiological and ecological factors contributing to the successful use of entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) for the control of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) under South African conditions(Stellenbosch : Stellenbosch University, 2011-12) De Waal, Jeanne Yvonne; Malan, Antoinette P.; Addison, M. F.; Addison, Pia; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) is a devastating pest of pome fruit in temperate regions of the world. Control of this pest, previously involved the extensive use of broad-spectrum insecticides. However, concerns over human safety, environmental impact, widespread dispersal of resistant populations of codling moth and the sustainability of synthetic pesticides in agroecosystems, has encouraged the development and use of alternative environmentally-friendly pest management technologies including the use of entomopathogenic nematodes. These nematodes are lethal pathogens of insects and belong to the families Steinernematidae and Heterorhabditidae, and are ideal candidates for incorporation into the integrated pest management programme currently being developed for residue-free pome fruit production in South Africa. The biological and ecological factors pertaining to the successful use of these nematodes for the control of codling moth were investigated in this study. Their use for bin-disinfestations was evaluated, focusing on the optimum handling conditions to ensure the survival and subsequent efficacy of the nematodes. The study proved that the local isolate SF41 of Heterorhabditis zealandica Poinar 1990 could be used for successful bin-disinfestation. The use of the same nematode isolate was also investigated for the disinfestation of mulch layers of diapausing codling moth larvae. An insect containment device which allowed for direct trial efficacy evaluation was identified and ecological factors pertaining to the successful use of nematodes for mulch disinfestation were investigated. The biological control potential of local nematode isolates, which had previously never been tested against codling moth larvae, was investigated in the laboratory under conditions as can be expected during orchard applications. The efficacy of the selected isolates was confirmed in field experiments. Innovative insect containment methods for above-ground trial efficacy evaluation in the field were investigated. Desiccation proved to be the most limiting factor to the survival and subsequent efficacy of the nematodes during field applications in temperate regions. The effect of low moisture levels on H. zealandica’s efficacy to control diapausing codling moth larvae was subsequently investigated and a starch-based formulation was further tested to overcome the issue of desiccation. Conclusive results indicated that there were several biological and ecological factors influencing the survival of nematodes and illustrated how these factors could be manipulated to overcome these issues and thereby ensure the efficacy of treatments. This is the first report of its kind to comprehensively investigate the use of South African entomopathogenic nematodes for the control of diapausing codling moth larvae and all results emanating from the study can be integrated into a framework for the commercial use of these nematodes in this regard in future.
- ItemBiological control of the banded fruit weevil, Phlyctinus callosus (Schönherr), using entomopathogenic nematodes and fungi(Stellenbosch : Stellenbosch University, 2018-11) Dlamini, Bonginkhosi; Addison, Pia; Malan, Antoinette P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: The overall aim of this study was to establish guidelines, from research undertaken mainly in the laboratory, and from field application, for the use of entomopathogenic nematodes (EPNs) and entomopathogenic fungi (EPF) to control the banded fruit weevil (BFW), Phlyctinus callosus (Schönherr), in vineyards and apple orchards in the Western Cape province. Discovering new species of entomopathogens is important, as more virulent, locally adapted species can be used to increase the potential of microbial control. The first objective of this study was to survey for EPNs and EPF strains/species in orchards and vineyards of the Western Cape, and to investigate their potential to control the BFW. The most virulent EPN species for the biological control of the BFW were selected in laboratory bioassays, and a field trial using Steinernema yirgalemense at different concentrations was conducted. In a further study, the best EPF strains for the biological control of the BFW were selected in laboratory bioassays. The most virulent EPN and EPF isolates were applied, in combination, to determine their interaction-effect on the mortality of BFW in the laboratory, as the final objective. In total, 70 soil samples were collected from deciduous fruit orchards and vineyards in the Western Cape. The soil samples were baited with mealworms, Tenebrio molitor (Coleoptera: Tenebrionidae) to trap EPNs and EPF, which were characterised by using morphological and molecular techniques, and evaluated for their potential to control the BFW adults. EPNs were isolated from 17 % (12) of the samples, with Heterorhabditis bacteriophora Poinar and Heterorhabditis safricana as the only two EPN species isolated. Heterorhabditis bacteriophora (53 % mortality) resulted in significantly higher (p < 0.05) mortality of adult BFW, compared to H. safricana (37 % mortality), in laboratory trials. EPF were trapped from 37 % (26) of samples, consisting of a total of 14 Beauveria bassiana isolates and 12 isolates from the Metarhizium anisopliae complex. A Metarhizium isolate (79 % mortality) resulted in significantly higher (p < 0.05) mortality of BFW adults, compared to B. bassiana (63 % mortality) in laboratory trials. Results obtained from the study indicate that the soil samples from the deciduous fruit orchards and vineyards from the Western Cape contained both EPNs and EPF that can be used to control BFW. Different EPN species were evaluated by laboratory screening for virulence against the different life stages of the BFW. A field trial to determine the performance of Steinernema yirgalemense, applied at different concentrations, followed. Results from a probit analysis showed S. yirgalemense to be six times more potent than Heterorhabditis noenieputensis, giving 95 % mortality of BFW larvae at a concentration of 400 infective juveniles (IJ) per insect, which was significantly higher (p < 0.05) compared to other concentrations. At a concentration of 100 IJs/insect, Steinernema yirgalemense, H. noenieputensis, and Steinernema feltiae resulted in significantly higher (p < 0.05) mortality of BFW larvae compared to the other EPNs, with no significant difference between each other. Heterorhabditis indica (70 % mortality) and H. baujardi (67 % mortality) resulted in significantly higher (p < 0.05) mortality of the BFW pupae, compared to H. noenieputensis (55 % mortality). In the case of adult BFW, Heterorhabditis indica (95 % mortality) and S. yirgalemense (94 % mortality) gave significantly (p < 0.05) higher mortality, compared to three other EPN species evaluated. In the field trials, S. yirgalemense, at 20 and 40 IJs/cm2, gave 69 % and 78 % mortality of BFW larvae, respectively. The results showed that all EPNs screened controlled the juvenile and adults stages of BFW. Steinernema yirgalemense was also shown to be capable of controlling BFW under field conditions, even at low concentrations. Different Different EPF isolates were tested at 1 × 106 conidia ml-1 for their virulence against the different life stages of the BFW. Results showed that Broadband® (Beauveria bassiana strain PPRI5339) (97 %) and Meta 69 (Metarhizium anisopliae) (93 %) gave significantly higher (p < 0.05) mortality of BFW larvae compared to Eco-Bb® (B. bassiana) (58 %), with no significant difference in mortality between Broadband® and Meta 69. In the case of pupae, Broadband® (92 %) gave significantly higher (p < 0.05) mortality, compared to Eco-Bb® (67.5 % mortality) and Meta 69 (65.8 % mortality). Broadband® (90 % mortality) gave significantly higher (p < 0.05) mortality of adult BFW compared to Eco-Bb® (69.2 % mortality) and Meta 69 (65 % mortality), of which neither differed from each other. When compared to a local EPF (M. anisopliae EA2), Broadband® (91.7 % mortality) gave significantly (p < 0.05) higher mortality of BFW adults, compared to EcoBb® (65 % mortality), Meta 69 (59.5 % mortality) and M. anisopliae isolate EA2 (64.2 % mortality), which did not differ significantly from one another. In a sand bioassay, Broadband® (85 % mortality) resulted in significantly (p < 0.05) higher mortality of BFW larvae compared to Eco-Bb® (55 % mortality) and Meta 69 (70 % mortality). The results indicated that all the EPF isolates tested were effective against juvenile and adults stages of the BFW, with Broadband® showing the most promise in controlling the BFW under laboratory conditions. The last objective of the study was to evaluate the combined use of the EPF; Eco-Bb®, Broadband®, Meta 69 and a local isolate M. anisopliae EA2, with the EPN, S. yirgalemense against BFW larvae and adults. The EPF were either applied alone, or at the same time as S. yirgalemense, or S. yirgalemense was introduced 1 and 2 weeks after fungal application; the EPNs were also applied alone. Results showed that 100% larval and adult mortality was obtained when S. yirgalemense was applied 1 or 2 weeks after Eco-Bb® and BroadBand® application. Synergistic interactions were noted when Eco-Bb® and S. yirgalemense, BroadBand® and S. yirgalemense, Meta 69 and S. yirgalemense, and M. anisopliae isolate EA2 and S. yirgalemense when applied 1 or 2 weeks after application of the EPF. Additive interactions were observed when the EPF and S. yirgalemense were applied simultaneously. Future research into the biological control of the BFW, using EPNs and EPF, should be focused on conducting large-scale field trials to demonstrate their potential use as biocontrol agents, within an integrated pest management programme. Both entomopathogens have shown outstanding potential to control the BFW when used alone, and in combination, could provide an economically viable control strategy against the BFW.
- ItemCharacterisation of nematode symbiotic bacteria and the in vitro liquid culture of Heterorhabditis zealandica and Steinernema yirgalemense(Stellenbosch : Stellenbosch University, 2013-03) Ferreira, Tiarin; Malan, Antoinette P.; Addison, Pia; Addison, M. F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Entomopathogenic nematodes have the potential to be outstanding biocontrol agents against agricultural pest insects. Combined with their bacterial symbionts, these biocontrol agents have proven to be very effective against numerous pests. The nematodes belong to the families Steinernematidae and Heterorhabditidae, and are ideal to be used in, and integrated with, pest management systems. There is a dire need for new and innovative methods to control agricultural pests, as numerous pest insects have developed resistance against broad-spectrum insecticides. Together with the environmental impact of these insecticides and the safety aspect regarding humans and animals, the need to develop new technologies, including entomopathogenic nematodes for pest management, is high. In this study, the associated symbiotic bacteria of three entomopathogenic nematodes species were isolated, and the potential of two nematode species to be successfully mass cultured in liquid medium was evaluated. Regarding the symbiotic bacteria, results from the study showed that bacteria species from all three nematode species, Heterorhabditis noenieputensis, Steinernema khoisanae and Heterorhabditis zealandica, were novel. Heterorhabditis noenieputensis was isolated in the Mpumalanga province during a previous survey conducted in citrus orchards. The bacterium isolated from this nematode belongs to the genus Photorhabdus, and bear closest similarity (98.6%) to the type strain of P. luminescens subsp laumondii (TT01T). Photorhabdus luminescens subsp. noenieputensis subsp. nov., derives its name from the area where the nematode was sourced, namely the farm Springbokvlei, near the settlement Noenieput close to the Namibian border. Thus far, 85 Steinernema spp. have been described worldwide, including S. khoisanae which was isolated in the Western Cape province of South Africa. Four S. khoisanae strains, namely SF87, SF80, SF362 and 106-C, were used for characterisating the new bacteria from different localities in South Africa. Using the neighbor-joining method, all the strains were aligned with 97% homology to the 16S rRNA sequences of several Xenorhabdus- type strains, indicating that they belonged to the same genus. The multigene approach was used to distinguish between the Xenorhabdus spp. and partial recA, dnaN, gltX, gyrB and infB gene sequences of the various strains were analysed. The bacterium species was named Xenorhabdus khoisanae sp. nov. after the nematode from which it was isolated. The results showed that the third bacterium species, which was isolated from H. zealandica, was new. The sequence of the bacteria strain clustered with the type strains of P. temperata and P. asymbiotica, indicate that it belonged to the genus Photorhabdus. This is the first study to show that H. zealandica associates with a luminescent Photorhabdus species, rather than with the known non-luminescent P. temperata. The potential of H. zealandica and Steinernema yirgalemense mass culture in liquid was investigated. Results illustrated that H. zealandica and its P. luminescens symbiont can be successfully cultured in liquid. However, two generations occurred during the process time, instead of the desirable one-generation. The growth curve of the symbiotic bacteria during the process time was measured, in order to determine when the stationary phase was reached, with the results showing this to occur after 36 h. Therefore, the optimum amount of time required for inoculating the IJs and for aiding in maximum infective juvenile (IJ) recovery is 36 h for adding the nematodes post pre-culturing of the bacteria. Future research goals should be to increase the percentage recovery in liquid culture, which would increase the number of nematodes produced per ml, which would, therefore, reduce the processing time significantly. The results from mass culturing the second nematode species, S. yirgalemense, indicated an asynchronous nematode development in the first generation. Growth curves were performed with the symbiotic bacteria that showed the exponential phase of Xenorhabdus started after 15 h, and that, after 42 h, the stationary phase was reached, with an average of 51 × 107 cfu·ml-1. Bioassays were performed to compare the virulence between in vitro- and in vivo-produced nematodes, with the results showing that the in vitro-produced nematodes were significantly less virulent than were the nematodes produced in vivo. The success obtained with the production of S. yirgalemense in liquid culture can serve as the first step in the optimising and upscaling of the commercial production of nematodes in industrial fermenters. The last aim of the current study was to determine when Xenorhabdus reached the stationary phase, when it is grown in a 20-L fermenter, as this would be the optimum time at which to add the IJs of S. yirgalemense. Such characteristics as the effect of stationary phase conditions on the bacterial cell density and on the DO2 rate in the fermenter were investigated. The results showed that the stationary phase of Xenorhabdus was reached after 36 h at 30˚C, which took 6 h less than did the same procedures followed with the Xenorhabdus sp. cultured in Erlenmeyer flasks on orbital shakers. This is the first step toward the liquid mass culturing of S. yirgalemense in industrial-size fermenters. Data from this study indicated the optimum amount of time that is required for adding nematodes to the bacterial culture in the fermenter, and for ensuring the optimum recovery of IJs, as well as a subsequent high yield of nematodes within a minimum processing time. This is the first report of its kind to investigate comprehensively the successful liquid culture of two South African entomopathogenic nematode species for the sole purpose of evaluating potential commercialisation. Results emanating from this study could be used as groundwork in future, in combination with similar research such as culturing nematodes intensively in large fermenters.
- ItemDeveloping an integrated management system for western flower thrips, Frankliniella occidentalis (Pergande), on deciduous fruit, using semiochemicals in a push-pull strategy(Stellenbosch : Stellenbosch University, 2016-12) Allsopp, Elleunorah; Addison, Pia; Dewhirst, Sarah Y.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Western flower thrips (WFT), Frankliniella occidentalis (Pergande), causes both feeding (russetting and silvering) and oviposition (pansy spot) damage to fruit. Despite routine insecticide applications from 20% bloom until petal fall, pansy spot and pitting damage was still being reported, particularly on plums. This study was initiated to determine the reason for the apparent failure of chemical control and the cause of pitting damage, and to investigate the feasibility of developing a push-pull system to minimize economic WFT damage by using deterrent plant essential oils and trap crops. Field trials in commercial plum orchards in the Western Cape confirmed that WFT oviposition causes pitting damage. The apparent failure of insecticide applications to prevent pansy spot and pitting damage was due to the fact that WFT entered plum blossoms even before the petals opened, where they were protected from contact insecticides applied at 20% bloom. No treatment threshold could be determined because no consistent significant relationship was found between blue sticky trap counts and WFT oviposition damage to plums. Sticky trap counts thus only serve to indicate presence or absence of WFT in an orchard. To reduce WFT oviposition damage, monitoring must start as soon as flower buds begin to swell, some blue sticky traps should be hung closer to the ground during the early season and, if WFT are present, the first spray application should be made as soon as blossoms reach balloon stage. To provide the “push” in a push-pull system, the potential of three plant essential oils to reduce WFT oviposition rate on plum blossoms was investigated. This study was the first to demonstrate that suspensions of thymol (10%), methyl salicylate (1% and 10%) and carvacrol (1% and 5%) significantly reduced WFT oviposition rate when applied to individual plum blossoms in laboratory bioassays. Significant results could not be obtained in semi-field trials using potted plum trees, mainly because the suspensions were unable to provide sustained release of the volatile essential oils at behaviourally effective concentrations. Phytotoxic damage to blossoms was encountered at higher concentrations of the essential oils. While thymol, methyl salicylate and carvacrol were shown to have potential as oviposition deterrents for WFT on plum blossoms, they could only be considered for commercial use if stable suspensions can be developed to deliver sustained release of behaviourally effective concentrations with no phytotoxic effects. An effective trap crop that provides the “pull” should be as attractive, or more attractive to WFT than plum blossoms. White clover, Trifolium repens L., was selected for investigation. The attractiveness of flower volatiles of clover flowers and plum blossoms, collected by means of air entrainment, was evaluated using a Y-tube glass olfactometer. Results showed that the volatiles of clover flowers and plum blossoms are both very attractive to WFT females. White clover shows potential as a trap crop for WFT, but a control system on heavily infested clover should be implemented to remove WFT and clover flowers should be cut before honeybees are brought in to ensure effective pollination. This study provided crucial information to improve the efficacy of early-season chemical control of WFT. Three essential oils were identified as potential oviposition deterrents for WFT on plum blossoms and white clover was identified as a potential trap crop. Development of suitable formulations of the essential oils is required before a push-pull system to manage WFT more sustainably in deciduous fruit orchards can be implemented.
- ItemThe development of a management strategy for the control of the Cape grapevine leafminer, Holocacista capensis (Lepidoptera: Heliozelidae), in South African table grape vineyards(Stellenbosch : Stellenbosch University, 2019-03) Steyn, Leigh Ami Isbell; Addison, Pia; Malan, Antoinette P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: The Cape grapevine leafminer, Holocacista capensis Van Nieukerken & Geertsema (Lepidoptera: Heliozelidae) has become a common pest on table grapes and wine grapes in the Western Cape province of South Africa, since it was first reported in 2012. The presence of cocoon casings on grape bunches intended for export makes them a pest of economic importance, although its recognised pest status does not reflect the severity of some of the infestations that have occurred in the Berg River region. To date, control strategies have consisted of insecticide applications or manual, labour intensive post-harvest removal of rooted cocoon casings from table grape bunches during the packing process. To aid in the development of an integrated pest management (IPM) strategy, this study focused on understanding aspects of cultural, chemical and biological control strategies, whilst considering genetic diversity and environmental variables that influence H. capensis populations. In agreement with other studies conducted on problematic leafminers, field trials indicated that ambient light intensity, climatic conditions and plant nutrient composition affected H. capensis populations in commercial vineyards. Correlations derived from the evaluation of temporal satellite imagery to determine the normalized difference vegetation index (NDVI), indicated the potential for the use of this technology for monitoring leafminer invasions in the future. A preliminary study on the genetics of the pest involved the extraction of DNA from 52 male moths collected from commercial vineyards and natural forests (using baited Delta traps) in and around the Western Cape. The study was able to confirm species identity and synonymy of the insects collected from field-placed traps. An insecticide screening trial, conducted in the laboratory using varying doses of a variety of commercially available insecticides, identified spinetoram (spinosyn), dichlorvos (organophosphate) and cypermethrin (pyrethoid) as good candidates for inclusion in an IPM strategy. High mortality (> 87%) was recorded at the lowest doses (a quarter of the recommended field dose). Entomopathogenic nematodes (EPNs) were screened in the laboratory as an alternative to a management strategy focused solely on the use of chemical applications. Using a 200 infective juvenile (IJ)/50 µl of distilled water solution, EPNs were able to penetrate leaf galleries (mines) and cause larval mortality. Three EPNs, Heterorhabditis baujardi Phan, Subbotin, Nyugen & Moens, Heterorhabditis indica Poinar, Karunakar & David and Heterorhabditis noenieputensis Malan, Knoetze & Tiedt, were able to cause > 86% mortality of leaf-mining larvae and have the potential to be adopted in an IPM strategy against H. capensis. The use of bunch covers as a physical control strategy was tested in the field, for cases where leafminer infestations are unavoidable and maximum residue limits (MRLs) have been reached, to preclude insecticide treatments. All covers tested proved to successfully reduce the presence of rooted cocoon casings on bunches. This study has provided a positive forecast for the success of future chemical and biological applications and has provided the groundwork for the development of an IPM strategy against H. capensis on grapevines.
- ItemEfficacy of entomopathogenic nematodes and fungi as biological control agents of woolly apple aphid, Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae) under South African conditions(Stellenbosch : Stellenbosch University, 2016-03) Stokwe, Nomakholwa Faith; Malan, Antoinette P.; Addison, Pia; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: The woolly apple aphid (WAA), Eriosoma lanigerum (Hausmann) is an important pest of apples, (Malus domestica Borkh.). Severe infestations by WAA can lead to colonies near spurs that can deposit honeydew on fruit, which serve as a substrate for sooty mould. If not controlled, it can lead to destruction of developing buds in the leaf axils and a reduction in tree vigour or formation of galls. Increasing interest in environmentally sustainable farming has increased the demand for environmentally friendly pest control methods. Therefore the use of naturally occurring biocontrol agents and more environmental friendly methods are needed. The study aims to determine the potential of entomopathogenic nematodes (EPNs) and entomopathogenic fungi (EPF) to control WAA. EPNs and EPF are naturally occurring and environmentally friendly microbials that have the potential to be developed into bio-pesticides. Research on the use of EPNs and EPF as biocontrol agents against E. lanigerum showed that they have potential to be used to control WAA. This is the first report on the use of EPNs and EPF to control WAA in South Africa. These findings are significant, especially to those interested in integrated pest management (IPM). The first objective of this study was to evaluate the virulence of endemic EPN species against WAA by conducting laboratory bioassays and to determine the effect of imidacloprid on the infectivity of EPNs. A total of seven entomopathogenic nematode isolates were evaluated for their potential as biological control agents for WAA in the laboratory, using a 24-well bioassay protocol screening method. From these, the two most virulent nematode isolates were selected. In all cases studied the degree of infection associated with mortality was less than 50% and the other tested nematode isolates were less successful. Although penetration, recovery of the non-feeding Infective Juveniles (IJ) to the feeding stage and development into the adult stage was observed in some cases, the nematodes failed to complete their life cycle inside the WAA. When this failure to develop and reproduce was investigated using direct screening with the associated symbiotic bacteria and insect extract, it became evident that the WAA haemolymph contains an inhibitory factor that prevented the symbiotic EPN bacteria from growing. WAA size was also shown to have an effect on insect mortality, with higher mortality observed in adults and low mortality for intermediates, while no mortality was observed for the crawlers. The two most virulent nematode isolates, Nguyen, Tesfamariam, Gozel, Gaugler & Adams, 2004 and Heterorhabditis zealandica Poinar, 1990 were not affected by the addition of imidacloprid, leading to the conclusion that EPNs and imidacloprid could potentially be applied as tank mix. The second objective of the study was to evaluate the use of two EPF, Beauveria bassiana and Metarhizium anisopliae, for the control of WAA in the laboratory. The five fungal isolates tested were pathogenic to WAA and they caused significant WAA mortality compared with the control. The commercial isolates Beauveria bassiana (Eco- Bb strain R444) and Metarhizium anisopliae (ICIPE 69) caused the highest rate of WAA mortality and were selected for further evaluation. When the effect of EPF concentration and exposure time of these two most virulent isolates were evaluated, it became evident that increased EPF concentration (1 × 107 to 1 × 1010 conidia ml-1) and exposure time increased WAA mortality. This lead to the conclusion that a relatively long incubation period and high EPF concentration are needed to achieve full efficacy of the these fungal isolates for controlling WAA. The third objective of the study was to evaluate the interaction between EPNs and EPF for the control of WAA and the effect of mulching on EPN efficacy in pot trials. Joint use of EPNs and EPF increased insect mortality when compared to treatments with only EPNs or only EPF, indicating an antagonistic effect. Combining S. yirgalamense with B. bassiana (Eco- Bb® strain R444) and M. anisopliae (ICIPE 69) provided no advantage for improved efficacy against WAA, which lead to the conclusion that M. anisopliae (ICIPE 69) or B. bassiana (Eco- Bb® strain R444) could be used for suppression of WAA. When the environment was manipulated by adding mulches, WAA mortality was slightly higher compared to the unmulched soil. However, these differences were not statistically significant. The fourth objective of the study was to evaluate the efficacy of S. yirgalamense, B. bassiana and M. anisopliae against WAA in the field. A single application of S. yirgalamense (80 IJs/cm2) B. bassiana (Eco- Bb® strain R444) (1g/L) and M. anisopliae (ICIPE 69) (200 ml/ha) effectively controlled WAA under South African field conditions. The EPF performed better than EPNs. Based on these results the success in controlling the root colonies resulted in greatly reduced infestations of the aerial parts of the apple trees in the trial. These studies attempted to determine if local EPNs and EPF are pathogenic to WAA and if they could be used to control it in the field. It was found that all the isolates tested were pathogenic to WAA in the laboratory and that S. yirgalamense, B. bassiana and M. anisopliae were the most effective isolates. They were able to control WAA under field conditions, although the degree of control was low. Therefore future studies should be designed to investigate the application and post-application conditions required for EPF to be effective with respect to WAA control and to ensure that the application of the fungi is economically viable. The role of the wetting agent in improving soil saturation, penetration and uptake of EPNs and EPF also requires to be investigated.
- ItemIntegrated management of false codling moth, Thaumatotibia leucotreta, on stone fruit and table grapes(Stellenbosch : Stellenbosch University, 2019-03) Steyn, Vernon Murray; Addison, Pia; Malan, Antoinette P.; Stenekamp, Daleen; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Integrated pest management (IPM) strives to control insect pests with a multifaceted approach that mirrors that of the ecology and endeavours to restore balance to the agricultural environment. To ensure the success of an IPM programme it is vital to understand the biology and the life cycle of the target insect. False codling moth (FCM), Thaumatotibia leucotreta is a tortricid moth with an extensive host range of more than 70 plants and is a key pest on citrus, stone fruit and table grapes. Insecticides are still relied upon for the control of FCM however, due to stricter regulations and their cascading environmental effects, there is a drive to reduce the chemical load in our agricultural environments. This encourages the need for a more sustainable approach such as IPM, which targets every stage in the life cycle of FCM. In this study, entomopathogenic nematodes (EPNs) and entomopathogenic fungi (EPF) were isolated from agricultural soils. The susceptibility of eggs and pupae to EPNs was investigated, and both entomopathogen types were screened against larvae. The EPNs proved to be the more potent pathogen and the larval stage was the least resilient against the pathogen. The EPN species that showed the most promise in laboratory trials were used as an in vitro cultured product and were tested in the field against FCM. The EPNs caused mortality of FCM larvae within 48 h and remained effective four weeks after application. Mating disruption is a nonchemical control technique that interferes with the mate-finding ability of insects in order to reduce mating events and is therefore an ideal candidate for the control of FCM. However, the effect of mating disruption has not been quantified against FCM in stone fruit and table grapes. Using multiple mark-release-recapture experiments, this is the first study to reliably quantify mating disruption in stone fruit and table grapes. Mating disruption proved to be a highly successful technique causing up to 99% disorientation of male FCM, but how the method alters FCM’s mate-finding ability was unclear. To determine FCM’s behavioural response to the addition of the female pheromone, quantitative tools and dosage-response profiles were used. The study proved that at low dosages the success of mating disruption is dependent on FCM density, however at high dosages there is a shift to non-competitive disruption causing mating disruption to remain effective even at high pest densities with few pheromone point sources. The integration of the techniques investigated here will ensure the effective control of FCM at each stage of the life cycle, ensuring low population growth that may lead to the successful suppression of this problematic pest.
- ItemA molecular, morphological and biological characterisation of the genus Globodera (Nematoda: Heteroderidae) in South Africa(Stellenbosch : Stellenbosch University, 2014-03) Knoetze, Rinus; Swart, Antoinette; Addison, Pia; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: A molecular, morphological and biological characterisation of the genus Globodera (Nematoda: Heteroderidae) in South Africa is presented. The aims of the study were to determine the spread of the genus in South Africa; to study the systematics and describe the characteristics of the group and to gain a more complete understanding of the biology of the group as agricultural pests. Surveys were conducted in the Cape Floristic Region and in all the potato-producing areas of South Africa. The surveys unearthed new species of cyst nematodes and determined the spread of Globodera rostochiensis in the country. Phylogenetic analysis of sequences from ITS-rDNA was used to infer phylogenetic relationships among cyst nematodes from South Africa. The analyses established the distinct phylogenetic positions of cyst nematode populations from South Africa relative to an array of other cyst nematode species and indicated the existence of four new species of cyst nematodes. Analysis of random amplified polymorphic DNA (RAPD) banding patterns revealed intraspecific genetic variation amongst populations of Globodera rostochiensis. In order to provide molecular protocols for the accurate identification of South African cyst nematodes, species-specific primers and restriction enzymes were tested for their ability to discriminate between local Globodera spp. A combination of the molecular, morphological and morphometric characteristics of these populations were used to describe three new species of cyst nematodes. Experiments to determine the effect of storage temperature on the viability and hatching of South African populations of G. rostochiensis, showed differences in the responses of different populations to different storage temperatures. Experiments to determine the effect of field conditions on the viability and hatching of South African populations of G. rostochiensis, indicated that a decline in viable eggs in cysts from different populations occur, but suggests that the cysts will be able to survive for much longer in these soils than was expected. Spontaneous hatch was the main contributor to the decline of viability of cysts in the soil. Recording of soil temperatures in different locations indicated that the average temperature at 20 cm depth was approximately 20°C, the optimum temperature for the reproduction of G. rostochiensis, as confirmed by in vitro reproduction tests, which also showed that multiplication and survival is influenced negatively when the temperatures rise above 25°C. Reproduction on differential potato clones confirmed the pathotype of all the South African populations of G. rostochiensis as Ro1. After assessing the reproduction of G. rostochiensis on indigenous solanaceous plants, it was concluded that none of these plants induce substantial hatch in G. rostochiensis, nor do they support multiplication of the nematode. The results of this project have an impact on inquiries at all taxonomic levels, while also having an essential practical application in nematology. Knowledge of the distribution, pathogenicity, survival potential and reproduction capacity of Globodera species in South African soils are valuable for the design of effective management strategies as well as regulatory measures.
- ItemOptimization of a mass-rearing system to produce codling moth, Cydia pomonella, for a Sterile Insect Release programme in South Africa(Stellenbosch : University of Stellenbosch, 2011-03) Stenekamp, Daleen; Addison, Pia; Addison, M. F.; University of Stellenbosch. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Codling moth, Cydia pomonella, is a worldwide pest and of major economic importance to the South African pome fruit industry. Sterile insect release is applied as a component of area-wide integrated pest management and includes the mass-rearing, sterilization and the release of the sterile insects. For sterile insect release, the improvements of rearing methods in terms of the quality of the diet ingredients and the economical aspect of the rearing method are examined. The effect of genetically modified maize meal, containing the Bacillus thuringiensis gene, in an artificial medium for codling moth rearing, is determined. The use of even a small amount of Bacillus thuringiensis resulted in larval mortality and prolonged development. These results are detrimental to a mass-rearing facility and must be considered by any rearing facility that uses genetically modified maize meal if the insect is sensitive to the gene. An alternative to maize meal in the artificial medium was tested and whole wheat flour was considered to be a suitable replacement. Agar agar is an expensive gelling agent used in the artificial medium. An alternative for agar agar (Kelcogel, Elastigel and carrageenen) is tested and the biological effect on codling moth is determined. Factors such as mortality, pupal and moth weight, longevity, fecundity and development time were used as quality parameters. Results showed that Elastigel was a suitable replacement for agar agar, with bigger pupae and moths, higher fecundity and increased longevity. The economical advantage of the replacement is a 40.91% reduction of the diet cost. The other gelling agents tested also gave acceptable results and can be considered if shortages of agar agar or Elastigel occur. A new method of mass-rearing codling moth larvae in a closed rearing system using large trays placed in a ventilated box is designed. This method is more cost and space effective as a smaller area is needed to rear a large number of moths. The risk of diet contamination is less because of the closed environment and more economical and effective air handling. This is the first report of its kind to describe the mass-rearing of codling moth in a closed environment and the risks involved in using genetically modified maize meal in an artificial diet for the codling moth. These results should be incorporated into existing mass-rearing facilities or taking into consideration when designing new mass-rearing facilities.
- ItemPerformance of sterilized Eldana saccharina Walker (Lepidoptera: Pyralidae) adults in mating and cage trials : further steps towards its control using the Sterile Insect Technique(Stellenbosch : Stellenbosch University, 2012-12) Mudavanhu, Pride; Conlong, D. E.; Addison, Pia; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.The sugarcane borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) is the most limiting factor in the South African sugar industry with losses to this insect pest estimated to be at least ZAR60 million per annum. Because of its cryptic nature as well as the fact that E. saccharina is both indigenous to Africa and occurs on several host plants, attempts to control or eradicate it using several available methods have not been very successful. However, the sterile insect technique (SIT) is one of the newer control methods that can be incorporated into an area-wide integrated pest management (AW-IPM) programme to achieve better control or eradication. The implementation of the SIT program needs to go through a series of well-researched phases in order to be successful. In the first of this multi-phase project, it was determined that E. saccharina is susceptible to ionizing radiation, and is thus a suitable candidate for the SIT development against it and that a sub-sterilizing dose of 200 Gy is sufficient to induce F1(inherited) sterility in male and complete sterility in female moths respectively. The results presented here are discussed in the context of further development of the SIT as an addition to the arsenal of tactics in an AW-IPM programme against E. saccharina. Based on these initial findings, the study examined the lek and mating behavior of male moths subjected to three radiation doses (150, 200, 250 Gy) against normal non-irradiated/fertile moths. Both mass-rearing and irradiation of E. saccharina led to a quantitative departure of male mating behavior away from that exhibited by their wild counterparts. However, treated males are still able to form leks and mate with wild females. Male E. saccharina irradiated at all three doses tested were found to be as active and competitive as wild males, but in some of the traits measured, performance diminished significantly with an increase in the radiation dosage. In general, the performance of moths treated at 200 Gy did not differ significantly from that of moths treated at 150 Gy and therefore the former dose is ideal for SIT development since it results in a lower residual F1 fertility than the latter. The level of mating competitiveness and compatibility was assessed under both laboratory and semi-field conditions in pairwise comparisons consisting of laboratory reared vs. wild (L-W), 200 Gy irradiated vs. wild (S-W) and laboratory reared vs. irradiated moths (L-S). Based on the results from the more robust field cage assays, the mating indices generated indicated that the mass-reared E. saccharina strain produced in South Africa has not yet evolved sexual behaviours suggestive of incipient pre-mating isolation barriers with local wild strains. Wild moths did not discriminate against either the partially sterile or laboratory reared moths and most importantly, the irradiated males mated significantly more than their wild counterparts regardless of the type of female. The irradiated insects could therefore achieve the purpose for which they are intended upon release into the field. Third, the critical thermal limits (CTLs) to activity at high and low temperatures (i.e. critical thermal maxima “CTmax” and minima “CTmin”) of different E. saccharina strains/treatments were investigated under standard experimental conditions. The effect of laboratory rearing and increasing radiation dosage on thermal tolerance of the adult stage of E. saccharina was explored. There were highly significant differences between the laboratory-reared and wild strain and also between non-irradiated and irradiated strains in both CTmax and CTmin. Laboratory reared E. saccharina moths were more heat tolerant compared to wild moths for both genders while in the case of CTmin, the reverse was true. Irradiation had a negative effect on both CTmax and CTmin. Moths treated at the lowest radiation dose were more cold and heat tolerant than those treated at higher dosages thereby reinforcing the importance of lower dosages rather than those that induce full sterility against E. saccharina. In general, gender effects on the CTLs were non-significant. Pilot sterile male releases in shade house trials to measure the impact of sustained releases of partially sterile adult males at an over-flooding moth ratio of 10T: 1U (treated to untreated),were conducted to measure their efficacy to stop E. saccharina incursions and suppress populations prior to testing in pilot studies under true season-long and area wide conditions. Results from the current study demonstrated that releasing partially irradiated (200 Gy) adult male moths at the afore mentioned release rate significantly reduced sugarcane stalk damage as well as lowered the number of fertile progeny from F1to succeeding generations in a stable E. saccharina population initiated in a cage house. There were more damaged internodes per stalk in the control than in the sugarcane receiving regular releases of partially sterile male moths. Overall, there were significantly more undamaged stalks in the treated sugarcane than the untreated control. Furthermore, there were significantly more larvae per stalk retrieved from the control compared to the treated sugarcane suggesting that the sustained release of steriles was efficacious in reducing emergence of fertile larvae in the succeeding generations. The results of this study indicate that there is considerable scope for the SIT against E. saccharina.
- 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.
- ItemPostharvest phytosanitary disinfestation strategies using thermal and atmospheric stress: commodity and insect tolerances(Stellenbosch : Stellenbosch University, 2019-12) Smit, Renate; Johnson, Shelley A.; Jooste, Mariana; Addison, Pia; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: South African chill sensitive horticultural products deemed for export cannot be exported using certain phytosanitary cold sterilisation regimes, without negatively affecting fruit quality. Low temperature phytosanitary treatments are required to control a variety of pests, however in some cases, cold temperature treatments are ineffective against insects that display high levels of thermal tolerance. Developing alternative phytosanitary treatments is therefore crucial, and maintaining a balance between desirable fruit quality and effective control of insect pests is an important consideration throughout the process. In the present study, the potential of two postharvest mitigation technologies were investigated to assess their potential in controlling targeted pests while maintaining fruit quality - CATTS (Controlled Atmosphere Temperature Treatment System) and ethyl formate fumigation. CATTS was investigated specifically as a potential postharvest mitigation treatment for chill sensitive plum cultivars. CATTS technology incorporates heat and atmospheric stress to control insect pests. Key phytosanitary pests of South Africa which require control include the grain chinch bug, Macchiademus diplopterus (Distant) (Hemiptera: Lygaeidae), the banded fruit weevil, Phlyctinus callosus (Schöenherr) (Coleoptera: Curculionidae) and the false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae). In the first part of this dissertation, different temperature treatments in combination with controlled atmosphere were tested and fruit was cold-stored using two different cold storage regimes, namely standard cold sterilisation and the dual temperature regime, to examine the effectiveness of the CATTS treatments and cold storage for phytosanitary control. Finding a balance to maintain fruit quality and kill both internal and external pests proved challenging. As a pre-conditioning benefit of heat treatments was observed during the first season, treatments were aimed at enhancing this effect during the second season, to enable the fruit to withstand low temperatures for longer periods to control internal pests. The second part of this dissertation is an in-depth investigation into the physiology of Macchiademus diplopterus. This was conducted to provide insight into the thermo-tolerant ability of this pest, as CATTS treatments were found to be ineffective for phytosanitary control. The compositional changes that occur during aestivation were examined through biochemical (macromolecules) and molecular (soluble protein identification) analyses. These were performed on the insects before entering aestivation and during the aestivation period. To examine the biochemical compositional changes the insect undergoes during thermal stresses, insects from early and mid-aestivation were treated with different CATTS treatments and cold storage regimes (cold sterilisation and dual temperature regime). The insect mortality and macromolecule content in each aestivation period provided insight into the different factors that influence its survival. A significant difference was observed in mortality and biochemical composition between early and mid-aestivating insects. Mechanisms identified that initiate defence and survival strategies during unfavourable conditions included heat shock protein and cryoprotectant synthesis. The high thermal tolerance of M. diplopterus therefore requires a different approach for phytosanitary control. The third and final part of this dissertation addresses that need. Fumigation using ethyl formate was investigated as a potential alternative to thermal treatments. The main aims were to examine, firstly, the potential of ethyl formate as a fumigant to control the M. diplopterus, and, secondly, the effect of ethyl formate on the fruit quality of selected stone and pome fruit cultivars. A central composite design (CCD) method was used to treat pome and stone fruit cultivars to assess phytotoxicity after fumigation. A range of ethyl formate concentrations and fumigation durations were tested in conjunction with various other factors such as pulp temperature, harvest maturity, time during the season in which the cultivar ripens and the effect of pre-ripening. No phytotoxic damage was observed on stone fruit. Pome fruit, in contrast, had a phytotoxic response, and the CCD model predicted fumigation limits for treatments. Ethyl formate fumigation is highly effective against M. diplopterus, providing an alternative treatment for this highly thermo-tolerant pest. Both postharvest mitigation technologies tested here provide valuable insight into the response of both the commodity and insect to the various treatments. Challenges for the application of both technologies have been elucidated, and are addressed and discussed. The research presented here represents significant steps taken towards having more effective postharvest disinfestation strategies available for phytosanitary control.
- ItemThe relationship between ants (Hymenoptera: formicidae), vine mealybug (Hemiptera: pseudococcidae) and parasitoids in vineyards of the Western Cape Province, South Africa(Stellenbosch : Stellenbosch University, 2008-12) Mgocheki, Nyembezi; Addison, Pia; Pringle, K. L.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.The mutual association between honeydew foraging ants and vine mealybugs in vineyards is detrimental to the biological control of the vine mealybug Planococcus ficus (Signoret). This study investigated the relationship between ants, vine mealybugs and their parasitoids to improve biological control of the vine mealybug. The investigation was carried out during two consecutive growing seasons (2005-2006 and 2006-2007) in two major wine grape growing areas of the Western Cape Province, Simondium (two farms) and Breede River Valley (one farm). A presence – absence cluster sampling system was used on a biweekly basis throughout both growing seasons from October to February on each of the farms. Additionally, yellow delta traps with vine mealybug pheromone, were used to catch parasitoids in vineyards. Prior to harvest, economic damage to grape bunches was assessed using a 0-3 damage rating index. Three ant species, Anoplolepis steingroeveri (Forel), Crematogaster peringueyi Emery and Linepithema humile (Mayr) foraged mainly on vine stems during both seasons, relative to other plant parts. Vine mealybugs of all stages were found on all sampling dates. Three species of primary parasitoids attacked the vine mealybug, including Anagyrus sp. near pseudococci (Girault), Coccidoxenoides perminutus (Timberlake) and Leptomastix dactylopii Howard. Bunch damage was significantly different between seasons in the Breede River Valley but not in Simondium. There was a negative linear relationship between ants and parasitoid activity in all vineyards. Spatial Analysis by Distance IndicEs (SADIE) was used to analyse spatial distribution of ants and parasitoids and ArcView, with its extension, Spatial Analyst, were used to map the gap, patch and local association indices where significant association and disassociation occurred. A significant association was found between C. peringueyi and parasitoids and L. humile and parasitoids. There was a significant disassociation between L. humile and C. peringueyi and between A. steingroeveri and C. peringueyi indicating interspecific hostility.
- ItemSpatio-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.
- ItemStatus of the invasive wasp species, Vespula germanica and Polistes dominula in South Africa, and the feasibility of various management strategies(Stellenbosch : Stellenbosch University, 2016-12) Van Zyl, Carolina; Veldtman, Ruan; Addison, Pia; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: The main objective of this study was to determine the current status of two invasive wasps, Vespula germanica and Polistes dominula, in South Africa and to explore the feasibility of implementing various management strategies to control and/or eradicate them. Both wasp species pose a potential threat to biodiversity and agriculture in the Cape Floristic Region (CFR), as well as being a nuisance to people. In an effort to identify suitable biocontrol agents, the pathogenicity of three likely indigenous entomopathogenic nematode (EPN) species and one likely indigenous entomopathogenic fungal (EPF) species was tested against both V. germanica and P. dominula larvae in a bioassay trial. The three EPN species were Heterorhabditis bacteriophora,H. noenieputensis and Steinernema yirgalemense. The fungal species tested was Beauveria bassiana. Both V. germanica and P. dominula larvae were highly susceptible to all of the biocontrol agents tested, and died of infection within 4 days after inoculation within EPN and within 7 days after innoculation within the EPF. The EPN Heterorhabditis bacteriophora which performed best in the bioassay trial, as well as the EPF, Beauveria bassiana, were then tested in the field to determine its ability to infect P. dominula larvae by spraying inoculum directly onto nests. Four treatments were applied, namely: an aqueous solution of the EPF, an aqueous solution of the EPN, a mixture of the EPF and EPN species, and a control of distilled water. The combination of EPF and EPN caused the highest mortality in both P. dominula larvae (31.39 %) and pupae (3.42 %) compared to the other treatments, but infection levels were much lower than those obtained under laboratory conditions. An unsuspected discovery was made, when it appeared that 13 % of all nests used in this trial were parasitized by an unclassified fly species, identified to be a species from the Tachinidae family. There was no significant difference between the ability of fly larvae that were treated with the control, to develop into adults over a period of 144 h, compared to those treated with the various biocontrol agents. Landmark-based geometric morphometric analyses were used to identify the potential origin of introduced V. germanica wasps and to determine the possible route of invasion followed in South Africa. Variation in forewing shape among wasp worker samples that were collected from five different countries, including South Africa, Australia, New Zealand, Argentina and France, was compared. An overall direct correlation between the wing shape and the geographic distance between two sites was found. This result suggests that the morphological variation in wasps from South Africa can be explained as isolation-by-distance. Results inferred that wasps had spread from Kirstenbosch to Somerset West, and thence through Stellenbosch to Franschhoek. The wing shape of wasps collected from Kirstenbosch, the area where the first V. germanica specimen was found, mostly resembled the wing shape of samples from France, compared to all the other overseas localities. Therefore, one could conclude V. germanica wasps were most likely transported from Europe to South Africa. The attractiveness of a range of lures and baits to V. germanica and P. dominula females collected in the field were tested using a Y-tube olfactometer. A combination of protein and carbohydrate-based baits were tested. Vespula germanica mostly preferred cooked ham, whereas P. dominula was mostly attracted to the odours emanating from their own nest.
- ItemA study on the biological and physiological traits of Bactrocera dorsalis, with special reference to its invasion potential into the Western Cape of South Africa(Stellenbosch : Stellenbosch University, 2018-03) Pieterse, Welma; Addison, Pia; Terblanche, J. S.; Manrakhan, Aruna; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Bactrocera dorsalis (Hendel) is of Asian origin and is present in the northern and north-eastern parts of South Africa, but is still absent in other areas of the country including the Western Cape Province. The Western Cape Province is the largest producer of deciduous fruit in South Africa, exporting 41% of the deciduous fruit grown in the province. South Africa earned about R7 billion in export revenue from deciduous fruit exports in 2015. Currently, Ceratitis capitata (Wiedemann) and Ceratitis rosa s.l. Karsch are economically the most important fruit fly species on deciduous fruit in the Western Cape Province of South Africa. However, there is currently a lurking threat of potential introduction of B. dorsalis in Western Cape Province and this is of great concern to the deciduous fruit industry. Bactrocera dorsalis has shown remarkable range expansion over the past 10 years within Africa, adapting to different climatic conditions. Bactrocera dorsalis was also found to be able to out-compete a number of Ceratitis species in Africa. The aim of this study was to determine the invasive potential of B. dorsalis in the Western Cape Province of South Africa. The thermal biology, utilisation of deciduous fruit and the competitive ability of B. dorsalis were studied. A simple morphology based identification tool for B. dorsalis larvae was also developed in order to aid in early detection of the pest. A detailed assessment of acute high and low temperature survival ability of four life stages of B. dorsalis and the plasticity thereof was carried out to test the hypothesis that traits of the thermal niche have contributed to the species‟ invasion ability. The extreme low and high temperatures at which c. 20% of the population of B. dorsalis survived were determined to be -6.5°C and 42.7°C, respectively, when using 2 h exposures. The egg stage was found to be the most resistant life stage to both high and low temperatures with 44 ± 2.3% and 60 ± 4.2% surviving the low and high discriminating temperature treatments respectively. The potential for adult hardening responses to mediate tolerance of extremes was also considered using a diverse range of acute conditions (using 2 h exposures to 15°C, 10°C and 5°C and 30°C, 35°C, 37°C and 39°C as hardening temperatures, and some treatments with and without recovery periods between hardening and discriminating temperature treatment). The results of these studies showed that although some significant hardening responses could be detected in certain treatments (e.g. after exposure to 37°C and 39°C), the magnitude of this plasticity was generally low compared to two other wide-spread and more geographically-range-restricted con-familial species, C. capitata and C. rosa. In other words, B. dorsalis adults were unable to rapidly heat- or cold-harden to the same extent as the other Ceratitis species examined to date. These results suggest a narrower thermal niche in B. dorsalis compared to these Ceratitis species - in both basal and plastic terms - and suggests that its geographic distribution might be more restricted as a consequence. The larval stage of fruit flies is the most commonly intercepted life stage, and identification of this stage using traditional morphological methods such as identification keys is difficult. This study investigated the use of shape analysis, a morphometric method, to identify the third instar larvae of four tephritid species commonly intercepted in fruit destined for export. Larval specimens of laboratory reared B. dorsalis, C. capitata, C. rosa s.s. and Ceratitis cosyra (Walker) were used. The mandibles of third instar larvae of all species were dissected out, dehydrated and mounted in Euparal. Images of the mandibles were captured and analysed using Elliptical Fourier Descriptors (in the SHAPE v.1.3 analysis programme). According to the cumulative eigenvalues, the first two Principal Components (PCs) contributed the most (65%) to the shape change. The first PC separates C. rosa s.s. and C. cosyra from C. capitata and B. dorsalis. Ceratitis capitata and B. dorsalis were separated by the second PC. This study showed that morphometrics, in the form of shape analysis of the mandibles, can be used in combination with measurements of the mandibles to distinguish between third instar larvae of B. dorsalis, C. capitata, C. rosa s.s. and C. cosyra. Nutritional stress and population density are some of the factors that can contribute to morphological changes in insects. This study evaluated the effect of four different fruit crops mainly cultivated in Western Cape Province, South Africa: Prunus persica (L.) Batsch, (Nectarine), Prunus domestica L., (Plum), Malus domestica Borkh., (Apple) and Pyrus communis L., (Pear) on the wing shape of B. dorsalis and C. capitata, the dominant fruit fly pest on deciduous fruit in the region. Geometric morphometric tools were used to compare the relative positions of landmarks on the wings of the flies. The results show significant differences in the shape of wings between males and females of both species, indicating sexual dimorphism. The distances between corresponding landmarks among the averaged wings of B. dorsalis and C. capitata varied highly significantly between individuals that were reared on nectarine, plum, apple and pear. It is as yet unclear how these results translate into fly fitness, but observing significant shape changes resulting from nutritional factors warrant further investigation. The development, reproduction and survival of B. dorsalis and C. capitata on main deciduous fruit types cultivated in the Western Cape were studied. For both species, adult emergence was over 90% on all crops, except for C. capitata on apple, which was at 84%. The ratio of male:female flies was about 50:50 for both species on all the fruit types. Bactrocera dorsalis had a higher net reproductive rate (Ro) on all deciduous fruit tested compared to C. capitata. The value of Ro was the lowest for C. capitata on apple and highest on plum. For B. dorsalis, Ro was lowest on nectarine and highest on pear. Bactrocera dorsalis adults generally lived longer than those of C capitata, irrespective of the fruit types that they developed from. These results indicate that all the fruit types tested were suitable for both B. dorsalis and C. capitata to complete their life cycles. The long period of egg production on apple and the high numbers of eggs deposited on pear makes these fruit types ideal bridging hosts for B. dorsalis to survive until other hosts become available. Interspecific competition regulates the distribution and abundance of a number of phytophagous insects. Ceratitis capitata is currently the dominant species on deciduous fruit in the Western Cape Province of South Africa. Studies were conducted to quantify adult and larval interactions between B. dorsalis and C. capitata on four deciduous fruit types (nectarine, plum, pear and apple). When B. dorsalis and C. capitata adults were evaluated separately, they infested deciduous fruit at more or less the same rates based on the number of pupae reared from the fruit. The only exception was on plum where B. dorsalis produced significantly more pupae and consequently adults from the fruit compared to C. capitata. When adults of the two species were mixed within a confined space, Bactrocera dorsalis was able to out-compete C. capitata in most treatments and crops. Ceratitis capitata was only able to out-compete B. dorsalis on pear. The highest mean numbers of adults of both species emerged from nectarine and plum, with the lowest number emerging from pear. The larvae of C. capitata were more successful in completing development than those of B. dorsalis when present in mixed ratios as larvae of the two species in plum. Ceratitis capitata larvae developed faster than B. dorsalis on all deciduous fruit types tested. Bactrocera dorsalis larvae were able to complete development more successfully in apple than C. capitata in the larval competition experiments. The competition studies between B. dorsalis and C. capitata demonstrated that on deciduous fruit, competition between the two species would be in favour of B. dorsalis at the adult stages (ovipositing females) and, depending on fruit types, in favour of C. capitata at the larval stages. Overall the probability of B. dorsalis invading the Western Cape and displacing C. capitata in deciduous fruit is bigger than the opposite happening. In case B. dorsalis becomes established in the Western Cape, the populations of the pest will probably be reduced to undetectable levels during the winter, with a bloom in the population in summer. As B. dorsalis completes more life cycles in Western Cape, it will probably adapt to the local conditions and become a bigger problem for fruit growers. Fruit like apple and pear are not good hosts for C. capitata, but might be better hosts for B. dorsalis, since B. dorsalis deposited a significantly higher number of eggs on pear, lived longer and produced low numbers of eggs over a long time on apple. This could increase the cost of spray programmes, since fruit types with low incidence of spraying could in the presence of B. dorsalis require more frequent control interventions.