Browsing by Author "De Waal, Jeanne Yvonne"

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    Biological 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.
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    Entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) for the control of codling moth, Cydia pomonella (L.) under South African conditions
    (Stellenbosch : Stellenbosch University, 2008-12) De Waal, Jeanne Yvonne; Addison, Pia; Malan, Antoinette P.; Addison, M. F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    The codling moth, Cydia pomonella (L.), is a key pest in pome fruit orchards in South Africa. In the past, broad spectrum insecticides were predominantly used for the local control of this moth in orchards. Concerns over human safety, environmental impact, widespread dispersal of resistant populations of codling moth and sustainability of synthetic pesticide use have necessitated the development and use of alternative pest management technologies, products and programmes, such as the use of entomopathogenic nematodes (EPNs) for the control of codling moth. Entomopathogenic nematodes belonging to either Steinernematidae or Heterorhabditidae are ideal candidates for incorporation into the integrated pest management programme currently being developed for pome fruit orchards throughout South Africa with the ultimate aim of producing residuefree fruit. However, these lethal pathogens of insects are not exempted from governmental registration requirements and have therefore not yet been commercialized in South Africa. A nontarget survey was conducted to find suitable isolates of EPNs from local soils and to test their effectiveness as control agents against the codling moth. Soil samples were collected from several habitats and regions throughout South Africa and nematodes were recovered using the insect baiting technique. All EPN isolates obtained were identified to species level using a molecular taxonomic approach. Entomopathogenic nematodes were recovered from 20 of the 200 soil samples (10 %). Of these, eight (40 %) yielded Steinernema spp., identified as three isolates of S. khoisanae and five undescribed Steinernema spp. The other 12 (60 %) of the samples were positive for Heterorhabditis spp. and included six isolates of H. bacteriophora, five H. zealandica and one H. safricana. These isolates were then evaluated in laboratory bioassays for their potential as microbial agents of codling moth under varying conditions. A morphometric study indicated that all natural openings (mouth, anus and spiracles) of final instar codling moth were large enough for the infective juveniles (IJs) of all tested EPN species to gain entry into the larvae.