Browsing by Author "Steyn, L. A. I."

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    Potential of South African entomopathogenic nematodes to control the leaf miner, Holocacista capensis (Lepidoptera: Heliozelidae)
    (MedPharm Publications, 2019) Steyn, L. A. I.; Addison, P.; Malan, A. P.
    The Cape grapevine leafminer, Holocacista capensis, a sporadic pest of economic importance, is found in South African table and wine grape vineyards. The cocoon casings, constructed by the final instar larvae, can be found attached to grape bunches, posing a phytosanitary risk for table grape export markets. The current study aimed to determine the susceptibility of leaf-mining H. capensis larvae toseven entomopathogenic nematode (EPN) species belonging to Steinernematidae and Heterorhabditidae. To determine nematode virulence occupied leaf-mining galleries were extracted from infested leaves and inoculated with 200 infective juveniles (IJs) in 50 μl of distilled water, for each of the EPNs screened. Concentration assays were conducted and and lethal dose was determined for the three most virulent species (Heterorhabditis baujardi, H. indica and H. noenieputensis), using concentrations of 0, 25, 50, 100, 200, and 400 IJs/leaf-mining larva. High mortality of leaf-mining larvae was obtained with H. baujardi(92%), H. noenieputensis (85%) and H. indica (83%). Almost double the number of H. noenieputensis (34 nematodes/insect) penetrated the insect larvae, in comparison with the other two EPNs. However, the relative potency of H. baujardi was 3.56 times higher than for H. indica, whilst that of H. indica was 2.57times higher than it was for H. noenieputensis. The results obtained in the laboratory were found to be encouraging, especially with regard to the nematodes’ ability to penetrate the leaf-mining galleries, and to infect the larvae successfully.
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    A review of leaf-mining insects and control options for their management, with special reference to holocacista capensis (lepidoptera: heliozelidae) in vineyards in South Africa
    (South African Society for Enology and Viticulture, 2020) Steyn, L. A. I.; Geertsema, H.; Malan, A. P.; Addison, P.
    A leaf-mining pest occurring on commercial varieties of Vitis vinifera in South Africa was investigated due to the presence of cocoons on fruit. The leaf miner, Holocacista capensis, was reported on grapevines in 2012. Since its discovery on commercial grape varieties, control strategies have consisted solely of insecticide applications. Despite the fact that the leaf-mining habit is taxonomically diverse and considered ancient, little is generally known of leaf-mining larvae. A review was conducted in order to better understand the leaf-mining strategy and amalgamate the current knowledge of other leaf-mining insects. The general evolutionary history within the full complement of taxa that display the leaf-mining habit is discussed. The review focuses on lepidopteran leaf-mining pests and discloses the known information associated with the first report and the impact of H. capensis in the Western Cape, South Africa. As no control methods have been identified for H. capensis in vineyards, various chemical, biological and cultural control strategies adopted for other leaf-mining pests were investigated. Control options, including the use of entomopathogenic nematodes (EPNs), parasitoids, physical and cultural control measures, were considered and are discussed. Alternate control methods are pertinent for the grape-growing industry to avoid the development of the insecticide resistance that is common amongst leaf miners. This review aims to consolidate the available literature and therefore aid in the development of an integrated pest management strategy to effectively control H. capensis in infested vineyards in South Africa.