Browsing by Author "Doubell, Marce"

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    Katydid (Orthoptera: Tettigoniidae) bio-ecology in Western Cape vineyards
    (Stellenbosch : Stellenbosch University, 2017-12) Doubell, Marce; Addison, Pia; Bazelet, Corinna S.; Terblanche, J. S.; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Many orthopterans are associated with large scale destruction of crops, rangeland and pastures. Plangia graminea (Serville) (Orthoptera: Tettigoniidae) is considered a minor sporadic pest in vineyards of the Western Cape Province, South Africa, and was the focus of this study. In the past few seasons (since 2012) P. graminea appeared to have caused a substantial amount of damage leading to great concern among the wine farmers of the Western Cape Province. Very little was known about the biology and ecology of this species, and no monitoring method was available for this pest. The overall aim of the present study was, therefore, to investigate the biology and ecology of P. graminea in vineyards of the Western Cape to contribute knowledge towards the formulation of a sustainable integrated pest management program, as well as to establish an appropriate monitoring system. No detailed surveys have as yet been undertaken to assess the assemblage structure of katydids in vineyards and to verify their taxonomic status. By conducting a survey in vineyards located in the greater Stellenbosch region of the Western Cape, the identities of the katydid species present and their pest status was determined. A monitoring method was developed by adapting a generic sampling system for monitoring key arthropod pests in vineyards. Due to the perfect camouflage of adult katydids within the vine canopy, surrogate methods for monitoring this pest were investigated. Besides determining the basic biology and ecology of P. graminea within vineyards, aspects of its physiological ecology with implications on its mating behaviour were investigated. Furthermore, natural enemies that could potentially be used as environmentally-friendly biological control agents against this pest were identified. Three Phaneropterinae species were identified, namely P. graminea, Eurycorypha lesnei Chopard and a Phaneroptera species. Due to the similarity between the Plangia and Eurycorypha species, an ID-key was compiled for easy identification by growers. Plangia graminea was found to be the primary katydid pest in vineyards monitored. There was only one generation per year, with an overwintering egg stage. The monitoring of katydid eggs could potentially be used to monitor P. graminea, as eggs were positively and significantly correlated with katydid numbers and could allow early prediction estimates of katydid populations in vineyards. Temperature appeared to be an important environmental factor enhancing population outbreaks, as it influenced katydid development, but could also affect mating success of male katydids. It was found that there was a significant metabolic cost associated with the mating calls of P. graminea males. This study identified two natural control agents that could potentially be incorporated into an integrated pest management program for the control of P. graminea, namely hymenopteran egg parasitoids and an entomopathogenic fungus. The outcomes of this study aim towards the development of a practical, sustainable and environmentally-friendly integrated pest management program. Future research should focus on validating a monitoring method in the field, establishing an economic threshold, testing the efficacy of entomopathogenic fungi in the laboratory and in the field, and investigating the mechanisms involved in habitat preferences of hymenopteran egg parasitoids.