Olfactory responses of the leafhopper vector Mgenia fuscovaria (Stål) (Hemiptera : Cicadellidae) to volatiles from aster yellows phytoplasma-infected and uninfected grapevine (Vitis vinifera L.)

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dc.contributor.advisor Kruger, Kerstin en
dc.contributor.coadvisor Glinwood, Robert en
dc.contributor.coadvisor Ignell, Rickard en
dc.contributor.postgraduate la Grange, Mari Roleen en
dc.date.accessioned 2017-06-05T12:10:54Z
dc.date.available 2017-06-05T12:10:54Z
dc.date.created 2017-05-02 en
dc.date.issued 2017 en
dc.description Dissertation (MSc)--University of Pretoria, 2017. en
dc.description.abstract The leafhopper Mgenia fuscovaria Stål (Hemiptera: Cicadellidae) is a vector of aster yellows phytoplasma (AY), 'Candidatus Phytoplasma asteris', in grapevine, Vitis vinifera L. (Vitaceae), in South Africa. In a previous study, M. fuscovaria was preferentially attracted to AY-infected compared to uninfected grapevine branches, although the mode of attraction was not determined. Phytoplasma infection may alter the volatile profiles of plants, rendering them more attractive to the insect vector. This may lead to an increase in the number of vectors transmitting the pathogen. The volatile compounds that attract or repel insect pests could be used in behavioural manipulation strategies to manage pests. The objective of this study was to determine the effect of AY-infection on the volatile composition of the grapevine cultivars Colombard and Chenin blanc in summer and autumn, and the associated behavioural and electrophysiological responses of M. fuscovaria towards these changes in volatile profiles. Volatile analyses of AY-infected and uninfected grapevine branches revealed both qualitative and quantitative differences. In summer, methyl salicylate was produced in significantly higher amounts or only produced in AY-infected branches in cv. Chenin blanc and cv. Colombard, respectively. Similarly, ethyl salicylate was recorded only from AY-infected branches of both cultivars during summer. There was a significant increase in the total volatile emissions in AY-infected compared to uninfected grapevine cv. Colombard, including several green leaf volatiles. The compounds that differed significantly between AY-infected and uninfected branches in autumn were produced exclusively or in greater quantities in uninfected branches. (E,E)-α-farnesene was the most abundant compound recorded in all cases. Grapevine branches infected with AY often had a greater mass than uninfected branches with the same leaf area. In behavioural studies, M. fuscovaria displayed no consistent preferences toward volatiles from AY-infected and uninfected grapevine branches cv. Colombard or cv. Chenin blanc in summer or autumn. In summer, there were no significant differences in the choices made by leafhoppers for both cultivars. In autumn, leafhoppers preferred purified air over AY-infected cv. Colombard branches and AY-infected cv. Chenin blanc branches over purified air. There was no difference in the choices made between male and female leafhoppers. In electrophysiological tests, M. fuscovaria antennae displayed weak responses to grapevine volatiles collected in summer. Consistent responses were identified to 1-octen-3-ol, phenol, (E,E)-α-farnesene, which is produced at elevated concentrations by AY-infected grapevine, and aromadendrene, which was only produced by AY-infected branches and not by uninfected branches cv. Colombard. For grapevine cv. Chenin blanc, insects responded to the co-eluting green leaf volatiles (E)-2-hexenal, (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol and 1-hexanol as well as nonane from uninfected branches. The results from this study suggest that M. fuscovaria is not preferentially attracted toward AY-infected grapevine branches based solely on olfactory cues. Based on the weak responses observed in electrophysiological and behavioural tests, as well as results obtained in studies on other leafhopper species, the observed attraction could be a result of visual cues rather than olfactory cues or a combination of both. en_ZA
dc.description.availability Unrestricted en
dc.description.degree MSc en
dc.description.department Zoology and Entomology en
dc.identifier.citation la Grange, MR 2017, Olfactory responses of the leafhopper vector Mgenia fuscovaria (Stål) (Hemiptera : Cicadellidae) to volatiles from aster yellows phytoplasma-infected and uninfected grapevine (Vitis vinifera L.), MSc Dissertation, University of Pretoria, Pretoria, viewed yymmdd <http://hdl.handle.net/2263/60819> en
dc.identifier.other A2017 en
dc.identifier.uri http://hdl.handle.net/2263/60819
dc.language.iso en en
dc.publisher University of Pretoria en
dc.rights © 2017 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. en
dc.subject UCTD en
dc.title Olfactory responses of the leafhopper vector Mgenia fuscovaria (Stål) (Hemiptera : Cicadellidae) to volatiles from aster yellows phytoplasma-infected and uninfected grapevine (Vitis vinifera L.) en
dc.type Dissertation en


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