The development of a management strategy for the control of the Cape grapevine leafminer, Holocacista capensis (Lepidoptera: Heliozelidae), in South African table grape vineyards

Steyn, Leigh Ami Isbell (2019-03)

Thesis (PhDConsEcol)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Die Kaapse wingerdbladmyner, Holocacista capensis Van Nieukerken & Geertsema (Lepidoptera: Heliozelidae), het 'n algemene plaag op tafel- en wyndruiwe in die Wes-Kaap provinsie van Suid-Afrika geword, sedert dit in 2012 gerapporteer is. Die teenwoordigheid van kokonne op druiwetrosse bestem vir uitvoer maak dit 'n plaag van ekonomiese belang, hoewel die erkende plaagstatus nie die erns van sommige van die besmettings, wat in die Bergrivierstreek voorkom, weerspieël nie. Tans bestaan die beheerstrategieë uit insekdoder toedienings of arbeidsintensiewe na-oes verwydering van gehegte kokonne op tafeldruiwe met die hand, tydens verpakking. Om te help met die ontwikkeling van 'n geïntegreerde plaagbestuurstrategi (IPM), het hierdie studie gefokus op aspekte van kulturele, chemiese en biologiese beheerstrategieë, terwyl die genetiese diversiteit en omgewingsveranderlikes wat H. capensis populasies beïnvloed, oorweeg is. Veldproewe het gevind het dat omringende ligintensiteit, klimaatstoestande en plantvoedingstof samestelling die bevolkings van H. capensis in kommersiële wingerde beïnvloed, wat ooreenstem met vorige studies wat op ander problematiese bladmyners uitgevoer is. Korrelasies wat afgelei is van die evaluering van temporale satellietbeelde om die genormaliseerde verskil-plantegroei-indeks (NDVI) te bepaal, het aangedui dat daar potensiaal is vir die gebruik van hierdie tegnologie vir die monitering van bladmyner voorkoms in die toekoms. In 'n voorlopige studie oor die genetika van die plaag, is DNA onttrek van vanuit 52 mannetjie-motte, wat versamel is met behulp van Delta-lokvalle in kommersiële wingerde en natuurlike woude in en om die WesKaap. Die studie kon die identiteit van die spesies bevestig, asook dat die mannetjies wat gevang is en dat almal wel H. capensis is. 'n Insekdoder-proef, wat in die laboratorium uitgevoer is, het verskeie dosisse van verskillende kommersieel beskikbare insekdoders getoets. Spinetoram (spinosyn), dichlorvos (organofosfaat) en sipermetrien (piretoid) is geïdentifiseer as goeie kandidate om ingesluit te word by 'n IPM-strategie. Hoë mortaliteit (> 87%) is aangeteken teen die laagste dosisse ('n kwart van die aanbevole veld dosis). As 'n alternatief vir ʼn bestuurstrategie wat uitsluitlik op die gebruik van chemiese middels gefokus is, is entomopatogeniese nematodes (EPNs) in die laboratorium getoets. Teen 'n konsentrasie van 200 infektiewe larwes (IJs)/50 μl gedistilleerde water, was EPNs in staat die blaargalerye (myne) binne te dring en larvale mortaliteit te veroorsaak. Drie EPNs, Heterorhabditis baujardi Phan, Subbotin, Nyugen & Moens, Heterorhabditis indica Poinar, Karunakar & David en Heterorhabditis noenieputensis Malan, Knoetze & Tiedt het > 86% mortaliteit by bladmynerlarwes veroorsaak en het dus die potensiaal om deel te word in 'n IPMstrategie teen H. capensis. Die gebruik van trosbedekkings as 'n fisiese beheerstrategie is in die veld getoets. Al die trosbedekkings was suksesvol om die kokonne op trosse te verminder en is dus ʼn goeie opsie in gevalle waar besmettings onvermydelik is en maksimum toelaatbare residuperke (MRL's) klaar bereik is. Hierdie studie dui op 'n positiewe vooruitsig vir die sukses van toekomstige chemiese en biologiese beheermaatreëls, sowel as ʼn basis vir die ontwikkeling van 'n IPM-strategie teen H. capensis.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105700
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