The bio-ecology of the Cape grapevine leafminer, Holocacista capensis (Lepidoptera: Heliozelidae), in the Western Cape

Torrance, Leigh Ami Isbell (2016-03)

Thesis (MScConsEcol)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: The Cape grapevine leafminer, Holocacista capensis Nieukerken & Geertsema (Lepidoptera: Heliozelidae), occurring on Vitis vinifera L., has recently become of economic importance in the Western Cape, South Africa. The leafminer is of quarantine importance as cocoons are often attached to grape bunches intended for export when grapevine infestation is severe. Fortnightly monitoring efforts have indicated the occurrence of several overlapping generations within a growing season which are likely to affect potential management strategies. Adult and larval abundances tend to increase as the grapevine growing season progresses and as temperatures increase. A peak in adult and live larval abundance is reached between February and March, usually after harvest. The severity of leafminer infestation may be affected by the location of a vine within a cultivated block and strong evidence suggests that structural aspects (i.e. the trellis system used) affect the invasion potential of H. capensis. The leafminer tends to overwinter in the larval or pupal life stage within a cocoon which is often sheltered under the bark on the stem of a grapevine, in leaf litter or in a small crevice of a trellis post. Male moths have been detected throughout the colder winter months suggesting that small fluctuations may affect the developmental rate of overwintering pupae depending on the shelter experienced by cocoons. It is a possibility that adults produce offspring in surrounding foliage or are sourced by such refuges, although it is likely that eclosed adults undergo diapause and contribute to the first generation of leafmining larvae as soon as conditions become favourable. Pheromone baited traps, placed throughout the Western Cape, have indicated the presence of the moth in two of the largest table grape producing regions, namely the Berg River and Hex River Valley. The overall distribution of the moth has proven to be far more extensive than previously thought and may be present throughout southern Africa based on herbarium samples that yielded symptoms of leafminer damage. Monitoring strategies should be conducted as early as possible within a grapevine growing season to avoid severe infestations and unnecessary chemical applications depending on the bunch infestation tolerance. At an economic threshold of 5% bunch infestation, the commencement of management strategies is recommended when 442 adult male moths are caught per trap per fortnight. Results suggest that bunch infestation could be prevented altogether if management strategies were implemented when less than 87 adult male moths are caught. In cases where bunch infestation has occurred and post-harvest cold treatments are considered, a cold-treatment exposure of no less than 26 days at -0.5°C should be considered if 100% mortality is desired. Parasitoid wasps associated with the leafminer have been identified and could potentially be used in the area-wide control of H. capensis. A variety of chemical compounds have been used to control leafminer infestations in the past, although preventative applications of spinetoram seem to have had the most success in preventing infestation. Management strategies in line with the ideals of current Integrated Pest Management strategies should be explored in future research endeavours.

AFRIKAANSE OPSOMMING: Die inheemse Kaapse wingerdblaarmyner, Holocacista capensis Nieukerken & Geertsema 2015 (Lepidoptera: Heliozelidae), wat op Vitis vinifera L. voorkom het onlangs van ekonomiese belang geraak in die Wes-Kaap, Suid-Afrika. Die blaarmyner se kwarantyn is van beduidende belang as ʼn potensiële kwarantynplaag omdat kokonne dikwels aan druiwetrosse kleef wat bestem is vir uitvoer, veral onder swaar bestemmings. Twee-weeklikse monitering het aangedui dat daar verskeie oorvleuelende generasies binne 'n enkele seisoen voorkom wat waarskynlik potensiële bestuurstrategieë beïnvloed. Volwassenes en larwe verspreidings neig om toe te neem soos die wingerdstok se groeiseisoen vorder en met toenemende temperature. 'n Hoogtepunt in die volwasse en lewende larwe getalle word bereik tussen Februarie en Maart, gewoonlik na oes. Die omvang van blaarmynerbesmetting mag beïnvloed word deur die posisie van die wingerdstok binne 'n bewerkte blok en sterk bewyse dui daarop dat strukturele aspekte (d.w.s die tipe traliewerkstelsel wat gebruik word) die inval potensiaal van H. capensis binne 'n besmette area grootliks beïnvloed. Die blaarmyner neig om te oorwinter in die larwe- of papie stadium binne die kokon wat dikwels beskut is onder die bas op die stam van 'n wingerdstok, in blaarmolm of in 'n klein kraak van die traliewerk. Manlike motte is tydens kouer wintermaande gevind wat daarop dui dat klein fluktuasies die ontwikkelingsbehoeftes en koers van oorwinterende papies beïnvloed, afhangende van die graad van beskutting wat motte ervaar. Dit is moontlik dat volwassenes nageslag produseer in die omliggende blare, of aangevul word deur sulke toevlugsoorde alhoewel dit hoogs waarskynlik dat nuwe volwassenes diapause ondergaan en so tot die eerste generasie van blaarmyner larwes bydra sodra toestande gunstig raak. Feromoon-aas lokvalle wat oor die hele Wes-Kaap geplaas is, het aangedui dat die mot in twee van die grootste tafeldruifstreke, naamlik die Bergrivier en Hexrivier Vallei, teenwoordig is. Oor die algemeen is die algehele verspreiding van die mot veel meer uitgebrei as voorheen gedink en mag die mot dwarsdeur Suider-Afrika teenwordig wees, gebaseer op herbarium monsters wat blaarmyner skadesimptome vertoon. Moniteerstrategieë moet so vroeg as moontlik gedoen word binne 'n wingerdstok groeiseisoen om ernstige besmettings en onnodige voorkomende chemiese toedienings, afhangende van die tros besmetting verdraagsaamheid, te vermy. By 'n ekonomiese drempelwaarde van 5% tros besmetting, word bestuurstrategieë aanbeveel wanneer 442 volwasse manlike motte gevang word per lokval oor twee weke. Resultate dui daarop aan dat as bestuurstrategieë geïmplementeer word wanneer daar minder as 87 volwasse manlike motte versamel is, kan tros besmetting heeltemal voorkom word. In gevalle waar tros besmetting plaasgevind het en na-oes koue behandeling oorweeg word, moet die koue behandeling blootstelling ten minste 26 dae lank wees teen -0,5°C indien 100% mortaliteit verlang word. Parasitiese wespe geassosieerd met die blaarmyner is geïdentifiseer en kan moontlik gebruik word in die gebied-wye beheer van H. capensis. 'n Verskeidenheid van chemiese middels is in die verlede gebruik is om blaarmynerbesmettings te beheer, alhoewel voorkomende programme met spinetoram blyk asof dit mees suksesvol is vir die voorkoming van blaarmynerbesmetting. Bestuurstrategieë in pas met die ideale van die huidige Geïntegreerde Plaagbestuur strategieë moet in toekomstige navorsing pogings ondersoek word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98322
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