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dc.contributor.advisorVan Der Linde, T. C. de K.
dc.contributor.advisorVan Der Westhuizen, A. J.
dc.contributor.advisorPotting, R. P. J.
dc.contributor.authorPrinsloo, Godfried Jacob
dc.date.accessioned2016-01-06T09:13:30Z
dc.date.available2016-01-06T09:13:30Z
dc.date.copyright2006-09-30
dc.date.issued2007-11-03
dc.date.submitted2009-09-30
dc.identifier.urihttp://hdl.handle.net/11660/1975
dc.description.abstractEnglish: Host plant resistance and biological control by means of natural enemies are becoming more favourable as high potential alternatives for chemical control of insect pests. Tritrophic studies (plant–herbivore-natural enemy) indicated that the application of host plant resistance and biological control to a particular pest could give significantly better or worse results than expected from each component respectively. Russian wheat aphid Diuraphis noxia (Kurdjumov) is a serious pest of wheat in South Africa since 1978. Plant resistant cultivars are being used against D. noxia since 1992. The introduction of parasitoids and predators for biological control of this pest automatically led to the development of an integrated pest control programme involving both control strategies. Nothing is known about interactions between resistant cultivars, D. noxia and natural enemies in South Africa. These interactions could have substantial influence on the efficacy of the control programme. The parasitoid Aphelinus hordei (Kurdjumov), introduced from the Ukraine, established in the Lesotho highlands after being released in the wheat production areas of the Free State Province. This parasitoid together with a native parasitoid Diaeretiella rapae (McIntosh), also parasitising D. noxia in South Africa, was included in a study on tritrophic interactions. A. hordei and D. rapae respectively have narrow and wide host ranges. Field studies on the interaction between A. hordei and resistant and susceptible cultivars indicated reduction in aphid population growth on each of the cultivars. Diuraphis noxia was highly parasitised on a susceptible cultivar Betta, while a positive interaction on resistant Gariep occurred, resulting in the enhancement of the resistance. A slightly lower percentage control was found on SST 333 in the presence of A. hordei. Volatile profiles emitted by infested Betta plants and resistant Elands and SST 333 plants, differed qualitatively (different volatiles) and quantitatively (concentration of volatiles). These differences caused behavioural differences between parasitoid species e.g. A. hordei could not distinguish infested from clean Elands, while D. rapae did. Diaeretiella rapae could not distinguish infested from clean SST 333 while A. hordei did. Aphelinus hordei could not distinguish between infested Betta and Elands, while D. rapae significantly preferred Betta to Elands. Parasitoids therefore responded to different volatiles from the same cultivars. This means that both A. hordei and D. rapae, use different volatiles or volatile combinations from the same plant-herbivore combination in host habitat location. Semiochemicals e.g. methyl salicylate, that act as insect behaviour-modifying chemicals, was tested in the laboratory and the field as potential control options against D. noxia. Volatile compounds released by plants could serve as signals attracting beneficial insects and induce a variety of responses in plants. A slow release wax pellet formulation named OX54 releasing methyl salicylate, menthol and 1,8-cineole was tested. Olfactometric studies showed that D. noxia and R. padi was repelled by each of the compounds although not released by their alternate host plants in South Africa. Both parasitoid species were repelled by some of the semiochemicals tested, but differences occurred between the two species. Aphelinus hordei did not respond to 1,8 -cineole, while D. rapae was not responding to menthol indicating that the different parasitoids differ in sensitivity to other semiochemicals. The repellence of the parasitoids by methyl salicylate indicated that these volatiles are not induced by D. noxia when feeding on wheat. Different host range of the parasitoids may be a reason for this reaction. OX54 and methyl salicylate respectively caused a delay in the immigration of D. noxia into resistant cultivar Elands during field trials, but on susceptible Betta an increase in infestation was found. Lower infestation on treated Elands resulted in a slight increase in yield compared to the control. The positive integration of host plant resistance and biological control can have two objectives namely synergistic reduction of pest densities and the protection of durability of resistance. Some resistant wheat cultivars to D. noxia seem to be highly resistant and the efficacy of natural enemies in these wheat fields is of utmost importance. The application of semiochemicals in these cases should also be investigated . Where resistant cultivars are less effective and hence have more durable resistance, the value of biological control is to enhance the effect of plant resistance on the reduction of the pest population in such a way that the effects of plant resistance and biological control are sufficient to prevent damage. The understanding and effective manipulation of agro -ecosystems in the wheat production areas of the Free State Province is therefore essential for the successful establishment of a successful integrated pest control programme.en_ZA
dc.description.abstractAfrikaans: Gasheer plant weerstand en biologiese beheer met behulp van natuurlike vyande neem in gewildheid toe as alternatiewe beheermetodes vir chemiese beheer. Trofiese vlak verwantskapstudies (tussen plant, herbivoor en natuurlike vyand) het aangedui dat die gesamentlike gebruik van plantweerstand en biologiese beheer op ‘n sekere plaag betekenisvol beter, maar soms ook swakker beheer tot gevolg het as wanneer die beheermetodes afsonderlik gebruik word. Die Russiese koringluis Diuraphis noxia (Kurdjumov) is sedert 1978 die belangrikste insekplaag van koring in Suid Afrika. Weestandbiedende koring kultivars word sedert 1992 as beheermetode vir D. noxia gebruik. Die invoer van parasitoïede en predatore vir biologiese beheer van D. noxia het vanselfsprekend tot die ontstaan van ‘n geïntegreerde plaagbeheerprogram gelei, waarin beide beheermetodes betrokke is. Geen inligting is bekend oor die wisselwerking tussen weerstandbiedende kultivars, D. noxia en natuurlike vyande in Suid Afrika nie. Hierdie wisselwerkings kan verreikende gevolge inhou vir die doeltreffendheid van die beheerprogram. Die parasitoïed Aphelinus hordei (Kurdjumov), wat uit die Oekraïne ingevoer is, het na vrystelling in die koringproduserende gebiede in die Vrystaat Provinsie en die hooglande van Lesotho gevestig. Hierdie parasitoïede is saam met ‘n plaaslike parasitoïed, Dia eretiella rapae (McIntosh), wat ook D. noxia in Suid Afrika parasiteer, in die studie gebruik. Aphelinus hordei en D. rapae het onderskeidelik ‘n meer beperkte en ‘n wye gasheerreeks. Veldproewe oor die interaksie tussen A. hordei, weerstandbiedende en vatbare kultivars het aangedui dat luispopulasies se groei afneem in die teenwoordigheid van die parasiatoïed. ‘n Groot aantal D. noxia is op vatbare Betta geparasiteer, terwyl daar ‘n positiewe interaksie met weerstandbiedende Gariep was wat die versterking van die weerstand tot gevolg gehad het. Die beheer van D. noxia op SST 333 in die teenwoordigheid van A. hordei was effens swakker as op die kontrole wat op ‘n klein negatiewe interaksie dui. Vlugtige reukstof profiele wat deur besmette Betta, weerstandbiedende Elands en SST 333 plante afgeskei word, verskil in kwaliteit (verskillende reukstowwe) en kwantiteit ( konsentrasie van reukstowwe). Hierdie verskille het gedragsverskille tussen parasitoïed spesies veroorsaak en wat daartoe gelei het dat parasitoïede swakker op sommige weerstandbiedende cultivars gereageer het. Die verskillende parasitoïede het ook verskillend op reukstowwe van dieselfde kultivars gereageer. Dit beteken dus dat A. hordei en D. rapae verskillende reukstof of reukstofkombinasies vanaf dieselfde plant-herbivore kombinasie gebruik om hulle gasheerhabitat te identifiseer. Reukstowwe wat as seine dien bv. metiel-salisilaat, kan ook as insekgedrags- veranderende stowwe dien en is ook in die laboratorium en veld getoets vir ‘n moontlike beheerstrategie teen D. noxia. Reukstowwe wat deur plante afgeskei word, kan as seine om natuurlike vyande aan te lok dien, maar kan ook ‘n verskeidenheid van reaksies in plante ontlok. ‘n Waskorrelformulasie wat reukstowwe stadig vrystel is getoets. Hierdie formulasie genaamd OX54, bevat metiel-salisilaat, mentol, en 1,8 cineole. Olfaktometriese toetse het bewys dat D. noxia deur hierdie stowwe afgeweer word, hoewel geeneen van hierdie stowwe deur alternatiewe gasheerplante in Suid Afrika geproduseer word nie. Beide parasitoïed spesies is ook deur die reukstowwe afgeweer, maar verskille het tussen spesies voorgekom. Aphelinus hordei het nie op 1,8-cineole gereageer nie, terwyl D. rapae nie op mentol gereageer het nie. Die afwering van die parasietoïede deur metiel-salisilaat, dui daarop dat die stof nie geïnduseer word wanneer D. noxia op koring voed nie. Verskille in gasheerreeks samestelling van parasitoïede mag veroorsaak dat hulle verskillend op hierdie stowwe reageer. Gedurende veldproewe het beide OX54 en metiel-salisilaat ‘n vertraging in die immigrasie van D. noxia na weerstandbiedende Elands teweeg gebring. Op vatbare Betta is egter ‘n verhoging in die besmetting gevind. Die laer besmetting op Elands het ‘n geringe verhoging in opbrengs in vergelyking met die kontrole tot gevolg gehad. Die positiewe integrasie van gasheerplantweerstand en biologiese beheer het twee doelwitte naamlik die sinergistiese vermindering van plaagpopulasies en die beskerming van standhoudende plantweerstand tot gevolg. Sommige kultivars het ‘n sterker weerstand en die doeltreffendheid van natuurlike vyande in die lande is belangrik vir beskerming van die weerstand. Die toediening van reukstowwe in hierdie gevalle moet ondersoek word. Waar die weerstand swakker is en meer standhoudend, moet natuurlike vyande bykomend die effek van plantweerstand verhoog en voorkom dat skade aangerig word. Kennis oor doeltreffende manipulasie van landbou eksosisteme in die koringproduserende gebiede van die Vrystaat Provinsie is dus belangrik vir die vestiging en doeltreffende werking van ‘n geïntegreerde plaagbeheerprogram.af
dc.description.sponsorshipAgricultural Research Councilen_ZA
dc.description.sponsorshipNational Research Foundation (NRF)en_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectThesis (Ph.D. (Zoology and Entomology))--University of the Free State, 2006en_ZA
dc.subjectRussian wheat aphid -- South Africa -- Free Stateen_ZA
dc.subjectRussian wheat aphid -- Biological controlen_ZA
dc.subjectDiuraphis noxiaen_ZA
dc.subjectAphelinus hordeien_ZA
dc.subjectDiaeretiella rapaeen_ZA
dc.subjectChemical ecologyen_ZA
dc.titleParasitoids and aphid resistant plants : prospects for Diuraphis noxia (Kurdjumov) controlen_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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