Control of the obscure mealybug, Pseudococcus viburni (Hemiptera: Pseudococcidae) using entomopathogenic fungi and nematodes
| dc.contributor.advisor | Stokwe, Nomakholwa F. | en_ZA |
| dc.contributor.advisor | Malan, Antoinette P. | en_ZA |
| dc.contributor.author | Mathulwe, Letodi Luki | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology. | en_ZA |
| dc.date.accessioned | 2021-10-27T10:24:34Z | |
| dc.date.accessioned | 2021-12-22T14:18:56Z | |
| dc.date.available | 2021-10-27T10:24:34Z | |
| dc.date.available | 2021-12-22T14:18:56Z | |
| dc.date.issued | 2021-12 | |
| dc.description | Thesis (PhDConsEcol)--Stellenbosch University, 2021. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae), the obscure mealybug, is a serious cosmopolitan, polyphagous agricultural insect pest of deciduous fruit crops. In South Africa, the mealybug negatively affects apple and pear production. Feeding of the mealybug on the arboreal parts of fruit trees results in different types of damage, such as early flower and fruit drop, leaf and fruit discoloration and, in severe cases, the premature death of the host plant shoot. On apples and pears, various life stages of the mealybug are often found in the fruit core and calyx, and on the pedicel. The mealybug extracts and ingests large amounts of phloem sap when feeding, then excretes the excess sap as a carbohydrate-rich sugary substance, which is known as honeydew, which falls onto the fruit, leaves and bark. This results in severe secondary damage, as it promotes the growth of sooty mould. Infestation of the fruit and the presence of sooty mould on the fruit have severe economic implications, as both stained and infested fruits are likely to be rejected or downgraded in pack- houses. Currently, the management of obscure mealybug in orchards relies on the use of both biological and chemical control. However, current management strategies have proven to be ineffective, as the mealybug has developed resistance to a range of chemical insecticides. Both entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPN) are effective biological control agents of various agricultural insect pests, as they cause epizootics in various insect orders. The main aim of this study was to assess the potential of both local and commercial EPF species and of local in vivo- and in vitro-cultured species of EPN as possible biological control agents of P. viburni. The pathogenicity of the entomopathogens was assessed under laboratory conditions, with the EPF being tested at a conidial concentration of 1 × 10⁷ conidia/ml, and EPN at a concentration of 200 infective juveniles (IJs) per insect. From the study, two local EPF isolates, namely Metarhizium pinghaense (5HEID) and M. robertsii (6EIKEN) were identified as the most effective EPF isolates against P. viburni, resulting in >90% insect mortality, a week after exposure to the entomopathogens. The local in vivo-cultured Heterorhabditis indica (SGS) was found to be the most effective EPN isolate against P. viburni, causing 79% insect mortality, 48 h post inoculation. Further evaluation assessing the effect of combined application of M. pinghaense or M. robertsii with H. indica against P. viburni was conducted under laboratory conditions, using both sequential and simultaneous exposure methods. For the sequential method, the entomopathogens were each applied in turns, using first either the EPF or the EPN, followed by the other entomopathogen, at different time intervals. For the simultaneous method, the mealybugs were exposed to both EPN and EPF simultaneously. The combined application of H. indica with M. pinghaense or M. robertsii was observed to result in increased mortality of P. viburni, relative to when they were applied individually. The simultaneous application of H. indica and M. pinghaense was the most effective combination method of the two entomopathogens against P. viburni, resulting in 95% mortality five days post inoculation. The sequential method of application of H. indica and M. robertsii was the most effective, resulting in >85% mortality of P. viburni after four and three days of exposure. The interaction between the entomopathogens, when used in combination, was found to have an additive effect in all combination exposures. The infective conidia of M. pinghaense and M. robertsii were mass cultured, using agricultural grains as solid substrates. Rice grains, inoculated using blastospores, were the best for mass culture and production of conidia of both M. pinghaense and M. robertsii. Oil carriers (liquid paraffin, coconut oil, canola oil and olive) and a mineral carrier (diatomaceous earth) were investigated as potential formulations for mass-produced conidia of both M. pinghaense and M. robertsii. The viability of the formulated conidia was assessed over a period of eight weeks, and the efficacy of the formulation against P. viburni being assessed at the end of eight weeks. Oil carriers were found to be the most effective formulation for conidia of both the fungal isolates, maintaining conidial viability of >95% over time. The conidia in all the oil formulations also induced high mortality, ranging between 60% and 90% for M. pinghaense, and 70% and 90% for M. robertsii, when used against P. viburni. The current study provides insight into the efficacy of both EPF and EPN as possible biological control agents of P. viburni. Further long-term evaluation of the efficacy of the tested isolates of M. pinghaense, M. robertsii and H. indica, used individually or in combination, against P. viburni under field conditions, will provide insight into the potential success of using the entomopathogens for the management of the mealybug in orchards, as well as providing information regarding the possible integration of the entomopathogens as biocontrol agents in an integrated pest management system against mealybugs. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae), die appelwitluis, is ʼn ernstige kosmopolitiese insekpes van landboukundige gewasse, veral van sagtevrugte. In Suid-Afrika het hierdie witluise veral ʼn negatiewe invloed of appel- en peerproduksie. Voeding van die witluis op die blare en vrugte kan lei tot ʼn reeks van skade, soos vroeë blom- en vrugval, verkleuring van blare en vrugte en, in ernstige gevalle, die vroegtydige dood van die gasheerplant. Op appels en pere word verskillende lewensfases van die witluis dikwels aangetref in die vrugkern en –kelk, sowel as op die stam. Die witluise neem groot hoeveelhede floëemsap op tydens voeding en skei dan oortollige sap uit as heuningdou, ʼn koolhidraatryke suikerstroop, wat op die vrugte, blare en bas aanpak. Heuningdou kan lei tot sekondêre skade aangesien dit die groei van roetskimmel bevorder. Infestasie deur witluise en die voorkoms van roetskimmel op die vrugte het ernstige ekonomiese gevolge, aangesien gevlekte sowel as witluisbesmette vrugte in pakhuise verwerp of afgradeer sal word. Tans berus die bestuur van appelwitluis in boorde op die gebruik van beide chemiese en biologiese beheer. Die huidige beheerstratgieë, maar veral chemie, is ondoeltreffend, aangesien witluise weerstand teen ʼn reeks insekdoders ontwikkel het. Beide entomopatogeniese swamme (EPF) en nematodes (EPN) word as effektiewe biologiese beheermiddels van verskillende landbou insekplae beskou, aangesien dit binne verskillende insekordes epidemies kan veroorsaak. Die hoofdoel van hierdie studie was om die potensiaal van beide plaaslike en kommersiële EPF-spesies, sowel as die plaaslike in vivo- en in vitro-geteelde spesies van EPN, as moontlike biologiese bestrydingsagente van P. viburni te evalueer. Die patogenisiteit van die entomopatogene is onder laboratoriumtoestande beoordeel, met die EPF wat getoets is teen 'n spoorkonsentrasie van 1 × 10⁷ spore/ml en EPN teen 'n konsentrasie van 200 infektiewe larwes (IJs) per insek. Uit die studie is twee plaaslike EPF-isolate van Metarhizium pinghaense (5HEID) en M. robertsii (6EIKEN) geïdentifiseer as die mees effektiewe EPF-isolate teen P. viburni, wat lei tot > 90% inseksterftes 'n week na blootstelling aan die entomopatogene. Die plaaslike in vivo-geteelde Heterorhabditis indica (SGS) was die doeltreffendste EPN-isolaat teen P. viburni, wat 79% inseksterftes veroorsaak het, 48 uur na inokulasie. Verdere evaluering van die effek van die gekombineerde toediening van die mees effektiewe EPF-isolate, M. pinghaense en M. robertsii, met die effektiewe EPN-isolaat, H. indica, teen P. viburni is uitgevoer onder laboratorium toestande, met behulp van beide opeenvolgende en gelyktydige kombinasie blootstellingsmetodes. Vir die opeenvolgende metode is die entomopatogene om die beurt toegedien deur eers die EPF of die EPN te gebruik, gevolg deur die ander entomopatogeen, met verskillende tydsintervalle. Vir die gelyktydige metode is die witluise gelyktydig aan beide EPN en EPF blootgestel. Die gekombineerde toediening van H. indica met M. pinghaense of M. robertsii het gelei tot 'n toename in sterftes van P. viburni, relatief tot wanneer dit afsonderlik toegedien is. Die gelyktydige toediening van H. indica en M. pinghaense was die doeltreffendste kombinasiemetode van die twee entomopatogene teen P. viburni, wat gelei het tot sterftes van 95%, vyf dae na inokulasie. Die opeenvolgende toedieningsmetode van H. indica en M. robertsii was die doeltreffendste, wat tot meer as 85% sterftes van P. viburni gelei het vier en drie dae na blootstelling. Daar is gevind dat die interaksie tussen die entomopatogene in alle kombinasieblootstellings 'n additiewe effek het. Massaproduksie van infektiewe spore van M. pinghaense en M. robertsii met verskeie grane as soliede substrate is ondersoek. Ryskorrels, geïnokuleer met blastospore, het die beste resultate vir massaproduksie van beide M. pinghaense en M. robertsii gelewer. Formulasies van die massa geteelde spore van M. pinghaense en M. robertsii in oliedraers (vloeibare paraffien, klapperolie, canola olie en olyfolie) en ‘n minerale draer (diatoomaarde) is getoets om te bepaal wat die beste formulasie is om die patogenisiteit en raklewe van massa geteelde swamspore vir toekomstige kommersiële veldtoediening teen P. viburni te behou. Die lewensvatbaarheid en effektiwiteit van die spoorformulasies teen P. viburni is vir beide EPF-isolate is oor 'n tydperk van agt weke ge-evalueer, Daar is gevind dat oliedraers die doeltreffendste formulasie van die swamspore van beide die swam- isolate is, wat meer as 95% lewensvatbaarheid behou. Die spore in al die olieformulasies het ook 'n hoë P. viburni sterftesyfer veroorsaak, wat gewissel het tussen 60% en 90% vir M. pinghaense, en 70% en 90% vir M. robertsii. Die huidige studie bied insig rakende die effektiwiteit van beide EPF en EPN as moontlike biologiese beheeragente van P. viburni. Verdere lang termyn evaluering van die doeltreffendheid van die getoetste isolate van M. pinghaense, M. robertsii en H. indica, afsonderlik of in kombinasie aangewend, teen P. viburni onder veldtoestande word benodig. Dit sal insig verskaf oor die moontlike sukses van die gebruik van entomopatogene vir die bestuur van die witluis in boorde, asook inligting oor die moontlike integrasie van entomopatogene as biologiese beheeragente in 'n geïntegreerde plaagbestuurstelsel teen witluise. | af_ZA |
| dc.description.version | Doctoral | en_ZA |
| dc.embargo.terms | 2023-02-28 | |
| dc.format.extent | xviii, 113 pages : illustrations (some color) | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/123743 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | Pseudococcus viburni -- South Africa | en_ZA |
| dc.subject | Fruit -- Diseases and pests -- Control -- South Africa | en_ZA |
| dc.subject | Mealybugs | en_ZA |
| dc.subject | Entomopathogenic fungi -- Classification | en_ZA |
| dc.subject | Insect nematodes -- Biological control -- South Africa | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | Control of the obscure mealybug, Pseudococcus viburni (Hemiptera: Pseudococcidae) using entomopathogenic fungi and nematodes | en_ZA |
| dc.type | Thesis | en_ZA |