The search for a biological control agent to control invasive Polistes dominula wasps in the Western Cape region, South Africa
Mhlongwe, Thobeka Rita (2018-03)
ENGLISH ABSTRACT: Polistes dominula (Christ) (Hymenoptera: Vespidae: Polistinae), also known as the European paper wasp is globally notorious as a highly invasive wasp, and invaded and established itself in five continents, with the exception of the Antarctica. Polistes dominula had a negative impact in invaded regions, where it has been reported to displace native wasp species by exclusive competition. The first record of P. dominula in South Africa was in 2008 in the Western Cape Province. Since then, it has expanded its range to more areas in the Western Cape. However, there have been no reports of this invader in other provinces in South Africa. Globally, there have been many methods used in the attempt to control invasive wasps. These methods include mechanical control, which involves the physical removal and destruction of nests, chemical control, which is the use of chemical pesticides, and biological control, which involves the use of a living organism to control the population of another. It has been found that mechanical control is labour intensive and chemical control is not environmentally friendly. This leaves biological control to be the best potential control strategy for the wasp. Research has been carried out to find natural pathogens of invasive wasps and there are many potential control agents that could be used. These include entomopathogenic nematodes, entomopathogenic fungi, viruses, bacteria and parasitoids. These biocontrol agents tend to be host specific, and there has been no biological control agent developed against P. dominula. In this study the fungi associated with P. dominula were isolated from the nests of wasps and identified. Most of the fungi isolated from the nest material were saprophytic fungi that are commonly found in soils and on plant material, with a few known to be pathogenic to plants and insects. The pathogenicity of selected fungi was tested against P. dominula second instar larvae and it was confirmed that, among the isolated fungi, B. bassiana was more virulent under laboratory conditions. This fungal isolate was able to kill 80% of the larval population within three days after exposure to the fungal treatment. Furthermore, a field trial was conducted to determine the pathogenicity of the B. bassiana isolate that was successful in infecting P. dominula larvae under laboratory conditions. This fungal isolate was, however, not able to establish under the unpredictable field conditions, as there was no visible proof of infection to the larvae that were treated with the fungal isolate. There are a number of biotic and abiotic factors that may hinder a fungal biological effect. In this study, temperature was one of the abiotic factors that played a role in hindering the fungal isolate from establishing in the field. Laboratory experiments showed that B. bassiana could only grow optimally at temperatures between 25 ˚C and 30 ˚C and at 40 ˚C fungal spores were not able to survive. The temperature in the field during the experiment, regularly reach above 30 ˚C. Biotic factors, including other living organisms, also have an effect on the success or failure of a biological control agent. In this study, a Bacillus species were isolated from the nest material and were found to inhibit the growth of B. bassiana. This study has provided valuable information by showing that the larvae are susceptible to the entomopathogenic fungi B. bassiana under laboratory conditions. Therefore, more research needs to be done to improve the performance of this pathogen in under field conditions.
AFRIKAANSE OPSOMMING: Polistes dominula (Christ) (Hymenoptera: Vespidae: Polistinae), ook bekend as die Europese papierwespe, is wêreldwyd bekend as ‘n indringerspesie. Hierdie wespe het al vyf kontinente ingedring en gevestig, met uitsondering van die Arktiese gebied. Polistes dominula het ‘n negatiewe impak op die areas waar hy indring deur die inheemse wespe te verplaas deur middel van kompetisie. Die eerste keer dat P. dominula in Suid-Afrika aangemeld was, was in die Wes-Kaap in 2008. Sedertdien het dit in meer gebiede van die Wes-Kaap gevestig, maar daar is nog geen teken van hierdie indringer in ander provinsies voorkom nie. Wêreldwyd is daar al verskeie metodes aangewend om indringerwespes te beheer. Dit sluit in meganiese beheers wat die fisiese verwydering en vernietiging van neste behels, chemiese beheer waar die gebruik van chemiese plaagdoders aangewend word; en biologiese beheer wat die gebruik van ‘n lewendige organisme vir die beheer van ‘n ander behels. Meganiese beheer kan arbeidsintensief wees en chemiese beheer is nie omgewingsvriendelik nie. Daarom is die beste potensiële strategie om wespes te beheer, dus die biologiese beheer. Verskeie navorsings is al uitgevoer om ‘n natuurlike patogeen vir indringerwespes te identifiseer. Daar is verskeie potensiële beheermiddels wat gebruik kan word. Hierdie sluit in entomopatogeniese nematodes, entomopatogeniese swamme, virusse, bakterieë en parasitoïede. Hierdie beheermiddels is geneig om gasheer spesifiek te wees en daar was tot dusver nog geen beheermiddel ontwikkel teen P. dominula nie. In hierdie studie is verskillende swamme wat met P. dominula assosieer, geïsoleer vanaf die neste en geïdentifiseer. Die meerderheid van die geïsoleerde swamme is saprofitiese swamme wat algemeen voorkom in grond en plantmateriaal. Slegs ‘n paar is bekend as patogene teen plante en insekte. Verskeie swam-isolate se patogenisiteit is teen P. dominula larwes getoets. Vanuit al die geïsoleerder swamme, het B. bassiana onder laboratoriumtoestande die hoogste virulensie getoon. Binne drie dae na die blootstelling aan hierdie swambehandeling, het 80% van die larwes doodgegaan. Verder is ‘n veldproef uitgevoer om die patogenisiteit van die B. bassiana-isolaat, wat suksesvol was onder laboratorium kondisies, te toets. Die onvoorspelbare veldkondisies het egter daartoe gelei dat die swam nie in die veldproef suksesvol was nie. Daar was geen sigbare bewys dat die larwes geïnfekteer is met die swam-isolaat nie. Daar is verskeie biotiese en abiotiese faktore wat die biologiese effek van swamme kan beïnvloed. In hierdie studie het temperatuur veroorsaak dat die swam nie in die veld suksesvol nie. Eksperimentele werk in die laboratorium het getoon dat B. bassiana optimaal groei by temperature tussen 25 ˚C en 30 ˚C. Die swamspore het nie by temperature bo 40 ˚C oorleef nie. Tydens die veldproef het temperature gereeld bo 30 ˚C gestyg. Biotiese faktore, soos ander lewendige organismes, het ook ‘n effek op die sukses of mislukking van ‘n biologiese beheersmiddel. In hierdie studie is ‘n Bacillus-spesie geïsoleer vanaf die nesmateriaal. Hierdie isolaat het die groei van B. bassiana effektief geïnhibeer. Hierdie studie verskaf waardevolle inligting deur te bewys dat die larwes vatbaar is vir die entomopatogeniese fungi, B. bassiana, onder laboratorium kondisies. Daarom word meer navorsing benodig om die effek van hierdie patogeen in die veld te verbeter.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103858
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