The search for a biological control agent to control invasive Polistes dominula wasps in the Western Cape region, South Africa

[摘要] 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.

[发布机构] Stellenbosch University