Status of the invasive wasp species, Vespula germanica and Polistes dominula in South Africa, and the feasibility of various management strategies

[摘要] ENGLISH ABSTRACT: The main objective of this study was to determine the current status of two invasive wasps, Vespula germanica and Polistes dominula, in South Africa and to explore the feasibility of implementing various management strategies to control and/or eradicate them. Both wasp species pose a potential threat to biodiversity and agriculture in the Cape Floristic Region (CFR), as well as being a nuisance to people.In an effort to identify suitable biocontrol agents, the pathogenicity of three likely indigenous entomopathogenic nematode (EPN) species and one likely indigenous entomopathogenic fungal (EPF) species was tested against both V. germanica and P. dominula larvae in a bioassay trial. The three EPN species were Heterorhabditis bacteriophora,H. noenieputensis and Steinernema yirgalemense. The fungal species tested was Beauveria bassiana. Both V. germanica and P. dominula larvae were highly susceptible to all of the biocontrol agents tested, and died of infection within 4 days after inoculation within EPN and within 7 days after innoculation within the EPF.The EPN Heterorhabditis bacteriophora which performed best in the bioassay trial, as well as the EPF, Beauveria bassiana, were then tested in the field to determine its ability to infect P. dominula larvae by spraying inoculum directly onto nests. Four treatments were applied, namely: an aqueous solution of the EPF, an aqueous solution of the EPN, a mixture of the EPF and EPN species, and a control of distilled water. The combination of EPF and EPN caused the highest mortality in both P. dominula larvae (31.39 %) and pupae (3.42 %) compared to the other treatments, but infection levels were much lower than those obtained under laboratory conditions. An unsuspected discovery was made, when it appeared that 13 % of all nests used in this trial were parasitized by an unclassified fly species, identified to be a species from the Tachinidae family. There was no significant difference between the ability of fly larvae that were treated with the control, to develop into adults over a period of 144 h, compared to those treated with the various biocontrol agents.Landmark-based geometric morphometric analyses were used to identify the potential origin of introduced V. germanica wasps and to determine the possible route of invasion followed in South Africa. Variation in forewing shape among wasp worker samples that were collected from five different countries, including South Africa, Australia, New Zealand, Argentina and France, was compared. An overall direct correlation between the wing shape and the geographic distance between two sites was found. This result suggests that the morphological variation in wasps from South Africa can be explained as isolation-by-distance. Results inferred that wasps had spread from Kirstenbosch to Somerset West, and thence through Stellenbosch to Franschhoek. The wing shape of wasps collected from Kirstenbosch, the area where the first V. germanica specimen was found, mostly resembled the wing shape of samples from France, compared to all the other overseas localities. Therefore, one could conclude V. germanica wasps were most likely transported from Europe to South Africa.The attractiveness of a range of lures and baits to V. germanica and P. dominula females collected in the field were tested using a Y-tube olfactometer. A combination of protein and carbohydrate-based baits were tested. Vespula germanica mostly preferred cooked ham, whereas P. dominula was mostly attracted to the odours emanating from their own nest.

[发布机构] Stellenbosch University