Biocontrol of wasps
Since 2014 Bob Brown and his colleagues at Landcare Research have been reinvestigating the potential for using natural enemies for the biological control of invasive social (common and German) Vespula wasps. The mite Pneumolaelaps niutirani, recently discovered infesting wasp nests in New Zealand, was the first potential agent investigated. To determine its range and prevalence throughout New Zealand the public were invited in the winters of 2014 and 2015 to send in any wasp queens they found overwintering. Inspecting these revealed that the mite is widely distributed from Northland to Southland.
In the summers of 2015 and 2016 wasp nests were excavated and examined for the mite. Photographs were also taken of the comb fragments of each nest to determine nest size by counting the number of cells. The results from the first season were very promising, with mite-infested nests being much smaller (average of c. 4,100 cells) than un-infested nests (average of c. 11,500 cells). However, in 2016 the small numbers of mites in the majority of nests appeared to have no correlation with nest size.
Bob’s team also observed mites feeding from the mouths of wasp larvae as they regurgitated their nutrient rich ‘soup’ for the rest of the colony to feed on. It would thus appear that the mite doesn’t directly feed on the wasps as a classic parasite would, but behaves more as a social parasite or commensal agent. This means the mite is unlikely to act as a classic biocontrol agent (a self-sustaining biocontrol solution that works in perpetuity). However, it may still end up being used as a control tool if it can act as a vector for wasp-specific pathogens, and this potential is being explored as part of the New Zealand’s Biological Heritage National Science Challenge.
In 2016 the team directed its efforts away from the mite to pursue the introduction of new genetic stock of Sphecophaga vesparum, a parasitoid wasp that attacks social wasps in their nests. The female parasitoids lay their eggs on the Vespula larvae just as they begin to pupate. When the eggs hatch, the parasitoid larvae migrate to the bottom of the cell and begin feeding on the pre-pupal Vespula. This life history makes them prime candidates for biocontrol of common wasps, and many thousands of them were introduced from Switzerland into New Zealand for this purpose in the 1980s. However, they appear to have only established in a handful of sites in the South Island.
A key reason for the team’s renewed interest in this parasitoid is recent research demonstrating that the common wasp was introduced into New Zealand from the United Kingdom and not from Switzerland. Preliminary work indicates that the United Kingdom is also the likely origin for New Zealand’s population of German wasps. Thus, enriching the parasitoid gene pool and matching ecotypes via new introductions from the United Kingdom may increase the parasitoid wasp’s effectiveness as a control agent of New Zealand’s Vespula wasp populations. Also, most of the really hard work on the parasitoid biology was carried out in the 1980s by researcher Barry Donovan, who documented its life cycle and developed techniques for rearing it. Currently, the newly imported parasitoids are in containment to ensure they are disease free and can survive on New Zealand-sourced wasp brood. Once they are approved for release from containment they will be released at multiple locations in the South Island.
This work is funded by the Ministry for Primary Industries’ Sustainable Farming Fund.
Sphecophaga vesparum larva (circled) feeding on a Vespula vulgaris pupae.
Sphecophaga vesparum female on wasp nest.
A newly emerged Sphecophaga vesparum male.
Bob Brown (Landcare Research) brownb@landcareresearch.co.nz
Ronny Groenteman