by Ian Bushell
At the beginning of October, at the Amateur Entomological Exhibition at Kempton Park, I was introduced to Dr R.L.Brown from New Zealand, who was doing research into potential biological control of wasps.
In New Zealand, Common wasps (Vespula vulgaris) and German wasps (V.germanica) are invasive aliens that have become one of the country’s most damaging and widespread invertebrate pests. Without native predators, the wasps have proliferated, particularly in the beech forests of the northern part of South Island, where they can reach a biomass as great as, or greater than, the combined biomasses of the forests’ birds and mammals.
Dr Brown had been in the UK for about three months searching for late season wasps’ nests to dig up, hoping to find the larvae of a particular hoverfly (Volucella inanis) that parasitises social wasps. He has permission to take the larvae back to New Zealand as part of a biological control project. As the Friends had recently found two wasps’ nests in the reserve, I said I was sure we could help him and gave him my phone number.
A few days later, with permission from the Countryside Team and after the requisite risk assessments, Countryside Officer Ali Rasey and I met Dr Brown in the reserve’s car park. We loaded his kit [bee suit, spades, containers etc,] into the Wiltshire Council Land Rover and set off. Both nests were alongside the tributary stream and Dr Brown was more than happy to dig them up.
We closed the path by the footbridge into Village Green, with walkers diverted over the bridge or up the Blackthorn tunnel, and, at the other end of the danger zone, we closed the path near the pond, with walkers diverted into Kestrel Field. Ali and I stood guard at either end of the closed section of path just to be sure, while Dr Brown kitted up and set to work.
The nest near the footbridge was of the Common wasp (Vespula vulgaris) and that nearer the pond Vespula germanica. Dr Brown dug out the Common wasp nest without any trouble and then moved on to the German nest. These were a bit more obnoxious and they attacked Countryside Officer Ali, bravely standing guard at the end of the path, and she got stung a couple of times.
All the collected combs were placed in containers after both nests had been treated and sealed back up. When we were packing up, a passer-by mentioned that they knew of a hornets’ nest in the reserve. Dr Brown was interested, so while Ali stayed by the nests to ensure the safety of the public, he and I walked down to Sleeper Field to have a look. Although the nest was big, it was more than two metres up in a tree and would have needed a chain saw to get at it.
But Dr Brown was very happy with his haul: he had found Volucella inanis larvae in both nests. To successfully introduce V. inanis as a biological control agent, he needs as wide a genetic base as he can find; a previous attempt at parasitoid introduction had failed possibly because the larvae came from a single adult source.
He has taken the Volucella larvae back to New Zealand, where they will pupate and hatch into adult hoverfly. There are always risks involved in the introduction of a non-native species for any reason, so the next part of the project will be conducted under closely controlled conditions. We will try to keep you up-dated.