Last updated 14:45 27/03/2014
MARTIN DE RUYTER/Fairfax NZ
Entomologists are frantically trying to drum up increased funding to fight a huge wasp problem that has been made even worse by the recent arrival of another invader.
Warm and dry weather stretching back well over a year is one reason for the large numbers of wasps this summer and early autumn. A second is the rapid spread of giant willow aphids which produce honeydew, a favourite wasp food.
In the past month or so wasps have hit the headlines numerous times after people discovered monster nests near their homes, or after the insects launched aggressive attacks.
Among the incidents:
* Sheep farmer Janet Kelland was attacked by hundreds of wasps after stepping on a nest in a remote area northwest of Taumarunui. At one point she feared she would not survive.
* New Plymouth woman Diana Cole watched a wasp nest grow bigger by the day on a wood chopping block. Then one day it rolled free onto her driveway and she took the opportunity to run it over, ending the problem.
* A nest containing thousands of wasps was found built around a ponga stump in a backyard in the Taranaki town of Normanby. Exterminator Neville Prestidge said it was the largest nest he had encountered in 14 years doing the job.
* Nine pupils from a Nelson primary school and a woman were taken to hospital after being stung when a wasp nest was disturbed at Tahunanui Beach.
Professor Phil Lester from Victoria University's School of Biological Sciences said the rapid spread of the invasive willow aphids, which had arrived in this country in the past few years, had made the wasp problem even worse than it would otherwise have been.
"It (willow aphids) seems like a massive problem. It's just making the wasp population worse. These aphids are effectively fuelling the wasps."
Now the willow aphids had come along, wasps were going to have to be a higher priority. "It's a huge problem."
"People end up in hospital fairly regularly, and people will die," Lester said.
"They're (wasps) really aggressive. They're probably the most harmful animal we have in New Zealand."
Researchers around the country and overseas were working on ways to control the wasp population.
At Victoria, research looking at potential biological control using pathogens and parasites was at an early stage.
"Many New Zealanders, including us entomologists, are pretty desperate for a wasp control option. So there's all sorts of avenues being investigated," Lester said.
For now, there were baits that could be used to kill wasps but a lack of registration of effective pesticides for wasp control limited their use. Pesticide companies needed to be on board to register toxic chemicals - poison baits - so it was legal to use them to kill wasps.
"There are chemicals around that are really, really, really effective but we need those to be registered," Lester said.
"It's a relatively quick fix that should really be happening quicker."
Ideally it would be preferable not to use large amounts of toxic, or even mildly toxic, chemicals in the environment.
"So my desire would be to work towards something that was environmentally sustainable, like a biological control agent, whether that's something in New Zealand that we could exploit, or something that we need to bring in from overseas."
Two invasive species of social wasps are the major problem in New Zealand.
German wasps are native to Europe and northern Africa. In this country they were first found at an air force base near Hamilton in 1945. Within a few years they had spread to most of the North Island and parts of the upper South Island.
Common wasps are native to Europe and parts of Asia. They were confirmed as established in Dunedin in 1983, although museum specimens show queens were collected from Wellington as early as 1978. They rapidly spread throughout New Zealand and almost completely displaced german wasps from beech forests in the upper South Island because of their superior competitiveness.
According to the Department of Conservation, wasp densities in South Island beech forests - covering more than 1 million hectares of conservation areas in the South Island - are the highest recorded anywhere on earth.
Researchers put those densities at up to 370 wasps per square metre of tree trunk and 34 nests per hectare. The high densities are due to the availability of honeydew being produced by insects.
Dr Darren Ward of Landcare Research said higher wasp numbers affected the breeding success of some birds and also had an impact on some lizard and bug populations.
"They do a lot more damage to the native environment. They eat a lot more food, usually native bugs, and they also eat the honeydew (produced by aphids) ... That's basically a really good sugar resource important for native birds, native lizards and native bugs, and the wasps get it first."
A group had been set up to lobby central government about the problem, while a study funded by DOC and the Ministry for Primary Industries was trying to put a figure on the economic cost of wasps, Ward said.
"Wasps don't just affect native habitats. They have quite a big health impact. They kill many, many thousands of beehives each year. They're also in vineyards and orchards. They will eat grapes and spoil fruit."
Lester and Ward are among authors of a paper published this year on critical issues facing New Zealand entomology, developed in consultation with the Entomological Society of New Zealand.
A list of nine priorities includes limiting the effects of invasive invertebrates, particularly german and common wasps in honeydew beech forests.
It had been estimated wasp abundance in the forests would need to be reduced by more than 80 per cent to conserve vulnerable invertebrate species, the paper said.
"We believe that a sustained, dramatic reduction of wasp densities is necessary for conservation, especially in honeydew beech forests."
Pesticides would be useful in relatively small areas, but biological control was the only viable option for sustained wasp control.
Lester and Ward were also among the authors of an article in the New Zealand Science Review last year which said that apart from the direct manual application of insecticides to nests, toxic baits had been the only successful control tool for wasps so far.
Researchers using a protein bait containing the broad-spectrum insecticide fipronil had been highly effective in controlling wasps, but commercial restrictions around end-uses of fipronil in this country had prevented any wasp bait products containing the toxin being manufactured for commercial purposes.
In a Landcare Research report Ward said social wasps were pests in may temperate regions of the world.
"Consequently, a sizeable amount of research effort has been focused on developing control strategies. However, despite these efforts, wasps continue to be a major problem."
Along with poisoned baits and biological control, possible ways to control wasp populations included interference with wasp pheromones - chemicals secreted by an organism to communicate with other members of the same species; and RNA interference, a natural biological process that could turn-off specific genes.