Controlling wasp populations with a new protein bait
Richard Toft has developed bait that is helping deal to the wasp problem in the native beech forests around Nelson and other parts of the country.
The German wasp (Vespula germanica) and common wasp (Vespula vulgaris) have been described as New Zealand's most abundant and devastating invertebrate pests.
The German wasp arrived in New Zealand soon after World War II. It was first sighted near Hamilton in 1945. The common wasp arrived in the 1970s, but insect ecologist Richard Toft at Entecol says genetic testing suggests there were up to 10 separate introductions. Despite arriving later, the common wasp has largely displaced the German wasp in beech forests. These wasps had no natural predators, few competitors, mild weather and an abundance of high-quality food.
Studies have found that, at their peak, there can be up to 40 nests per hectare of beech forest. A nest can produce thousands of queens and thousands of workers, and there are about a million hectares of beech forest in the South Island.
Based on these figures, there could be up to 40,000,000,000 (40 billion) wasp queens in the beech forest at the height of summer, and many more workers.
Richard Toft says the impact of that amount of wasps on the ecosystem has "got to be catastrophic". A Department of Conservation study, published last year, estimated that wasps cost New Zealand about $130 million a year.
Richard has spent nearly three decades as an insect ecologist. He has previously worked at DSIR and Landcare Research. He says wasps are drawn to the South Island beech forest by honeydew, a sugary drop excreted by scale insects that burrow into the bark of the beech tree.
Honeydew is an important food source for native birds like tui and bellbirds, as well as some lizards and insects, however, each summer, vespula wasps consume about half of the beech honeydew.
The introduction of foreign wasps has also impacted on the ability of people to enjoy the outdoors in summer. German and common wasps can deliver a painful sting with an injection of venom.
A new bait, known as Vespex has been introduced to try and beat the wasp problem. It is a low toxicity, protein-based bait that's laid in bait stations during late January and February, when wasps change to a protein-based diet.
Vespex was developed with DOC and in 2015, Richard and DOC staff ran a series of trials that produced excellent results.
Wasps require protein to feed their growing larvae, and will scavenge for good quality protein sources to take back to the nest. Vespex is an attractive and palatable protein bait to wasps – combined with a potent, but slow-acting insecticide called fipronil.
The wasps gather the bait from bait stations and take it back to their nests, where it is shared through the colony, including the queen. It's safe for bees and pets.
Vespex has been remarkably successful in wiping out wasps during trials in five locations across the South Island, including Abel Tasman and Nelson Lakes national parks, achieving between 95 and 100 per cent wasp eradication.
The timing for an effective baiting campaign is dependent on knowing when the wasp population in your area has a high demand for protein. This is determined via a simple activity testing procedure – which involves putting out a cheap protein source like cat food and watching out for wasp interest.
If the number of wasps that start feeding on the protein reaches a pre-determined threshold, then its time to put out the bait. The threshold levels of protein foraging behaviour is rarely reached before mid January, and often in early February. Cut off for baiting wasps is around mid April when their interest in protein begins to wane.
Richard says that Vespex has usually done its job within a week. It is recommended that the bait is removed after a maximum of 8 days.
DOC runs a wasp control programme in the Nelson Region. In late 2016 a community initiative lead by the Nelson Mail was launched to tackle the wasp problem. In conjunction with the Tasman Environment Trust, the organisations are working together to help wipe out wasps in the area.