Managing the wasp menace
The importance of pollinating insects such as bees contrasts markedly with the destructive impact another insect has on New Zealand’s biodiversity.
Some of the highest wasp densities in the world occur in New Zealand and these invaders continue to cause big environmental, social and economic impacts. Wasps have no natural enemies, our winters are mild, and there is an abundance of food for which they can out-compete our native insects and birds. The average density of wasp nests in a beech forest that has honeydew is about 12 nests per hectare, which equates to about 10,000 workers per hectare. In some areas the number of nests has been as high as 50–60 per hectare; the equivalent of 25–30 nests in an area the size of a football field. Landcare Research staff estimate that in beech forest with honeydew, the biomass of social wasps (about 1100 g/ha/yr) is greater than that of all the native birds plus stoats and rodents put together. All those wasps eat huge numbers of native insects and consume large quantities of sugary honeydew. By eating so much, wasps upset the natural food chain of the forest.
Landcare Research entomologist Richard Toft is studying the ecology and control of the four introduced wasp species with the goal of finding ways for managers to reduce densities to environmentally acceptable levels.
‘We are currently developing wasp baiting technologies by testing a range of more environmentally friendly toxins to see if we can pair one with our current wasp bait. We are also working to develop more cost effective strategies for baiting wasps,’ he says.
Mr Toft has also been working with AgResearch to prolong the field life of wasp bait, which will allow control of wasps at lower wasp densities and over a greater range of habitats. The trials have proven successful, prolonging the palatable field life of the bait by at least 400%.
‘We have also been exploring novel methods to include natural insect pathogens in baits. The idea is that these “biocides” will reduce the need for toxic chemicals, providing a safer, more environmentally friendly way to reduce wasp numbers. We’ve produced a shortlist of pathogens that are lethal to developing wasp larvae, and the first set of these biocides-in-baits will be ready for preliminary field trialling in wild nests this year.’
A number of different toxins to mix with bait have been trialled against wasps but with limited success. That’s largely because wasps are fussy eaters and some toxins become repellent when mixed with baits at concentrations required to obtain wide-area control. In order for toxic baits to be effective they have to work slowly enough to allow time for the bait to be spread around members of the community but toxic enough to be lethal in small amounts, a balance that is not easy to find.
Another approach is the use of odour technologies and this could lead to entirely new solutions where wasps are controlled through the widespread delivery of behaviour-disrupting pheromones specific to wasps. ‘Landcare Research has recently begun a new collaborative arrangement with Plant & Food Research that will specifically focus on odour technologies,’ Mr Toft says.
Richard Toft