Wasp season expected to have little sting

Media Release 18 January, 2001

Wasp season expected to have little sting

Landcare Research predicts that wasp numbers will be low at the peak of the wasp season, in February and March.

New Zealand has some of the highest densities of common and German wasps in the world. These introduced wasps prey on and compete with native fauna, disrupt human activities, and reduce productivity in forestry, tourism and bee-keeping.

Landcare Research insect ecologist, Dr Richard Harris, says the prediction has been made in conjunction with AgResearch population modeller Dr Nigel Barlow. Dr Barlow says the current model predicts there should be about eight nests per hectare in the honeydew beech forests favoured by wasps, compared with the 12 usually found. Dr Harris says that reports from the Auckland area indicate there are not many wasps around, and in the Nelson region, wasp numbers in honeydew beech forests are similar to last year, when they were fairly low.

*Wasp densities depend a lot on the spring weather* says Dr Harris. *There were several rain events around the nest founding time, and these have reduced the number of nests*.

*There will be hot spots around the country where wasp numbers are high. But many areas can look forward to their third year in a row with relatively low wasp densities*.

Dr Harris says it is possible that New Zealand is *behind the invasion front* of the common wasps that swarmed into the country in the 1970s. *Numbers may never again reach the huge levels they did in the late 80s.

*However, there*s no evidence that poisoning or biocontrol agents that we*ve released over the years to attack the wasps are responsible for this decline in population*.

Dr Harris says like most of New Zealand*s introduced pests, wasps are here to stay. *We can*t get rid of them, but we can treat hot-spots.

*Poison baiting can kill 80 - 100% of wasp colonies within the treated area. However, re-invasion by foraging workers lessens the actual wasp reduction. And queen wasps can travel at least 30 kilometres per year, so any reduction is short term.

*At the moment, there is no registered wasp bait in New Zealand, as a product developed in the 1990s has been withdrawn. We are currently researching a new product that should soon fill the gap*.

Dr Harris says so far, biocontrol agents released into the environment have failed to make much impact on the wasp pests. A wasp parasitoid (a parasite that kills its host) was introduced more than 10 years ago, but has not measurably reduced wasp density. Two other strains have yet to make an impression. Landcare Research is also investigating the potential of modifying the bacteria already present in the gut of the wasp, so that it attacks the wasp, but is still specific just to wasps.

ENDS For more information, contact: Dr Richard Harris Landcare Research Nelson ph: wk: (03) 548 1082 hm: (03) 546 7864 HarrisR@landcare.cri.nz

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