Fight against a migrant invasion
Aotearoa’s history is littered with migrant invasions over-running natives, including rabbits, ferrets, possums, gorse and pakeha.
Science can’t do much to reestablish the pre-eminence of indigenous humans, but it may offer some defence against other unwelcome migrants.
Greater Wellington regional council’s biosecurity staff have successfully introduced 13 insect, rust and fungi species which feed on pest plants and have plans for more.
The council’s environmental wellbeing committee was told last month that the council was taking the lead on the introduction of Honshu white admiral butterfly to control the spread of Japanese honeysuckle.
The honeysuckle is an invasive weed causing concern throughout New Zealand.
Greater Wellington biosecurity officer Harvey Phillips said a group supported by most of New Zealand’s regional councils collectively decided when a pest plant had become so well-entrenched that physical or chemical measures could not bring it under control and something else was needed.
The Greater Wellington council has applied to introduce the Honshu white admiral, but the Horizons council would champion an agent to control field horsetail.
‘‘Problem plants are identified. Landcare then look at a survey to see if there is anything on that land the can be used.’’
Testing was virtually complete and the Honshu butterfly was expected to be introduced last next summer, proved the Environmental Protection Authority approved it.
Imported plants are often innocuous in their homeland so Landcare goes back to there to find an agent that naturally controls its spread, and brings samples back to a secure environment in New Zealand, Mr Phillips said.
Rusts and fungi were tested in Auckland, where there were facilities to contain spores and insects are tested at Lincoln, first to ensure they stay on the host plant and then to see if they attacked closely-related native plants.
The imported pest Old Man’s Beard is closely-related to native clematis, so most of its natural control agents would also attack New Zealand natives.
‘‘ The safety issue is huge because once you’ve got it out there working it won’t stop, regardless of later decisions,’’ Mr Phillips said. ‘‘We can’t afford any mistakes.’’ An insect in captivity may stay with its preferred food source, ignoring similar nearby natives but in the wild, when its preferred plant is unavailable, may turn to native alternatives.
‘‘Even those little jumps are a bit scary,’’ Mr Phillips said. Not all species jumps are bad. Green thistle beetle was introduced to control California thistle, but it was known to also feed on Scotch thistle and variegated thistles, both introduced pest plants.
‘‘That was acceptable,’’ Mr Phillips said.
‘‘Luckily, there are no closelyrelated native plants to thistles.’’
Tradescantia, commonly known by the less politically- correct name wandering Jew, proved a problem.
Green thistle beetles were successfully tested but there was a problem.
‘‘The first insects they brought in had a gut bug.’’ he said.
‘‘They were allowed to introduce the beetle but not the gut bug.’’
The gut bug would have been able to transfer to native beetles, and it took years to breed a beetle free of it.
‘‘I can’t emphasise enough the safety precautions Landcare take to make sure we don’t put an insect out that’s going to attack ornamental, economic or native plants.’’ Mr Phillips said.
When the agent is approved Mr Phillips finds a suitable site to establish a breeding population and then redistributes it throughout the region.
Broom shoot moth was released on reserve land near Porirua last December to control tradescantia.
Green thistle beetle was released in Rangitumau, Wairarapa in 2009 to help landowners control Californian thistle.
Gastarbeiter: A Honshu white admiral butterfly at work.