Possums in Western Australia are developing a resistance to the poison known as 1080, found at low levels in some plants in the state, now prompting researchers to compare genetics to possums in Aotearoa.
1080 has killed millions of the Australian pests in New Zealand, with the Department of Conservation (DOC) dropping about 1.5 tonnes of the poison across 700,000 hectares of public conservation land per year.
Possums, alongside other pest predators like rats, stoats and cats, kill about 25 million native New Zealand birds per year.
Possums “eat a lot of eggs, a lot of chicks and nests and they do a lot of damage to native plants as well”, Predator Free 2050 science director Dan Tompkins told 1News.
“Right now without 1080, we would not achieve possum eradication for New Zealand.”
Exposures to 1080 in West Australian plants have meant it now takes “160 times the dosage is needed to kill a Western Australian possum than an Eastern Australian possum”, Massey University evolutionary ecologist Steve Trewick said.
He is among a group of New Zealand scientists researching the genetics, and implications, of this resistance.
Possums in Aotearoa don’t come from Western Australia but have the same genes.
“We don’t know whether the exact same alleles that are present in Western Australian possums are present in the possums in New Zealand, but we know that the genes are there, and we know that all of those genes have variation. And we know that there are lots of different ways that variation can result in resistance.”
“At best you get something like 90 per cent kill [rates] when an aerial drop is done,” Trewick said.
But it is not known how long it will take for the survivors of 1080 drops to become the dominant population in Aotearoa, he said, and “this is a huge problem”.
Higher doses of 1080 poison are also easier for possums to detect.
“So it’s not surprising that when you alter even slightly those exposure levels, the possums will just say, no, I won’t eat that poison.”
Pest control resistance has already caused headaches in Aotearoa, as surviving rabbit populations fight off caliciviruses.
Trewick said that rabbits in Australia, introduced in recent centuries, are also showing resistance to 1080 poison.
However, in a statement DOC said: “Evolution in Western Australian brushtail possums has occurred over many millennia and is likely to be different from any process occurring in New Zealand in response to aerial possum control with 1080.
“DOC is aware that resistance to 1080 may become a problem, but we have not observed this … Where reduced possum kill rates for individual operations are detected, it is difficult to separate bait shyness and preference for other foods from true resistance to the toxin.”
And Predator Free 250 is confident the country can rely on 1080 for now.
“Possums they can live for 10, 12, 15, even up to 20 years for extremely long individuals and so they are slowly reproducing. And so the number of generations that will happen between now and 2050 is very few,” Tompkins said.
Research 15 years ago estimated there were 30 million possums in New Zealand, but DOC said it did not know exactly how many possums were on the country’s shores now.
DOC Predator Free 2050 manager Brent Beaven said: “We don’t yet have the tools, technologies, and methods to completely eradicate rats, possum and mustelids from Aotearoa New Zealand. The Predator Free programme is currently focussed on developing the tools and technology and strategies to achieve eradication and trialling methods to remove introduced predators from discrete areas and defend them from reinvasion.”
And while 1080 has prompted protests in New Zealand, possible back-up plans are also divisive.
Scientists overseas have developed genetic controls to kill some pest insects, but the tech is currently not ready, nor is it allowed, for possums in New Zealand.
“I think that these sorts of technologies should be thought of as another tool in our toolbox … They’re going to be an option and perhaps an option when everything else has failed,” Genomics Aotearoa director Peter Dearden said.