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Collage: Tina Tiller
Collage: Tina Tiller

ScienceSeptember 9, 2021

New tactics against predators and pests promise to be more effective and humane

Collage: Tina Tiller
Collage: Tina Tiller

New Zealand is ready to think outside the trap-box when it comes to getting rid of pests. That means trialing everything from sterilisation to putting the fear in cats and making plants invisible (sort of).

Neuroendocrinologist Greg Anderson says the country is on the brink of something catastrophic. “Half of New Zealand’s native species are extinct already and many of the rest are endangered,” the University of Otago professor says. “With the current [pest control] technology we’re just holding our ground at best. We need something radical to turn the tide.”

Anderson says the problem with mammalian pests in Aotearoa is that they’re great at making babies. His solution to our pest problem is a one-dose oral paste that permanently sterilises predators, regardless of sex or species.

He and his team – consisting of reproductive biologists, a chemist and a bait developer – have just been granted $1m through the Ministry of Business, Innovation and Employment’s Endeavour Fund to develop such a paste. It’s one of 69 projects to receive funding this round.

There are a slew of advantages to sterilisation over poisoning or trapping, says Anderson.

Baits or traps are OK but some predators, like stoats, will sneak into a nest of newly-born kits and mate with all the females before those young have even had the chance to leave the nest and encounter any traps.

And this sterilisation paste would only work on mammals, not birds. “That’s a god-send for New Zealand’s forests,” Anderson says, referring to the rare cases where birds fall victim to poisons destined for rats or stoats.

Plus, predators can become wary of bait after only eating a bit of it – not enough to kill them, end up feeling sick, and then learn to avoid the bait later on. They also tell their predator mates about it so they avoid the bait too. With a sterilisation paste the animals wouldn’t know anything had happened.

The fact that a pest animal wouldn’t feel the paste’s effects also makes it potentially more humane than poisons, which can leave an animal feeling sick, thirsty, in pain or breathless.

Finally, it’s a one-size-fits-all solution in that it would work on all mammal pests. That means no customising traps to fit a particular pest’s size or shape and more individuals can be targeted at a time. “The wider we can spread this [to pests], the better,” Anderson says.

A NZ stoat with a chick. (Photo: David Hallet/Department of Conservation)

His team will spend the first of the next three years homing in on a chemical formulation that targets a particular receptor in the mammal reproductive system. They’ll test it on animal cells in a dish, then move on to testing it on rats and mice in the lab, before tackling the tricky task of turning it into an edible paste where the active ingredients don’t get destroyed by the animals’ acidic stomachs.

There will be a few details to figure out when it finally comes time to potentially implement the paste, including making sure that it’s spread out in a way that pet cats don’t inadvertently lick it up. “We wouldn’t want to sterilise those animals but that can be managed. The Department of Conservation and the people who currently administer 1080 have decades of experience managing [distribution],” says Anderson. He adds that the effects could be reversible too.

But there may be a way to deal with cats as well: by scaring them away. Another project to receive MBIE funding will trial using sounds and smells to deter cats away from areas where native wildlife roam.

The project, led by wildlife ecologist Patrick Garvey from Manaaki Whenua – Landcare Research, will test out these scare tactics in different areas of the country.

Areas of interest include the perimeter of eco-sanctuary Zealandia, in Wellington, where birds that leave the protected sanctuary are being picked off by cats; and potentially the Te Atatu peninsula or other areas of Auckland where shorebirds like dotterel aren’t having success breeding because of the felines. Garvey is currently working with councils, iwi and DOC to pin down which sites they’ll use.

Garvey says the first step will be to figure out the right sounds and scents for deterring cats but that won’t bug native species. They’ll do this in large outdoor arenas before moving their experiments out into the wild.

Then they’ll find ways to place the sounds and smells so that they’re not freaking out native species as well. “This is a very important consideration as we want to ensure native wildlife are not impacted,” he says. They’ll also monitor the sites throughout the study to make sure birds and other non-target species aren’t disturbed.

The researchers will also fit cats with tracking collars and capture their movements on camera traps to see if the technique is working. That is, that cats are staying away. They’ll also monitor what’s going on at bird breeding sites using cameras to see if scaring away cats leads to better breeding success for the birds.

Native wildlife isn’t the only group to suffer at the paws of predators. Crops too come under attack from various insects. Chemical ecologist Ashraf El-Sayed, from Plant & Food Research, leads a team trying to make plants invisible to pest insects.

A group at Plant & Food had previously noticed that insect-infested apple trees protected their neighbours by changing the neighbouring trees’ physiology, down to the gene expression level, and stopping them giving off insect-attracting odours.

They think this is thanks to the infested plant giving off a particular chemical signal that puts the neighbouring plants in stealth mode.

“Can we achieve what we’ve seen [the plants doing] but using a chemical signal we’ve created?” proposes El-Sayed.

If they could, it would mean an alternative to insecticides, which can in some cases leave toxic residues in food, water, air or soil, lead to insects becoming immune to them or runoff into the surrounding environment.

El-Sayed and his team have identified some specific components to that chemical signal but there are more to uncover. The first year of their MBIE-funded project will identify those compounds then test which bouquet produces the physiological stealth-mode response they’ve seen.

The final stage will see whether the mix actually protects plants – specifically pip fruits like apples and pears, and plants in the cabbage family – against a specific plant-eater or a range of plant-eaters.

El-Sayed says the project is harnessing the amazing ability of plants that often go unnoticed. “People usually look at plants as objects, not living things. No, not at all. Plants are living organisms that react and respond to all sorts of stimuli,”

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