Sex pheromone lures fatal attraction

There are two key animal instincts – feeding and reproducing. Landcare Research scientist Dr Janine Duckworth is using the latter to increase the effectiveness of possum traps, minimise the use of poisons such as 1080, and aid in the vision of a predator-free New Zealand.

Who would’ve thought urine could help pest control?

Luckily the idea struck Landcare Research’s Dr Janine Duckworth.

She came up with the concept of using possum urine of “ready-to-mate” females to attract the pests – which cost the economy more than $100m every year – to traps.

And it works, according to preliminary results from a Landcare Research-led study.

Increased kill rate:

Field trials in Kaituna Valley, on Canterbury’s Banks Peninsula, have found it’s increased the kill rate by as much as 25 per cent compared with traditional food-based lures, such as icing sugar.

In pen trials, male and female possums reacted to the urine of in-heat females by sniffing, touching or pawing the area. Females spent on average around 80 seconds investigating the smell, and males over 2 minutes (140 seconds). Duckworth said the scent appeals to both sexes as males are interested in exploring the odour for mating purposes, and females for territorial reasons.

Duckworth came up with the innovative idea in 2010 after Landcare Research helped the Department of Conservation (DOC) rid Kapiti Island of a pesky male stoat that had evaded food-based lures for around 3 months. Landcare Research sent bedding from a ready-to-mate female stoat in their captive stoat colony and within about 10 days the male stoat on Kapiti was caught.

Animal instinct:

Duckworth said the lures would be particularly useful in helping trap low densities of pests in areas where food was abundant.

“They’re always trying to find a mate, and that’s a lot more difficult when there aren’t many animals in the area, so we tried to take advantage of that.”

It is hoped the new lure may also be successfully developed to use with stoats. This is yet to be trialled.

Duckworth said poison remained the most effective means of controlling possum numbers over large areas. However, trapping was preferred near towns and cities. The pheromone lure would be particularly useful in these areas.

It also has the advantage of only attracting possums, as opposed to food-based traps, which also enticed rats, and reducing the risk to non-target animals, particularly native birds.

Possums are considered a pest as they pose a major threat to New Zealand’s biodiversity by eating native plants and the eggs of native birds, as well as being the main source of Bovine tuberculosis (TB) in cattle.

Synthetic lures:

Duckworth worked with research associate Andrew Twidle at Plant and Food Research (PFR) to develop a synthetic version of the pheromone lure.

“We couldn’t go around and use possum urine all the time, because it’s not that easy to collect,” she said.

“We looked for the compounds that were present in the females but not present in the males (urine) and that made life a lot easier for us because there were only about 11 compounds.”

These were then tested and whittled down to five compounds that were particularly attractive to both male and female possums.

Twidle said once the key compounds for possums were identified it was “really lucky” that they were already commercially available.

“This made the process quite straightforward,” he said.

“These were then mixed in similar ratios to those observed in female urine.”

Further trials:

Landcare Research, in conjunction with Zero Invasive Predators (ZIP) and PFR, will conduct an extensive field trial of the synthetic lure at Bottle Rock, in Marlborough, later this year.

ZIP business manager Phil Bell said the trial had just been approved by the Environmental Protection Authority (EPA), “so we are keen to get it underway”.

World first:

If successful it will be the first pheromone lure for possums.

Twidle said it was “exciting” to be part of the “world first”.

Most pheromone products were developed around insects, with only a few targeted at vertebrates, he said.

“There are thousands of pheromone and communication chemicals known for insect pests, whereas for the vertebrates to date only a few pheromones have been identified, so it’d be a real breakthrough for us.”

Predator-free ambition:

Duckworth hoped the new lure may aid in the vision of a predator-free New Zealand.

Prime Minister John Key recently announced the ambitious goal of making New Zealand predator free by 2050. This included having developed a scientific means capable of eradicating a small pest species by 2025.

“New potent species-specific lures may be the key to improving encounter and interaction rates with traps and monitoring devices for better, more effective pest control in the future and to make the goal of a predator-free New Zealand more attainable,” Duckworth said.

“Also, we’re going to be dealing with populations of possums at very low densities and it may be hard to find that last possum or stoat so if we use a non-food based lure, like a pheromone lure, this may be a very good way to find that last individual and kill it.”

Landcare Research Managing Invasives portfolio leader Dan Tompkins felt increasing interaction rates was vital.

A study looking at the effectiveness of rat traps in the Eglinton Valley, in the South Island, found only 1 in a 100 approaches resulted in a rat being caught, he said.

“So there’s a real need in the ways that we can improve the success of these devices and Janine’s work into lures is one way to do so. If we can increase those interaction rates between pests and devices like traps and tunnels then we can really increase the impact we have on those pest populations.”

Tompkins said pheromone lures were proving effective as they tapped into animals’ two key instincts.

“Pheromone lures generally are believed to be effective because there’s two basic necessities in life for most things – feeding and reproducing. Pheromone lures are linked to reproduction and breeding and the necessity of finding a mate – this drives most species – so that’s why it’s a very good lure to use.”

The project is funded by Landcare Research Capability Funding and OSPRI’s TBfree New Zealand programme, and the proposed field trial in collaboration with ZIP.