They might have started as a small, local infestation but Argentine ants have swarmed their way through the North Island and now have Plant and Food Research scientists hot on their trail with natural pheromone lures.
While obviously native to South America, since turning up in New Zealand in 1990 the insects have found much of the North Island more than comfortable enough to establish massive colonies that have moved beyond being simply a nuisance.
Plant and Food Research doctoral invasive pest researcher Lloyd Stringer said the symbiotic relationship between sap-sucking insects like mealy bugs and the Argentine ant could be particularly problematic for plant-based industries.
“The bugs excrete a honeydew that provides a carbohydrate source for the ants.
“The ants essentially farm the bugs for their energy source, helping them to increase in number to the detriment of the plant.”
He and fellow researchers had studied how pheromones could be used to disrupt the ants’ ability to forage for food sources and might hold promise for commercial application and for deterring other insect species.
The research exposed ants from five colonies to varying levels of a commercially available pheromone.
Typically, ants secured a food source through one ant heading out of the colony, finding food and laying a pheromone trail back to the colony nest to lead the others back.
Researchers determined that laying down the pheromone over a certain concentration was similar to putting a sensory fog around the ants.
It overloaded their pheromone detectors, causing them to lose direction and orientation from the trail.
Ultimately, they would not make it back to the nest and the direction of the food source would be lost. The benign distraction left the ants lost and disoriented.
The researchers also found the ants did not switch from pheromone cues to touch cues when the sensory overload took place and that their detection was essentially provided through the pheromone trail.
Stringer said researchers were surprised at how little pheromone the ants were capable of following.
“They will follow up to about a hundred-fold pheromone strength before it becomes too strong and they lose direction.”
The interaction of Argentine ants had the chill of a B-grade science fiction movie to it, with collective nests of ants tending to act as a single colony rather than fighting each other for food resources.
“You could take Argentine ants from the South Island and place them up in the north and they would all work together. The population is effectively one massive colony.”
The researchers also had some success with pheromone treatment of another distinctly unwanted ant, the imported red fire ant.
Recognised as a significant environmental, human and economic hazard if it ever became established here, it had so far been found on only four occasions, in 2001, 2004, 2006 and 2007.
“They have required a specially made pheromone but are probably harder to control using pheromones alone as they also use other sensory cues to get around.”
Field trials had been done to determine the potential for a commercial application of the pheromone work and researchers were working on wider applications for pheromones as non-pesticide control methods for high-value export crops and to protect against other unwanted intruders.
Pheromones have great potential to find new incursions and be used for the eradication of new pests.
For example mass trapping or lure-and-kill methods or for pests such as the brown marmorated stink bug that was knocking on NZ’s door.
Pheromones could also provide a socially acceptable control tool, such as the sterile insect technique – essentially contraception for pests.
In populated urban areas where a lot of the new pests were found, the use of pheromones was more acceptable than aerial spraying to rid districts of incursions.
“And for commercial growers using pheromones to control problem pests there are higher returns for their crops because of lower chemical residues.”
Stringer said there was potential for Plant and Food Research to commercialise pheromone products with a partner or to support NZ pheromone companies and industries to bring overseas products to the NZ market.
