Argentine Ants

The highly invasive Argentine ant causes significant problems for apiarists and horticulturalists. Already in certain areas of Northland, apiarists no longer keep hives due to the prevalence of these pests.

Victoria University researchers, led by Professor Phil Lester have identified a novel virus on the Argentine ant and are looking to this virus and others for their potential to use as a biocontrol.

“Some people refer to them as the Genghis Khan of the ant world. They come along and kill off all their competitors and other species within the area and take over the landscape,” says Phil in a recent Radio New Zealand interview.

The Argentine ant was first observed in NZ in the early 90’s by an entomologist moonlighting as a musician. Performing at Mt Smart Stadium, she looked down at an ant and thought “that’s a weird ant”. That weird ant was the Argentine ant – an ant listed in the top 100 of the world’s worst invasive species. This little brown ant has now spread throughout the North Island and as far as Christchurch in the South. The populations can be spread across several hectares and are worse in warmer areas.

While a headache for households particularly in warmer areas, it’s apiarists and horticulturalists that stand to lose the most from this invader. The ant raids honeybee hives for honey and will in cases attack honeybee brood-stock. The prevalence of this ant means that certain areas in Northland are no longer used for honeybee hives.

Unfortunately the Argentine ant did not arrive alone – it brought piggybacking microbes with it, including a number of viruses. Like the varroa mite, the ant is a vector for the Deformed Wing Virus that has decimated honey bee colonies around the world.

The Argentine ant threatens the honey industry and impacts on the honey bee as a pollinator in the horticulture industry and poses further threats to horticulture through it’s farming of aphids, mealybugs and scale insects.

The ant ‘farms’ these insects – warding off predators like ladybirds in order to benefit from their honey dew excrement. This results in higher populations of both insects.

Due to the invasive ant’s association with higher abundances of pests like mealybug, it may well prove to facilitate the spread of diseases like Grapevine LeafRoll Disease. Mealybugs carry the virus for this disease – the virus in turn attacks the grape vines and the only solution is to uproot and dispose of the affected vines.

Researchers at Victoria University observed degrees of Argentine ant colony collapse in Wellington. The ants have shown a remarkable prowess and can cover several hectares, but there was evidence of these colonies reducing significantly. It was presumed that the ants were likely to be suffering from a disease. Their susceptibility to disease was further likely in light of their low genetic diversity and the fact that colonies will intermingle.

Professor Phil Lester’s team looked at the ant and have discovered it is a host to several viruses – one being the Deformed Wing virus. They’ve identified a novel virus that they’ve christened LHUV-1 (pronounced love-one).

Postdoctoral research fellow Monica Gruber worked on the initial study that identified these viruses. Monica is presently working to identify other viruses and she is also further defining the LHUV-1 virus. This work includes extending the genome of the LHUV-1 virus and identifying the genome of the other viruses.

The research is looking for the opportunity to develop a naturally-derived species-specific insecticide. However one spanner in the works with the LHUV-1 virus is that it has been identified as being related to the Deformed Wing virus that decimates honey-bee populations. Phil is very clear that they do not want to manipulate a virus that might impact other species like the honeybee.

“This virus hasn’t been seen before, but it’s related to other viruses that can devastate populations of other insect species. If it is specific to these invasive ants and managed correctly it could be used as a biopesticide both in New Zealand and overseas,” Professor Lester says.

Concurrent research at Phil’s lab is also looking at Argentine ant immunity with the idea that “knocking down an immune gene” will make the ant more susceptible to a biocontrol developed from a virus. Other research is looking at the behaviour of the ant with a view to understanding why it is so successfully invasive.

Other work by Monica Gruber and associate Antoine Felden is examining if humans, by moving this ant around the world, have selected for ‘invasiveness’ in this ant. Perhaps only the most inquisitive and aggressive genotypes have been selected when humans have moved them around the globe?