Resistance to neonicotinoid insecticides has for the first time been confirmed in Australian populations of green peach aphid (GPA), a serious broadacre cropping pest.
The discovery means that GPA is known to have resistance to four different chemical mode of action groups – synthetic pyrethroids, carbamates, organophosphates and now, neonicotinoids.
GPA is a widespread pest of canola and a range of pulse crops, causing damage by feeding and transmitting viruses, including Beet Western Yellows Virus which decimated canola crops in parts of South Australia, Victoria and New South Wales in 2014. It is also a common pest in horticulture.
Resistance to neonicotinoid insecticides – commonly used in the grains industry in seed treatments – was recently confirmed by scientists involved in research undertaken on behalf of the Grains Research and Development Corporation (GRDC) and Horticulture Innovation Australia (HIA).
The work has been led by Melbourne-based scientific research organisation cesar, in collaboration with researchers at CSIRO.
Entomologist Dr Paul Umina, of cesar, says resistance to neonicotinoids has now been confirmed in a number of GPA populations across Australia. Specimens taken from both canola and vegetable crops tested positive for resistance.
Dr Umina says the discovery – while not unexpected – further limits the opportunities and options for control of GPA and underlines the need for sound management resistance strategies and integrated pest management practices to ensure long-term access to available chemistries.
“Our findings don’t mean that neonicotinoids are dead in the water; they are still a valuable tool,” Dr Umina said.
“But the discovery does serve as a reminder that all chemicals are vulnerable to resistance development, particularly when dealing with a species like GPA which is known to have a high propensity to develop insecticide resistance.”
The mechanism underlying neonicotinoid resistance in Australian GPA populations has been identified as metabolic resistance which, fortunately, means that functionally resistance levels are low to moderate.
Dr Umina says there is another mechanism conferring neonicotinoid resistance in GPA, which leads to a very high level of resistance, and complete field failures.
“In good news, this high-level resistance, which is found overseas, hasn’t been detected in Australia. By adopting resistance management strategies, we can significantly reduce the likelihood of this resistance evolving in Australian GPA.”
Dr Umina says Transform, a sulfoxaflor foliar insecticide, remains an effective means to control GPA in canola crops.
Dr Siobhan de Little, a senior consultant with cesar, says it took researchers some time to establish the methodologies necessary to confirm resistance to neonicotinoids.
“We used a relatively new laboratory-based methodology in combination with genetic testing to confirm aphid populations were in fact resistant,” Dr de Little says.
“But it is not a discovery in isolation when you consider it in the context of what we already know in terms of GPA and its resistance to other chemical groups.”
GPA has high levels of resistance to pyrethroids and carbamates, and while resistance to organophosphates is broad across Australia, levels of resistance to this group are lower.
Insecticide resistance almost always evolves due to the overreliance on a particular chemical leading to strong selection.
Dr de Little says Australia now joins four other continents – North America, Asia, Europe and Africa – in having confirmed GPA resistance to neonicotinoids.
Dr Umina encourages growers to continue to follow the GPA Resistance Management Strategy, which aims to minimise the selection pressure for resistance in GPA. This strategy was developed by the National Insecticide Resistance Management (NIRM) working group of the Grains Pest Advisory Committee, a GRDC-funded project which provides strategic advice to the GRDC on pest issues.
He also urges growers to keep a close eye on next year’s canola crops as they establish.
“If aphids are seen surviving on young canola plants that have been treated with neonicotinoid insecticide seed treatments, growers are urged to contact cesar (phone 03 9349 4723).”
Suspect populations can be tested for resistance relatively quickly using new diagnostic tools.
Photo: A Weeks (cesar)