Spring has arrived, and with it comes increased numbers of bluegreen aphid in southern Australian pastures and legume crops.
We’ve previously reported on the evolution of insecticide resistance in bluegreen aphid in lucerne.
And this year, for the first time, resistant strains of the aphid have been discovered in Victorian lentil crops, leaving growers with limited options to protect their fields.
The growing challenge of bluegreen aphid insecticide resistance
Bluegreen aphid, Acyrthosiphon kondoi, is a pest of lucerne, pulses, medics, clovers, and pastures, damaging plants through feeding and spreading plant viruses.
For years, growers have leaned on insecticides to keep these pests in check. However, this over reliance on a small number of chemicals has created a persistent selection pressure, driving the evolution of resistance.
In 2021, Cesar Australia and Lucerne Australia made a worrying discovery: bluegreen aphid had evolved resistance to three major insecticide classes—carbamates, organophosphates, and synthetic pyrethroids. Initially, these resistant populations were identified in South Australia and New South Wales (NSW).
By 2022, the scope of resistance had expanded. For the first time, resistant bluegreen aphid were found in Victoria, and their reach had spread further west to the Eyre Peninsula. New resistant populations were also discovered in NSW, marking a troubling trend.
What started as an issue for lucerne seed and forage crops has now grown into a broader concern, with researchers finding resistant bluegreen aphid in lentils and sub-clover in 2023.
And the trend shows no signs of slowing down. This year, new outbreaks of resistant aphid populations have been discovered, with concerning implications for management strategies.
Key development: bluegreen aphid resistance found in Victorian lentil fields
For the first time, insecticide resistant bluegreen aphid have been discovered in Victorian lentil crops.
Led by Dr. Evatt Chirgwin and the team at Cesar Australia, recent research has revealed resistant populations in key pulse-growing regions across the Wimmera and Mallee, including Nhill, Horsham, and Kerang.
These populations showed resistance to all major insecticide mode of action groups registered for lentil crops in Victoria. This includes carbamates (1A), organophosphates (1B), and pyrethroids (3A). While the resistance to carbamates (such as pirimicarb) was generally weaker, it still poses a serious challenge for growers relying on these chemical options.
This marks a significant shift. In previous years, testing in these areas showed no signs of resistance, suggesting that this spread is a recent development.
Resistance also remains a common problem in lucerne paddocks, with bluegreen aphid collected from South Australian lucerne showing particularly high frequencies of resistance. Further, new resistant populations continue to be discovered across South Australia, including the South East, Mid-North, and Eyre Peninsula regions.
Limited chemical control options for resistant bluegreen aphid in lentils
Whilst sulfoxaflor (Transform) is registered for use on bluegreen aphid in lucerne and some pulse crops, the discovery of resistance in bluegreen aphid to all key insecticide groups used in lentil crops, leaves growers with limited chemical options.
The overall effectiveness of carbamates, organophosphates, and pyrethroids is becoming increasingly inconsistent. For growers who’ve relied primarily on these chemicals for aphid control, this is a serious challenge.
Movento® (spirotetramat) was previously approved under an emergency permit (PERMIT NUMBER – PER93824) following the discovery of insecticide-resistant bluegreen aphid in lentil crops in South Australia in 2023, but the jurisdiction of this permit is limited to this state.
While there are still some susceptible aphid populations in south-eastern Australia, meaning chemicals may still provide adequate control, the trend is clear; insecticide resistance is a growing problem, and will continue to be an issue in the future.
Alternative approaches
Managing bluegreen aphid requires a proactive and integrated approach to limit damage and to maintain the effectiveness of pest control strategies.
One effective cultural control strategy is to manage green bridges before sowing. Pests persist between growing seasons in weeds and volunteer plants, so controlling them reduces the chance of future outbreaks.
Using bluegreen aphid-resistant cultivars in high-risk areas or seasons is another key strategy.
During spring and autumn, monitor crops closely, noting that other aphid species such as pea aphid (Acyrthosiphon pisum), spotted alfalfa aphid/spotted clover aphid (Therioaphis trifolii), cowpea aphid (Aphis craccivora) and faba bean aphid (Megoura crassicauda) may also be present in the same crops as bluegreen aphid. Differentiating them from bluegreen aphids can be a challenge —particularly from pea aphid – but is a key step in identifying what chemicals will be most effective when managing an aphid outbreak.
To ensure you’re addressing the correct pest, consult the GRDC crop aphids back pocket guide, or in samples to us here at Pestfacts- we’re here to provide accurate identification and help you make informed control decisions.
If bluegreen aphid populations approach or exceed action thresholds, consider the role of beneficial insects in your crop, which can often manage aphid populations effectively.
One key player is Aphidius ervi, a tiny parasitoid wasp that can parasitise over 300 aphids in her lifetime. Already available commercially, we’ve also found high levels of natural parasitism across 25 locations in South Australia, NSW, and Victoria, in crops like clover, lucerne, vetch, and lentils. It’s worth checking parasitoid activity by sweep netting or looking for aphid mummies (parasitised aphids). If the beneficials are thriving, consider holding off on spraying.
Generalist predators such as ladybird beetles and lacewings contribute to natural pest control. But beneficials are highly sensitive to broad-spectrum chemicals like organophosphates and pyrethroids. For more information, check out the beneficial chemical toxicity table.
When chemical control is necessary, the best practice is to alternate between different modes of action. This approach helps to minimise the risk of resistance evolution. Relying too heavily on chemicals like organophosphates, carbamates, and pyrethroids, can exacerbate resistance evolution. Growers are strongly encouraged to reduce the use of these chemicals.
Help develop better management recommendations
Information on how to collect and post aphid samples is outlined in the aphid collection guidelines, or please contact Evatt Chirgwin (email: echirgwin@cesaraustralia.com, phone: 0487292556).
Acknowledgements
The research informing this article has been funded by AgriFutures Australia and the GRDC. Cesar Australia is conducting this research in collaboration with Lucerne Australia. We thank the growers and agronomists who assisted with sample collections and chemical history information, and Dr Evatt Chirgwin, who leads the bluegreen aphid research projects.
Cover image: Photo by Evatt Chirgwin, Cesar Australia
