Stephanie Ann Veskoukis 
New research has found insecticide-resistant bluegreen aphids in more crop types than previously reported and has uncovered key information on the biocontrol options for this pest.
Growers and agronomists of lucerne, medics, clovers, lupins, vetch, lentils and faba bean pastures and crops are urged to stay up to date with resistance status and management options for bluegreen aphids.
In this article, we’ll cover where and what crop types resistant populations have been found in, what naturally occurring predators can help control them, and how you can help improve regional recommendations by posting in bluegreen aphid samples for free resistance testing.
Newfound resistance
In 2021, Cesar Australia and Lucerne Australia discovered the first international cases of bluegreen aphid (Acyrthosiphon kondoi) evolving resistance to the insecticides registered and regularly used to control them (carbamates, organophosphates, and pyrethroids). More information on our preceding research can be found here.
Following investments from AgriFutures Australia and the GRDC, we are continuing to investigate the crop types and locations that insecticide-resistant bluegreen aphid populations have spread to.
Insecticide-resistant bluegreen aphid populations have now been found at 12 locations across Victoria, South Australia, and New South Wales. So far, insecticide-resistant populations have been most common in South Australia, where 8 resistant populations have been discovered. Only one of the five populations tested in Victoria have shown resistance.
Not only a lucerne issue
Previously, insecticide-resistant bluegreen aphids had only been detected in lucerne seed and forage crops. However, our recent work discovered resistant bluegreen aphids in two crop types for the first time: lentils and sub-clover.
This is the first confirmation of resistance in other crop types.
Accordingly, growers of all crops prone to bluegreen aphid attacks should be vigilant and aware that the chemical control options registered for bluegreen aphids differ across crop types (see management advice below).
Positive takeaways and activities on the horizon
While the discovery of new insecticide-resistant bluegreen aphid populations is concerning, some reassuring patterns have also emerged from our research.
New susceptible populations have also been found, indicating the resistant strain (or strains) of bluegreen aphids have not become completely dominant across southern Australia. Therefore, in some regions, organophosphates and carbamates may still provide effective bluegreen aphid control.
The magnitude of resistance has not increased in the newly collected populations compared to previous ones, indicating that bluegreen aphid populations have not evolved a higher level of resistance to any of the chemicals tested, yet.
Spring will see us conducting more surveillance, and more resistance tests (also known as bioassays).
So if I find bluegreen aphids, what are my options?
Most prominent during spring, bluegreen aphids feed on the upper leaves, stems and terminal buds of host plants. They are often confused with green peach aphids or pea aphids, but can be distinguished by their long antennae, very long siphunculi, and lack of black markings on the knee joints (seen in pea aphids).
If upon monitoring, you find that bluegreen aphid populations are approaching or exceeding action thresholds, consider the beneficials present in your crop (more details below) prior to chemical control.
If chemical control is needed, alternating modes of action and using selective chemistry continues to be the best way to prevent resistance evolution. Sulfoxaflor (Transform) is registered for use on bluegreen aphid in lucerne and some pulse crops. Flonicamid (MainMan) is under a limited emergency permit to control insecticide resistant bluegreen aphid in the later stages of lucerne seed production.
An emergency use permit for spirotetramat (e.g. Movento) has also been approved for bluegreen aphid control in South Australian lentil crops.
If you’re unsure about which aphids you have in a crop, and would like support with pest identification please send through a PestFacts report or some sample specimens, and one of our entomologists will confirm the species for you.
New biocontrol research
Biocontrol can be effective at suppressing aphid populations and will help lessen the risk of further insecticide resistance evolving in the future.
Growers and agronomists are increasingly harnessing naturally occurring predators (i.e., natural enemies) of pests as a key component of their pest management strategies. However, controlling bluegreen aphids with natural enemies has some challenges, because besides generalist aphid predators (e.g., ladybugs & lacewings) limited information is available on which naturally occurring species attack bluegreen aphids.
Cesar Australia and Lucerne Australia are investigating one of the most effective and widespread groups of natural enemies of aphids – parasitoid wasps. Parasitoid wasps deposit their eggs inside living aphids, which then hatch and eat their aphid hosts from the inside out: forming aphid mummies. When the wasp is fully developed, it emerges through the aphid shell, and flies off to repeat the cycle.
The project has now collected bluegreen aphid mummies in 9 locations across SA, VIC and NSW. Samples were collected from clover, lucerne, vetch and lentil crops. Surprisingly, the wasps that have been reared, collected and identified from the bluegreen aphid mummies have all been one species of parasitoid wasp: Aphidius ervi.
Aphidius ervi is a common parasitoid species across southern and eastern Australia, and are known to parasitise other aphid pests of pasture seed crops (like the pea aphid). Each female wasp can parasitise over 300 aphids in her 2-3 week lifetime.
Although further data is needed, these preliminary results indicate a possible lack of diversity in bluegreen aphid parasitoids. This result differs to other Australian grain aphids, which are usually parasitised by multiple species (often > 4) of parasitoid wasp.
If this lack of parasitoid diversity is also observed in future collections, management methods – particularly chemical usage – may need to be carefully planned to support A.ervi in crops and seasons where bluegreen aphid outbreaks are most likely.
Help develop better management recommendations
Post us your bluegreen aphids for free resistance testing this spring!
We are continuing to collect and test new bluegreen aphid populations for insecticide resistance. To ensure we are testing from the most diverse and industry-relevant regions, we need the help of growers and agronomists.
If you encounter any bluegreen aphids, whether you suspect they’re resistant or not, sending in samples would support this work and allow us to gain a better understanding of how resistance is evolving over time.
Your help will allow us to provide regional and crop specific recommendations for bluegreen aphid control and help mitigate the risk of future resistance.
Information on how to collect and post aphid samples are outlined in the aphid collection guidelines.
For information on collecting and posting samples, please contact Dr Evatt Chirgwin (email: echirgwin@cesaraustralia.com or phone: 0487292556).
Acknowledgements
The research informing this article has been funded by AgriFutures Australia and the GRDC. Cesar Australia are 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 SARDI
