Samantha Ward A recent study spearheaded by Cesar Australia has unveiled an important discovery for pest management: the presence of low-level resistance to sulfoxaflor in green peach aphid (Myzus persicae) can be found across Australia.
This noteworthy finding represents an important development in understanding resistance evolution in the green peach aphid and raises questions about the potential implications for agricultural practices in the industry.
Pesticide Predicaments
Green peach aphid is a major troublemaker for farmers across Australia and can be a costly control consideration. It poses a serious threat to a variety of crops across broadacre and horticulture, impacting crop yield through both direct feeding and, most importantly, transmission of plant viruses.
To keep this pest in check, farmers often turn to insecticides. Commonly employed are broad-spectrum actives, including organophosphates, synthetic pyrethroids, carbamates, and neonicotinoids. These are typically applied during pre-emergence and establishment stages, when green peach aphids are most likely to cause trouble, as seedlings are susceptible to feeding damage and virus risks are elevated.
Here’s the problem, though: relying too much on chemical control has meant that the green peach aphid has become a champion at evolving resistance. In fact, it’s now one of the top 10 invertebrate species exhibiting insecticide resistance globally.
Insights into Sulfoxaflor
Sulfoxaflor was approved for use in 2013. Considered effective against green peach aphids, it serves as an important option when this pest exhibits resistance to other chemical treatments. Additionally, sulfoxaflor has become a crucial element in resistance management tactics, such as chemical rotations.
In 2018, the first case of low-level resistance to sulfoxaflor emerged in Western Australia (WA), following reported field failures which were linked to poor spray coverage and suspected rate cutting. This discovery prompted Cesar Australia, together with Corteva Agriscience and the GRDC, to assess the distribution and phenotypic levels of sulfoxaflor resistance in Australian green peach aphid populations.
The latest study from this project, led by Dr. Samantha Ward, revealed that sulfoxaflor resistance has persisted in the field, has become more widespread, and is now present in multiple populations across Australia.
Resistance Surge
Between 2019 and 2022, green peach aphid populations were gathered from major agricultural regions in Australia, predominantly from canola and horticultural crops. These populations underwent genotyping to identify their clonal types. (Now, clonal types might sound fancy, but it’s essentially understanding the unique genetic groups these aphids belong to).
Once the aphid genetics were known inside out, the resistance status to sulfoxaflor for each population was determined in the lab, where the chemical was directly applied at various concentrations to the aphids’ back using a tiny syringe.
Of the 35 populations tested, seven exhibited low-level resistance to sulfoxaflor, or around 20% of all samples. This is in addition to four populations identified with resistance previously from WA. Importantly, this work revealed sulfoxaflor resistance was widespread, being detected in Queensland, New South Wales, Victoria, and South Australia in addition to WA. In some cases, these resistant populations were separated by distances longer than a road trip from Perth to Melbourne (that’s more than 3000 km!)
Moreover, the study revealed resistance across two distinct clonal types, both prevalent throughout Australia and constituting the vast majority of green peach aphid populations collected in the last decade. This, along with the wide geographic range reached over such a short duration, points to the likelihood of resistance arising from both the movement of resistant individuals to new locations and new independent evolution events.
Fortunately, the majority of field populations tested in this study were found to be susceptible to sulfoxaflor. So, for now, sulfoxaflor is holding its ground and keeping crops safe in most situations. But to address the evolving challenges caused by resistance, it will be important to keep a close eye on the situation and be ready to change tactics.
Resisting Resistance
This discovery underscores the importance of being smart about how we use insecticides. Unfortunately, these green peach aphid populations with resistance to sulfoxaflor are also resistant to pyrethroids, organophosphates, carbamates, neonicotinoids, and some are also resistant to spirotetramat and other Group 23 chemicals. So, the challenge is – how do growers tackle these aphids without relying just on the usual chemical arsenal?
What really works is a well-thought-out plan. Opting for a comprehensive approach through integrated pest management (IPM) and resistance management strategies is the most effective way to protect crops in the long term and slow down or prevent the evolution of insecticide resistance. It’s time to steer clear of those “insurance” sprays. They might seem like a quick fix, but they’re not cutting it anymore.
Instead, focus on practices such as rotating insecticides, including sulfoxaflor, to prevent aphids from getting too comfortable with one mode of action; this will prolong the longevity of chemical control options available. Additionally, it is critical when using chemical options that application is optimised to ensure spray coverage adequately targeting the pest. If control failures occur, avoid respraying with the same mode of action. Avoid cutting rates at all costs! And wherever possible, avoid the use of broad-spectrum pesticides that wipe out everything, including beneficial insects. Finally, set some rules and employ thresholds to decide when it’s absolutely necessary to bring out the spray.
In a nutshell, it’s time to keep ahead of the game when it comes to resistance management and go for the smart, long term game plans using a mix of tactics such as chemical, cultural, and biological to keep crops safe.
When in doubt, always consult the Best Management Practice Guide and look out for the updated version of the green peach aphid resistance management strategy, which should be available shortly.
Support your beneficial insects by utilising the Beneficials Chemical Toxicity Table.
Acknowledgements
Thanks to Samantha Ward (Cesar), Paul Umina (Cesar) and Rob Annetts (Corteva) for reviewing the article.
This research was conducted by Cesar Australia and CSIRO scientists Samantha Ward, Tara Jalali, Anthony van Rooyen, Jenny Reidy-Crofts, Karyn Moore, Owain Edwards and Paul Umina. This research was undertaken as part of a Grains Research and Development Corporation investment, ‘Insecticide resistance in the green peach aphid: national surveillance, preparedness and implications for virus management (CES2001-001RTX)’ together with Corteva Agriscience.
The full study can be accessed at here.
For more information, contact Dr. Samantha Ward at sward@cesaraustralia.com.
Cover image: Green peach aphid, photo by Andrew Weeks
