Insecticide Resistance

Staying Ahead of the Curve: Understanding Insecticide Resistance in Green Peach Aphids

The idea of trying to predict the future is something that conjures up more images of oracles, crystal balls, and witches, rather than scientists in lab coats. But scientific research, especially with the aid of modern technology, often investigates what could happen in the future based on what we know to be happening now. Think ‘climate modelling’, for example – using current data to forecast future conditions.

When it comes to invertebrate pests in cropping systems and the growing issue of insecticide resistance, understanding how to best manage pests into the future, including which chemicals are likely to continue to work long-term, is hugely beneficial.

This forward-thinking approach inspired one of the recent projects conducted by research entomologists at Cesar Australia, investigating resistance evolution in green peach aphids (Myzus persicae).

The study

Researchers Marielle Babineau and Lisa Kirkland carried out a two-year study to better understand the risk of green peach aphid evolving resistance to two relatively new insecticides on the market in Australia: flonicamid (MainMan® 500 WG) and afidopyropen (Versys® 100 DC) .

The green peach aphid is notorious for evolving resistance to insecticides, with over 80 chemicals worldwide that are no longer as effective at controlling them.

This feat is even more concerning when you consider that the vast majority of green peach aphid populations worldwide, including Australia, are asexual. That is, their reproduction doesn’t involve the mixing of genes between parents, which can speed up the evolution of adaptive traits. Rather, the development of resistance in green peach aphid is heavily reliant on novel genetic mutations which just happen to allow the population to better handle exposure to a chemical. 

Knowing this, Babineau and Kirkland designed an experiment aimed at encouraging several colonies of green peach aphid to evolve resistance to flonicamid and afidopyropen. The goal was twofold: (1) to see how easily resistance could evolve, and (2) if a resistant population did emerge, to characterise the mechanism of resistance so that resistance management strategies could be adapted.

Aphid colonies on bok choi in our controlled-temperature room. Courtesy of Lisa Kirkland.

The experiment was set up to artificially ‘select’ for traits that allow the aphids to better tolerate exposure to the two chemicals. This was done by regularly exposing aphid colonies to flonicamid or afidopyropen, in the form of foliar sprays, every second generation (roughly every four weeks) between February 2022 and October 2023.

The green peach aphid colonies were made up of a mix of five genetic clones which are prevalent in Australian grains regions, in order to increase the chances of finding a clone that could evolve resistance.

Every ten generations, the colonies’ responses to flonicamid and afidopyropen were tested by conducting a laboratory bioassay where aphids were exposed to a range of chemical doses, and their survival rates assessed. This allowed the researchers to understand how sensitive the aphids were to the chemicals at that time.

Green peach aphids on bioassay dishes. Courtesy of Lisa Kirkland.

By comparing the colonies’ responses over time, as well as by comparing the ‘selected’ colonies to ‘unselected’ colonies (which were not exposed to insecticides), researchers could observe in real time whether there was any evidence for resistance evolving. 

Key discovery

Surprisingly, despite green peach aphid’s track record of evolving resistance, and despite considerable efforts to push their limits, Babineau and Kirkland were unable to artificially create a colony resistant to either flonicamid or afidopyropen. 

Practical takeaways for pest management

This is promising news for the longevity of these chemicals’ efficacy in Australian crops, but these findings need to be taken with caution. The inability to create a resistant colony does not indicate that resistance to flonicamid and afidopyropen cannot or will not evolve in the future.

The study was unable to test all Australian clones of green peach aphid, and the number of individuals in the laboratory colonies were a mere fraction compared to field populations.

However, the results suggest a lower likelihood of resistance to these chemicals evolving quickly in areas with low genetic diversity. 

Slowing the evolution of insecticide resistance is best tackled by employing control tactics beyond just chemicals. If insects aren’t exposed to chemicals, there’s no reason for resistance traits to persist. This might include releasing beneficial insects and letting nature take its course, or removing weeds that act as a ‘green bridge’ between seasons.

If chemical use is warranted, rotating chemical groups is key to staying one step ahead of resistance. Additionally, selecting a chemical (such as afidopyropen and flonicamid) that are softer on beneficial insects can be win-win!

If you’re interested in ways to slow resistance in green peach aphid on your farm, keep an eye out for an updated resistance management strategy coming soon.


This study was performed by Lisa Kirkland, Marielle Babineau, Samantha Ward, Anthony van Rooyen, Evatt Chirgwin, Luis Mata and Paul Umina. This work was supported through investments from the Grains Research and Development Corporation, ISK Biosciences and BASF Crop Solutions Australia. The published paper reporting this work in full can be found at:

Cover image: Photo by Andrew Weeks, Cesar Australia

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