The need for an integrated strategy to control blue-green aphids has been heightened by the discovery of new pesticide-resistant populations in lentil crops in Victoria’s Wimmera and Mallee regions.

Recent research led by Dr Evatt Chirgwin (Cesar Australia) found new resistant populations in these important pulse-growing regions after previous testing showed no resistance there – indicating this is a recent development.

The Wimmera and Mallee populations have now been found to be resistant to all major insecticide groups registered for lentil crops in Victoria, including carbamates (1A), organophosphates (1B) and pyrethroids (3A). Although resistance to carbamates (for example, pirimicarb) is weaker, it still presents a challenge for control.

While the majority of aphid populations in south-eastern Australia remain susceptible to these chemicals, the increasing incidence of insecticide resistance is of growing concern for pest management.

Blue-green aphids (Acyrthosiphon kondoi) are common pests of pulses and pastures, damaging plants through feeding and transmitting plant viruses.

Insecticides

Insecticides have long been used to keep  blue-green aphids in check, but some no longer provide reliable control.

Cesar Australia and Lucerne Australia first found blue-green aphids resistant to carbamates, organophosphates and synthetic pyrethroids in South Australia and New South Wales in 2021.

By 2022, resistance had spread to Victoria and the Eyre Peninsula, SA, with further detections in NSW. What began as a challenge in lucerne and forage crops expanded, with resistant blue-green aphids next detected in lentils and subclover in SA in 2023.

By 2024, insecticide-resistant blue-green aphids were in multiple Victorian lentil crops, raising concerns for ongoing management.

Figure 1: Locations of insecticide-susceptible and insecticide-resistant blue-green aphids in south-eastern Australia, as of 2024.

Source: Evatt Chirgwin, Cesar Australia

Figure 2: Locations where Aphidius ervi has been found parasitising blue-green aphid.

Source: Evatt Chirgwin, Cesar Australia

Alternative approaches

Effective management of blue-green aphids requires a proactive, integrated strategy to minimise damage and preserve pest control efficacy.

Key strategies include managing the green bridge over summer months to reduce pest prevalence in weeds and crop volunteers,  and using aphid-resistant crop cultivars  where available.

Growers are encouraged to monitor crops in spring and apply economic thresholds to guide control decisions.

Accurate aphid identification is a key step in selecting effective products. It is also important to remember that other aphids, such as the pea aphid (Acyrthosiphon pisum), often co-occur with blue-green aphids. But unlike blue-green aphids, pea aphids do not have insecticide resistance in Australia. Identification guides for both species can be found on the Cesar Australia website.

One way to help keep blue-green aphid populations below economic thresholds is to facilitate the presence of beneficial insects. For example, the parasitoid wasp Aphidius ervi has been found parasitising blue-green aphid populations across southern Australia and in multiple crop types.

Monitoring the abundance of parasitoids and other common predators (for example, lacewings, hoverflies and ladybeetles) alongside aphid numbers can help determine whether spraying is needed.

The Cesar Australia website offers identification guides for beneficial insect species and the chemicals least likely to harm them.

When chemical control is necessary, rotating between modes of action is  crucial to minimise the likelihood of resistance evolving in new populations. An over-reliance on a small number of insecticides will increase the possibility  of insecticide resistance developing.

More information: Cesar Australia

Acknowledgements: The research informing this article has been supported by AgriFutures Australia and GRDC. Cesar Australia is conducting this research in collaboration with Lucerne Australia.