Grower concerns trigger research into bluegreen aphid resistance to insecticides

Bluegreen aphids (Acyrthosiphon kondoi) are a major pest of lucerne and other legume crops. These tiny pests feed directly on the foliage, damaging the plant and spreading harmful viruses through infected crops. Currently, lucerne seed growers have access to a limited range of insecticides to control bluegreen aphid populations. During the past two years, several growers and agronomists in New South Wales and South Australia have reported that currently registered insecticide sprays are no longer effectively controlling bluegreen aphid populations.

Dr Evatt Chirgwin, Cesar Australia is leading the AgriFutures supported project on Understanding bluegreen aphid resistance in the pasture seeds industry. Dr Chirgwin is testing bluegreen aphid populations collected from key lucerne-growing regions in New South Wales and South Australia for signs of evolutionary resistance.

“Our previous investigations through collaborative research with CSIRO, and funded by the Grains Research and Development Corporation, suggest these field populations may have evolved resistance to insecticides,” said Dr Chirgwin.

“So far, results from this project strongly suggest that all three field-collected populations of bluegreen aphids have evolved resistance to organophosphates (omethoate and chlorpyrifos) and carbamates (pirimicarb). These field populations were collected in 2020 and 2021 after we received reports from producers of chemical control failures. We will now test for bluegreen aphid resistance to a third group of insecticides – pyrethroids.”

While the evolution of insecticide resistance is reasonably common in some species of crop pests, such as green peach aphids, the resistance reported in bluegreen aphids as part of this project appears to be the first of its kind in this species.

“To better understand the mechanism underlying insecticide resistance in bluegreen aphids, we are also undertaking some preliminary molecular work. To do so, we are exploring whether any shifts in the DNA of the bluegreen aphid samples collected from our three field populations differ to a reference population of bluegreen aphids, which we know remains susceptible to current chemical control options.”

“A better understanding of what molecular mechanisms create resistance in bluegreen aphid populations will help us determine the likelihood these populations will have cross-resistance to other insecticides with different modes of action.”

The project team is also keen to determine just how far resistance may have spread to get a clear understanding of the potential impact.

“We’d like to develop a ‘map of resistance’ so to speak, so we can better understand which regions are most at risk during the coming season,” said Dr Chirgwin.

Growers experiencing issues with bluegreen aphid control are encouraged to contact Cesar Australia to help with the development of this resistance map.

 

Recommendations based on science

The rapid response to industry concerns around emerging resistance is allowing the research team to gather the critical information required to formulate a plan for lucerne growers to better manage bluegreen aphids going forward.

“Based on the findings of our experiments, we will provide recommendations to AgriFutures Australia and Lucerne Australia for managing bluegreen aphids in the short term and identify any additional work required to solidify long-term control options,” said Dr Chirgwin.

Katrina Copping, Lucerne Australia’s Executive Officer, has highlighted the importance of investing in the science behind reports of resistance to any agricultural chemicals before making industry-wide management recommendations.

“Without confirmation regarding what is happening in the field we are flying blind —this is imperative to informing future management strategies for the industry,” said Katrina. “The results of this preliminary research will ensure future investment in bluegreen aphid control is well directed.”

Katrina believes the collaboration between AgriFutures Australia and Lucerne Australia is critical for the lucerne seed industry. “Bluegreen aphids can be a major issue for lucerne seed growers and if we cannot achieve adequate control, it can negatively impact yield,” she said.

Emergency use permit for MainMan® offers an alternative option

Since the preliminary research project started Lucerne Australia has sought an emergency use permit for MainMan® — a Group 29 insecticide registered for the control of aphids in other crops, including apples, pears, cotton, cucurbits, potatoes and canola.

“This emergency permit will provide growers with another option for this season until the full results from the project have been delivered,” said Katrina.

“The willingness of the Australian Pesticides and Veterinary Medicines Association to respond so quickly to our call for an emergency permit indicates the level of industry-wide concern regarding the lack of options to protect the industry against pests, such as bluegreen aphids.

“The lucerne seed industry is a relatively small player on the broader rural industries stage and there has been concern leading into this season. This will give growers confidence until we can better understand insecticide resistance and implement management strategies accordingly.”

In the meantime, Dr Chirgwin and the project team will continue their work to identify any evolutionary DNA changes occurring in the resistant aphid populations. They are also testing the impact of other potential insecticide options, which could assist with future aphid management.

“Our bioassays will be finalised in the next few weeks and the results will form the basis of our recommendations back to AgriFutures Australia and Lucerne Australia,” said Dr Chirgwin.

Emma Rodham, AgriFutures Australia Program Manager is working closely with Lucerne Australia and Cesar Australia to respond quickly to grower concerns.

“I really commend Lucerne Australia for the strong relationship with its members, which supports such a rapid and proactive response to a key industry issue,” she said.

“This preliminary research paves the way for ongoing investigations into bluegreen aphid resistance and control. These results come at a good time to allow the Program to continue our investment in bluegreen aphid research.  AgriFutures works with industry and with our research partners to identify and address such issues to ensure our industries remain viable and profitable. ”

“The AgriFutures Pasture Seeds Program’s Open Call is open now until 24 March; we encourage researchers to consider research needs in this space and across the pasture seeds industry and make a submission to the Open Call.”

To read more about the AgriFutures Pasture Seeds Program Open Call visit: AgriFutures Pasture Seeds – Open Call for Research 2022 | AgriFutures Australia

Dr Chirgwin will give an update on the team’s research at the upcoming Lucerne Australia Field Day on Wednesday, 2 March 2022 in Keith South Australia. Find out more and register: https://www.lucerneaustralia.org.au/event/new-upcoming-event/

Growers experiencing issues with bluegreen aphid control are encouraged to contact Dr Chirgwin via email on echirgwin@cesaraustralia.com

To read more about AgriFutures Pasture Seed Program, visit: www.agrifutures.com.au/rural-industries/pasture-seeds/