Understanding the magnitude and spread of insecticide resistance in bluegreen aphids (Acyrthosiphon kondoi)

Take home messages

  • The bluegreen aphid (BGA; Acyrthosiphon kondoi) is a widespread pest of lucerne, pastures and grain legumes.
  • Reports from growers and preliminary research suggest some field populations of BGA could be evolving resistance to current insecticides registered for BGA control in Australia.
  • Research is underway to determine if control failures following insecticide applications targeting BGA is due to insecticide resistance.
  • If BGA has evolved insecticide resistance, growers will require new management strategies to be developed so they can confidently protect their crops from this pest.

Background

Bluegreen aphids (BGA; Acyrthosiphon kondoi; Figure 1a) are widespread pests in Australian crops of lucerne, pastures, and grain legumes (Bailey 2007; Clouston et al. 2016; Edwards 2001). Typically, BGA are most abundant during spring, but they can also be problematic in autumn and winter (Figure 1b; Humphries et al. 2012; Lodge and Greenup 1980). BGA cause both direct and indirect damage to crops (Valenzuela and Hoffmann 2015). Direct damage to crops occurs through feeding – mostly on upper leaves, stems and terminal buds (Bailey 2007) – which removes essential nutrients from plants, causing stunted growth, leaf curling and leaf drop. BGA also indirectly damage crops in two ways. Firstly, BGA secrete honeydew on plants which can facilitate secondary fungal growth, ultimately inhibiting photosynthesis and decreasing plant growth (Bailey 2007). Secondly, BGA can spread plant viruses, including cucumber mosaic virus (CMV) and bean yellow mosaic virus (BYMV)(Garran and Gibbs 1982).

Figure 1. a) Bluegreen aphid adult (non-winged). Photo by Andrew Weeks, Cesar Australia. b) Lifecycle, critical monitoring and management periods for the bluegreen aphid.

Figure 1. a) Bluegreen aphid adult (non-winged). Photo by Andrew Weeks, Cesar Australia. b) Lifecycle, critical monitoring and management periods for the bluegreen aphid.

Results and discussion

In the past, growers have successfully protected their crops from BGA by spraying organophosphate and carbamate-based insecticides that efficiently control these aphids. However, over the last few years, we have received reports from multiple growers and agronomists in New South Wales and South Australia that have experienced poor control of BGA with these commonly used insecticides (Table 1). Our preliminary investigations suggest these populations may be evolving resistance to organophosphates, Chemical control failures can occur due to a number of reasons, for example spray application issues, low quality chemical and/or environmental reasons. Therefore, further research is required to confirm whether reported control failures are due to evolved insecticide resistance versus other factors.

Table 1: Recent reports of bluegreen aphid insecticide control failures.

State

Approximate location

Date first reported

Crop

Insecticides used

NSW

Forbes

Aug 2019

Clover

chlorpyrifos, omethoate, pirimicarb

NSW

Combaning

Jun 2020

Lucerne

omethoate

NSW

Canowindra

Oct 2020

Lucerne

chlorpyrifos, omethoate, pirimicarb

SA

Wanbi

Sep 2020

Lucerne

chlorpyrifos, omethoate

SA

Willalooka

Dec 2020

Lucerne

chlorpyrifos

SA

Keith

Jan 2021

Lucerne

chlorpyrifos, alpha-cypermethrin

SA

Laffer

Mar 2021

Lucerne

chlorpyrifos

SA

Jamestown

Nov 2021

Lucerne

omethoate

While the evolution of insecticide resistance is a reasonably common occurrence in some aphid pests (for example, green peach aphids; Myzus persicae), to our knowledge, insecticide resistance has not occurred in BGA previously. Therefore, these reports might constitute the first cases of resistance for BGA globally. We will commence a study in January 2022 (funded by AgriFutures) to quantify chemical tolerances and characterise target gene variation in field populations of BGA. Firstly, we will use laboratory-based bioassays to determine whether BGA populations from key cropping areas in NSW and SA have evolved resistance to organophosphate and carbamate-based insecticides. We will quantify how resistant these populations are by comparing their chemical tolerances to a susceptible BGA population. If these populations are resistant, we will then investigate the heritability of resistance (for example, does the resistance persist over multiple aphid generations). Additionally, we will characterise variation in the target gene, ace (acetylcholinesterase), to determine if any known resistance mutations have evolved in this gene. We will present preliminary results of our bioassays at the February GRDC Grains Research Update.

If our research confirms BGA populations have evolved insecticide resistance, developing updated BGA management approaches must be prioritised to ensure growers can protect their crops from future outbreaks. Such management approaches may involve the registration of new insecticides for BGA, new cultural and biological methods to help growers control BGA populations, and better guides to help monitor and identify BGA within lucerne and grain crops.

Conclusion

While confirmation is required, the anecdotal evidence suggests BGA populations may be evolving some level of resistance to insecticides. In turn, growers may lack a sustainable method of protecting their crops from BGA outbreaks into the future. Upcoming research will rigorously test whether resistance has evolved in BGA populations collected from NSW and SA. As such, we request any information that growers and agronomists can provide on experienced BGA control failures, including details on location, crop type, and insecticide usage.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support. We thank the many growers and agronomists, as well as SARDI, for freely providing information about chemical field failures involving BGA. Thanks also to those that have sent BGA samples to our laboratory for testing. AgriFutures has committed funding to explore BGA resistance in 2022.

Useful resources

Bluegreen aphid information and identification guides on pestnotes

References

Bailey PT (2007) 'Pests of field crops and pastures: identification and control.' (CSIRO Publishing: Melbourne)

Clouston A, Edwards O, Umina P (2016) An insecticide baseline study of Australian broadacre aphids. Crop and Pasture Science 67(2), 236-244.

Edwards O (2001) Interspecific and intraspecific variation in the performance of three aphid species on five-grain legume hosts. Entomologia Experimentalis et Applicata 100(1), 21-30.

Garran J, Gibbs A (1982) Studies on alfalfa mosaic virus and alfalfa aphids. Australian Journal of Agricultural Research 33, 657-664.

Humphries AW, Peck DM, Robinson SS, Rowe T, Oldach K (2012) A new biotype of bluegreen aphid (Acyrthosiphon kondoi Shinji) found in south-eastern Australia overcomes resistance in a broad range of pasture legumes. Crop and Pasture Science 63(9), 893-901.

Lodge GM, Greenup LR (1980) Seedling survival, yield and seed production of three species of annual medics exposed to lucerne aphids. Australian Journal of Experimental Agriculture and Animal Husbandry 20(105), 457-462.

Valenzuela I, Hoffmann AA (2015) Effects of aphid feeding and associated virus injury on grain crops in Australia. Austral Entomology 54(3), 292-305.

Bluegreen aphid information and identification guides on PestNotes

Contact Details

Paul Umina
95 Albert Street, Brunswick VIC 3056
0405 464 259
pumina@unimelb.edu.au
@cesaraustralia

Evatt Chirgwin
95 Albert Street, Brunswick VIC 3056
0487 292 556
echirgwin@cesaraustralia.com
@evattchirgwin

GRDC Project Code: CES2001-001RTX,