With insecticide resistance on the rise, it is important for the Australian agricultural industry to keep up-to-date on current trends and management practices to best respond to resistance risks, Dr Lizzy Lowe* writes.
In grains and pasture-based systems, reliance on a select number of chemical options for management of key insect pests has created strong selection pressure that drives the evolution of resistance. There are now dozens of agricultural pests with documented resistance in Australia. This includes major pests such as the cotton bollworm (Helicoverpa armigera), diamondback moth (Plutella xylostella), green peach aphid (Myzus persicae) and red legged earth mite (Halotydeus destructor).
The evolution of resistance in pest species not only reduces the number of effective insecticide options available, but it also places additional selection pressure on the remaining chemical actives as growers are forced to utilise these alternative insecticides more regularly. In this article we will look at insecticide resistance in two aphid grain pests as an example of the ongoing challenges of resistance in pest management.
Green peach aphid is widespread across Australia and is damaging to a range of horticultural and broadacre crops. It has a very wide host range, including oilseeds, lupins, pulse crops, broadleaf weeds and some broadleaf pastures. They are also common in many horticultural crops including crucifer vegetables. The broad geographic distribution and host range, as well as the resistance to numerous chemical mode of action groups, makes green peach aphid an ongoing management challenge.
Populations of green peach aphid in Australia are known to have evolved high-level resistance to synthetic pyrethroids and carbamates, and low-level resistance to organophosphates and neonicotinoids. The problem is widespread, with resistance to all four of these chemical groups detected in populations in Western Australia, South Australia, Victoria, NSW, Tasmania and Queensland.
In addition to these existing resistances, recently low-level resistance to sulfoxaflor (Transform) has evolved in some field populations in Western Australia and new research has found populations of green peach aphid with resistance to spirotetramat (Movento) in Queensland vegetable crops.
These findings are noteworthy because neither spirotetramat nor sulfoxaflor resistance have been found in green peach aphids anywhere else in the world, despite being widely used to manage this pest in a range of crops in other countries.
The bluegreen aphid (Acyrthosiphon kondoi) is a pest of lucerne, lupins, medics, clovers, and pastures. It feeds directly on the foliage, damaging the plant and spreading harmful viruses through infected crops.
Farmers have access to a limited range of insecticides to control bluegreen aphid populations, but up until now these have been effective at protecting crops from damage. However, recently some bluegreen aphid populations in South Australia and NSW have evolved insecticide resistance.
Although the full status of resistance in the field remains unclear, multiple populations of bluegreen aphids have been detected with resistance to organophosphates (omethoate and chlorpyrifos), carbamates (pirimicarb), and pyrethroids.
These field populations were collected in 2020 and 2021 after farmers reported chemical control failures. This resistance in bluegreen aphid is thought to be the first of its kind in this species. Cesar Australia is undertaking new research to map the spread of insecticide-resistant bluegreen aphids across Australia, which will allow us to provide regional-specific recommendations on this new resistance issue.
The rise in insecticide resistance in crop aphids means extra consideration should be given to how these pests are managed in the future. For a species like green peach aphid, which has a high propensity to evolve new resistances, this means only spraying insecticides when absolutely needed and rotating insecticides from different mode of action groups in those instances where multiple sprays are required in a single season.
If spraying, high water volumes, correct nozzle selection and appropriate ground speeds will help to ensure the chemical gives the expected efficacy. It is critical that the full label rate is used, as lower rates will often be insufficient and increase selection pressure for further resistance.
It is possible to reduce damage by selecting cultivars that are more resistant to aphid feeding damage and controlling weeds around crops during summer and early autumn to remove alternate aphid hosts between growing seasons. Management should also be supported via regular monitoring in crops during vulnerable growth stages.
Natural enemies, including ladybird beetles, parasitoid wasps, hoverflies, and lacewings, can be very effective at supressing aphid populations. Therefore, if chemical management is required, it’s best to choose chemicals which are less toxic to these beneficial insects. More information can be found in the grains beneficials chemical toxicity table on the Cesar Australia website.
Understanding the distribution of insecticide resistance in aphid pests is important to ensure farmers can make informed chemical application decisions regarding their local resistance risks and reduce the likelihood of control failures. Growers who experience control failures with green peach aphids or bluegreen aphids are encouraged to contact Cesar Australia for free resistance testing.
Acknowledgements:
Our research into bluegreen aphids has been undertaken in conjunction with Lucerne Australia, CSIRO and The University of Melbourne, with financial support from AgriFutures and GRDC. Our research into green peach aphids has been undertaken in conjunction with CSIRO and the University of Exeter (UK), with financial support from GRDC, Bayer CropScience, Corteva Agriscience, ISK and BASF. We would like to thank all the farmers and advisors who have provided samples for resistance testing.
*Dr Lizzy Lowe is extension lead at Cesar Australia.
