Insecticide resistance increasing in aphids

Photo of green peach aphids

Insecticide resistance among green peach
aphids is under investigation. Population
screening has shown resistance is
increasing to all three chemical groups
used to control the pest.

PHOTO: CESAR

Recent GRDC-funded research has uncovered widespread resistance among green peach aphid populations to pirimicarb, synthetic pyrethroids and organophosphates in Victoria, South Australia, New South Wales, Queensland and Western Australia. 

Scientists, led by the research company cesar, have been investigating green peach aphid insecticide resistance in cropping regions over the past 12 months. The confirmation of widespread resistance to pirimicarb is particularly concerning for pulse and oilseed growers because this chemical has been a fallback for aphid populations resistant to other chemical groups. 

Pirimicarb is aphid-specific and less harmful to other invertebrates when applied to crops, so is compatible with an integrated pest management (IPM) approach. 

In 2010, the first documented case of resistance to pirimicarb in Australia was identified in a green peach aphid population from WA. 

This was the first confirmed instance of green peach aphid resistance to carbamates in Australia, although tolerance to pirimicarb was identified some years previously by state agricultural entomologists in WA and in other states. 

The current research team screened 36 populations over an area spanning more than 1700 kilometres across eastern Australia and an area of 800km in WA.

Key points
  • Insecticide resistance in populations
    of green peach aphid has increased
    in Australia
  • Green peach aphid is a pest of canola
    and some pulse crops
  • To reduce the risk of further resistance
    problems avoid the use of
    ‘insurance sprays’
  • Apply insecticides only after careful
    monitoring and correct identification of
    pest species

Dr Paul Umina of cesar says that of the 27 populations tested in eastern Australia, 13 showed high resistance to synthetic pyrethroids, indicating resistance to this chemical group has become more common over the past five to 10 years.

Organophosphate resistance, observed in Australia for many years, has also been identified in populations across all states.

“Most alarming was the discovery that 11 populations in eastern Australia were resistant to pirimicarb,” he says.

Green peach aphid resistance to insecticides has been known overseas for some time, but the widespread resurgence of resistance to all three chemistries is something that has increased only recently.

Dr Umina says the levels of resistance identified were far greater than what was anticipated. “In some populations, aphids exhibited more than 10,000 times the resistance to synthetic pyrethroids than the control populations.”

In WA, pirimicarb resistance has been found to be widespread across vegetable-growing areas in the south west. 

Department of Agriculture and Food, WA (DAFWA), PestFax coordinator Peter Mangano says grain growers have experienced significant issues with resistance in green peach aphid this season. 

There have been almost 20 reported chemical control failures involving green peach aphid across the year, mostly in seedling and establishing canola crops. 

Mr Mangano says green peach aphid damage has been most noticeable in isolated patches within crops where high densities of the aphids have been found on the undersides of leaves. 

These patches have generally increased in size with time, resulting in thinned and stunted plant growth and in many cases bare patches within crops. Monitoring green peach aphid populations and reducing ‘insurance sprays’ will help to prolong the lifespan of insecticides used to control green peach aphid.

Ongoing work

Damaging viruses

Aphids damage crop plants through their
feeding activities, as well as from viruses
they transmit.The green peach aphid is
an economically damaging crop pest and
carries several viruses such as cucumber
mosaic virus, bean yellow mosaic virus
and beet western yellows virus (BWYV).
The combination of aphid feeding and
BWYV alone can result in yield losses
of up to 50 per cent in canola.

The next research steps will be to understand if individual aphids have resistance to all three chemistries and to explore the genetic makeup of green peach aphid populations.

Dr Umina says: “If we discover that individual aphids have resistance to organophosphates, synthetic pyrethroids and carbamates, it will mean the likely reproduction of fully resistant offspring, as green peach aphids can reproduce asexually to produce clones of themselves. This will have significant implications for the ability of growers to control green peach aphid in crops.”

The work, conducted in conjunction with CSIRO, the South Australian Research and Development Institute, the NSW Department of Primary Industries, the Department of Agriculture, Fisheries and Forestry Queensland and DAFWA, is screening other species of crop aphids as well. 

Monitor and report

Growers are encouraged to keep an eye out for any control difficulties when applying chemicals as per label instructions, and to rotate insecticide classes to prevent resistance from developing further. 

If you have crop aphids that survive registered rates of pesticide treatments or suspect that you have resistant green peach aphids, contact Dr Paul Umina or CSIRO’s Dr Owain Edwards.

More information:

Dr Paul Umina
03 9349 4723,
pumina@cesaraustralia.com

Dr Owain Edwards
08 9333 6401,
owain.edwards@csiro.au

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GRDC Project Code CES00001

Region North, West, South