Insecticide resistance in fall armyworm (FAW) remains at low levels in central and northern Queensland grain growing regions, but experts warn that ongoing vigilance is key to maintaining efficacy and control.

This has been a key finding from a GRDC investment with New South Wales Department of Primary Industries and Regional Development (NSW DPIRD) in collaboration with the Department of Primary Industries Queensland (DPIQ) focusing on insecticide resistance surveillance in FAW and Helicoverpa armigera.

FAW, a serious pest of cereals and pulses, was detected in Australia in February 2020 and has since established populations in northern areas of Queensland, the Northern Territory and Western Australia. Seasonal outbreaks have also impacted some growing regions of northern NSW.

Dr Lisa Bird with fall armyworm samples at the Tamworth laboratory. Photo: NSW DPIRD

NSW DPIRD Senior Research Scientist Dr Lisa Bird said the resistance surveillance work had a strong focus on the cropping regions of central and northern Queensland where there was a high risk of FAW incursions.

“FAW is a tropical pest, so it is exposed to a lot of selection pressure from insecticide use in those areas,” she said.

“Our collaboration with researchers from DPIQ provides essential field capacity for collecting and sending samples from northern regions to the testing laboratory in Tamworth.

“Our aim is to track any changes in insecticide resistance frequency so we can extend those messages back to industry in a timely manner to raise awareness of potential resistance outbreaks and provide information to help maximise the effectiveness of spray applications.

Dr Bird said it was ‘fantastic news’ that there had been no changes in resistance since the discovery of FAW in Australia, particularly given its strong track record of developing insecticide resistance overseas.

Global reliance on chemical control of FAW has resulted in resistance to at least 29 insecticide active ingredients in six mode-of-action groups.

“We use an F2 screening method in our resistance testing, which enables us to pre-emptively detect resistance at very low frequencies,” she said.

“It also enables us to detect recessive resistance genes which can lie dormant in populations. In other words, we have the capacity to identify and predict resistance risks before spray failures occur in the field.

“This proactive approach delivers an early warning systems to industry and growers so they have the opportunity to adapt their chemical control strategies to minimise impacts on productivity.”

FAW can be an extremely challenging pest to manage with insecticides due to the frequency of egg lays and concealed feeding sites of larvae (in the whorl, silks and cobs of maize), rendering chemical control only partially effective.

Registered or permitted insecticides that currently provide effective control of FAW include Group 5 products with spinosyns as the active ingredient, Group 28 products containing chlorantraniliprole, cyantraniliprole and tetraniliprole, Group 6 products containing emamectin benzoate and Group 22A products containing indoxacarb.

Dr Bird said Australian growers were fortunate to have access to highly efficacious products but should not take that for granted.

“Like any pesticides, we need to think about sustainable practices so we can retain access to those products,” she said.

Dr Bird has published a ‘Top Tips for Management of FAW’ resource on the NSW DPIRD website.

It advises growers to approach control of FAW with an integrated pest management (IPM) focus and to take advantage of natural enemies in crops. This involves making spray decisions that conserve beneficial insects that help to suppress FAW in crops.

In addition, it also advises growers to know which products are not effective on FAW. For example, FAW is resistant to synthetic pyrethroids such as alpha-cypermethrin. Growers are advised to avoid these products because they will not control FAW and will destroy naturally occurring beneficial insects in crops.

“Overuse of selective insecticides will increase resistance levels in FAW and Helicoverpa armigera, which is another important pest of grain crops,” Dr Bird said.

“Growers should use a planned approach to insecticide selection and chemical rotation in maize and sorghum to maximise the effectiveness of applications and minimise resistance risk.”

Dr Bird said there were increasing instances of resistance in a related species – cluster caterpillar or Spodoptera litura – which is a significant pest in coastal pulse growing regions.

“We are starting to see changes in sensitivity to some insecticides in S. litura which has resulted in variable levels of control across the northern tropics,” she said.

“This is a scenario we want to avoid with FAW. A continued program of F2 screening will be important for identifying any emerging issues early, well before field failures of insecticides occur”.

Resistance testing is available in 2024-25 for FAW and H. armigera.

Growers who experience a control failure or suspect resistance should contact the NSW DPIRD insecticide resistance team at Tamworth for instructions on how to submit samples for testing.

Resistance surveillance for sustainable management of Helicoverpa and fall armyworm in grains is a co-investment with the Cotton Research and Development Corporation.

Further resources on FAW are available via the GRDC website.