Early research to guide insecticide use for fall armyworm

image of fall armyworm
New research into fall armyworm’s (FAW) insecticide sensitivities will help guide grower and agronomist decision making in the paddock to effectively manage the rapidly spreading pest. Photo: Lyle Buss, University of Florida.

New results from research into fall armyworm’s (FAW) insecticide sensitivities and genetic make-up are set to help guide grower and agronomist decision making in the paddock to effectively manage the rapidly spreading pest.

FAW (Spodoptera frugiperda) is a highly migratory, invasive pest that was first reported in Australia in February 2020 and quickly established across parts of northern Australia’s tropical and sub-tropical regions, including northern Queensland, the Northern Territory, and parts of Western Australia (WA). It has now been detected in southern WA and New South Wales.

A comprehensive research project into FAW’s insecticide sensitivities and genetic make-up is being led by Australia’s national science agency CSIRO with co-investment by the Australian Centre for International Agricultural Research (ACIAR), Grains Research and Development Corporation (GRDC), Cotton Research and Development Corporation, FMC Australasia and Corteva Agriscience.

Early results released by the research partners indicate FAW in Australia currently shows no evidence of resistance to the important insecticides chlorantraniliprole, emamectin and spinetoram.

Independent studies by NSW Department of Primary Industries (NSW DPI) have confirmed these findings and resulted in diagnostic tests to increase capacity for detecting future changes in resistance to these important selective insecticides.

The preliminary CSIRO data on live FAW demonstrated significantly lower sensitivity (approx. 50 times less sensitive) to alpha-cypermethrin than the Helicoverpa armigera (H. armigera). Consistent with this, more detailed research conducted by NSW DPI shows strong evidence of widespread metabolic resistance to the two synthetic pyrethroids registered for FAW, alpha-cypermethrin and gamma-cyhalothrin. These findings indicate that synthetic pyrethroids are unlikely to control FAW in the field.

Genetic markers of resistance to Group One pesticides, organophosphates and carbamates, have also been detected in some FAW samples from WA and Queensland. Genetic analysis detected two copies of this known resistance mutation in approximately half of the individuals from Queensland and WA populations. Small reductions in sensitivity to methomyl observed in live FAW larvae as compared with H. armigera may be consistent with the presence of this mutation.

While these results don’t necessarily confirm widespread field resistance they highlight the need for careful management of Group One pesticides including to potentially slow the further selection of this mutation in the field.

Given the levels of resistance to broad-spectrum insecticides in FAW, growers should strongly consider avoiding these chemicals and instead opt for integrated pest management strategies to help optimise the cost of controlling FAW by taking advantage of natural enemies present in crops.

A common foliar Bacillus thuringiensis (Bt) kurstaki formulation was also assessed, with FAW up to 25 times less sensitive in the laboratory compared to H. armigera and cluster caterpillar (Spodoptera litura).

GRDC Biosecurity Manager Jeevan Khurana said improved understanding of FAW’s genetic make-up, insecticide sensitivities and current resistance status was critical to developing sustainable management strategies.

“FAW has developed resistance to commonly used insecticides in other parts of the world, making management difficult,” Dr Khurana said.

“This new knowledge will provide critical information to help guide insecticide use to reduce resistance risk. As always, growers are encouraged to judiciously select and rotate products to reduce selection pressure.”

Another key part of this research into FAW in Australia has been a genetic analysis of the similarities and differences in the populations found here compared with South-East Asian countries where samples were collected and analysed with the support of ACIAR.

“Analysis of the genetic make-up of Australian FAW has provided further evidence that the pest arrived via natural dispersal rather than any alternate pathway such as human-assisted routes involving trade or people movement,” Dr Khurana said.

“Historically, this insect pest has been classified as either rice-preferred or corn-preferred fall armyworm. However, strain typing of individuals in this study suggests that Australian FAW is a hybrid of the separate corn and rice strains described in the Americas.

“The confirmation and potential implications of this are still being explored by several groups here and around the world.”

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