RESEARCH supported by the Grains Research and Development Corporation (GRDC) will lead to a better understanding of how pesticide resistance in redlegged earth mites (RLEM) spreads.
The Department of Agriculture and Food Western Australia (DAFWA) recently announced that four new farms in WA have confirmed populations of RLEM resistant to synthetic pyrethroid (SP) chemicals, including bifenthrin and alpha-cypermethrin.
A total of 12 WA farm properties, mostly between Esperance and Cranbrook and one at Boyup Brook, now contain RLEMs confirmed to be resistant to SPs.
DAFWA entomologist Svetlana Micic is conducting research into RLEM resistance in collaboration with Paul Umina from the Centre for Environmental Stress and Adaptation Research (CESAR) at The University of Melbourne.
“The research into RLEM resistance is an important investment for the GRDC, which is looking to provide answers to farmers into best practice management options for RLEM,” Ms Micic said.
She said that while many of the SP resistant RLEM populations in WA were believed to have developed independently, more information was needed on how far resistant populations could spread.
“I am collecting mites from points surrounding known ‘source points’ of resistant mites to find out how far the resistant populations can spread,” Ms Micic said.
“I will survey locations at various distances from the source points and RLEM collected from these locations will be screened by CESAR for resistance.”
Dr Umina said some populations of mites were up to 240,000 times more resistant to SPs than mites from nearby properties.
“Importantly, this resistance has been demonstrated to have a genetic basis, meaning it can be passed on to future generations of RLEM and threatens to become a long-term problem,” he said.
“In recent years the increased usage and reliance on low cost insecticides has accelerated the selection pressure placed on pest populations.”
Ms Micic urged growers to control weeds along fencelines and within paddocks to help minimise the numbers of RLEMs, which feed on many common weeds.
“Unsprayed and undergrazed pastures in spring are known to be favourable sites where RLEM can produce populations of more than 50,000 mites per square metre, while adjoining crop situations, where weeds have been sprayed, can support numbers less than 1000 per square metre,” she said.
Ms Micic said growers should also rotate chemicals to minimise the risk of resistance developing and limit ‘insurance’ or prophylactic spraying unless there is a genuine risk of pest problems.
“Repeated applications of one type of insecticide provide intense selective pressure for insects to develop resistance,” she said.
In addition to RLEM research work being conducted on WA farm properties, populations of RLEM will be screened in eastern Australia.
The RLEM research is being conducted in conjunction with other GRDC funded research in WA comparing an integrated pest management (IPM) approach to pest management with conventional pesticide usage.