Spray failures mite mean resistance

Author: Natalie Lee | Date: 01 May 2015

DAFWA is increasing its testing of mites for resistance to organophosphate insecticides, as well as for resistance to synthetic pyrethroids

Growers who notice any instances of insecticides failing to control redlegged earth mites (RLEM) this season are encouraged to arrange for the pests to be tested.

Given increasing levels of insecticide resistance in RLEM in Western Australia, growers are also urged to adopt integrated pest management tools including non-chemical control measures.

Department of Agriculture and Food (DAFWA) entomologist Svetlana Micic encouraged growers to notify her if they suspected RLEM had survived registered rates of insecticides, so arrangements could be made to have samples of mites tested for resistance.

Ms Micic conducts research into RLEM as part of a national project led by cesar, in collaboration with the University of Melbourne, CSIRO and The University of WA, funded by the Grains Research and Development Corporation (GRDC).

Over recent years, DAFWA has confirmed 49 WA properties as having RLEM resistant to synthetic pyrethroids (SPs).

Ms Micic said that as well as screening RLEM for resistance to SPs, DAFWA’s RLEM screening program would this year use more rates and insecticides from the organophosphate (OP) group (Group 1B), which includes dimethoate and omethoate.

“To date, growers with SP resistant RLEM have been able to control them using OP insecticides,” she said.

“But in 2014 a Capel property was found to have RLEM that survived both OP and SP insecticides, and subsequent testing by cesar showed these mites were 30 times more resistant to omethoate than a susceptible population.

“The Capel populations were found to be still susceptible to chlorpyrifos and other chemicals in the OP group, and will undergo further testing this year.”

Ms Micic said DAFWA had also observed increasing levels of omethoate tolerance in RLEM populations from other WA properties.

GRDC funded research has shown SP resistance in RLEM can be passed through generations, but it is not yet known if omethoate tolerance is heritable.

Ms Micic encouraged growers to consider integrated pest management tools for RLEM including:

  • Growing crops that do not support large populations of mites (for example, cereals) before susceptible crops such as canola are planted
  • Heavily grazing pasture paddocks through spring in the year prior to sowing crops susceptible to RLEM (for example, canola).
  • Decreasing weeds that will host mite populations during the crop phase and around fence lines
  • Using insecticidal seed dressings. There are now seed dressings available from the OP, neonicitinoid, fipronil, and SP/neonicitinoid groups.
  • If sprays need to be applied, rotate chemical groups within the season and between years

Growers who suspect that RLEM have survived registered rates of insecticides on their properties can contact Ms Micic on, 9892 8591 or 0427 772 051, so arrangements can be made to have samples of the mites tested for resistance.

More information about RLEM is available at a GRDC Hot Topic or by searching ‘RLEM’ on the DAFWA website.

Contact Details

For Interviews

Svetlana Micic, DAFWA
08 9892 8591


Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827

GRDC Project Code UM00049

Region West