Testing advised for RLEM survivors

Author: Natalie Lee | Date: 21 Jun 2013

Western Australian growers who observe redlegged earth mites (RLEM) surviving insecticide treatments are advised to arrange testing for resistance levels.


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Department of Agriculture and Food (DAFWA) entomologist Svetlana Micic, who conducts RLEM research supported by the Grains Research and Development Corporation (GRDC), said mites had hatched in areas of the grainbelt that had received recent rainfall and experienced at least seven days of temperatures below 20 Celsius. 

She encouraged growers to contact their local DAFWA office if they had difficulty controlling the mites, which could indicate resistance to synthetic pyrethroid (SP) chemicals including bifenthrin and alpha-cypermethrin.

Ms Micic said that from 148 WA properties tested from 2006 to 2012, 29 had been confirmed with RLEM populations resistant to all SPs.

“However, the incidence of RLEM resistance to SP insecticides in WA could be more widespread than these figures suggest and each year we find more properties with resistant redlegged earth mites,” she said.

“Research by the University of Melbourne has shown that SP-resistant RLEM are up to 240,000 times more tolerant to SP insecticides than susceptible RLEM and this resistance is genetic – surviving through several generations.

“Fortunately, tests have shown that WA’s SP-resistant RLEM populations do not have cross resistance to other insecticide groups, such as organophosphates (OPs) and can be controlled with these products.”

As part of a GRDC-funded project, DAFWA researchers will continue to test properties across the State where RLEM are found to survive insecticide treatments.

“Under this project I am also researching the extent and geographical spread of RLEM resistance to help develop integrated management strategies to deal with this pest,” Ms Micic said.

She said that to prolong the efficacy of all insecticide groups, it was vital to rotate products within and between seasons to minimise the risk of resistance developing and to limit ‘insurance’ or prophylactic spraying unless there was a genuine risk of pest problems.

“Every time an SP is used to control pests such as weevils, caterpillars and aphids, RLEM also receive a dose of this insecticide, despite not necessarily being the primary target,” Ms Micic said.

She said research had shown that weedy habitats - including in-crop weeds and weeds along fencelines – could host residual populations of RLEM that could re-infest surrounding paddocks.

“Growers looking to control RLEM should control weeds right throughout the season so there are fewer breeding opportunities for mites to carry over to the following year,” she said.

“Unsprayed and under-grazed pastures in spring are also known to be favourable to RLEM.”

More information about RLEM resistance is available from the DAFWA Farmnote Prevent redlegged earth mite resistance at http://www.agric.wa.gov.au/PC_94450.html or the GRDC Insecticide Resistance Management and Invertebrate Pest Identification Fact Sheet at www.grdc.com.au/GRDC-FS-IPM-SW

Contact Details

For Interviews

Svetlana Micic, entomologist, DAFWA
08 9892 8591

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

Caption: Late sown canola crops are especially susceptible to redlegged earth mite (RLEM) infestation.
Caption: Predatory snout mite (left, on its back), RLEM (centre) and Balaustium mite (right).  Photo: Pia Scanlon, DAFWA.

GRDC Project Code UM00033; DAW00177; CES00001; SCF00002