Insecticide Resistance

Detecting pyrethroid resistance in redlegged earth mites: a simple in-field test 

Insecticides are valuable tools in protecting crops and pastures from a variety of pests, contributing to increased yields and quality. However, the intensive and often repeated use of insecticides places selection pressure on pest populations to evolve resistance.  

One such species is the redlegged earth mite (RLEM), which is an important crop establishment pest. Insecticide resistance in RLEM is a growing issue in many Australian grain and pasture-growing regions, particularly resistance to synthetic pyrethroids.  

Pyrethroid resistance may appear as reduced chemical effectiveness or complete failure in the field. Ongoing monitoring in the field is important to detect emerging issues. Until recently however, it was a lengthy process for farmers to confidently determine if their mite populations were resistant to pyrethroids – relying on laboratory tests that are conducted by trained experts. 

Fortunately, a straightforward and accessible method has recently been developed to identify pyrethroid resistance in RLEM populations.  

Photo by Andrew Weeks, Cesar Australia

What do we know about pyrethroid resistance in RLEM?  

Insecticide resistance in the RLEM was first detected in WA to synthetic pyrethroids. Since this discovery in 2006, ongoing surveillance shows that resistance in the RLEM has emerged over a wide area of the southern grain-growing regions of Australia

The underlying mechanism responsible for pyrethroid resistance in RLEM results in all pyrethroid chemicals currently registered to control RLEM becoming completely ineffective. Additionally, research has shown that this resistance can persist in the field for a long time, even in the absence of further pyrethroid use.  

Continuous monitoring is therefore essential to detect emerging issues and adapt pest management strategies accordingly. The ability to identify pyrethroid resistance early on allows farmers to make informed management decisions – including correct chemical usage. 

How does the test work? 

The test, develop by the Cesar Australia team, utilises easily obtainable materials and requires no special training.  

The key ingredients are insecticide granules that contain 2g/kg Bifenthrin (e.g. David Grays Antex granules, Richgro Ant Killa insecticide granules), which are widely available at supermarkets and hardware stores.  

The procedure involves the collection of mites, exposing these to insecticide granules, and subsequent observation of the mites’ after 1 hour.  

Click here to access the grower guide.

Managing RLEM with resistance 

If resistance is confirmed through the in-field test, farmers will need to rethink their management options for RLEM. Updates are currently underway to the RLEM Resistance Management Strategy

In the meantime, there are several decision aid tools to guide farmers in managing RLEM. The complex lifecycle of RLEMs gives rise to critical monitoring periods. 

Prior to sowing, the seasonal pest risk tool provides an overview of pre-emptive management strategies to control RLEM populations ahead of the critical plant establishment period.  

After sowing in autumn, the RLEM hatch timing tool provides an indication of when crop monitoring should increase, by predicting when mite eggs are likely to hatch.  

If populations remain high in spring, the TimeRite® tool can be used to ensure any necessary sprays are applied at the correct time in spring to reduce RLEM numbers surviving through to the next season. 

For queries and additional information, please email us at: 


This guide was developed with the support of the Grains Research and Development Corporation, through investment CES2010-001RXT ‘Future options for the control of RLEM in Australian grain crops’, with contributions from The University of Melbourne, CSIRO and the Western Australian Department of Primary Industries and Regional Development. 

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