Grains Research and Development

Date: 20.01.2014

DNA helps explain mite adaptation

Author: Catherine Norwood

Photo of a redlegged earth mite

Redlegged earth mites are only one millimetre in size and can be identified from other mites by their bright red legs.

PHOTO: A. Weeks, CESAR

The story of the redlegged earth mite’s (RLEM) march across Australia is a story of adaptability and a changing climate is unlikely to end that tale, Dr Matthew Hill says.

Predicting the response of RLEM (Halotydeus destructor) to climate change was the focus of his GRDC-sponsored PhD, recently completed at the University of Melbourne.

The RLEM arrived in Western Australia in 1917, and as part of his research Dr Hill has investigated how it has evolved since then and particularly during the past 50 years.

Tracing the DNA, he says the RLEMs in Australia are most genetically similar to the mites from the Stellenbosch region, about 50 kilometres east of Cape Town in South Africa. But since arriving in Australia, the mites have evolved to withstand a greater climatic range than they would have experienced in their native habitat.

Dr Hill says an extensive survey was undertaken of RLEMs in Australia in the 1960s, and it was thought at that time that the mites had reached the limits of their range.

However, in the 1990s, the RLEM was discovered further inland than scientists had originally thought possible. “It has adapted to survive within a wider thermal window,” Dr Hill says.

“Its protective diapause phase has helped it to survive higher temperatures and there is also new evidence of increased frost tolerance. This is important as an indicator of population persistence for RLEM found in new areas such as inland New South Wales.”

Collating the data from extensive surveys of RLEM and applying genetic markers has allowed him to model the invasion process of the RLEM and investigate the ecological processes that have aided its spread.

He says the research has revealed a high level of gene flow between different RLEM populations – favourable traits are widely dispersed, which has allowed it to colonise new regions. This indicates that RLEM is likely to remain a significant pest in the grains industry under increased climate variability. His work has also led to further GRDC-supported research at the University of Melbourne, examining how the traits of increased temperature tolerance are transferred between RLEM populations and how this process might parallel the spread of pesticide resistance in RLEM populations.

Understanding and predicting these responses should help develop management strategies that can take into account shifts in the frequency of outbreaks and persistence of pests, as well as changes to the interaction between species – especially beneficial species that might provide biocontrol options.

More information:

Dr Matthew Hill,

hillmp@sun.ac.za

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GRDC Project Code GRS00154, UM00043, UM00049

Region Overseas, South, West, North