Multiple cryptic species of Bryobia mites inhabit vast areas of agricultural landscapes in Australia signifying possible management challenges for farmers.
Support of the presence of a diverse species complex of Bryobia mites in Australia was recently published in Pest Management Science identifying several broad genetic lineages within Australia that exhibited important ecological differences, including their distribution, climatic suitability and response to insecticides.
This research was led by Cesar Australia in conjunction with the University of Melbourne and WA Department of Primary Industries and Regional Development, and supported through the Grains and Research and Development Corporation.
Identifying Bryobia mites
Bryobia mites belong to a complex of cryptic species with > 130 species described worldwide. Identifying between species is difficult due to the lack of suitable morphological characteristics and relies heavily on genetic markers.
In Australia, Bryobia mites are a significant pest of pastures and winter grain crops, with seven putative species identified in these agricultural commodities. However, this is based on limited sampling mostly from the state of Victoria, with little known about the broader biogeographic and abundances of the different Bryobia taxa across Australia.
In this study we further explored the species status and distribution of Bryobia mites throughout the Australian pasture and winter grain growing regions and examined the chemical responses of multiple field populations. Over 210 populations of Bryobia mites was examined collected from Victoria, Western Australia, Tasmania, New South Wales, South Australia and Queensland.
This research produced a comprehensive dataset identifying 47 unique haplotypes across all mites sampled within Australia. These grouped into four distinct genetic lineages, with one lineage showing support for the presence of multiple species, while the other lineages likely representing distinct species.
These lineages exhibited different distributions, with three of the four putative lineages showing different climatic envelopes, as inferred from species distribution modelling. Two of the lineages exhibited a broad distribution being found in most Australian states, while the other two lineages were restricted to eastern regions of Australia. Differences in the climatic envelopes inhabited by Bryobia lineages may help inform management strategies in the absence of rapid field diagnostic.
Response to insecticides
Bryobia mite populations also showed varied responses to a widely used insecticide (the organophosphate, omethoate), but not to another chemical (the pyrethroid, bifenthrin) when examined using laboratory bioassays. Differences in response to omethoate were evident between lineages, suggesting important insecticide tolerance disparities between the genetic lineages of Bryobia mites.
These findings potentially explain inconsistencies experienced by Australian farmers when attempting to control these mites with insecticides registered in grain crops and pastures.
This research demonstrates the importance of developing management strategies that consider genetic lineages separately and the need for the development of tools to readily distinguish Bryobia mites in the field.
The cryptic diversity present in Australian Bryobia mites is likely to complicate the formulation of management strategies against this pest and highlights the importance of further research into this complex group of mites.
If you have questions or want to find out more information, you can contact Dr Aston Arthur on firstname.lastname@example.org.
We thank Hao Van La, Jamie Hopkinson, Melina Miles, Timothy Callan and Mark Golder for assistance with mite collections, Rachael Impey for assistance with DNA extractions, and Hazel Parry and Sonia Sharma for technical advice. This work was in conjunction with the University of Melbourne and WA Department of Primary Industries and Regional Development supported by the Australian Grains Research and Development Corporation.