Wheat curl mite
Photo by M Schiffer, University of Melbourne
The wheat curl mite is a microscopic, cigar-shaped mite. It is the principal vector of the damaging cereal virus, wheat streak mosaic virus, which is a disease that in severe cases may cause up to 100 per cent yield loss with early and widespread infection of young wheat plants. The mites are dispersed by the wind and colonise the youngest tissue of a wheat plant. These mites cause little direct feeding damage. Mild summers with adequate rain for volunteer cereal and grass growth favour mite survival and virus build up between wheat crops. Controlling volunteer cereals and grasses over summer is the main tool in controlling wheat curl mites by eliminating the potential green bridge for mites.
Given their tiny size, the exact distribution and occurrence of wheat curl mites is difficult to ascertain, however they have been found in grain growing areas of southern Australia including Victoria, South Australia, New South Wales, Western Australia and the eastern part of Tasmania.
Mites are extremely small (<0.3 mm in length), have a cigar shaped cream coloured body and are wingless. They have only two pairs of legs located at the front of their body and cannot be seen without the aid of a microscope. The mite is the primary vector for wheat streak mosaic virus (WSMV).
Wheat curl mites are extremely small and can only be seen with a microscope, making in-paddock identification difficult.
Wheat curl mites are the primary vector for wheat streak mosaic virus (WSMV), a disease which may cause up to 100 per cent yield loss with early and widespread infection of young wheat plants.
Wheat curl mites complete their lifecycle in 8-10 days, and each female lays 12-20 eggs. This rapid rate of development means a single female can produce more than 3 million descendants within 60 days under ideal conditions. Populations increase rapidly at temperatures around 25°C, but are limited by temperatures above 30°C and below 15°C. Lifespan under ideal conditions is typically eight to 10 days, but it can survive for up to three months in cold conditions where reproduction is significantly slowed.
Wheat curl mites are less active in colder weather or when temperatures are below 10°C. The optimum temperature range for mite activity is 24-27°C. Due to their size they rely on wind for their dispersal within and between crops. Wheat curl mites colonises the youngest tissue of a wheat plant and acquire WSMV when feeding on infected plants, carrying it to other plants. Wheat curl mites can transmit at least five more viruses including wheat spot mosaic virus, wheat spot chlorosis pathogen, cereal spotting, triticum mosaic virus and high plains virus.
Similar to Top
Wheat curl mites are very difficult to detect due to their small size. Under a microscope they resemble other small eriophyoid mites.
Crops attacked Top
Primarily wheat, but also barley and triticale. There also have many alternative hosts including wild oats, barley grass, annual ryegrass, small burr grass and cocksfoot.
Unless found in extremely high numbers, wheat curl mites generally cause little direct damage in the field other than the characteristic leaf curling and the occasional trapping of the flag leaf.
Wheat shows the most obvious symptoms of wheat streak mosaic virus (WSMV), and is the preferred host of the wheat curl mite (the primary vector of the virus). In addition to wheat, cereal varieties such as barley, oats, millet and cereal rye, and several grass varieties are also susceptible to WSMV infection. Crops are most susceptible to virus infection from emergence until early tillering. Development of virus symptoms often does not occur until later in the season, when temperatures exceed 10°C. WSMV can cause stunted growth or cause plants to die prematurely. Early infection can cause grain to become small and shriveled. Infection can also cause wheat heads to develop no grain. Along with WSMV, wheat curl mites are also known to vector at least 5 other viruses including wheat spot mosaic virus, wheat spot chlorosis pathogen, cereal spotting, triticum mosaic virus and high plains virus.
Wheat curl mite can only be seen with a microscope, making in-paddock identification difficult. Given their minute size, the presence of wheat curl mites is almost always first noticed by plants showing symptoms of WSMV. Monitor crops in spring when temperatures begin to increase. The two main symptoms to identify WSMV are leaf mottling and leaf streaking. Plants infected with WSMV develop light green streaks parallel to the veins. The streaks develop into blotches, which tend to form yellow and green mosaic patterns.
Economic thresholds Top
There are no economic thresholds established for this pest.
Management options Top
There are currently no known biological control agents for wheat curl mites in Australia.
Mild summers with adequate rain for volunteer cereal and grass growth favour mite survival and virus build up between wheat crops. Controlling volunteer cereals and grasses over summer is the main tool in controlling wheat curl mites by eliminating the potential green bridge for mites. This is particularly important in virus prone areas where cereals are going to be planted the following season. Where possible, delay autumn sowing until temperatures are too cold for mite activity. WSMV is also seed borne, and seed can be tested for the virus prior to sowing.
While research is under way, there are no WCM/WSMV-resistant wheat varieties available in Australia.
The main tool in controlling wheat curl mites is controlling volunteer cereals and grasses over summer.
Currently there are no insecticides registered for wheat curl mites. Research from overseas suggests that mites do not respond well to insecticides.
Wheat curl mites are usually well protected within leaf whorls and pesticides are unlikely to be effective in controlling mites.
This article was compiled by Paul Umina (cesar) and Sandra Hangartner. The Australian Wheat Streak Mosaic Cycle was reprinted from GRDC (2009).
References/Further Reading Top
Bailey PT. 2007. Pests of field crops and pastures: Identification and Control. CSIRO Publishing, Melbourne, Australia.
Carew M, Schiffer M, Umina PA, Weeks A and Hoffmann A. 2009. Molecular markers indicate that the wheat curl mite Aceria tosichella Keifer may represent a species complex in Australia. Bulletin of Entomological Research 99, 479-486.
Coutts BA, Strickland GR, Kehoe MA, Severtson DL and Jones RAC. 2008. The epidemiology of Wheat streak mosaic virus in Australia: case histories, gradients, mite vectors, and alternative hosts. Australian Journal of Agricultural Research 59: 844–853.
Coutts BA, Cox BA, Thomas GJ and Jones RAC. 2014. First Report of Wheat mosaic virus Infecting Wheat in Western Australia. Plant disease 98: 285.
Coutts et al. 2009. Wheat streak mosaic virus and wheat curl mite, Farmnote no. 342, Department of Agriculture and Food WA.
Dwyer GI, Gibbs MJ, Gibbs AJ and Jones RA. 2007. Wheat streak mosaic virus in Australia: Relationship to Isolates from the Pacific Northwest of the USA and Its Dispersion Via Seed Transmission. Plant disease 91: 164-170.
Ellis MH, Rebetzke GJ, Kelman WM, Moore CS and Hyles JE. Detection of Wheat streak mosaic virus in four pasture grass species in Australia. Plant Pathology 53: 239.
GRDC. 2009. The wheat curl mite. Fact Sheet; www.wheatcurlmite.org
Halliday RB and Knihinicki DK. 2004. The occurrence of Aceria tulipae (Keifer) and Aceria tosichella Keifer in Australia (Acari: Eriophyidae). International Journal of Acarology 30: 113-118.
Lanoiselet VM, Hind-Lanoiselet TL and Murray GM. 2008. Studies on the seed transmission of wheat streak mosaic virus. Australasian Plant Pathology 37: 584-588.
Miller AD, Umina PA, Weeks AR and Hoffmann AA. 2012. Population genetics of the wheat curl mite (Aceria tosichella Keifer) in Australia: implications for the management of wheat pathogens. Bulletin of Entomological Research 102: 199-212.
Navia D, Santos de Mendonca R, Skoracka A, Szydlo W, Knihinicki D, Hein GL, Valle da Silva Pereira PR, Truol G and Lau D, 2013. Wheat curl mite, Aceria tosichella, and transmitted viruses: an expanding pest complex affecting cereal crops. Experimental and Applied Acarology 59: 95-143.
Richardson K, Miller AD, Hoffmann AA and Larkin P. 2014. Potential new sources of wheat curl mite resistance in wheat to prevent the spread of yield-reducing pathogens. Experimental and Applied Acarology 64: 1-19.
Schiffer M, Umina PA, Carew M, Hoffmann AA, Rodoni B and Miller A. 2009. The distribution of wheat curl mite (Aceria tosichella) lineages in Australia and their potential to transmit wheat streak mosaic virus. Annals of Applied Biology 155, 371-379.
Skoracka A, Kuczynski L, Santos de Mendonca R, Dabert M, Szydlo W, Knihinicki D, Truol G and Navia D. 2012. Cryptic species within the wheat curl mite Aceria tosichella (Keifer) (Acari : Eriophyoidea), revealed by mitochondrial, nuclear and morphometric data. Invertebrate Systematics 26: 417-433
Umina PA and Schiffer M. 2007. Pest mite raises curly questions. Australian Farm Journal 16, 42-43.
|February 2015||1.0||Paul Umina (cesar) and Sandra Hangartner||Bill Kimber (SARDI)|
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