Wheat curl mite, Aceria tosichella
Order: Acari
Family: Eriophyidae
Description
Wheat curl mites are white, cigar-shaped arthropods whose bodies taper near the head and rear. All eriophyid mites have two pairs of legs located near the head. These mites are too small to be seen with the naked eye.
Quick Facts
- Wheat curl mite is a pest of great economic significance in Colorado because it transmits several viruses of wheat: the wheat streak mosaic (WSMV), high plains wheat mosaic (HPWMoV), and Triticum mosaic (TriMV) viruses.
- These mites can use wild and cultivated plants as alternate hosts. Effective management depends on the removal of volunteer crops and grassy weeds – i.e., eliminating the ‘green bridge’.
- A hand lens with 10x magnification or greater is needed to see wheat curl mites since they are too small to be seen with the naked eye.
A single eriophyid mite adult. Wheat curl mites are eriophyid mites, which have long cylindrical bodies and two pairs of legs. The wheat curl mite is a pest of great economic significance in Colorado because it transmits several plant viruses that can devastate wheat, sometimes resulting in 100% yield loss. This pest is very difficult to suppress using insecticides owing to the leaf curling these mites cause in wheat. Therefore, effective management depends on preventing wheat curl mite infestation, which is best accomplished through cultural control. Image credit: Brian Kunkel, University of Delaware, Bugwood.org
Leaf curling in wheat leaves caused by wheat streak mosaic virus. Image credit: Marie Langham, South Dakota State University, Bugwood.org
Leaf curling in wheat leaves caused by wheat streak mosaic virus. Image credit: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
Side by side comparison of healthy winter wheat (left) and winter wheat inoculated with wheat streak mosaic virus (right). Image credit: Mary Burrows, Montana State University, Bugwood.org
Wheat leaf infected with wheat streak mosaic virus. Chlorotic streaks and speckles are symptoms of infection. Image credit: Erik Stromberg, Virginia Polytechnic Institute and State University, Bugwood.org
Life history and habits
Adult wheat curl mites, immature stages, and eggs can overwinter on wheat and surrounding perennial grasses. In the spring, egg laying occurs along leaf veins. These mites prefer tender leaf tissues and will begin feeding on new leaves as they emerge. It takes an average of 8-10 days to complete development.
When wheat plants dry, wheat curl mites move to the upper parts of the plant that still contain green tissue. Wind currents transport mites to oversummering hosts such as corn, volunteer wheat, barnyard grass, stinkgrass, witchgrass, and green foxtail.
Viruses transmitted by wheat curl mite
Important viruses transmitted by wheat curl mites in Colorado are the wheat streak mosaic (WSMV), high plains wheat mosaic (HPWMoV), and Triticum mosaic viruses (TriMV). When feeding on an infected plant, mites can acquire the virus where it remains active through the mite’s development. However, the virus is not passed down to offspring. These viruses often exist as a complex in Colorado wheat, with the potential for drastic yield loss when wheat crops are simultaneously infected with WSMV and TriMV. Temperatures of 23.9-26.7° C (75–80° F) are highly favorable for mite reproduction and WSMV replication.
WSMV
WSMV is a resilient virus and can survive in a variety of environments. This includes areas that do not produce wheat because the virus can use native grasses as alternative hosts. WSMV also survives in seeds; however, seed transmission rates are very low. WSMV relies primarily on wheat curl mites for transmission.
On average, 2-3% of yield loss is expected from infection with WSMV only. However, in severe mite infestations wheat streak mosaic virus can cause 100% yield loss when infection occurs in the fall. Symptoms are likely to be caused by TriMV in varieties resistant to WSMV.
TriMV
This virus has caused major problems recently due to drought. Unlike WSMV, there are currently no TriMV resistant wheat varieties. In 2010 and 2011, field surveys were conducted in wheat producing states like Colorado to determine the incidence of TriMV and how frequently plants are also co-infected with WSMV. The survey results indicated that 91% of plants infected with TriMV were also infected with WSMV. For more information, the full study is available here.
Injury
Wheat curl mite feeding injury causes leaf curling, in which leaf margins form a tight roll. Symptoms of viral infection appear as discoloration of wheat leaves. If leaves display chlorotic speckles or streaks (see images) and stunted growth, this indicates that the plant may be infected with WSMV. Plants are likely infected with TriMV if discoloration and stunted growth are observed in WSMV resistant wheat varieties.
Management
Effective WSMV management depends on minimizing the amount of viable host plants for virus and mites. Therefore, volunteer wheat and grassy weeds that emerge before harvest should be treated with herbicides or tilling a minimum of two weeks before planting in the fall. Since corn can serve as a reservoir for mites and WSMV, wheat should not be planted next to late maturing corn fields.
Some wheat varieties are more resistant to the wheat streak mosaic virus. Resistant varieties include Joe, Clara CL, and Oakley CL. However, the resistance genes are less effective when temperatures exceed 23.9°C (75°F).
Unfortunately, there are no viable chemical management options for controlling wheat curl mites, therefore prevention is the most effective management option. Volunteer wheat and alternative host plants should be destroyed, and winter wheat planted at least two weeks later. Early planting should be avoided to minimize the length of time wheat curl mites can transmit the virus. Later planting can also help control mite outbreaks since wheat curl mite populations growth increases at temperatures between 21.1-26.7°C (70-80°F) but decreases at or below 10°C (50°F).
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
Amrine, J. 2013. Eriophyid mites. Washington State University. Available https://s3.wp.wsu.edu/uploads/sites/408/2015/02/PLS-89-Eriophyid-Mites.pdf
Colorado State University. 2022. Eriophyid Mites. Colorado State University: Extension – Plant Talk Colorado. Available https://planttalk.colostate.edu/topics/insects-diseases/1400-8-eriophyid-mites/
Cranshaw, W. 2013. Insect and Mite Galls. Colorado State University: Extension – Fact sheet 5.557. Available https://extension.colostate.edu/topic-areas/insects/insect-and-mite-galls-5-577/
Davis, R. 2011. Eriophyid Mites: bud, bluster, gall and rust mites. Utah State University – Cooperative Extension. Available https://extension.usu.edu/pests/uppdl/files/factsheet/eriophyid-mites2010.pdf
Sloderbeck, P. E., Michaud & R. J. Whitworth. 2018. Wheat Pests. Kansas State University: Department of Entomology. Available https://entomology.k-state.edu/extension/insect-information/crop-pests/wheat/curlmite.html
Varenhorst, A., 2022. Managing Wheat Curl Mite. South Dakota State University Extension. Available https://extension.sdstate.edu/managing-wheat-curl-mite
Royer, T. 2021. Mites in Small Grains. Oklahoma State University Extension. Available https://extension.okstate.edu/fact-sheets/mites-in-small-grains.html#:~:text=Brown%20wheat%20mites%20are%20more,and%20withered%20(Figure%203)
Roberts, R. 2022. Colorado Wheat Disease Newsletter. Colorado State University. Available https://coloradowheat.org/wp-content/uploads/2022/06/062122-disease.pdf
Jones-Diamond, S. 2022. 2021 Colorado Winter Wheat Variety Performance Trials. Colorado State University Extension. Available https://agsci.colostate.edu/csucrops/wp-content/uploads/sites/18/2022/06/wheatreport-2022-WFD.pdf
Seifers, D. Satyanarayana, T., and Roy, F. 2013. University of Nebraska-Lincoln – Plant Pathology Department. Available https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1316&context=plantpathpapers