Tolerance of the eriophyid mite Aceria salsola to UV-A light and implications for biological control of Russian thistle

Authors: Moran, Patrick; Wibawa, Maria - Irene; Smith, Lincoln

Submitted to: Experimental and Applied Acarology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2017
Publication Date: 12/1/2017
Citation: Moran, P.J., Wibawa, M.I., Smith, L. 2017. Tolerance of the eriophyid mite Aceria salsola to UV-A light and implications for biological control of Russian thistle. Experimental and Applied Acarology. 73(3-4):327-338. https://doi.org/10.1007/s10493-017-0205-z.
DOI: https://doi.org/10.1007/s10493-017-0205-z

Interpretive Summary: Russian thistle is a shrub that is native to Europe and Asia and invasive in western North America, especially in deserts and rangelands, where it outcompetes the local native plants and takes over their habitat. Although cattle can eat young plants, mature live and dead plants are covered in thorns and contain toxins that can harm livestock. In addition, this invasive weed provides food and shelter for insects that are crop pests and that transmit diseases to crops, making it difficult to control the insect pests. Dead plants break off of their roots and roll in the wind, forming 'tumbleweeds' that many see as a classic symbol of 'Wild West' American deserts and small towns. However, these dead shoots cause great harm by spreading seed, clogging irrigation canals, blocking highways, and creating a fire hazard. In California alone, millions of dollars are spent each year to control Russian thistle with chemical herbicides. The USDA-ARS and collaborators in southern and eastern Europe discovered a tiny, microscopic mite (a sort of lice for plants) that feeds on shoot tips, distorting their growth and stunting the entire plant. In order to gain permission to release the mite into the field in the U.S. for biological control of Russian thistle, scientists must show that the mite will not feed on other plants, especially native desert species. Previous tests in a quarantine laboratory indicated that the mite could reproduce on horned seablite, a U.S. native plant. However, in a field test back in Europe, no reproduction occurred on horned seablite. In the outdoor tests the mites were exposed to UV light present in sunlight, whereas in the lab there was no UV light. In this study, scientists hypothesized that exposing the mites feeding on plants in the lab to UV light in the long wavelength range (315-400 nanometers, also known as "UV-A") would reduce their ability to feed on horned seablite, but not Russian thistle. In feeding and reproduction tests lasting five weeks, the mites developed populations that were 3 to 20-fold higher on Russian thistle than on horned seablite, under both normal lighting and enhanced UV-A lighting, and up to 55-fold higher on Russian thistle than on another plant species. However, some mite reproduction did occur on horned seablite, even on plants exposed to UV-A, indicating that other components of the field environment, such as likely more harmful UV-B light, could limit the ability of the mite to feed on this 'non-target' native plant, and these factors need to be simulated in future lab-based tests.

Technical Abstract: Aceria salsolae (Acari: Eriophyidae) is being evaluated as a candidate biological control agent of Russian thistle (Salsola spp., Chenopodiaceae), a major invasive weed of rangelands and dryland crops in the western U.S. Prior laboratory host range testing under artificial lighting indicated reproduction on non-native B. hyssopifolia and a native plant, Suaeda calceoliformis. However, in field garden tests in the native range, mite populations released on these ‘nontarget’ plants remained low. We hypothesized that UV-A light, which can affect behavior of tetranychid mites, would affect populations of the eriophyid A. salsolae differently on the target and nontarget plant species, decreasing the mite’s realized host range. Plants were infested with A. salsolae under lamps that emitted UV-A along with broad-spectrum light, and the size of mite populations and plant growth compared to infested plants exposed only to broad-spectrum light. Russian thistle supported 3- to 55-fold larger mite populations than the nontarget plants regardless of UV-A treatment. Mite populations did not differ between UV-A-exposed and non-exposed Russian thistle and S. calceoliformis, while UV-A exposed B. hyssopifolia supported seven-fold larger populations. Main stems on nontarget plants grew two- to six-fold faster than Russian thistle under either light treatment, and the two nontarget plants, but not Russian thistle, attained greater plant volume under the control light regime. Although Russian thistle was always the superior host, UV-A light did not reduce the ability of A. salsolae to reproduce on the two nontarget species, suggesting that UV-B or other environmental factors are more important in the field.