Acaricide efficacy and resistance in South Carolina tomato populations of twospotted spider mite

Authors: Schmidt, Rebecca; SNIPES, ZACK - Clemson University; BERGERON, PAUL - Washington State University

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2020
Publication Date: 5/31/2021
Citation: Schmidt-Jeffris, R.A., Snipes, Z., Bergeron, P. 2021. Acaricide efficacy and resistance in South Carolina tomato populations of twospotted spider mite. Florida Entomologist. 104(1):1-8. https://doi.org/10.1653/024.104.0101.
DOI: https://doi.org/10.1653/024.104.0101

Interpretive Summary: Twospotted spider mite is an important pest of tomatoes in the southeast US, which is primarily managed using specific pesticides (acaricides). Spider mites are known for their ability to rapidly develop pesticide resistance. Therefore, information on acaricide efficacy and resistance is important for growers in developing management plans. Researchers at the USDA-ARS in Wapato, in collaboration with Clemson University and Washington State University, conducted a two-year field study to evaluate the effectiveness of acaricides registered for use on tomato. They also tested three separate populations of twospotted spider mite for acaricide resistance by comparing the acaricide susceptibility of these populations to a known-susceptible laboratory colony. The most effective treatments in the field study were abamectin, fenpyroximate, and cyflumetofen. Bifenazate and bifenthrin had lower efficacy than other products and acaricide resistance was a suspected cause. Resistance screening detected resistance to bifenthrin and abamectin in all three populations tested, but resistance to bifenazate was not found. It is possible that the populations of twospotted spider mites in the field trials were resistant to bifenazate and those that we collected to screen for resistance were not. Additional screening will be required to determine if bifenazate resistance is present in South Carolina populations of spider mites, but this study does not indicate that this is occurring. Growers that experience field failures should first confirm that other issues, such as inadequate coverage or calibration errors, are not to blame for poor acaricide performance.

Technical Abstract: Twospotted spider mite, Tetranychus urticae Koch (Trombidiformes: Tetranychidae) is a key pest of vegetable crops in the southeastern US. Spider mites can cause significant yield loss in tomato due to reduced photosynthetic capacity and direct feeding damage (“gold fleck”). Use of acaricides is the primary control method, but acaricide resistance is a serious concern. We sought to characterize efficacy of acaricides registered for use on tomato by conducting two field trials in South Carolina in 2015-2016. The most effective treatments were abamectin, fenpyroximate, and cyflumetofen. Bifenazate and bifenthrin had lower efficacy than other products and acaricide resistance was a suspected cause. Therefore, three spider mite populations were collected from grower fields in 2017, subjected to dose-response screening, and compared to a known-susceptible population. Probit analysis revealed that all populations were resistant to bifenthrin at levels that would likely result in field failure. All populations were resistant to abamectin, with the LD50 of one population above field rate. Resistance to acequinocyl and spiromesifen was also present in all populations, but LD50 values were well below field rate. Based on our results and known non-target effects of bifenthrin and abamectin on predatory mites, growers should avoid using these products for spider mite management. Poor performance of bifenazate in the efficacy study could not be attributed to resistance, although it is possible that the populations from the efficacy study were resistant and those screened for resistance were not. Many acaricides registered in tomato appear to be effective for mite management in South Carolina.