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ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #420369
Research Project: Development of Superior Hops and Resilient Hop Production Systems

Location: Forage Seed and Cereal Research Unit

Title: Effect of imidacloprid application timing on twospotted spider mite (Acari: Tetranychidae) on hop

Author
item Woods, Joanna
item RICHARDSON, BRIANA - Oregon State University
item KAUR, NAVNEET - Oregon State University
item Dorman, Seth
item Gent, David

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2025
Publication Date: 4/17/2025
Citation: Woods, J.L., Richardson, B.J., Kaur, N., Dorman, S.J., Gent, D.H. 2025. Effect of imidacloprid application timing on twospotted spider mite (Acari: Tetranychidae) on hop. Journal of Economic Entomology. 118(3):1441-1445. https://doi.org/10.1093/jee/toaf079.
DOI: https://doi.org/10.1093/jee/toaf079

Interpretive Summary: The twospotted spider mite is a cosmopolitan pest in agricultural systems. Populations of this pest often are regulated by a complex of predators, but this regulation can be disrupted by various factors common in modern, high-intensity, agricultural systems. In this research, we sought to understand if use of a specific insecticide, imidacloprid, could induce more severe outbreaks of twospotted spider mites on hop and, if so, if this effect could be mitigated by altering the timing of its use. Over three years of field studies, we found that a single application of this pesticide could sometimes induce more severe occurrences of spider mites. However, this effect was year dependent and moderated by the specific timing of the application. We detected relatively small and transient effects on predatory arthropods, which suggests that the mechanism underlying the observed effect might be indirect. Practically, avoiding application of imidacloprid when twospotted spider mite densities are increasing (generally June in Oregon) should minimize risk of secondary outbreaks of this organism.

Technical Abstract: Imidacloprid and other neonicotinoids have been associated in secondary pest outbreaks of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Imidacloprid is commonly applied in hop for the suppression of various pest organisms. A three-year study was conducted in western Oregon to determine the impact of a single foliar application of imidacloprid on twospotted spider mites and their predators in hop when made in mid-May versus mid-June. Applications made in June generally resulted in greater densities of twospotted spider mites as compared to applications made in May or when plants were nontreated, although this effect was year-dependent. Predatory mites (Acari: Phytoseiidae) were present at low levels and seemingly were not impacted by imidacloprid application. Orius spp. (Hemiptera: Anthocoridae), Stethorus spp. (Coleoptera: Coccinellidae), and other macropredators were minimally reduced in one year on two dates. Given the small impact on the key predator groups, the mechanisms of imidacloprid-induced secondary outbreak of twospotted spider mite appears to involve factors other than direct toxicity to predators. Practically, avoiding application of imidacloprid when twospotted spider mite densities are increasing (generally June) should minimize risk of secondary outbreaks of this organism.