The cellar spider, Holocnemus pluchei (Scopoli) isa non-native species found in abundance in the southwestern United States. It is often the dominant species under the eaves and on the walls of homes. Requests for control of cellar spiders and are common for pest management professionals, sometimes representing >50% of summer service calls. We tested four IPM strategies, sweeping and vacuuming, and two low-impact water-based sprays as control methods. The sprays included a botanical + pyrethrins and a permethrin emulsion. Treatments were made one time in June when there were large numbers of spiders present. Fifteen-foot sections of eaves on 13 separate buildings on the U.C. Riverside campus infested with H. pluchei were treated or left as untreated controls. Spiders per section were counted before treatment and at 2 wk and 1, 2, 3 and 4mo after treatment. As expected, the number of spiders in the untreated sections gradually increased throughout the summer. They declined in fall. Permethrin, 0.5%(maximum label rate) nearly eliminated the spiders from every section for the duration of the study. Compared to the number of spiders in the untreated sections, the botanical spray, a single sweeping, or vacuuming had a measurable but marginal effect, reducing the number of spiders to a level approximately intermediate between the untreated sections and the permethrin spray treatment. Laboratory contact spray tests showed that<1/10 maximum label rates of pyrethrins, permethrin and other pyrethroids kill 100% of H. pluchei within a day. However, this high level of activity was only partially substantiated in the field. Webbing may shelter some spiders from direct spray and summer heat may reduce the effectiveness of low rates of spray. This study suggests that H. pluchei on homes may be controlled with single permethrin spray. Sweeping or vacuuming cobwebs coupled with treatment with a low rate of low-impact spray may also be effective. A single sweeping or vacuuming was not highly effective, but multiple sweepings that reduce webs and crush spiders may be.

Michael K. Rust, Richard S. Vetter and Donald A. Reierson. Department of Entomology, University of California Riverside

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