A bark disk bioassay was used to assess the effectiveness of different insecticides for control of overwintering adult native elm bark beetles, Hylurgopinus rufipes (Eichoff) (Coleoptera: Curculionidae). Insecticides were applied to the base of the trunks of living American elm trees, Ulmus americana L., and bark disk samples were removed at intervals with a hole saw. Adult H. rufipes were exposed in bioassay chambers for which the bark disks formed the floor of the chamber. In September 2005, chlorpyrifos, permethrin, and a water control were applied to trees in five replicated blocks, and bark disk samples were taken at intervals over the following 725 d. In September 2006, chlorpyrifos, permethrin, carbaryl, bifenthrin, and a water control were applied to trees in six replicated blocks, and disk samples were removed at intervals up to 1,163 d after application. In both experiments, beetle mortality was 100% on chlorpyrifos-treated disks removed up to 725 d after treatment and, in the 2006 trial, declined thereafter. The pattern of mortality in the bifenthrin treatment did not differ significantly from that in the chlorpyrifos treatment in the 2006 experiment. Average corrected mortality on disks treated with permethrin or carbaryl declined below 100% by 11 d after application. On disks removed in the May following treatment, 248 d after application, average corrected mortality was 42–44% on permethrin-treated disks and 26% on carbaryl-treated disks.
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Vol. 104 • No. 3