Effectiveness of two systemic insecticides for protecting western conifers from mortality due to bark beetle attack.

Bark beetles (Coleoptera: Curculionidae, Scolytinae) are important tree mortality agents in western coniferous forests. Protection of individual trees from bark beetle attack has historically involved applications of liquid formulations of contact insecticides to the tree bole using hydraulic sprayers. More recently, researchers looking for more portable and environmentally safe alternatives have examined the effectiveness of injecting small quantities of systemic insecticides directly into trees. In this study, we evaluated trunk injections of experimental formulations of emamectin benzoate and fipronil for preventing tree mortality due to attack by western pine beetle (Dendroctonus brevicomis LeConte) on ponderosa pine (Pinus ponderosa Dougl. ex Laws.) in California, mountain pine beetle (Dendroctonus ponderosae Hopkins) on lodgepole pine (Pinus contorta Dougl. ex Loud.) in Idaho, and spruce beetle (D. rufipennis [Kirby]) on Engelmann spruce (Picea engelmannii Parry ex Engelm.) in Utah. Fipronil appeared ineffective for protecting P. ponderosa from mortality due to D. brevicomis over the 3 years in California because of insufficient mortality of untreated, baited control trees the first 2 years and high mortality of the fipronil-treated trees in the third year. Emamectin benzoate was effective in providing protection of P. ponderosa from D. brevicomis during the third year following a single application. To our knowledge, this is the first demonstration of the successful application of a systemic insecticide for protecting individual conifers from mortality due to bark beetle attack in the western United States. Estimates of efficacy could not be made during both field seasons in P. contorta because of insufficient mortality in control trees. Both emamectin benzoate and fipronil were ineffective for protecting P. engelmannii from D. rufipennis. Lower ambient and soil temperatures and soil moisture may have limited chemical movement and thus efficacy at the Idaho and Utah sites.