Microbial control of Agrilus planipennis (Coleoptera: Buprestidae) with Beauveria bassiana strain GHA:: field applications

The effects of Beauveria bassiana strain GHA, applied as BotaniGard ES, on newly colonised and well-established populations of emerald ash borer, Agrilus planipennis (Coleoptera: Buprestidae) were evaluated in the field using foliar and trunk sprays in Michigan in 2004-2005. Results from field trials at a newly colonised white ash site showed a 41% reduction in A. planipennis population in fungal-treated trees compared with that of untreated controls. In addition, fungal infection was also found in 20% of the larval population within 14 days of incubation under laboratory conditions. At a site with a well-established Agrilus planipennis population in green ash trees, larval density was reduced by 47% for trees treated with the fungus compared with that of the controls; 21% of larvae from the current generation were found infected after 14 days of laboratory incubation. Fungal-treated green ash trees also produced fewer adults emerging in the next generation, with a 63% reduction in adult density observed in treated trees compared to that of controls. As a result, fungal-treated trees sustained 42% less crown dieback than did controls. A. planipennis larval density was negatively correlated with trunk height above the ground, and positively correlated with log diameter. Results of laboratory leaf bioassays on A. planipennis adults showed that fungal conidia persisted well under field conditions, with mortality of 78-100% at 7 - days post - exposure for leaves collected between 2 and 264 h after application. Potential strategies for using B. bassiana strain GHA for managing A. planipennis are discussed.