1 COLD HARDINESS OF EMERALD ASH BORER, AGRILUS PLANIPENNIS: A NEW PERSPECTIVE

This study was designed to assess the cold hardiness of emerald ash borer larvae, the overwintering stage of the insect. We began by measuring larval supercooling points, the temperatures at which larvae freeze. We found that larvae collected from naturally infested trees in St. Paul, MN between late October and early December had an average supercooling point of-25°C (-13°F). Research elsewhere indicates that when these insects freeze, they die. Our laboratory assessments of cold hardiness were confirmed during field tests. Naturally infested logs were held outdoors in St. Paul, MN (low winter air temp=-28°C) and near Grand Rapids, MN (-34°C) for ca. 5.5 weeks. Approximately 40 % of larvae from logs in St. Paul were inactive or brown, both evidence of death; approximately 90 % of larvae from logs near Grand Rapids were inactive or brown, compared with the approximately 10 % that showed evidence of death prior to exposure or after being held under cool, non-lethal conditions. Overwintering mortality may help to minimize the damage caused by emerald ash borer in areas with extremely cold winter climates. Emerald ash borer, Agrilus planipennis Fairmaire was detected in North America initially i