Augmentation of native North American natural enemies for the biological control of the introduced emerald ash borer in central Canada

Abstract

Agrilus planipennis Fairmaire (Col: Buprestidae) (EAB) has been spreading rapidly throughout North America, killing millions of ash trees, Fraxinus spp. L. (Oleaceae). Eradication is not viable, so biological control using natural enemies is now the leading management strategy. Little information is available on whether native parasitoids and predators can be manipulated to increase EAB mortality. We moved freshly cut ash logs infested with EAB parasitoids to field sites where there was no record of EAB mortality by native North American natural enemies. Changes in EAB parasitism, EAB density, and woodpecker predation were monitored over the following three years. Higher parasitism of EAB by Phasgonophora sulcata Westwood (Hym: Chalcididae) (16.67 ± 16.67%) and Atanycolus spp. Foerster (Hym: Braconidae) (48.18 ± 4.29 %) was observed in all plots over three years after native parasitoids were released. However, no reduction was seen in EAB density between the treatment and control plots or over time. There was no significant relationship found between predation by woodpeckers and year or between control and parasitoid-release plots. However, woodpecker predation increased significantly with EAB density. Movement of ash logs containing native parasitoids to sites newly infested by EAB, but with low native natural enemy populations, can increase long-term EAB mortality as an added component in management strategies to slow its spread.