Larval development and parasitism of emerald ash borer in Chionanthus virginicus (Oleaceae): Implications for biological control.

Emerald ash borer (Agrilus planipennis Fairmaire) is an invasive wood-boring beetle that has killed millions of ash trees (Fraxinus spp.) across North America. In 2014, emerald ash borer was discovered attacking white fringetrees (Chionanthus virginicus L.) in Ohio, indicating a host range expansion. Since then, emerald ash borer activity in white fringetree has been confirmed in additional states, posing a potential threat to this native tree in natural and managed ecosystems. Though emerald ash borer can complete a full life cycle in white fringetree, there has been little research into the comparative success with which emerald ash borer develops in this novel host versus ash, or how introduced biocontrol agents will respond. We conducted laboratory and field infestations of white fringetree and ash in Delaware to compare the timing of emerald ash borer larval development and the associated response of larval parasitoids. In lab-infested white fringetree bolts, emerald ash borer developed slowly, with no larvae reaching the mature J-shaped larval stage (JL) during the 14-wk lab study, compared with all surviving larvae developing to the J-shaped larval stage in ash. Field results showed delayed emerald ash borer development and reduced survival in white fringetree, with just 1 larva out of 158 reaching the JL stage over 2 growing seasons. There was no parasitism of emerald ash borer larvae in lab- or field-infested white fringetree, likely because few larvae in this host reached instars suitable for larval parasitism. Overall, this study suggests that emerald ash borer populations in white fringetree are not self-sustaining, though further studies should be conducted using larger fringetree material, as small sizes may negatively impact larval survival.