Wet spots on trunk
Flatheaded alder borer, bronze birch borer, twolined chestnut borer, bronze poplar borer, honeylocust
borer Agrilus spp.
Flatheaded alder borers attack alders, bronze birch borers infest birch, twolined chestnut borers
attack oak and chestnut, and bronze poplar borers infest Populus spp. Wet, dark, and gnarled
growth often appears on the infested bark. Adult emergence holes, often D-shaped and about 0.13
inch in diameter, are left in bark.
Oak twig girdler Agrilus angelicus
Oak twig girdler is a flatheaded borer that attacks oaks in California. Infestations produce scattered
patches of whitish brown leaves throughout the canopy. Leaves are dead, but have not been chewed
and exhibit no surface scraping. A flattened, spiral tunnel, possibly containing dark brown frass
and a larva, should be visible in twig girdler-infested oaks.
Borer beneath bark
Pacific flatheaded borer and flatheaded appletree borer Chrysobothris spp.
Chrysobothris spp. are attracted to diseased, stressed, or injured trees of more than seventy
species including ceanothus, cotoneaster, manzanita, maple, oak, rose, sycamore, and willow. Appletree
borers are found throughout the United States; Pacific flatheaded borers occur only in the western
states. Larvae excavate just beneath bark in the cambial area and may bore deeper into wood as they