Ash Bark Beetle

    Ash Bark Beetle (Western)

    Hylesinus californicus 

    ash bark beetle

    Western ash bark beetle (T. H. Atkinson,

    bark beetle galleries

    Ash bark beetle galleries (Swiss Federal Institute for Forest, Snow, and Landscape Research,


    Pest Description

    • adults: ~ 1/6 inch long; dark with white to yellow scales; clubbed antennae
    • larvae: white grubs with no legs and a brown head capsule

    Host Plants, Diet & Damage

    • ash
    • feed on sapwood and phloem layers under the bark
    • typically attack smaller branches, but can attack the trunk
    • prefer highly stressed trees
    • leaves above the damaged areas will turn color and die
    • if the main stem is attacked, tree death may occur
    • create small round holes in limbs
    • galleries can be found under bark
    • can introduce fungal pathogens

    Biology, Life Cycle & Damaging Life Stage

    • overwinter as late-stage larvae under the bark or as adults in bark notches
    • larvae and adults become active in mid- to late-spring
    • adults mate and eggs are laid within a gallery that encircles and girdles the branch
    • larvae hatch and burrow outward from parental gallery
    • typically one generation per year
    • adults and larvae damage limbs and occasionally the main stem

    IPM Recommendations

    • Control is generally not warranted.
    • Remove and discard infested branches prior to beetle emergence.
    • Reduce stress on ash trees.
    • Apply insecticides (carbamates; pyrethroids) to the bark and branches to prevent damage to susceptible trees in areas of active ash bark beetle activity.

    For more information, see our Bark Beetles fact sheet.