Cambium Miners: Appearance, Territory, Damage and Life Cycle

Latin Name: Phytobia

Appearance: Adults are a gray moth that flies in early summer and measures around 6 mm in length. Larvae that are slender and semi-transparent. They feed and mine beneath the cambium of new canes as well as canes that have developed from past seasons. As a result of mining, new cane tips may be stunted or died. Adults can be seen flying in the early summer. The larval mine is a long, thin tunnel that bends at both ends to form a small elliptical. When the larva has completed a circle, it generally returns to the original mine to feed and grow it.

Hosts Plants:  In the north, white ash is favored, whereas in the south, green ash is desired. Other ash species are likely to be harmed to a lesser degree.

Territory: Eastern United States

Damage Insect Cause: Injury is generally invisible in standing trees. When the bark is removed, tan to brown mines on the white, inner phloem and xylem surface become evident. The mines in the branches and upper bole are typically small, threadlike, and straight to serpentine. Many mines become more sinuate and zigzag at the middle and lower bole. In addition to these patterns, pectinate and bipectinate-shaped mines may be present in the roots. The wood grain covering the mines becomes warped and somewhat bulging or bloated as the mines fill and heal over. Furthermore, in most mines, most of the brown deposit fades or bleaches, becoming practically colorless.

Life History and Habits: Small twigs are used to lay eggs. Maggots mine in the cambium and inner bark of the stem, all the way down to the roots. Maggots of the second instar spend the winter in the roots. Maggots that have matured leave through the bark and develop puparia in the soil. Pupation occurs in the northern hemisphere in May and June, but it happens in Mississippi from February to April. One year is required to complete the life cycle.