Some ambrosia beetles attack healthy trees, but most prefer weakened, injured, or dying trees and fresh-cut logs (fig. 18). They bore into the sapwood and reduce tree and log values for wood products; some spread fungal pathogens. Larvae feed on a moldy fungus called ambrosia that adult females culture on the gallery walls. Small piles of boring dust or strings of compacted frass may be present on the bark. There are two or more generations per year. Adults can be trapped with pheromones. Logs should be processed promptly.

Larvae vary from dark pink or reddish gray to dusky green, with a dark-brown head and thoracic shield. They are about 25 mm long when full grown (fig. 19). The American plum borer is widely distributed throughout the United States, Canada, and parts of Mexico. Weepy sap spots appear on the bark, followed by accumulations of reddish frass in bark crevices (fig. 19). Lifting the bark will expose larval burrows, frass, larvae, and white, silken cocoons. This borer prefers trees in poor health, especially those with mechanical injuries to the bark and canker diseases. Good cultural practices help minimize infestation. Direct controls may be needed to protect valuable trees.