Apparently-healthy or inapparently-stressed? Ambrosia beetles as indicators of stressed trees in ornamental nurseries

Xylosandrus germanus and Xylosandrus crassiusculus can attack more than 120 and 200 species of nursery trees, respectively. However, recent studies have demonstrated that only certain tree species are attacked in a given year and location. While such trees may appear "apparently-healthy" at the time of attack, they could instead be "inapparently-stressed" and emit stress related volatiles that signal their vulnerability to ambrosia beetles. Ethanol is the most attractive volatile compound currently known for X. germanus and X. crassiusculus, and both species have an efficient and rapid ability to locate trees emitting this olfactory cue. The ability of extreme climatic events and improper growing conditions to induce the emission of ethanol and thereby predispose trees to attack by ambrosia beetles will be discussed.