Response of the oak ambrosia beetle Platypus quercivorus (Coleoptera: Platypodinae) to volatiles from fresh and dried leaves

Bark and ambrosia beetles use trees as hosts, and the preferred host condition—whether healthy, weakened, or dead—varies among beetle species. Though attraction to volatiles from trees under favorable conditions have been well studied in beetles, only a few studies have examined the repulsion of volatiles from trees under unfavorable conditions. We focused on this aspect by using the oak ambrosia beetle, Platypus quercivorus, as a model. This beetle attacks healthy oaks, causing Japanese oak wilt. Previous studies have suggested that leaf volatiles are important cues to detect the hosts of this beetle. Therefore, we used a Y-tube olfactometer to evaluate the beetle response to volatiles from fresh and dried leaves of their hosts and non-hosts. Volatile components were analyzed by gas chromatography-mass spectrometry (GC–MS). In the Y-tube, P. quercivorus preferred fresh leaf volatiles to clean air and did not generally prefer dried leaf volatiles. This preference was observed regardless of whether the source was a host or non-host. The degree of attraction to fresh leaf volatiles increased when the counterpart of the Y-tube was changed from clean air to dried leaf volatiles, suggesting a repelling effect of the dried leaf volatiles. The GC–MS results showed a clear difference in the chemical components of the volatiles from fresh and dried leaves. Common chemicals among the dried leaf volatiles of hosts and non-hosts, such as trans-2-hexenal, have been suggested as candidate repellents for P. quercivorus. The results suggest the possible use of dead branches to avoid beetle infestation.