Volatile compounds from Salix spp. varieties differing in susceptibility to three willow beetle species

The volatile compounds emitted by leaves of 10 willow varieties that differ in their susceptibility to damage by blue (Phratora vulgatissima), brassy (P. vitellinae), and brown (Galerucella lineola) willow beetles were examin ed both before and after mechanical damage and correlated with feeding pref erences of these beetles determined under laboratory conditions. Three comp ounds were identified from intact undamaged leaves of six willow varieties, namely cis-3-hexenyl acetate, cis-3-hexenol, and benzaldehyde. After mecha nical damage, the yield and number of volatile compounds increased for all varieties. There were significant differences among willow varieties for bo th the concentration of cis-3-hexenyl acetate and the relative proportion o f this compound to cis-3-hexenol (green leaf volatile ratio). The 10 variet ies collectively showed a significant negative correlation between the rela tive resistance of each variety to blue and brown willow beetles and the yi eld of cis-3-hexenyl-acetate from damaged plants. The green leaf volatile r atio of damaged plants was also negatively correlated with the relative res istance of willow variety to these two beetle species.