Herbivore‐induced volatile emission in black poplar: regulation and role in attracting herbivore enemies

Abstract

After herbivory, plants release volatile organic compounds from damaged foliage as well as from nearby undamaged leaves that attract herbivore enemies. Little is known about what controls the volatile emission differences between damaged and undamaged tissues and how these affect the orientation of herbivore enemies. We investigated volatile emission from damaged and adjacent undamaged foliage of black poplar (Populus nigra) after herbivory by gypsy moth (Lymantria dispar) caterpillars and determined the compounds mediating the attraction of the gypsy moth parasitoid Glyptapanteles liparidis (Braconidae). Female parasitoids were more attracted to gypsy moth-damaged leaves than to adjacent non-damaged leaves. The most characteristic volatiles of damaged versus neighbouring undamaged leaves included terpenes, green leaf volatiles and nitrogencontaining compounds, such as aldoximes and nitriles. Electrophysiological recordings and olfactometer bioassays demonstrated the importance of nitrogenous volatiles. Under field conditions, parasitic Hymenoptera were more attracted to traps baited with these substances than most other compounds. The differences in volatile emission profiles between damaged and undamaged foliage appear to be regulated by jasmonate signalling and the local activation of volatile biosynthesis. We conclude that characteristic volatiles from damaged black poplar foliage are essential cues enabling parasitoids to find their hosts.

Beetle feeding induces a different volatile emission pattern from black poplar foliage than caterpillar herbivory

“…Turning to groups of compounds, the proportion of aromatic compounds emitted from beetle-damaged foliage was higher than for caterpillar-damaged leaves. 10 In contrast, the proportion of green leaf volatiles was smaller than from caterpillar-damaged leaves. To identify the most important compounds that distinguish the caterpillarinduced from the beetle-induced volatile blends, we employed the Random Forest algorithm (Breiman 2001).…”

“…The same experimental set-up as described in Clavijo McCormick et al 10 was applied but the trees were infested with Phratora vulgatissima leaf beetles (Fig. 1A).…”

“…Beetles were allowed to feed for 41 h before volatiles were collected and analyzed as described in. 10 …”

“…10 The blend released from damaged black poplar foliage was qualitatively and quantitatively different from that of undamaged adjacent foliage and foliage of non-damaged control trees. Female Glyptapanteles liparidis wasps, which are parasitoids of Lymantria dispar caterpillars, were attracted to the volatiles from damaged leaves, and EAG experiments and behavioral assays revealed that this species was especially attracted to minor, nitrogen-containing compounds.…”

“…Female Glyptapanteles liparidis wasps, which are parasitoids of Lymantria dispar caterpillars, were attracted to the volatiles from damaged leaves, and EAG experiments and behavioral assays revealed that this species was especially attracted to minor, nitrogen-containing compounds. 10 As members of natural floodplain forests in Europe, black poplar trees harbor an enormous diversity of arthropods and are almost constantly under attack by different species of herbivorous insects. Whether these trees are capable of releasing herbivore species-specific volatiles thus has important consequences for herbivore enemy attraction.…”