Qualitative and quantitative variation among volatile profiles induced by Tetranychus urticae feeding on plants from various families

Many plant species are known to emit herbivore-induced volatiles in response to herbivory. The spider mite Tetranychus urticae Koch is a generalist that can feed on several hundreds of host plant species. Volatiles emitted by T. urticae-infested plants of 11 species were compared: soybean ( Glycine max), golden chain ( Laburnum anagyroides), black locust ( Robinia pseudo-acacia), cowpea ( Vigna unguiculata), tobacco ( Nicotiana tabacum), eggplant ( Solanum melalonga), thorn apple ( Datura stramonium), sweet pepper ( Capsicum annuum), hop ( Humulus lupulus), grapevine ( Vitis vinifera), and ginkgo ( Ginkgo biloba). The degree to which the plant species produced novel compounds was analyzed when compared to the odors of mechanically damaged leaves. Almost all of the investigated plant species produced novel compounds that dominated the volatile blend, such as methyl salicylate, terpenes, oximes, and nitriles. Only spider mite-infested eggplant and tobacco emitted a blend that was merely quantitatively different from the blend emitted by mechanically damaged or clean leaves. We hypothesized that plant species with a low degree of direct defense would produce more novel compounds. However, although plant species with a low direct defense level do use indirect defense to defend themselves, they do not always emit novel compounds. Plant species with a high level of direct defense seem to invest in the production of novel compounds. When plant species of the Fabaceae were compared to plant species of the Solanaceae, qualitative differences in spider mite-induced volatile blends seemed to be more prominent in the Fabaceae than in the Solanaceae.