## 3 Results and Discussion  
The volatiles induced by \(P\). _japonica_ feeding were analyzed by GC-MS and the volatile components were identified as phenylacetonitrile, (_E_)-\(\beta\)-ocimene, linalool, DMNT and (_E_,_E_)-\(\alpha\)-farnesene, as shown in Figure 1 and Table 1. Volatile emission was not observed from either undamaged leaves or mechanically damaged leaves. These results suggest that volatile emission will be induced by a herbivore-specific factor, an elicitor present in the oral secretion of \(P\). _japonica_. It is known that a fatty acid-amino acid conjugate, volicitin, is a strong elicitor that is widely distributed in lepidopteran caterpillars [16] and also found in cricket and fruit fly [17]. Volicitin induces the emission of volatile blends composed of terpen, green leaf volatiles and indole [4]. Inseptin is a peptidic elicitor found in oral secretions of lepidopteran larvae, _Spodoptera frugiperda_, which promote either defense-related phytohormone production or herbivore-induced volatile emission, such as DMNT [7]. Caeliferins have been identified as nonlepidopteran elicitors from the American bird grasshopper, _Schistocerca americana_, which also induce volatiles from plants similar to caterpillar feeding [5]; however, there is no example in which the elicitor was identified from Coleoptera and that the elicitor induces nitrile emission from plants. Four terpenes, (_E_)-\(\beta\)-ocimene, linalool, DMNT and (_E_,_E_)-\(\alpha\)-farnesene, have been found as _P. japonica_ feeding-induced volatiles from the leaves of grape, _Vitis labrusca_ and crabapple, _Malus_ spp. [18,19]; however, _F. sachalinensis_ is an unique species that emits phenylacetonitrile infested by the same herbivore, _P. japonica_. Although it has not been determined whether these terpenes attract beetles, the beetles prefer the leaves of _V. labrusca_ and _Malus_ spp. infested by _P. japonica_ feeding than undamaged leaves [18,19] and thus, the herbivore-induced volatiles are likely to serve as host location cues for the beetles. The above terpenes are well-known volatiles induced by insect feeding, while there are only a few examples in which phenylacetonitrile was found as an herbivore-induced volatile. Phenylacetonitrile has been found from insect-infested Manchurian ash, _Frazinus mandshurica_[10] and _Brassica_ spp. [8,20], and mite-infested apple leaves [21]. Phenylacetonitrile found from caterpillar-infested _B. rapa_ has been shown to attract parasitoid wasps [20]. Phenylacetonitrile is also known as one of the floral scent components of Orchidaceae, such as _Diaphananthe pellucida_[22] and Cactaceae [23]. This volatile compound may be a potential chemical cue to attract various types of insects, for example, natural enemies, flower-visiting insects, and herbivores. after MeJA treatment. The emission of two terpenes increased and reached almost maximum 18 h after MeJA treatment. The increase of phenylacetonitrile emission, which initially lagged behind those of terpenes, was time dependent during the experimental period (24 h, Figure 2). All of the volatile emission triggered by MeJA was suppressed under constant dark conditions to 29-39% of that under constant light conditions (data not shown). It is suggested that light is essential for volatile production and/or emission together with activation of the JA signaling pathway. As _P. japonica_ diurnally infests the leaves of _F. sachalinensis_, it is reasonable for _F. sachalinensis_ to response under light conditions. It could also be favorable for _P. japonica_ to use photoperiod volatile emission from _F. sachalinensis_ as an attractant. Plant nitriles are known as one of the degradation products of glucosinolates, mostly found in the Brassicaceae family. In this system, glucosinolates are initially hydrolyzed by myrosinase which catalyzes the glucosinolates when plant tissue is physically damaged by cutting, grinding or chewing [24]. In _F.