Fatty acid-amino acid conjugates (FACs), first identified from beet armyworm Spodoptera exigua larvae (Alborn et al., 1997), have been found in noctuid as well as sphingid caterpillar oral secretions and especially volicitin [N-(17-hydroxylinolenoyl)- L-glutamine, 17OH-volicitn] and its biochemical precursor, N-linolenoyl- L-glutamine, are known elicitors of induced volatile emissions in corn plants. We conducted FAC screening of 29 lepidopteran species and found FACs in 19 of these species (Yoshinaga & Mori et al., 2010). Thus, FACs are quite commonly synthesized through a broad range of lepidopteran caterpillars. From an evolutionary perspective, it is presumed that volicitin and the other FACs, although consequently unfavorable to the insect in the plant-herbivore interactions, are produced because they are essential part of the primary metabolism of the insects. In this context, we suggested that FACs in Spodoptera litura play an active role in nitrogen assimilation by regulating the amount of glutamine in the larval midgut (Yoshinaga & Mori et al., 2008). The benefits of the physiological function of FACs for the herbivores need to outweigh the costs caused by induction of plant defense