# Volatiles Emission by _Crotalaria nitens_ after Insect Attack
## 3 Discussion
Some plants recognize the attack of the caterpillar by the presence of molecules such as volicitin or its derivatives, present in the oral secretion of _Spodoptera exigua_ (Hubner) (Lepidoptera: Nocutiadese), which induce the emission of HIPVs from corn [44] or cotton [45] leaves. The results of the present study suggest that _C. nitens_ plants distinguished the attack of the _U. ornatrix_ caterpillars and activated a series of biochemical reactions that promoted volatile compounds release [1]. However, further research is required to determine whether the HIPVs induction was generated by specific molecules, enzymes, or microorganisms from the caterpillars' saliva. The volatiles released by _C. nitens_ leaves had been reported as herbivory-induced volatiles in other plants [46]. HIPVs are detected by insects to locate/avoid plants to use as oviposition sites [33; 34; 47]. In the present work, the blend of the HIPVs emitted by _C. nitens_ leaves after the caterpillar wounding significantly reduced the oviposition of the conspecific moths in damaged plants (28%) preferring to lay the eggs on those undamaged (72%). These results were akin to those reported in other species of Lepidoptera. For instance, [PERSON] et al. [30] observed that _H. virescens_ moths selected non-infested tobacco plants (_Nicotiana tabucum_) to lay the eggs (80%) and avoided the infested plants. The same behavior was registered for _T. ni_[31], _M. sexta_[32], _Manduca quinquemiculta_ ([PERSON]) (Lepidoptera: Sphingidae) [2], or _Spodoptera frigiperda_ ([PERSON]) (Lepidoptera: Nocutiidae) [48]. Changes in either the presence or relative abundance of the volatile compounds emitted by the plant upon caterpillar damage could have a completely different meaning for the moth, causing the plant not to be recognized as host [47]. Indeed, herbivore-induced volatiles of _C. nitens_ included linalo1 (11-13%), an oxygenated monoterpene known to have oviposition-deterrent properties against many insect species [2; 49; 50]. _trans_-\(\beta\)-Ocimene and DMNT, emitted by _C. nitens_ leaves in relative amounts of 9-19%, have shown to be repellents of stemborer moths, including _Busseola fusca_ ([PERSON]) (Lepidoptera: Nocutiidae), and attractants of pest's natural enemies in the push-pull system in maize crops [23], and DMNT also deterred moths of the leaf worm, _Spodoptera littoralis_ ([PERSON].) (Lepidoptera: Nocutiidae) from damaged plants of cotton (_Gossypium hirsutum_ L.). The ability of moths to recognize changes in plant volatiles could have the benefit of avoiding host plants already infested with insects, which reduces the competition for food resources of their future offspring [30; 47]. Other HIPVs identified in the present work have shown to be involved in the interaction between different organisms. GLVs, which first appeared due to herbivory or mechanical damage, have been reported in damaged leaves of maize seedlings [5; 35], _A. thaliana_[51], cotton [52], and black poplar (_Populus nigra_) [53], among others. GLVs have ecological functions such as attracting or repelling insects [54], _cis_-hex-3-enyl acetate showed to increased herbivory defenses in maize [55] and activated defense genes in black poplar [56]. _trans_-\(\beta\)-Caryophyllene has been reported as repellent of _Diaphorina citri_,a bacteria-spreading insect in citrus crops [57], and to induce resistance against microbial pathogens in neighboring plants [58]. Linalool, _trans-\(\beta\)_-ocimene, DMNT, and methyl salicylate attracted female mite (_Pltroseiulus persimilis_), a natural predator of another mite (_Tetranychus urticae_), considered a pest in lima bean plants (_Phaseolus lunatus_) [59]. Although _C. nitens_ emitted few amounts of _allo_-ocimene (0.18%), this compound has shown antifungal properties in _A. thaliana_[60]. \(\alpha\)-Humulene reduced the mating ability of _Ceratitis capitata_ females and males, a pest of various crops in the Mediterranean [61], and the _trans_-nerolidol was tested to induce resistance against herbivores and pathogens in tea plants [62].