[Edited_by_A._Ciancio,_C.N.R.,_Bari,_Italy_and_K.(Bookos.org)

HERBIVORY & PLANT DEFENSE
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performance under laboratory condition (Thaler et al., 2001). This induced resistance
often suppressed many communities of herbivores. The information on the plant
biochemistry, insect preference, performance and abundance may hence be helpful in
developing practical tools for insect management, through natural or induced plant
defense mechanisms (Thaler et al., 2001).
The amounts of signalling molecule may affect the efficacy of defense
metabolites. Quantitative relationships between induced JA levels and volatile
emissions in maize during Spodoptera exigua herbivory have been reported by
Schmelz, Alborn, Banchio, and Tumlinson (2003a). JA induced emission of indole
and sesquiterpenes (volatiles) limited the plant ethylene emission and also controlled
excessive volatile production. In another study (Schmelz, Alborn, & Tumlinson,
2003b), volicitin from the herbivore oral secretion induced JA levels, and
sesquiterpene volatiles were more excessively stimulated in maize than through
mechanical damage in absence of volicitin. Relatively more significant increase in
ethylene levels were recorded during beet army worm herbivory, than either by
wounding or volicitin treatments (Schmelz et al., 2003b).
Engelberth, Alborn, Schmelz, and Tumlinson (2004) reported that airborne
signals alert plants against insect herbivore attack. Green leafy volatiles including
six carbon aldehydes, alcohols and esters were commonly emitted by plants in
response to mechanical damage or herbivory. These volatiles induced intact
undamaged neighbouring corn seedlings to rapidly produce JA and emit
sesquiterpenes. These green leaf volatiles played a key role in plant – plant
signalling and plant-insect interactions. Heil (2004) reported that JA induced
defenses in lima bean (Phaseolus lunatus) was beneficial under natural condition.
Finally, Howe and Jander (2008) observed that herbivore insects use diverse
feeding strategies to obtain nutrients from their host plants. Plants responded to
herbivory with the production of toxins and defensive proteins that target
physiological processes in the insect. This strategy appears as a highly dynamic form
of immunity, initiated by the recognition of insect's oral secretions and emission of
signals from injured plant cells.
5.2. Plant Receptor Molecules
Cowpea (Vigna radiata) attacked by the fall armyworm Spodoptera frugiperda
perceived herbivory through inceptins, a proteolytic fragments of chloroplastic ATP
synthase γ-subunit regulatory regions (Schmelz et al., 2006). Inceptins (feasibly the
receptor molecule) induced volatile, phenylpropanoid and protease inhibitor
defenses in cowpea, against fall armyworm. It was also noted that S. frugiperda
larvae having previously ingested chloroplastic ATP synthase γ-subunit proteins
induced cowpea defenses after herbivory.
5.3. Defense Genes in Plants
Intracellular levels of free linoleic and linolenic acids increased in tomato leaves on
wounding (Conconi, Miquel, Browse, & Ryan, 1996). The intracellular signalling