Plant Communication Initiated By Herbivore Interaction

 Alterations in phenotype limit the possibility of continued herbivory. staff/hopa/alwe3983/web/main_en.htm

 Predators of herbivores are drawn to the plant; they remove the herbivores.  Parasitoids are drawn to the plant; they attack the herbivores and keep them from eating as much- this increases the number of seeds produced

 Herbivores can be lured to the plant instead of herbivore predators.

 Jasmonic Acid ◦ A hormone necessary to stimulate indirect defense  Extrafloral nectar (EFN) ◦ Beckons ants ◦ Beckons carnivorous arthropods  For example, parasitic wasps

 Chemicals that are important in sending information ◦ Within a species ◦ Interspecies  Origin of the word is “semion”, meaning a “signal or mark”  One example: ◦ Undamaged wheat seedlings lure aphids ◦ Wheat seedlings that are being attacked by a significant number of aphids dispense odors that keep aphids away US_Navy_ N-0068T- 114_Storekeeper_Seaman_Virginio_Torres_from_Orland oUS_Navy_ N-0068T- 114_Storekeeper_Seaman_Virginio_Torres_from_Orland o,

Diagram by Pare and Tumlinson from the journal Plant Physiology, October 1999, Volume 121, page 326 Insect herbiv Insects secrete compounds from their mouths when eating such as volicitin. This causes the plant to diffuse volatiles that then attack predators of herbivores, such as parasitic wasps.

 Volatiles have structural semblances  They are distinct from volatiles diffused by ◦ Undamaged plants ◦ Plants not being eaten by herbivores  This implies stimulation of biosynthetic pathways ◦ That are related ◦ That are found in a variety of plant types ◦ That are perceptible by a wide range of insect parasitoids and predators

 Factors affecting amount or condition ◦ Degree of injury ◦ Behavior of insects when attacking plant  Factors affecting blend of a volatile compound ◦ Type of insect ◦ Juvenile or adult insect stage  Other compound classes ◦ Aldehydes ◦ Short chain alcohols

 Secreted in minutes after tissue injury  Stimulates extrafloral nectar (EFN) release in non-injured parts of injured plants  Stimulates other local plants  Can cause a “defensive response” alone  Can be necessary to stimulate a “defensive response  Gaseous nature of volatiles speeds communication in the damaged plant itself ◦ More rapid movement than an internal communication system

 Lima bean plants and apple trees that are injured by spider mites diffuse HI-VOCs that lure predatory mites  Corn and cotton plants diffuse HI-VOCs that lure hymenopterous parasitoids (wasps) when under attack by Lepidoptera larvae ◦ These parasitoids destroy the larvae by laying eggs in the larvae. This also ensures that more wasps will hatch  Female wasps can learn to detect different compounds when they successfully lay their eggs at a particular site where the compound is being released (4)

 Environmental conditions that cause a plant to produce more HI-VOCs ◦ “water stress” (in lima bean plants)  Environmental conditions that cause a plant to produce fewer HI-VOCs ◦ Low light intensity (in corn, cotton and lima beans) ◦ Shorter days (in corn, cotton and lima beans) ◦ Significant amounts of fertilizers (in celery plants)

 Scientists have speculated about why plants would waste metabolic energy to do this.  It is thought this is actually more like eavesdropping on a plant that is “warning” non-damaged parts of itself.

1. Heil, Martin and Silva Bueno, Juan Carlos. (2007). “Herbivore-Induced Volatiles as Rapid Signals in Systemic Plant Responses”. Plant Signal Behav May–Jun; 2(3): 191–193. Retrieved from: 2. Wayra G Navia-Giné, Wayra et al. (2009). “Insect-induced gene expression at the core of volatile terpene release in Medicago truncatula”. Plant Signal Behav July; 4(7): 639–641. Retrieved from: Dicke, Marcel and vanLoon, Joop. (2003). “Multitrophic effects of herbivore-induced plant volatiles in an evolutionary context”. Plant Signaling and Behavior. Retrieved from: Pare, P.W. and Tumlinson, J.H. (1999) “Plant Volatiles as a Defense against Insect Herbivores”. Plant Physiol October; 121(2): 325–332. Retrieved from: