Green leaf volatiles (GLV) are organic compounds released by plants. 
Some of these chemicals function as signaling compounds between either plants of the same species, of other species, or even different lifeforms like insects.
Green leaf volatiles are involved in patterns of attack and protection between species.  They have been found to increase the attractive effect of pheromones of cohabiting insect species that protect plants from attacking insect species. For example, corn plants that are being fed on by caterpillars will release GLVs that attract wasps, who then attack the caterpillars.  GLVs also have antimicrobial properties that can prevent infection at the site of injury.
GLVs include C6-aldehydes [(Z)-3-hexenal, n-hexanal] and their derivatives such as (Z)-3-hexenol, (Z)-3-hexen-1-yl acetate, and the corresponding E-isomers.