This is a "sweet" example of how a tree can force ants to only be able to survive on that species of tree through manipulating their diet! Acacia trees in South America provide housing for mutualistic ants in their thorns - the ants protect the tree from herbivores by attacking anything that tries to damage the tree, and the tree provides the ants nectar to feed on in return.
However, the tree has altered its nectar so it contains an enzyme (chitinase) that disables production of another enzyme (called invertase) in ants that allows ants to digest sucrose, which is the sugar that is a major component of the nectar they feed on. THEN, the acacia provides invertase with the sucrose in its nectar (other plant species only have sucrose in their nectar and not invertase) so that the ants can drink the acacia nectar and use the invertase (which the ants can no longer produce themselves) to digest the sucrose! After an adult ant has fed from the acacia tree just once, it can never survive from feeding on nectar from other plant species again.
http://news.nationalgeographic.com/news/2013/11/131106-ants-tree-acacia-food-mutualism/
However, the tree has altered its nectar so it contains an enzyme (chitinase) that disables production of another enzyme (called invertase) in ants that allows ants to digest sucrose, which is the sugar that is a major component of the nectar they feed on. THEN, the acacia provides invertase with the sucrose in its nectar (other plant species only have sucrose in their nectar and not invertase) so that the ants can drink the acacia nectar and use the invertase (which the ants can no longer produce themselves) to digest the sucrose! After an adult ant has fed from the acacia tree just once, it can never survive from feeding on nectar from other plant species again.
http://news.nationalgeographic.com/news/2013/11/131106-ants-tree-acacia-food-mutualism/