Chemical defense of the mint plant, Teucrium marum (Labiatae)

The mint plant, Teucrium marum (family Labiatae), sometimes called cat thym e, contains two methylcyclopentanoid monoterpenes, dolichodial and teucrein . The former compound is potently anti-insectan. It is repellent to ants (M onomorium pharaonis) and induces preening reflexes in flies (Phormia regina ) and cockroaches (Periplaneta americana). Evidence is presented suggesting that dolichodial, which is presumed to be the plant's chief defensive agen t, is stored in the tiny epidermal capsules that beset the leaves. It is on ly when the leaves are injured land the capsules ruptured) that the leaves become repellent. Teucrein, in contrast, has no anti-insectan potency. It i s present predominantly in the leaf buds, unlike dolichodial, which is pres ent mostly in mature leaves. It is argued that teucrein is the storage comp ound from which dolichodial is generated during leaf development.