The Role of the Extrafloral Nectaries of Catalpa Speciosa in Limiting Herbivory and Increasing Fruit Production

The leaves of Catalpa speciosa (Bignoniaceae) have extrafloral nectaries that are active from early June to September. Peak nectar secretion occurs in late June and early July when the eggs and young larvae of the first generation of the principal herbivore, Ceratomia catalpae (Sphingidae), are present. Leaves that have been damaged by this herbivore secrete significantly more nectar than undamaged leaves. The nectaries are visited by various species of ants, ladybird beetles, and a parasitoid. These predaceous insects attack and/or remove the eggs and young larvae of the herbivore. A series of ant exclusion experiments show that branches without ants have significantly fewer larvae removed, have significantly more leaf herbivory, and produce significantly fewer mature fruits than control branches (with ants). These data suggest that secretion of extrafloral nectar by C. speciosa and its subsequent harvesting by insects is mutually beneficial to both the plant and the predaceous insects.