Insect visitation of peduncular and petiolar extrafloral nectar glands on castor bean (Ricinus communis L.) plants in Southern California

Abstract

Castor bean (Ricinus communis L.) is a myrmecophytic plant species with specialized extrafloral nectar (EFN) glands that serve to attract predatory insects, which in return defend plant-tissues against herbivores. The EFN glands on castor bean plants are located along the leaf petioles as well as on the peduncles of its imperfect (unisexual) flowers. This field-project evaluates the richness, diversity, and species assemblage of insects visiting EFN glands located on (female and male) flower peduncles and leaf petioles on castor bean plants growing in a Southern California coastal landscape. We detected that EFN glands on female-flower peduncles were visited by an insect community that was distinct from that of the other two EFN gland types on castor bean.  Additionally, the insects visiting EFN glands on male-flower peduncles more closely resembled those observed visiting EFN glands on leaf petioles. We conclude that the observed differences in the biotic defense of foliar and unisexual floral tissues on castor bean are congruent with the optimal plant-defense strategy of a monoecious pioneer species.\r\r\tKey words: Ant-plant interactions, monoecious, mutualism, myrmecophyte, plant-defense optimality, sexual dimorphism.