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. Key words: Ant-plant interactions, monoecious, mutualism, myrmecophyte, plant-defense optimality, sexual dimorphism.
Highlights
Extrafloral nectar (EFN) glands are specialized plant structures that secrete nectar but are neither part of the flower structure nor associated with pollination (RicoGray and Oliveira, 2007)
Intraspecific comparisons of the insect communities visiting castor bean EFN glands located on female-flower peduncles, male-flower peduncles, and leaf petioles, showed marked differences in terms of species richness, diversity and composition
Based on the relative slopes of each rank-abundance curve, the species evenness was highest among insects visiting female-petiolar EFN glands
Summary
Extrafloral nectar (EFN) glands are specialized plant structures that secrete nectar but are neither part of the flower structure nor associated with pollination (RicoGray and Oliveira, 2007). EFN glands are visited by a large variety of predatory insects, such as ants, wasps and parasitoids (Del-Claro et al, 2013), which often serves to increase both the predation and parasitism rates of herbivorous insects feeding on plants bearing. The primary literature advances at least four hypotheses regarding the evolutionary role of EFN glands: (1) they help plants excrete excess carbohydrates (Beattie, 1985); (2) they attract predatory insects to defend plant tissues from herbivores (Byk and Del-Claro, 2011); (3) they deter ants from interrupting or interfering with pollination (LeVan et al, 2013); and (4) they discourage ants from tending phloem-feeding insects, such as Mealybugs (Becerra, 1989).
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