Flower Defenses Against Nectar-Pilferage by Ants

Abstract

ro determine palatability, floral nectars from 25, and floral tissue extracts from 17, plant species of wet and dry forests of Costa Rica were offered to foraging ants in pairwise tests with sugar solutions. Nectars from all 25, and floral tissues from 10, species were analyzed chemically to ascertain the presence of potentially attractive and deterrent substances. In general, floral nectars are palatable to ants, whereas floral tissues showed highly variable palatability. We observed ants foraging in flowers of only 10 species of plants. Defense from nectar thievery by chewing insects seems most often to involve varying degrees of chemical and morphological modification of floral parts, rather than by the production of deterrent compounds in the nectar itself. FLOWERS THAT OFFER NECTAR as a primary reward to pollinators are common in the tropics. Nectar is generally nutritious and energy-rich, and pollination and seed set regularly occur as a result of the nectargathering activities by a wide array of animals, including many hymenoptera. Ants, however, are only rarely considered reliable pollinators (Kerner von Marilaun 1878, Proctor and Yeo 1972, Hickman 1974, Faegri and van der Pijl 1979), even though they are extremely abundant in a wide variety of habitats and are notorious for their skill in locating even small amounts of sugar. It is surprising that observations in the tropics reveal ants foraging for nectar in flowers only occasionally (van der Pijl