HERBIVORY AND DETRITIVORY ON FRESH-WATER MACROPHYTES BY INVERTEBRATES - A REVIEW

Aquatic macrophytes have been viewed as important to invertebrates as substrates for periphyton and epiphytic food, refuges from predation, heterogeneous substrates for co-existence, and upon senescence and death as detrital food sources. Direct herbivory on living macrophytes has been considered unimportant and has been understudied until recently. A review of the literature shows that, when looked for, invertebrate herbivory of macrophytes is more common than generally thought. Most herbivory on macrophytes is usually by specialized oligophagous herbivores which are placed phylogenetically in families and orders of primarily terrestrial insect groups (secondary invaders) that include a number of pest herbivores in terrestrial systems (e.g., chrysomelid and curculionid beetles, aquatic lepidopterans, and specialized dipterans). Herbivores from primarily aquatic invertebrate groups (primary aquatic invertebrates) are often generalists and also detritivores. These patterns and the use of macrophyte detritus by primary aquatic invertebrates do not appear to be determined by a low food quality of aquatic macrophytes, but are more likely related to deterrent chemicals present in both terrestrial and aquatic plants. In order to more clearly ascertain the importance of aquatic macrophytes as food and their interrelations with aquatic invertebrates, more mechanistic studies are needed of aquatic herbivores, herbivore damage to plants, and the secondary chemistry of aquatic plants.