The Nutritional Requirements of Phytophagous Insects : Why do Insects Feed on Plants?

Observations on phytophagous (plant-eating) insects showed that what the insect eats and how much it eats largely determines its economic importance. The food ingested and digested by the insect must fulfil its nutritional requirements for normal growth and development to occur. These requirements are complex and although most nutrients must be present in the diet, some may be obtained from other sources. Some nutrients may be accumulated and carried over from earlier stages of development, others may be synthesized by the insect from different dietary constituents, while others may be supplied by micro-organisms. A number of substances, particularly amino acids and vitamins, are essential for any development to occur, others while not essential, are necessary for optimal development. The balance between different constituents is also important. In the absence or imbalance of certain requirements growth may not occur, or may be impaired, or moulting may not occur. Phytophagous insects therefore feed to satisfy their requirements for essential nutrients and in doing so destroy enormous amounts of economic food and fibre. In addition to discussing dietary requirements and why phytophagous insects feed on plants, this paper reviewed dietary deficiencies and the problems associated with devising chemically defined artificial diets for phytophagous insects