The Importance of Osmosis in Nectar Secretion and its Consumption by Insects

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Abstract
SYNOPSIS. Nectar is a simple food consisting of varying proportions of sucrose, glucose and fructose dissolved in water. The mechanisms of its secretion are poorly understood. Osmosis may explain why hexose-rich nectars are produced in larger volumes and are more dilute than sucrose-rich nectars. Unless protected, nectar tends to equilibrate with ambient humidity, and the concentrations available to flower visitors can vary from 7–70% w/w. Most nectars are osmotically concentrated, especially when rich in hexose sugars. The only digestion needed is sucrose hydrolysis, and monosaccharides and water are rapidly absorbed across the midgut of insects. Large flying insects feeding on nectar produce an excess of water which must be eliminated by evaporation and excretion. Animals which utilise this attractively packaged and easily digested food source may have osmoregulatory problems when nectar concentrations do not match their water requirements.

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