THE IMPORTANCE OF OSMOSIS IN NECTAR SECRETION AND ITS CONSUMPTION BY INSECTS

Nectar is a simple food consisting of varying proportions of sucrose, glucose and fructose dissolved in water. The mechanisms of its secreti on are poorly understood, Osmosis may explain why hexose-rich nectars are produced in larger volumes and are more dilute than sucrose-rich n ectars, Unless protected, nectar tends to equilibrate with ambient hum idity, and the concentrations available to flower visitors can vary fr om 7-70% w/w, Most nectars are osmotically concentrated, especially wh en rich in hexose sugars. The only digestion needed is sucrose hydroly sis, and monosaccharides and water are rapidly absorbed across the mid gut of insects. Large Eying insects feeding on nectar produce an exces s of water which must be eliminated by evaporation and excretion. Anim als which utilise this attractively packaged and easily digested food source may have osmoregulatory problems when nectar concentrations do not match their water requirements.