Spectrophotometric Analysis of Sugars Produced by Plants and Harvested by Insects

SummaryA spectrophotometric method for assaying minute quantities of sugar in solution has been modified for use on nectaries of plants and on insects which gather nectar. A flower is rinsed (or an insect crushed) in a measured amount of water; 1 ml of sample solution is added to 1 ml of 5% phenol and 5 ml concentrated sulphuric acid. After 45–60 min the absorbance at 490 nm is measured with a spectrophotometer, and translated into weight of sugar by means of a standard curve. Hundreds of samples can be gathered each day, frozen, and analysed (100/day) during a slack season. As an example, results are given for the sugar content of Tilia nectar as the flower ages.