Field methods for sampling and storing nectar from flowers with low nectar volumes

Abstract

Although several methods of sampling and storing floral nectar are available, little information exists on sampling and storing nectar from flowers with low nectar volumes. Methods for sampling and storing nectar from the flowers of species with low floral nectar volumes (Eucalyptus species. Sampling with microcapillary tubes, blotting up with filter paper, washing and rinsing were compared to determine masses of sugars recovered and differences in sugar ratios. Storage methods included room temperature, refrigeration and freezing treatments; the addition of antimicrobial agents benzyl alcohol or methanol to some of these treatments was also evaluated. Nectar samples were analysed using high-performance liquid chromatography and the masses of sucrose, glucose and fructose in each sample were determined. Masses of sugars varied significantly among sampling treatments, but the highest yielding methods, rinsing and washing, were not significantly different. A washing time of 1 min was as effective as one of 20 min. Storage trials showed that the sugar concentration measurements of nectar solutions changed rapidly, with the best results achieved for refrigeration with no additive (sucrose and fructose were stable for at least 2 weeks). Sugar ratios, however, remained relatively stable in most treatments and did not change significantly across 4 weeks for the methanol plus refrigerator and freezing treatments, and 2 weeks for the refrigeration treatment with no additive. Washing is recommended for nectar collection from flowers with low nectar volumes in the field (with the understanding that one wash underestimates the amounts of sugars present in a flower), as is immediate analysis of sugar mass. In view of the great variation in results depending on nectar collection and storage methods, caution should be exercised in their choice, and their accuracy should be evaluated. The use of pulsed amperometric detection, more specific than refractive index detection, may improve the accuracy of nectar sugar analysis.