NECTAR PRODUCTION, COMPOSITION, ENERGETICS AND POLLINATOR ATTRACTIVENESS IN SPRING FLOWERS OF WESTERN NEW YORK

High Performance Liquid Chromatography (HPLC) was used to determine specific sugar ratios (fructose, glucose and sucrose) in nectars of nine families of flowering plants. All nectars contained all three sugars with the exception of that of Asclepias. Asclepias nectar was nearly a pure sucrose solution. Sucrose/hexose ratio was correlated with flower morphology, with tubular flowers having more sucrose and open flowers having more hexose. Open flowers contained nectar whose concentration was more affected by relative humidity than tubular flowers. Available nectar in unbagged flowers was found in volumes of 0. Ito 5 Al (17.5 to 68.2% sugar). Total sugar available per blossom amounted to 0.07 to 3.54 mg. We note that care must be taken in converting % concentration to mg sugar. Energetic yield was not as variable as the other measures and ranged from 0.72 to 3.58 cal/,ul. Total daily nectar production was measured in five families and 24-hr sugar production varied from 0.64 to 5.52 mg per flower. Insect nectar feeders frequently searched many blossoms with little or no reward, but were rewarded sufficiently at rare "lucky hit" blossoms which contained relatively large nectar rewards. Insect pollinators did not seek nectars of specific sucrose-hexose ratios, but instead took nectar where caloric reward and accessibility made it most profitable. POLLINATION iS successful in many plant species as a consequence of pollinators seeking nectar. Yet little data are available on nectar properties and production in flowering plants of the northern United States. Data on nectar are lacking even for important agricultural plants, the pollination success of which is highly dependent on animal pollinators. Although much work has been done on nectars in southern and soutwestern states (e.g., Oertel, 1944; v6n Handel, Haeger and Hansen, 1972; Baker and Baker, 1975, 1979; Loper, Waller and Berdel, 1976), Finland (Kapyli, 1978), Germany (Beutler, 1953; Huber, 1956) and England (Wykes, 1953; Corbet et al., 1979), "our knowledge of nectar is very limited" (Robinson and Oertel, 1975, p. 286) particularly in the northern United States. I Received for publication 5 July 1980; revision accepted 25 October 1980. Supported by SUNY Research Foundation grant 7266A (EES). We thank H. D. Hammond and C. Gehris for help in identifying plant specimens, and the following specialists for reading an earlier draft of the manuscript and for their helpful suggestions: L. Walter Macior, University of Akron; Stephen L. Buchmann and Gordon D. Waller, U.S.D.A., SEA Tucson, AZ; Robert W. Shuel, University of Guelph, Guelph, Ontario; Herbert G. Baker and Irene Baker, University of California, Berkeley; and H. David Hammond, State University of New York, Brockport. Most studies on nectar have been on total sugar content and have not dealt with sugar ratios until recently (Baker, 1978; Baker and Baker, 1979, and unpubl. data), attractiveness or availability to pollinators, factors affecting production, or non-sugar constituents, although flavonoids, amino acids, lipid and volatiles in nectar have recently been reported (Baker and Baker, 1975; Baker, 1977; Erickson et al., 1979; Scogin, 1979), as have microclimate effects (Corbet, Unwin and Pr's-Jones, 1979; Corbet et al., 1979). Research on nectar is reviewed by Shuel (1970, 1975, and unpubl. data) and Baker and Baker (unpubl. data) who note that specific constituents of nectars influence the preference of foragers. Waller, Carpenter and Ziehl (1972), for example, found that high K+ content in onion nectar reduced honey bee visitation. These constituents, then, may directly affect pollination. Shuel and Baker and Baker further emphasize the necessity for basic biological data on nectar and its secretion. In this paper we describe some aspects of nectar production, amounts of nectar available and its constituency, including qualitative and quantitative analyses of sugars. Finally, we correlate these data with field observations of visits by nectarivores. The results contribute