On optimal nectar foraging by some tropical bees (Hymenoptera: Apidae)D.W. Roubika, D. Yanegab, M. Aluja Sa, S.L. Buchmannc and D.W. Inouyed
a Smithsonian Tropical Research Institute, Balboa, Panama
b Illinois Natural History Survey, 607, E Peabody Drive, Champaign, IL 61820, USA
c Carl Hayden Bee Research Center, 2000, East Allen Road, Tucson, AZ 85719, USA
d Department of Zoology, University of Maryland, College Park, MD 20742-4415, USA
Abstract - Sugar concentration in nectar foraged by 13 Euglossini, 16 Meliponini and 8 Centridini (Apidae) was monitored in floristically rich habitats. For 6 Meliponini, sugar solution profitability by imbibement rate was compared to nectar choice (figs 1-4, tables I-IV). In addition, foraging assays tested meliponine response to 10 amino acid solutions (table V, fig 5). Optimal nectars were 35-65% sugar among bees, and apparently their modal forage. Bees also accepted suboptimal nectar, or were 'rate maximizers'. Two species had modes well below the means, indicating facultative selection of dilute nectars. For pollination, heterogeneity and optimal nectar sweetness are likely key mechanisms causing forager fidelity. Mean sugar contents were 38, 44 and 48 for Euglossini, Meliponini and Centridini, respectively; modes averaged 3-4% higher. All bees used nectars of 30-45% sugar; some also used nectars of 10-15 or 65-70% sugar; others did not use nectar of over 60% sugar. Amino acid solutions of 35-80 mM concentration did not generally affect attractiveness, but Melipona avoided glutamic acid, glycine, serine, alanine and proline, responding comparably to 20-40% sugar solutions contrasted with 50% concentration.
Key words: nectar composition / optimal foraging / pollination