ON OPTIMAL NECTAR FORAGING BY SOME TROPICAL BEES (HYMENOPTERA, APIDAE)

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 wa s compared to nectar choice (figs 1-4, tables I-IV). In addition, fora ging assays tested meliponine response to 10 amino acid solutions (tab le V, fig 5). Optimal nectars were 35-65% sugar among bees, and appare ntly their modal forage. Bees also accepted suboptimal nectar, or were 'rate maximizers'. Two species had modes well below the means, indica ting facultative selection of dilute nectars. For pollination, heterog eneity and optimal nectar sweetness are likely key mechanisms causing forager fidelity. Mean sugar contents were 38, 44 and 48 for Euglossin i, 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 att ractiveness, but Melipona avoided glutamic acid, glycine, serine, alan ine and proline, responding comparably to 20-40% sugar solutions contr asted with 50% concentration.