Many ants forage at extrafloral nectar on plants and provide the plant with some measure of protection from herbivory. These nectars contain sugars, amino acids and, often, other compounds. The role of amino acids in attracting ants to extrafloral nectars was studied by baiting with Karo-syrup-based solutions. Control (without amino acids) and experimental (with amino acids) solutions were placed in second growth forest in Trinidad, W.I. The number of ants visiting the solutions was counted at fiveminute intervals for 45 min. In tests of solutions with only one amino acid, bothLeptothorax sp.andMonomorium sp.visited solutions with alanine, arginine, serine, cysteine, methionine or aspartic acid more frequently than sugaronly controls.Monomoriumpreferred control solutions to tyrosine solutions;Leptothoraxpreferred control solutions to histidine solutions.Leptothoraxdid not discriminate between control and tyrosine solutions;Monomoriumdid not discriminate between control and histidine solutions. However, in six of eight tests of combinations of amino acids, ants visited control solutions more frequently than experimental solutions. These results suggest that ants can act as selective agents, favoring plants with particular amino acids in their nectars.
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