Extrafloral Nectaries: A Defense against Ant-Homoptera Mutualisms?

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Abstract
We propose that extrafloral nectaries may sometimes function to defend plants from ant-Homoptera mutualisms by weaning ants onto a plant-controlled diet of nectar. According to this hypothesis, extrafloral nectaries can be favored even in the absence of ant defensive behavior. As evidence we cite the following observations: 1) Many studies have shown no net, defensive benefit to plants of nectar feeding ants. 2) Many nectar-feeding ants tend Homoptera which are major plant disease agents and which may profoundly alter plant architecture and physiology. 3) Ants can be distracted from tending Homoptera by feeding them sugar and they may even destroy the Homoptera. 4) Nectar has very similar chemical composition to honeydew and its collection does not require the extensive husbandry that tending Homoptera does. 5) Nectar production has been documented to increase during infestations of Homoptera. 6) It is more difficult to produce chemical defenses against sap feeders than against chewing insects.