Homopterans

Ants are notorious for the habit of maintaining colonies of homopterans on plants (Figure 7). The principal families involved are the Membracidae or treehoppers, the Cicadellidae (Jassidae) or leafhoppers, the Psyllidae or “lerps,” the Fulgoridae or planthoppers, the Aphididae or plant lice, the Coccidae or soft scales, and the Pseudococcidae or mealybugs. Together they represent thousands of different interactions with ants, the majority still undescribed and unstudied. Interactions between homopterans and ants have been reviewed by Way (1963) and many are fundamentally mutualistic. The Homoptera secrete honeydew on which the ants feed. In return, the ants provide a number of vital services to the homopterans.

Homopterans take sap directly from the phloem through the slender mouthparts. Phloem contents are under several atmospheres of hydrostatic pressure and little effort is required for ingestion. However, the animals are capable of regulating their intake (Kennedy & Fosbrooke 1972). Changes in the chemical constitution of the sap occur during its passage through the homopteran gut so that when it becomes available to ants as honeydew it contains a variety of sugars, organic acids, alcohols, plant hormones, salts, vitamins, amino acids, and amides (Brian 1977). The main nitrogenous components of honeydew are amino acids, but these fluctuate widely according to the condition of the host plant (Mittler 1958; Llewellyn, Rashid, & Leckstein, 1974). However, a low nitrogen content in the sap stimulates the homopterans to increase the rate of feeding.