Costs and benefits of gregarious feeding in the meadow spittlebug, Philaenus spumarius

Abstract

Abstract 1. To study the function of group living in a non‐social animal, costs and benefits of feeding in different group sizes (one to eight) were measured for nymphs of the meadow spittlebug (Philaenus spumarius) on tall goldenrod (Solidago altissima).2. In a controlled greenhouse experiment, the number of nymphs per plant had a significant influence on their mass as adults. Adult mass increased as group size went from one to five nymphs per plant, but fell as the group size increased beyond five. In contrast, the density of nymphs on a plant had no effect on the duration of nymphal development.3. Nymphal mortality increased linearly as the number of nymphs increased from one to eight per plant.4. These performance results suggest that the optimal group size of spittlebug nymphs reflects a compromise between bottom‐up influences (e.g. overcoming physical barriers to feeding on xylem) and within‐trophic‐level influences (e.g. avoiding competition for limited plant resources).5. In a survey of local populations of goldenrod, spittlebug nymphs were found to be slightly but significantly aggregated among host‐plant individuals. In addition, when more than one nymph occurred on a plant, the nymphs tended to feed in shared spittle masses.6. It is concluded that the aggregated dispersion pattern of spittlebug nymphs reflects an adaptive balance of coping with potentially conflicting demands from different trophic levels.