Balanced Polymorphism in the Meadow Spittlebug, Philaenus spumarius

The meadow spittlebug, Philaenus spumarius, is one of the commonest field insects in many parts of North America, Europe, and Asia. The adults occur in a variety of sympatric color forms. 2. Four color forms were found in samples collected in alfalfa fields and in an abandoned field in southeastern Michigan. One of these forms occurs only in females. 3. No significant seasonal change in the relative frequency of three of the forms was found (a) in a seasonally declining population in the alfalfa fields, and (b) in a seasonally fluctuating population in the abandoned field. Nor were there any significant changes in relative frequency in samples collected on the abandoned field during four successive years. The relative frequency of the forms was not significantly different in the two habitats during one year. 4. A state of balanced polymorphism seems to exist in these populations. Possibly the relative frequency of the forms is determined by selection by predators.