Herbivore deme formation on individual trees: a test case

Neil S. Cobb, Thomas G. Whitham

Research output: Contribution to journalArticlepeer-review

41 Scopus citations


We examined the deme-formation hypothesis, which states that sessile herbivores on long-lived hosts become locally adapted to the defensive phenotypes of individual trees. We showed a five-fold increase in resistance by individual pinyon pines (Pinus edulis) to the pinyon pine needle scale (Matsucoccus acalyptus). Although such variation could represent a significant selection pressure favoring deme formation, two lines of evidence led to rejection of the hypothesis. First, there were no significant differences in mortality among scale populations in a reciprocal transfer experiment. Second, a seven-year experiment showed that mortality of newly founded, incipient scale populations was similar to established scale populations. While our experiments fail to support the deme-formation hypothesis, they do demonstrate significant variation in the resistance traits of a natural tree population. Although we feel that demeformation is still probable in this system, it is likely to occur on a larger geographic scale than individual trees as proposed by Edmunds and Alstad.

Original languageEnglish (US)
Pages (from-to)496-502
Number of pages7
Issue number4
StatePublished - Dec 1993


  • Deme formation
  • Fine-scale adaptation
  • Host plant resistance
  • Matsucoccus acalyptus
  • Pinus edulis

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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