The influence of population density on communal gall sharing and parasitism rates for the manzanita leaf-gall aphid (Tamalia coweni)

Host-parasite interactions are a rich area of ecological research, and often central to the understanding of the species involved. The manzanita leaf-gall aphid, Tamalia coweni (Hemiptera: Aphididae) induces galls on the immature leaves of its host plants, shrubs of the genus Arctostaphylos (Ericaceae). These galls are subject to parasitism by a wide variety of species, including a close relative, Tamalia inquilinus. T. coweni frequently achieves high population densities, sometimes with more than ten galls sharing a single leaf. However, parasitism of these galls has not been explored as a potentially density-dependent process. The current research builds upon preliminary data that suggest a correlation between T. coweni gall density and parasitism rates. Additionally, it explores the unusual tendency of T. coweni to communally share galls with conspecifics, and whether this behavior has a relationship with population density.