Variability in the parasitoid community associated with galls of Diplolepis variabilis (Hymenoptera: Cynipidae): a test of the distance decay hypothesis Jordan A. Bannerman, 1 Joseph D. Shorthouse, Jason Pither, Robert G. Lalonde Abstract—Galls of Diplolepis variabilis (Bassett) (Hymenoptera: Cynipidae) on their host plant Rosa woodsii Lindley (Rosaceae) support a diverse community of parasitoid and inquiline wasps that exploit the gall inducer and the gall itself. Here, we studied quantitative variation in local structure of the gall community in the Okanagan Valley of southern British Columbia, Canada, from the United States border north, to test the hypothesis that dispersal limitation would generate a distance decay in gall community similarity. We also explored gall community richness in relation to latitude, as the northern range limit of the gall inducer occurs within our study area. We found that gall communities exhibited strikingly similar composition across the study region, with most of the major inquilines and parasitoids present across the gall’s range. However, the increased richness of rare parasitoid taxa near the northern range limits of D. variabilis generated a marginally significant positive relationship between gall community richness and latitude. Overall, our study suggests that dispersal constraints do not influence the composition of the Diplolepis Geoffroy gall community at regional scales, and that gall communities offer useful models for studying the association between community structure and range limits. Re ´sume ´—Les galles de Diplolepis variabilis (Bassett) (Hymenoptera: Cynipidae) sur leur ho ˆte Rosa woodsi Lindley (Rosaceae) contiennent une communaute ´ diverse de gue ˆpes parasitoı ¨des et inquilines qui exploitent l’insecte gallige `ne et la galle elle-me ˆme. Nous e ´tudions la variation quantitative de la structure locale de la communaute ´ des galles dans la valle ´e de l’Okanagan du sud de la Colombie-Britannique, a ` partir de la frontie `re des E ´ tats-Unis vers le nord, afin de tester l’hypothe `se selon laquelle la restriction de la dispersion cre ´e un de ´clin de la similarite ´ entre les communaute ´s des galles en fonction de la distance. Nous examinons aussi la richesse des com- munaute ´s des galles en fonction de la latitude, parce que la limite nord de l’aire de re ´partition de l’insecte gallige `ne se trouve dans notre re ´gion d’e ´tude. Les communaute ´s des galles pre ´sentent des compositions remarquablement semblables dans toute la re ´gion d’e ´tude et la plupart des inquilins et des parasites importants sont pre ´sents sur toute l’aire de re ´partition de la galle. Cependant, la richesse accrue de taxons rares de parasitoı ¨des pre `s des limites nordiques de l’aire de re ´partition de D. variabilis produit une relation positive significative entre la richesse de la communaute ´ des galles et la latitude. Globalement, notre e ´tude indique que les contraintes a ` la dispersion n’influencent pas la composition de la communaute ´ des galles de Diplolepis Geoffroy aux e ´chelles re ´gionales et que les communaute ´s des galles repre ´sentent des mode `les utiles pour l’e ´tude des associations entre la structure des communaute ´s et les limites des aires de re ´partition. J.A. Bannerman, 1 Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada V5A 1S6 J.D. Shorthouse, Department of Biology, Laurentian University, Sudbury, Ontario, Canada P3E 2C6 J. Pither, Department of Biology, Biodiversity and Landscape Ecology Research Facility, University of British Columbia Okanagan, 3333 University Way Kelowna, British Columbia, Canada V1V 1V7 R.G. Lalonde, Department of Biology, University of British Columbia Okanagan, 3333 University Way Kelowna, British Columbia, Canada V1V 1V7 1 Corresponding author (e-mail: jab32@sfu.ca). doi:10.4039/tce.2012.48 Received 7 November 2011. Accepted 15 December 2011. Can. Entomol. 144: 635–644 (2012)  2012 Entomological Society of Canada 635