title: Parasitoids of the goldenrod gall moth: effects of scale on spatial density dependence.
abstract: A parasitoid assemblage consisting of four hymenopteran species caused larval and pupal mortality of the host Gnorimoschema gallaeosolidaginis. In the absence of discrete host patches, the relationship between densities of hosts and parasitized hosts was examined on scales of 0.25, 1, 4, 16 and 25 m2within a 400 m2plot and between ten 16 m2plots within a 1·3 km2area. Within the 400 m2plot, positive density dependence was observed on scales of 1, 4 and 16 m2. Rates of parasitism were found to be density independent across the ten 16 m2plots. The nature of parasitoid and host spatial patterns were examined at the 400 m2plot by using Goodall's (1974) paired-quadrat variance function, and by fitting the observed distribution of galls and parasitized galls to the Poisson and negative binomial on three scales. Postive density dependence at the 400 m2plot occurred in the context of a host density gradient and may indicate aggregation of search time by parasitoids. However, significant responses on scales of 4 and 16 m2may only reflect the sum of parasitoid responses on lower scales because of this gradient. Predominance of significant responses on a 1 m2scale may be related to the high degree of variation in host density, and limits to active searching range of parasitoids.
authors.affiliation: Department of Zoology, University of Toronto, M5S 1A1, Toronto, Ontario, Canada.
authors.forename: Lorne D
authors.initials: LD
authors.lastname: Rothman
authors.affiliation: Department of Entomology, Royal Ontario Museum, 100 Queen's Park, M5S 2C6, Toronto, Ontario, Canada.|Department of Zoology, University of Toronto, M5S 2C6, Toronto, Ontario, Canada.
authors.forename: D Christopher
authors.initials: DC
authors.lastname: Darling
keywords: Density dependence; Gnorimoschema gallaesolidaginis; Gradient; Parasitoid; Scale