The distribution of risk and density‐dependent mortality in the galls of Eurosta solidaginis, the goldenrod gall fly

Abstract

ABSTRACT. This paper explores the net effect of a suite of mortality factors on a sedentary prey, the larvae of the goldenrod gall fly, Eurosta solidaginis Fitch (Diptera: Tephritidae). Mortality is caused by unknown factors early in larval development, two species of parasitoid wasp (Hymenoptera: Eurytomidae), an inquiline beetle larva (Coleoptera: Mordellidae), and during the winter months downy woodpeckers Picoides pubescens (L.). Distribution of mortality among galls relative to prey (gall) distribution was measured and discussed with respect to the distribution of relative risk of predation. Galls are by and large contagiously distributed among quadrats, and mortality is distributed in a comparable pattern to that of galls. The pattern of mortality on Eurosta larvae is neither density‐dependent nor aggregated independently of gall distribution. Persistence in the system is probably a result of a combination of other factors such as adult mortality and early larval death which may have intergenerational density‐dependent effects, and the linkage of locally unstable sub‐populations via migration.