The pattern, rate, and range of within-patch movement of a stem-galling fly

J. T. Cronin, University of North Dakota
K. Hyland, University of North Dakota
W. G. Abrahamson, University of North Dakota


1. Information on the movement of insects is critical to understanding the spatial spread, dynamics, and genetic structure of their populations, as well as their interactions with other species. With this in mind, the movement behaviour of the stem-galling fly Eurosta solidaginis Fitch (Diptera: Tephritidae) was investigated. 2. Fluorescent-marked adults were released at a single location within pure patches of the host plant, tall goldenrod Solidago altissima, and their distributions censused repeatedly throughout the day. 3. Following their release, male and female flies redistributed themselves in a manner that was well described by a simple-diffusion model. The diffusion rate was independent of fly density and time since flies were released. 4. Female flies dispersed at a significantly faster rate, and therefore farther on average, than males. Based on the diffusion model, it was estimated that at 2.5-3.0 h post release, males and females had a median dispersal distance of only 2.0 and 2.5 m respectively. Furthermore, 95% of the males were estimated to have dispersed no more than 5.9 m, and females no more than 6.4 m. 5. Post-release censuses suggested that flies were most active during mid morning, disappeared from the site at a rate of 10-15% per hour (most likely due to mortality), and survived for less than 2 days. Based on the rate of spread, diel activity, and liberal estimates of longevity in the field, 50% of the ovipositing females were predicted to have had a maximum lifetime range of movement within a patch of hosts of ≤ 51 m (95% were expected to have been limited to ≤ 130 m). 6. These data are used to assess whether the absence of a positive correlation between host-plant preference and offspring performance in this system could be due to the limited scale of dispersal of this species relative to the spatial scale at which its oviposition behaviour has been studied.