Date: 3/30/99

Time: 10:35

Type: Symposium

Number: 108

Population dynamics and movement patterns of two phytophagous prairie beetles

*M.J. St Pierre and S.D. Hendrix, Department of Biological Sciences, University of Iowa , Iowa City, IA 52242-1297
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Little is known about how phytophagous prairie insects cope with the large-scale fragmentation of their habitat, although they comprise a large proportion of the biodiversity of prairie communities. In summer, 1998 we conducted mark-recapture experiments with two phytophagous beetles to determine their population dynamics and their ability to track their spatially variable host plants. The study species were Rhyssematus lineaticollis Say (Coleoptera: Curculionidae), a small (5-8mm long) roughened weevil herbivore of Asclepias syriaca, and Chrysochus auratus Fabricius (Coleoptera: Chrysomelidae), the goldsmith beetle, a common herbivore of dogbanes (Apocynum sp.) in Iowa. In the case of R. lineaticollis, we observed no dispersal between patches of A. syriaca greater than 50m apart and even dispersal between plants within a patch was infrequent. In large A. syriaca patches (>100 plants), a second summer generation occurs which may be absent in smaller patches (<40 plants). Weevil numbers were low (<10 weevils per 100 plants) throughout the study (late June - early September) and few were recaptured after their initial marking, resulting in population estimates with low confidence. For C. auratus, observed dispersal distances, dispersal frequencies and mating frequencies differed significantly between a prairie remnant and a railroad right-of-way. Greater movement and higher mating frequencies were seen at the railroad right-of-way, where the plants appeared to be more vigorous. At the prairie remnant, peak abundance occurred earlier and beetle numbers dropped of much more dramatically than at the railroad site.

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