Intraspecific variation in herbivore fitness can generate populations locally adapted to different host species, or even individual plants. To test for occurrence of deme formation, local host species adaptation, and interspecific variation in host quality, we quantified survival and fecundity of pine needle scale, Chionaspis pinifoliae (Fitch), on red (Pinus resinosa Ait.) and Scots pine (P. sylvestris L.) in unmanipulated populations, as well as intra- and interspecific reciprocal host transfer experiments. Intraspecific transplants generated no evidence for deme formation on red or Scots pine as scale performance on natal and conspecific hosts did not differ, possibly because host uniformity and proximity may not have generated requisite environmental heterogeneity and genetic isolation. We did observe evidence for local adaptation to Scots, but not red pine. Survival of scales originating on Scots was 6 times higher on conspecific hosts relative to scales transferred from red to Scots pine; their fecundity was also higher, but the effect was not as strong. However, parental effects also contributed to this pattern, at least partially. In all experiments, Scots pine was a much better host than red pine, which is consistent with previous hypotheses that the long coevolutionary history between pine needle scale and red pine has selected for host defenses. These results add to previous studies that question the importance of deme selection in interactions between scales and trees, but do suggest that bottom-up effects contribute substantially to the variation in pine needle scale population dynamics frequently observed on different host species.
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