Does deer browsing affect Tamalia galling aphid populations on manzanita (Arctostaphylos spp.) host plants?

In natural systems, interactions among herbivores sharing common food resources have important ecological implications. The interactions among insects, mammals, and their host plants may affect the dynamics of the herbivore populations. Under some conditions, Columbian black-tailed deer (Odocoileus hemionus columbianus) browse on manzanita shrubs (Arctostaphylos spp.) in the Big Chico Creek Ecological Reserve (BCCER) near Chico, California. The manzanita leaf-gall aphid (Tamalia coweni) induces galls, either along new leaf edges, or, occasionally, along the midrib vein. My field observations suggest that deer browsing extends the season for the aphid by promoting the growth of new foliage. In some cases, deer browsing on manzanita plants appears to have a positive effect on aphid populations. The purpose of this study is to establish the trophic relationships among leaf-galling aphids, Columbian black-tailed deer, and manzanita plants by examining the responses of leaf-galling aphids on manzanita plants to browsing by the deer. In field trials, I have established vertical partitioning on 70 sampling plants, such that each plant is divided into regions either subject to browsing, or excluded from browsing. Here I present data on Tamalia aphid populations as a function of browsing by black-tailed deer.