Population dynamics of the northern tamarisk beetle (Diorhabda carinulata) in the Colorado River Basin

This report details two studies that examine the spread of the introduced tamarisk beetle over parts of the Southwestern United States. The first chapter documents plant phenology and beetle abundance and movement along the Dolores and San Juan Rivers, two major tributaries of the Colorado River. This study demonstrates that D. carinulata population-movement patterns can be highly influenced by the availability of beetle food resources and that local beetle “boom and bust” events are common. The second study demonstrates that the extent and timing of tamarisk defoliation are predictable on the basis of (1) abiotic cues for D. carinulata activity, (2) spatial distributions and abundances of D. carinulata across a site, and (3) movement of D. carinulata as a result of available tamarisk foliage. A significant positive correlation exists between the spatial distributions of D. carinulata populations in the fall and those of the first generation of larvae in the following spring, suggesting that the extent of tamarisk defoliation as a result of abundant larval populations is predictable. The results of these two studies will enable conservationists to better understand the variable timing of tamarisk defoliation events across a landscape and provide a template to forecast tamarisk defoliation levels and rates in areas that have yet to be colonized by D. carinulata.