The influence of Tamarix ramosissima defoliation on population movements of the northern tamarisk beetle (Diorhabda carinulata) within the Colorado Plateau: Chapter 18

The northern tamarisk beetle (Diorhabda carinulata) was introduced to the Colorado Plateau within the Colorado River Basin in 2004, in an effort to control invasive/exotic tamarisk (Tamarix ramosissima) plants. Since release, there has been rapid beetle colonization and subsequent defoliation of tamarisk along the Colorado River corridor. We collected plant phenology and beetle abundance data from the Dolores and San Juan rivers, two major tributaries of the Colorado River, to document tamarisk defoliation and beetle movement patterns. We found D. carinulata population movement patterns to be highly influenced by the availability of food resources, with local beetle boom and bust events appearing common. Beetles were able to defoliate from 35-65 km of river corridor tamarisk habitat each year. Following intensive tamarisk defoliation of large riparian reaches, beetles displayed a pattern of temporary abandonment in the following year with recolonization of that habitat in the subsequent year. Larvae were found primarily in areas that had partial defoliation, while adults occurred throughout the river corridor but most often on the leading edge of defoliated habitats. Understanding this type of beetle behavior and movement patterns will be useful in the management of areas where D. carinulata has been established, and in areas where it has not yet colonized. This will also assist land managers to further understand how defoliation and the presence of D. carinulata influence tamarisk-dominated habitats within Colorado Plateau riparian ecosystems.