Effect of the classical biocontrol agent Diorhabda carinata on generalist arthropod predators in saltcedar (Tamarix spp.)

Classical biocontrol has faced criticism for inadequately addressing potential risks of importing nonnative plant predators for control of exotic weeds. Although host plant specificity is well studied before their introduction, other potential deleterious effects have been proposed, including damage to community structure through altering food web dynamics. If arthropod biocontrol agents explode in numbers, generalist arthropod predator populations could exploit the new food source in a numerical response, potentially leading to a trophic cascade.  The larger tamarisk beetle Diorhabda carinata was imported from Asia and released to control the invasive shrub species complex Tamarix spp. along rivers in the Texas panhandle, and recently crossed into Oklahoma. By comparing these newly colonized areas to those not yet reached by the beetle, I aim to achieve three objectives. First, to measure the population response in the field of two generalist arthropod predators demonstrated to feed on the beetle in lab trials (a green lacewing, Chrysoperla rufilabrus and a reduviid, Zelus tetracanthus), through abundance sampling of beetles and predators. Second, to quantify the potential and actual predation rate of these two species on the beetle using a combination of qPCR gut content analysis and sleeve cage studies. Third, to identify the frequency of intraguild predation and cannibalism using sleeve cage studies at different predator/prey density ratios, to better reveal complexities of food web dynamics. I anticipate that the two predator species will show different population abundance response curves based on dissimilar life history traits, and that intraguild predation will influence actual field dynamics.