Using Tamarisk Beetle Pheromone Lures to Reduce Re-growth of Tamarisk Following Tree Cutting
Cynthia Brown1*, Hannah Ertl2, Dan Bean3, Zeynep Ozsoy4, Farley Ketchum Sr.5, and Emily Swartz6
1Colorado State University Department of Agricultural Biology/ Graduate Degree Program in Ecology, 1177 Campus Delivery, Fort Collins, Colorado, USA
2Trees, Water & People Indigenous Lands Program, 633 Remington Street, Fort Collins, Colorado, USA
3Colorado Department of Agriculture Palisade Insectary, 750 37 8/10 Road, Palisade, Colorado, USA
4Colorado Mesa University Department of Biological Sciences, 1100 North Avenue, Grand Junction, Colorado, USA
5Ute Mountain Ute Tribe Environmental Programs Department Colorado, 520 Sunset Boulevard, Towaoc, USA
6Colorado State University Department of Forest and Rangeland Stewardship,1472 Campus Delivery, Fort Collins, Colorado, USA
Tamarisk (Tamarix spp.), an invasive phreatophyte prevalent in riparian areas across the southwestern United States, threatens native cottonwood (Populus spp.) galleries, which are critical ecological and cultural resources. Tamarisk is notorious for re-sprouting after being cut, even when treated with herbicide. We used green leaf volatile (GLV) compounds and beetle aggregation pheromone (PHE) to attract tamarisk beetles (Diorhabda spp.). We hypothesized that the presence of pheromone lures would attract tamarisk beetles and result in reduced tamarisk re-sprout vigor through increased herbivory. Tamarisk trees in both pheromone treated and untreated plots (N = 4 each) were cut or masticated, but not treated with herbicide, 1 or 3 years before this study, respectively. We hung 10 GLV lures in each treatment plot, approximately equidistant from three target trees, during spring tamarisk leaf-out at the beginning of June 2022. We hung one PHE lure in each of the three target trees on three dates, approximately 3 weeks apart, mid-June and through the end of July 2022. We counted beetles and measured tree canopy volumes in pairs of pheromone treated and untreated (control) plots. Repeated measures, mixed effect analysis of variance detected no difference in beetle numbers between trees with and without pheromone lures (p = 0.83), but trees with pheromone lures had smaller canopy volumes than those without lures (p < 0.0001). Thus, tree defoliation, but not beetle numbers, indicated reduced growth due to pheromone lures. We did not take measures to prevent beetles from visiting control trees without lures. We suspect they moved between pheromone treated and untreated trees because the study areas were too small to separate them by distances greater than beetle flight ranges. We had limited statistical power to detect treatment effects due to the small size of the study. Despite mixed results, there is enough evidence supporting our hypothesis to repeat the study on a larger scale. Please contact the presenting author if you would like the land you manage to be involved in future research.