Biology subjects

Bean, D. W.

Publications and source records attributed to Bean, D. W..

4 recordsLinked to original sources

bioRxiv2025

Integrated management of Canada thistle (Cirsium arvense) in the Great Plains and Intermountain West using a biocontrol agent (Puccinia suaveolens)

Canada thistle [Cirsium arvense (L.) Scop.] is an invasive perennial plant that threatens agricultural landscapes and natural ecosystems worldwide. The extensive regenerative root system of Canada thistle complicates control efforts, with current strategies having limited success. Puccinia suaveolens (Pers.) Rostr (syn. Puccinia punctiformis (F. Strauss) Rohl), an obligate biotrophic rust fungus, has shown potential as a biological control agent by systemically infecting the root system, reducing root mass and shoot growth, and limiting vegetative regeneration; however, its efficacy when integrated with other control methods remains unclear. We conducted experiments from 2020 to 2022 at two sites in Colorado and Utah to evaluate P. suaveolens efficacy when applied alone and in combination with mowing, tillage, and herbicide. Treatments were applied in Fall (2020 and 2021), with monitoring of thistle stem density, vegetative cover, as well as P. suaveolens incidence before and after treatments through 2022. While P. suaveolens alone contributed to a decrease in thistle density, it was less effective compared to herbicide treatments, and its impact when integrated with mowing or tillage was inconsistent. Herbicide application (alone and when combined with P. suaveolens) generated the greatest immediate reduction in thistle stem density and vegetative cover, although it resulted in the greatest amount of bare ground exposure. Grass coverage present within treated plots varied significantly between treatments, ranging from 0-75%, with the highest percentage observed in herbicide treatments compared to control and tillage in both years. Forb cover remained below 10% across treatments and years. Although P. suaveolens continues to show promise as a biological control agent, further research is needed to improve efficacy, and optimize integration with other control strategies.

ecology↗

bioRxiv2023

Scaling use of the rust fungus Puccinia punctiformis for biological control of Canada thistle (Cirsium arvense (L.) Scop.): First report on a U.S. statewide effort

Canada thistle (Cirsium arvense (L.) Scop., CT) is one of the worst weeds threatening temperate regions of the world. A host-specific rust fungus, Puccinia punctiformis (F. Strauss) Rohl., is known to cause systemic disease of CT, ultimately killing individuals and reducing stand densities. In 2013, it was demonstrated that fall inoculation of rosettes with coarsely ground leaves bearing P. punctiformis telia can successfully initiate epiphytotics. In the same year, a cooperative project between the Colorado Department of Agriculture and United States Department of Agriculture was initiated, in which CT patches across the state of Colorado (USA) were inoculated and tracked over subsequent years for changes in stem density. Here, we report our findings from 8 years (2014-2021) of monitoring effort. At most sites (N = 87), CT stem densities declined, from a mean ({+/-} SE) of 87.9 ({+/-} 6.5) stems to 44.7 ({+/-} 4.2). These declines however were spatially-autocorrelated, and likely attributable to local growing conditions, as mean annual daily maximum temperature and standard deviation of elevation, as well as climatic conditions around the times of both treatment and monitoring, were found to be important predictors of CT decline. Further, we observed that the amount of inoculum deployed, timing since last release, and method in which it was spread locally at a site were also associated with the magnitude of CT stem decline. These results are indicative of the value of P. punctiformis as a CT biological control agent. The name Cirsium arvense dieback (CADB) is proposed herein to describe the agriculturally important decline in CT stem densities attributable to this previously un-named systemic disease.

pathology↗

bioRxiv2023

Adaptation at the edge: Patterns of local adaptation and genetic variation during a contemporary range expansion

During range expansion, differences can evolve between populations at the core and expanding edge of a range. While theory and experimental work has focused on range expansions across uniform environments, natural range expansions often occur over environmental gradients, which present novel selection pressures. We seek to understand how genetic variation expressed in different environments may constrain adaptation during range expansion across environmental gradients, by testing whether long-established populations are better adapted to their local environments than newly established populations in the expanding edge. We study the timing of winter dormancy in a beetle introduced for biological control (Diorhabda carinulata), expanding from areas with cold winters to areas with milder, shorter winters. In a reciprocal environment experiment, core populations showed a pattern of local adaptation, but only some edge populations showed a similar pattern, indicating these populations vary in their degree of adaptation. Expressed genetic variation of dormancy timing in a core population was high in a local (core) environment but disappeared in a novel (edge) environment. These results show that adaptive evolution has been rapid, likely fueled by high heritability, but long-distance movement may hinder adaptation by reducing the heritable genetic variation on which selection can act.

evolutionary biology↗

bioRxiv2021

Hybridization and range expansion in tamarisk beetles (Diorhabda spp.) introduced to North America for classical biological control

With the global rise of human-mediated translocations and invasions, it is critical to understand the genomic consequences of hybridization and mechanisms of range expansion. Conventional wisdom is that high genetic drift and loss of genetic diversity due to repeated founder effects will constrain introduced species. However, reduced genetic variation can be countered by behavioral aspects and admixture with other distinct populations. As planned invasions, classical biological control (biocontrol) agents present important opportunities to understand the mechanisms of establishment and spread in a novel environment. The ability of biocontrol agents to spread and adapt, and their effects on local ecosystems, depends on genomic variation and the consequences of admixture in novel environments. Here we use a biocontrol system to examine the genome-wide outcomes of introduction, spread, and hybridization in four cryptic species of a biocontrol agent, the tamarisk beetle (Diorhabda carinata, D. carinulata, D. elongata, and D. sublineata), introduced from six localities across Eurasia to control the invasive shrub tamarisk (Tamarix spp.) in western North America. We assembled a de novo draft reference genome and applied RADseq to over 500 individuals from laboratory cultures, the native ranges, and across the introduced range. Despite evidence of a substantial genetic bottleneck among D. carinulata in N. America, populations continue to establish and spread, possibly due to aggregation behavior. We found that D. carinata, D. elongata, and D. sublineata hybridize in the field to varying extents, with D. carinata x D. sublineata hybrids being the most abundant. Genetic diversity was greater at sites with hybrids, highlighting potential for increased ability to adapt and expand. Our results demonstrate the complex patterns of genomic variation that can result from introduction of multiple ecotypes or species for biocontrol, and the importance of understanding them to predict and manage the effects of biocontrol agents in novel ecosystems.

evolutionary biology↗