Airborne eDNA Reflects Human Activity and Seasonal Changes on a Landscape Scale

Recent research on environmental DNA (eDNA), genetic material shed by organisms into their environment that can be used for sensitive and species-specific detection, has focused on the ability to collect airborne eDNA released by plants and carried by the wind for use in terrestrial plant populations, including detection of invasive and endangered species. Another possible application of airborne eDNA is to detect changes in plant communities in response to activity or changes on a landscape-scale. Therefore, the goal of this study was to demonstrate how honey mesquite, blue grama, and general plant airborne eDNA changes in response to human activity on a landscape-scale. We monitored airborne eDNA before, during, and after a rangeland restoration effort that included honey mesquite removal. As expected, restoration activity resulted in a massive increase in airborne honey mesquite eDNA. However, we also observed changes in abundance of airborne eDNA from the grass genus Bouteloua, which was not directly associated with the restoration project, and we attribute these changes to both human activity and seasonal trends. Overall, we demonstrate for the first time that activity and changes on a landscape-scale can be tracked using airborne eDNA collection, and we suggest that airborne eDNA has the potential to help monitor and assess ecological restoration projects, track changes due to global warming, or investigate community changes in response to encroachment by invasive species or extirpation of threatened and endangered species.

Treatment life and economic comparisons of honey mesquite (Prosopis glandulosa) and huisache (Vachellia farnesiana) herbicide programs in rangeland

Herbicides have been a primary means of managing undesirable brush on grazing lands across the southwestern United States for decades. Continued encroachment of honey mesquite and huisache on grazing lands warrants evaluation of treatment life and economics of current and experimental treatments. Treatment life is defined as the time between treatment application and when canopy cover of undesirable brush returns to a competitive level with native forage grasses (i.e., 25% canopy cover for mesquite and 30% canopy cover for huisache). Treatment life of industry-standard herbicides was compared with that of aminocyclopyrachlor plus triclopyr amine (ACP+T) from 10 broadcast-applied honey mesquite and five broadcast-applied huisache trials established from 2007 through 2013 across Texas. On average, the treatment life of industry standard treatments (IST) for huisache was 3 yr. In comparison, huisache canopy cover was only 2.5% in plots treated with ACP+T 3 yr after treatment. The average treatment life of IST for honey mesquite was 8.6 yr, whereas plots treated with ACP+T had just 2% mesquite canopy cover at that time. Improved treatment life of ACP+T compared with IST life was due to higher mortality resulting in more consistent brush canopy reduction. The net present values (NPVs) of ACP+T and IST for both huisache and mesquite were similar until the treatment life of the IST application was reached (3 yr for huisache and 8.6 yr for honey mesquite). At that point, NPVs of the programs diverged as a result of brush competition with desirable forage grasses and additional input costs associated with theoretical follow-up IST necessary to maintain optimum livestock forage production. The ACP+T treatments did not warrant a sequential application over the 12-yr analysis for huisache or 20-yr analysis for honey mesquite that this research covered. These results indicate ACP+T provides cost-effective, long-term control of honey mesquite and huisache.

Delineating the Asphondylia prosopidis Complex (Diptera: Cecidomyiidae): Possible Biological Control Agents of Honey Mesquite

The Asphondylia prosopidis Cockrell complex with its fungal associate produces four distinct bud galls on honey mesquite (Prosopis glandulosa). They are considered as potential biological control agents to reduce seed production of invasive mesquites. Previous studies suggest that the complex may consist of more than one gall midge species or biotype. Therefore, before conducting host specificity tests, it is essential to understand the relationships among the gall midges in the complex. Each gall type was collected from sympatric regions in Arizona, New Mexico, and Texas for four years. Here we show that midges producing each gall type were clearly separated based on phylogenetic analysis using DNA sequences in the cytochrome oxidase subunit I region. Furthermore, we confirmed that morphological differences between pupae from each gall type were discernible, although variable, using a scanning electron microscope. Based on these differences, we suggest that the A. prosopidis complex consists of four different gall midge species, three of which are cryptic species. Among them, Asphondylia species producing a barrel gall type and A. prosopidis producing the original gall type are potential biological control agents of P. glandulosa because they are multivoltine species with four to five generations per year that complete their annual life cycle exclusively on flower buds of mesquite.