Location: Pest Management Research
Project Number: 3032-21220-003-004-I
Project Type: Interagency Reimbursable Agreement
Start Date: Jul 12, 2019
End Date: Sep 30, 2023
We propose to quantify large scale variation in biological control agent distribution and plant genetic structure for Leafy Spurge (Euphorbia esula L., EUES). This weed remains a top concern for western stakeholders despite decades of active management and a widely successful biocontrol program. Biological control remains the most cost effective means of long term EUES management (Hyder et al. 2008), but agent success varies. Environmental conditions and host-plant genotypes have been associated with lower agent success. Whether demonstrated local scale patterns and native range data reflect true limitations to biocontrol agents in the introduced range remains uncertain. We need consistent data over a broad scale to determine if suggested patterns correlate with overall similar trends in EUES infestation size and agent abundance, versus associations dependent on the range of habitats or conditions sampled (i.e., Schwartz et al. 2017). This information will be crucial for identifying key weaknesses in successful EUES management with biocontrol, and prioritizing research on additional agents still in the development pipeline. We will select a range of previous biological control release sites across three states to address 4 objectives: 1) Characterize habitat variables and the current status of leafy spurge infestations where agents have been released. 2) Quantify the variance in agent communities and abundance across sites. 3) Identify the genetic structure and variation within EUES patches across sites. 4) Evaluate potential correlations between habitat conditions, patch genetic structure, and agent presence.
We will quantify variation in agent presence and abundance, EUES infestation (patch size, density and frequency), and EUES patch genetic structure across a broad spatial gradient in North Dakota, Montana, and Idaho. Within each state, we will select a range of previous biological control release sites that provide a replicated series of vegetation and soil conditions that maximize critical gradients associated with variation in agent success. Replicating habitat conditions within states will allow us to gauge variation at scales similar to previous studies. Replicating habitat conditions across states will ensure we’ve sampled a large climate gradient that should reduce site-specific variation that obscures large scale correlations. Field Sampling. Year 1: At each site, the size and distribution of local patches will be assessed using a DJI Matrice 100 quadcopter drone with a high resolution visual lens. We will designate a “focal patch”, a leafy spurge infestation area with at least one side of 10 m length and least two stems/m2, in the vicinity of the original release(s). We will take 5 soil samples within each focal patch to analyze soil nutrients and texture. Each plot will be assessed using the protocol utilized in Weed et al. (2017; SIMP), and swept to verify agent presence. Ten individual plants per focal patch will be collected along the SIMP transect for genetic analysis using DNA sequence and Amplified Fragment Length Polymorphism (as in Gaskin et al. 2009). Additionally, these plants will be assessed for evidence of agent presence in the roots. Sites where leafy spurge has been extirpated will be excluded from further surveys, as will sites with no agent presence or with EUES densities below those required to establish a focal patch. Year 2 and 3: A minimum of 10 sites per state will be further sampled for genetic structure, variation in agent presence and abundance, and across patch variation. Each focal patch will be assessed with the SIMP method, and swept for insects, in five parallel transects a minimum of 2 m apart, between mid-June and July each year. We will count the number of sweeps required to sample the patch, as distribution of EUES is expected to vary within the focal patch, and abundances will be quantified on a per-sweep basis. Variation in leafy spurge cover (patch size) and biomass (patch quality) will be assessed by drone flights over the focal patch (ground-truthed with the SIMP data), and extended across a 0.5-km radius area surrounding the focal patch as the center point. This additional sampling will allow us to incorporate how greater abundance of EUES in the local landscape may affect patterns of agent abundance within patches. Insect sampling and patch variability will be sampled in both Years 2 and 3 to reduce the effect of yearly variation on project goals.