Performing Department
(N/A)
Non Technical Summary
We are developing new and sustainable IPM strategies for a regionl invasive and emergent insect problem, the oystershell scale (OSS; Lepidosaphes ulmi), which negatively affects aspen (Populus tremuloides) in the Interior West. Aspen is a wide-ranging tree species in North America and is highly valued for ecosystem services. Rapid climate change has likely contributed to the emergence of OSS, which now threatens aspen sustainability in the Southwest and Intermountain West. We will conduct research to develop IPM through these objectives: 1) describe the influence of temperature on OSS life cycle timing, voltinism, and survival across an elevational gradient at two latitudes; 2) evaluate the efficacy of silvicultural and insecticides interventions in reducing OSS populations and aspen decline and document potential non-target insecticide effects; 3) assess OSS outbreaks, including aspen mortality rates, and OSS infestation and severity patterns across a latitudinal gradient; 4) develop and deliver extension and outreach materials for land managers and the public. To meet our objectives, we will use both experimental and field sampling strategies, including previously installed monitoring plots and a before-after-control-intervention study design in treated and untreated areas. Our results will provide a better understanding of OSS biology and distribution in natural aspen stands across latitudes, effectiveness of silviculture and insecticide management tools for mitigating OSS-caused aspen mortality, and initial development of an IPM for OSS in aspen.
Animal Health Component
(N/A)
Research Effort Categories
Basic
50%
Applied
(N/A)
Developmental
50%
Goals / Objectives
Our overarching goal is to develop a research-based IPM program for OSS in aspen that is ecologically and socially acceptable and effective for mitigating OSS-related mortality in aspen. Specifically, we will:Evaluate how temperature affects OSS life cycle timing, voltinism, and survival across elevational gradients at two latitudes. Rationale: Knowledge of OSS life cycle timing is critical to effective implementation of management strategies. Little is known about OSS phenology and voltinism, particularly across elevations in aspen forests of the Southwest and Intermountain Regions. Appropriately timed insecticide treatments require detailed information on life-stage timing.Evaluate the efficacy of silvicultural and insecticide interventions in reducing OSS infestation severity and aspen mortality and document non-target effects of insecticides. Rationale: Forest managers began implementing reactive silvicultural treatments to mitigate OSS in 2019, with additional treatments planned for 2023-2025. The first insecticide application is planned for 2024; to our knowledge, insecticides have never been used in natural aspen stands in the Interior West. We need to understand both effectiveness of treatments and potential non-target impacts prior to wide-spread adoption of treatments.Assess OSS outbreaks, including aspen mortality rates, and OSS infestation and severity patterns across a latitudinal gradient. Rationale: We have been monitoring OSS in Arizona since 2019 and know it has begun causing mortality of aspen in Nevada, Utah and Idaho (Williams 2021). Beyond generalized infestation locations, no data are available related to the extent of aspen decline and mortality due to OSS in these areas. Without a better understanding of extent and severity, we lack the information to prioritize areas in need of IPM deployment.Develop and deliver extension and outreach materials for land managers and the public. Rationale: We have been working toward OSS management but lack a comprehensive multidisciplinary outreach component. Delivering diverse OSS outreach and extension materials and programming on a unified platform will facilitate knowledge transfer among researchers, land managers, pest management professionals, and the general public.
Project Methods
Objective 1. Evaluate how temperature affects OSS life cycle timing, voltinism, and survival across elevational gradients at two latitudes. Sampling will consist of counting OSS crawlers, young and maturescales, and presence of eggs. Designated study sites occur at one of three elevations (low, mid and high). Twig and/or bark samples will also be collected at each site to allow more accurate counts of individuals by life stage, sex ratio, and presence of parthenogenetic reproduction, as well as egg counts. At least one site at each latitude will be sampled throughout the winter months. A Hobo datalogger will be installed at each site and hourly temperatures recorded throughout the length of the study. A degree day model for individual life stages will be developed by accumulating proportions of individual life stages and associated degree days through time at each of the six sites. We will initially use a cumulative Weibull distribution for predicting the observed cumulative degree required for an observed cumulative proportion of individual life stages. Other pertinent distributions will also be tested and statistically evaluated for comparative fit to the observed data using simple linear regression (lm function, R).The crawler lifestage will be important to management strategies so we will focus on this lifestage. To estimate potential differences across latitudes that may indicate thermal adaptation of OSS via range expansion, separate models will initially be fit for the Flagstaff and Utah sites. If significant differences in degree day requirements are not found between the latitudes, data for all sites will be pooled for model development. Daily maximum and minimum historical temperatures downloaded from nearby NOAA weather stations will be used to analyze historical trends in climate suitability for OSS in AZ and UT based on our model. These results will inform the role of climate change in OSS invasion of aspen forests. To determine temperature survival thresholds of OSS, we will use a subset of the previous twig samples described from different latitudes and elevations each season (spring, summer, fall and winter) and place them in temperature controlled chambers in the Forest Entomology lab at Northern Arizona University. We will expose samples to various temperature extremes for 24 hours, remove them from the chamber, place at room temperature (25°C) and determine survival of OSS after 48 hours. Initial study temperatures to be tested include 0, -10, -20, and -30°C and later at a finer scale (increments of 5 or 3°C). Lower lethal temperatures (LLT50 values) will be obtained for OSS collected at each elevation and season, along with a control (room temperature) for each treatment/day of experiments. The temperature resulting in 50% mortality of experimental populations will be determined for the low exposure temperatures using Probit analysis in minitab (Minitab Inc.). Significant differences in mortality will be identified by non-overlapping 95% fiducial limits. Results will determine cold-induced mortality thresholds of OSS lifestages, and used in the development of phenology models and range maps.Objective 2. Evaluate the efficacy of silvicultural and insecticides interventions in reducing OSS populations and aspen decline and assess non-target effects of insecticides. We will re-measure previously established plots to assess early efficacy of silvicultural treatments after 1-year and 5-years (when possible) using a series of ANOVAs to test for differences among treatments in OSS severity, aspen stem mortality by size class, and aspen abundance by size class, within a single time period. We will also construct mixed effect linear models to assess differences among treatments and measurement periods for the same variables. Two exclosures will have insecticide application on five trees (treated trees) and five trees in each will be selected as untreated control trees, for a total of 20 study trees. Following insecticide application, Crawler emergence will be monitored within marked off sampling areas on each aspen trunk without clearing away the scales. OSS infestation will be recorded to assess dinotefuran efficacy by three methods. 1) We will take pictures of the marked sampling areas to count scales on the photos. 2) Bark scrapings will be used to collect scales to determine if the scales adhered to the bark are still alive. 3) Individual trees will be rated for OSS severity. To determine the concentration of dinotefuran moving in the aspen tree and begin understanding insecticide movement within aspen, we will collect foliage samples from study trees. These samples will be composited during processing for a total of one foliage sample per tree for insecticide residue analyses. Pre-treatment baseline samples will be collected from a limited number of trees. Dinotefuran concentrations will be compared between treated and untreated trees over time using a mixed model ANOVA to determine if dinotefuran is translocating within the tree in statistically higher concentrations over time. We will conduct non-target monitoring in the same units. We will use four methods for this initial evaluation of non-target effects: 1. Bark scrapings used for OSS population assessment will also be used to determine if predatory mite abundance and percent OSS mortality from parasitoid wasps differs between treated and untreated trees over time. A limited number of pre-treatment baseline bark scraping samples will be collected the year before applications. A mixed model ANOVA will assess mite and parasitoid wasp data between treated and untreated trees over time. 2. Dinotefuran and dinotefuran metabolite concentration in soils around trees. Comparisons will be made between treated and control trees. Pre-treatment baseline samples will be collected from around a limited number of aspen trees. A mixed model ANOVA will compare insecticide concentration data between treated and untreated trees at the two distances from the tree over time. 3. Non-target ground-dwelling arthropod communities will be assessed to determine if dinotefuran treatments are affecting abundance and taxa richness. Three pitfall traps will be installed around each tree at 1 m from the trunk for two years post-treatment. A mixed model ANOVA will assess ground-dwelling arthropod data between treated and untreated trees over time. 4. Surface water will be sampled to monitor whether dinotefuran and dinotefuran metabolites are present. Water samples will be collected before and after treatments at three locations: two surface waters sites downstream and nearest to the Dinotefuran applications and a paired surface water control site nearby. Water samples will be collected five times during the study: once pre-treatment twice during each monsoon season during the two-years post-treatment or possibly during aquatic invertebrate monitoring in the spring.Objective 3. Assess OSS outbreaks, including aspen mortality rates, and OSS infestation and severity patterns across a latitudinal gradient. We will use the aspen monitoring protocol and OSS severity rating system currently being implemented in Arizona to install new permanent monitoring plots in the Intermountain West. We will install one transect with three plots per transect, in ten areas known to be infested by OSS and nearby areas with uninfested aspen that represent different aspects, elevations and time since disturbance, for a total of 60 permanent plots. Plot installation protocol will follow those described above for Objective 2. We will assess OSS severity and extent through descriptive statistics and an updated distribution map. To understand the drivers of OSS in the Intermountain West, we will test for differences between infested and uninfested plots using appropriate paired t-tests. Variables compared will include live and dead aspen density by size class and severity of biotic and abiotic factors.