Data of emerald ash borer caught in six trapping systems at 16 site‐years were compared to assess their relative sampling efficiency. One sample scheme was chosen against which the other five were compared, and their relative efficiencies estimated. Recommendations for the use of the emerald ash borer samplers were made based on the relative efficiency analysis results. Two sampling schemes were found to have density‐dependent efficiency relative to the other four schemes and are most sensitive at low population densities, therefore, making them most useful for detection. Of the other four schemes, two are sufficiently more efficient to be recommended for monitoring established populations. The results of a global Taylor power law (TPL) analysis of the sample data suggest a loss of information of density‐dependent sampling efficiency by TPL when its parameter is b = 2. This limits the use of TPL to evaluate the sampling efficiency of insect samplers.

Societal Impact Statement Climate change is altering ecological systems, including the phenology of flowering plants. Shifts in the bloom date of cherry trees are a global concern considering their cultural, agricultural, and horticultural importance. Ornamental cherry is a prominent component of the University of Washington campus (Seattle, USA), providing an opportunity to engage volunteers in citizen science that quantifies shifts in bloom in the Pacific Northwest. These phenological shifts affect horticultural systems, cherry festival planning, and synchrony with pollinators, with direct implications on local economies, tourism, and landscape resilience for future generations. Summary We monitored cherry bloom date on the University of Washington campus, Seattle, USA, in three flowering cherry species and cultivars to develop a predictive model for estimating bloom, and to quantify changes in bloom date in Somei‐yoshino cherry ( Prunus x yedoensis ) between 1966 and 2024. We worked with citizen scientists to record bloom date, and for Prunus x yedoensis , bloom phases, using ArcGIS Field Maps between 2012 and 2024. We also examined newspaper archives to reconstruct the observed bloom date for Prunus x yedoensis prior to 2012. We used a published modeling framework to develop species‐ and cultivar‐specific models to predict bloom. We observed different thresholds for chill and heat requirements across flowering cherry species and cultivars, and general congruence between observed and model‐predicted bloom dates for each. Using the longer time series in Prunus x yedoensis , we observed that warmer winters slowed the accumulation of required chill units, while warmer springs led to required heat units accruing more rapidly. The net effect of warming winters and springs resulted in a delay in the bloom date of Prunus x yedoensis by ~2 days per decade between 1966 and 2024. Shifts in the bloom date of flowering plants could result in phenological asynchrony with pollinators, with cascading effects across ecosystems. Further research is needed to understand the complex responses of flowering plants to shifting climatic conditions.

Herbivores are commonly classified as host specialists or generalists for various purposes, yet the definitions of these terms, and their intermediates, are often imprecise and ambiguous. We quantified host breadth for 240 non-native, tree-feeding insects in North America using phylogenetic diversity. We demonstrated that a partitioning of host breadth: (1) causes 67% of non-native insects to shift from a generalist to specialist category, (2) displays a reduction in host breadth from the native to introduced range, (3) identifies an inflection point in a model predicting the likelihood of non-native insect ecological impact, with a corresponding change in behaviour associated with specialists versus generalists, and (4) enables three models for strong prediction of whether a non-native forest insect will cause high impacts. Together, these results highlight the primacy of how herbivore host recognition and plant defences mediate whether novel host interactions will result in high impact after invasion.

Pollinators are an essential component of ecosystem function, and declining bee populations are a global conservation concern. Despite this importance, there is a lack of understanding regarding the distribution of native bee species across western North American landscapes. This study documents new records of Melissodes nigracauda LaBerge, Dufourea dilatipes Bohart, Atoposmia abjecta abjecta Cresson, Coelioxys funerarius Smith, Dianthidium cressonii Dalla Torre, Dianthidium singulare Cresson, Osmia cyaneonitens Cockerell, and Stelis heronae Sheffield. These eight new records supplement the ~565 bee species previously documented in Washington state.

Enhancing tree diversity may be important to fostering resilience to drought-related climate extremes. So far, little attention has been given to whether tree diversity can increase the survival of trees and reduce its variability in young forest plantations. We conducted an analysis of seedling and sapling survival from 34 globally distributed tree diversity experiments (363,167 trees, 168 species, 3744 plots, 7 biomes) to answer two questions: (1) Do drought and tree diversity alter the mean and variability in plot-level tree survival, with higher and less variable survival as diversity increases? and (2) Do species that survive poorly in monocultures survive better in mixtures and do specific functional traits explain monoculture survival? Tree species richness reduced variability in plot-level survival, while functional diversity (Rao's Q entropy) increased survival and also reduced its variability. Importantly, the reduction in survival variability became stronger as drought severity increased. We found that species with low survival in monocultures survived comparatively better in mixtures when under drought. Species survival in monoculture was positively associated with drought resistance (indicated by hydraulic traits such as turgor loss point), plant height and conservative resource-acquisition traits (e.g. low leaf nitrogen concentration and small leaf size). Synthesis. The findings highlight: (1) The effectiveness of tree diversity for decreasing the variability in seedling and sapling survival under drought; and (2) the importance of drought resistance and associated traits to explain altered tree species survival in response to tree diversity and drought. From an ecological perspective, we recommend mixing be considered to stabilize tree survival, particularly when functionally diverse forests with drought-resistant species also promote high survival of drought-sensitive species. Rising climate extremes, such as drought, can cause major uncertainty in the survival of young trees. Tree diversity can reduce survival variability and stabilize tree survival. Functionally diverse communities with drought-tolerant species can promote the survival of drought-sensitive species.image

The health of solitary bees is dependent on the pollen they consume, driving their development from larvae to pupae. Nutrients such as proteins and lipids play an important role in bee development and could be an important key in conservation efforts to support declining populations. We examined the concentration of protein, total lipids, and 13 individual lipid classes in pollen provisions collected from the native solitary nesting bee, Osmia lignaria Say, at 22 sites in urban and rural landscapes in western Washington over three years and during two distinct foraging periods. The results indicate that protein concentrations in pollen did not significantly affect larval development. We detected higher lipid concentrations in the second foraging period, which was also associated with increased larval developmental success. Using Next-Generation sequencing on collected pollen, we also ascertained the plant genera in pollen and observed that plant richness did not differ significantly between the two foraging periods even though levels of lipid concentrations did. Individual lipid classes may play a role in the successful development of O. lignaria, as hexosylceramide and cholesterol ester were positively associated with O. lignaria larval developmental success, which emphasizes the need for additional studies on the role of individual lipid classes on bee development.

Over the past several decades, forests worldwide have experienced increases in biotic disturbances caused by insects and plant pathogens – a trend that is expected to continue with climate warming. Whereas the causes and effects of individual biotic disturbances are well studied, spatiotemporal interactions among multiple biotic disturbances are less so, despite their importance to ecosystem function and resilience. Here, we highlight an emerging phenomenon of “hotspots” of biotic disturbances (that is, two or more biotic disturbances that overlap in space and time), documenting trends in recent decades in temperate conifer forests of the western US. We also explore potential mechanisms behind and effects of biotic disturbance hotspots, with particular focus on how altered post‐disturbance recovery (successional pathways) can have profound consequences for ecosystem resilience and biodiversity conservation. Finally, we propose research directions that can elucidate drivers of biotic disturbance hotspots and their ecological effects at various spatial scales, and provide insight into this new knowledge frontier.

AbstractThe study of the spatial dynamics of forest insects has a long history, and many forest insect species have served as model systems for studying conceptual processes of population biology and ecology. Because forest insect population data were often collected from georeferenced locations, even prior to the development of geodatabases and spatial statistical software, they provide an important historical resource for understanding insect population dynamics and changes in those dynamics through time. Advances in spatial statistics have furthermore enabled forest entomologists to consider forest insect dynamics over multiple spatial and temporal scales, and vast spatial and temporal extents. In this chapter, we first introduce the importance of scaling in studies of spatial dynamics, and review spatial pattern formation in forest insect populations. We conclude the chapter by addressing metapopulation dynamics, and the concept of spatial synchrony in outbreaking forest insects.

Old-growth forests in the Pacific Northwest host a variety of epiphytes on their branches and stem. Given the common and often large epiphytic biomass associated with Acer macrophyllum (Pursh) in this region, we evaluated how seasonal weather changes and urbanization (metal and nitrogen deposition), affect canopy epiphytic N2 fixation in the Hoh Rainforest of the Olympic Peninsula and in urban parks and forests in Seattle. We collected Isothecium stoloniferum (Brid.) samples from both the Hoh Rainforest and Seattle at four periods from April 2016 through January 2017. Moss-associated N2 fixation rates were measured in the laboratory using the acetylene reduction assay and trace metal concentrations in the moss were analyzed using NO3 + H2O2 digestion. We found levels of N2 fixation were highest during the spring sampling period. Elevated levels of heavy metals were observed in I. stoloniferum samples collected in the urban canopies in Seattle where N2 fixation rates were low, suggesting N2 fixation is sensitive to the bioaccumulation of heavy metals. In A. macrophyllum canopies, I. stoloniferum was found to yield 0.1130 g N m−2 yr−1 in canopy branches within the Hoh Rainforest and only 0.0009 g N m−2 yr−1 on branches in Seattle. These results highlight a rarely explored source of biological N2-fixation in temperate rainforests and suggest that epiphytic N2-fixation may contribute bio-available nitrogen in A. macrophyllum stands. N2-fixation in canopy bryophytes was found to be highly sensitive to urban pollution, possibly due to bioaccumulation of heavy metals in bryophyte tissue.

Spring-emerging bees depend upon the synchronized bloom times of angiosperms that provide pollen and nectar for offspring. The emergence of such bees and bloom times are linked to weather but can be phenologically mismatched, which could limit bee developmental success. However, it remains unclear how such phenologically asynchrony could affect spring-emerging pollinators, and especially for those that forage over a relatively short time period. We examined the relationship between weather and host plant selection on the native spring-foraging solitary bee, Osmia lignaria , across 3 years at urban and rural sites in and around Seattle, Washington, USA. We used community science weather data to test the effects of precipitation, wind, and temperature on O. lignaria oviposition and developmental success. We also collected pollen data over two distinct foraging periods, early and late spring, and used Next-Generation Sequencing to identify plant genera from pollen. Among the weather variables, precipitation during the early foraging period adversely affected larval developmental success and adult bee emergence success, but not oviposition. Using DNA metabarcoding, we observed that increases in the number of plant genera in pollen increased adult emergence in both foraging periods, but not oviposition or larval development. We also observed that foraging bees consistently visited certain genera during each foraging period, especially Acer , Salix , and Rubus . However, pollen collected by O. lignaria over different years varied in the number of total genera visited, highlighting the importance of multi-year studies to ascertain bee foraging preferences and its link to developmental success.

Among insects, symbionts such as bacteria and fungi can be linked to their physiology and immature development, and in some cases are part of a defense system against parasites and diseases. Current bacterial and fungal symbiont associations in solitary bees are understudied, especially in the Pacific Northwest region of the USA. We collected pollen provisions from the native spring-foraging solitary bee, Osmia lignaria Say, across two distinct foraging periods over 2 years at 22 sites along an urban-to-rural gradient in western Washington. We then used next-generation sequencing to identify bacterial and fungi within pollen provisions and assessed the effect of their richness and diversity on O. lignaria larval development success and adult emergence. We detected a significantly positive relationship between bacterial diversity in pollen with O. lignaria larval developmental success, and higher bacterial richness and diversity during the later foraging period. Fungal generic richness and diversity decreased with increasing plant richness. Although neither was associated with O. lignaria developmental success, we did detect Ascosphaera spp. known to be pathogenic to O. lignaria and other bee species. Neither bacterial or fungal richness or diversity was affected by site type when classified as urban or rural. This study provides new information on bacterial and fungal symbionts present in pollen provisions of a native solitary bee when foraging across urban and rural areas of the Pacific Northwest.

Understanding and predicting the spread of invading insects is a critical challenge in management programs that aim to minimize ecological and economic harm to native ecosystems. Although efforts to quantify spread rates have been well studied over the past several decades, opportunities to improve our ability to estimate rates of spread, and identify the factors, such as habitat suitability and climate, that influence spread, remain. We review emerging sources of data that can be used to delineate distributional boundaries through time and thus serve as a basis for quantifying spread rates. We then address advances in modeling methods that facilitate our understanding of factors that drive invasive insect spread. We conclude by highlighting some remaining challenges in understanding and predicting invasive insect spread, such as the role of climate change and biotic similarity between the native and introduced ranges, particularly as it applies to decision-making in management programs.

Botanical gardens have extensive spatial databases of their plant specimens; however, the fungi occurring in them are generally unstudied. Botanical gardens, with their great plant diversity, undoubtedly harbor a wide range of symbiotic fungi, including those that are plant-pathogenic. One such group of fungi is powdery mildews (Erysiphaceae). The powdery mildews are among the most prevalent and economically important plant pathogens in the world, with an estimated 906 species in 19 genera. They are known to infect more than 10,000 species of flowering plants and although some species occur across a range of hosts, many are associated with specific plants. Powdery mildews have undergone a long and dynamic coevolution with their host plants, resulting in co-speciation. Botanical gardens provide a living laboratory in which to study these fungi, leading to a wealth of undiscovered fungal diversity. Furthermore, monitoring pathogens in botanical gardens has led to important ecological findings related to the plant sciences and plant protection. Between 2018 and 2022, a collaborative citizen science project was established with 10 botanical gardens in the United States and Mexico. A total of more than 300 powdery mildew specimens were collected on 220 different host taxa. We sequenced the entire internal transcribed spacer (ITS) and large subunit (LSU) rDNA loci and phylogenetically and morphologically analyzed these collections revealing 130 species, of which 31 are likely unknown to science. This research highlights the importance of botanical gardens as a reservoir of fungal diversity. Future research will further elucidate the coevolutionary relationship between powdery mildews and their hosts and extend the current study to evaluate other plant pathogens and fungi in botanical gardens.

Biological invasions by insects entail several processes including spread and outbreaks that can cause widespread tree mortality. These processes are commonly viewed as a linear sequence because we often lack the mechanistic understanding needed to partition them. We explored an invasion that occurred over a large enough spatial scale and time frame to examine the conditions under which spread rates may be uncoupled from outbreak severity. Lymantria dispar is an invasive generalist folivore that has spread continuously from its initial point of introduction in North America at variable rates. Since its establishment in Wisconsin, USA in 1998, L. dispar has spread more rapidly there than any other region, but has never irrupted into regionwide outbreaks. In contrast, L. dispar spread more slowly elsewhere, in part due to strong mate-finding Allee effects, but periodically undergoes highly damaging, landscape-scale outbreaks in susceptible forest types. We conducted a 10-year study across 45 stands in northern Wisconsin with a high composition of favorable hosts. We quantified population trends of life stages, natural enemy abundance and impacts, and radial tree growth increment, and assessed biotic and abiotic factors as putative drivers of the decoupling between spread rates and outbreak severity. We then compared the results from these rapid-spread, low-impact sites with those from slow-spread, high-impact sites in Michigan and Pennsylvania, USA. The abundance and richness of natural enemy communities in Wisconsin were either equivalent to or less than those communities reported elsewhere, reducing the likelihood that greater top-down control explains the absence of outbreaks. We also found no differences in larval developmental time or drought that could increase the effects of natural enemies among the different regions. Rather, higher overwintering mortality due to more extreme and frequent lethal minimal temperatures in Wisconsin appeared most responsible for the lack of outbreaks. Overall, it appears that the combination of strong mate-finding Allee effects and low overwintering mortality elsewhere is a more substantial hindrance to spread than are weak mate-finding Allee effects and high overwintering mortality in Wisconsin. Once populations are established, the net contributions of these constraints become reversed: mate-finding limitations become only a minimal challenge whereas regional differences in winter survival best explain differences in outbreak frequency. These results suggest that spread rates of invasive insects should not be used as a proxy for predicting their local or overall impact, and that management efforts should be tailored to underlying processes determining their region-specific relative importance.

Lymantria dispar (L.), formerly known in the U.S.A. as the gypsy moth, has been a major pest species in North American forests for > 100 years. Due to the economic and ecological consequences of L. dispar outbreaks, many aspects of its population biology and ecology have been studied. However, as L. dispar continues to spread into new areas, it remains important to understand its invasion dynamics in newly established populations where prior research is lacking. In this study, we used a 16-year spatially-referenced dataset to quantify the spatial dynamics of L. dispar population growth rates along its expanding population front from Minnesota to North Carolina. We then used this information in a spatially-explicit modeling framework to quantify the role of temperatures, primary and secondary L. dispar host plant density, and the fragmentation of primary and secondary host plants, on L. dispar population growth rates. Across the invasion front, temperatures were significant predictors of growth rates. The basal area of host plants, often used to predict L. dispar risk, was not a significant predictor in any region along the invasion front. Instead, primary and secondary host plant cohesion (i.e., reduced fragmentation), were significant predictors of growth rates, with the exception of areas where host plants are generally scarce. The results highlight geographical differences in how temperature and host plant fragmentation affect L. dispar growth rates, and underscore the role that secondary host plants can play in establishing populations. The results inform the development of improved risk models of L. dispar invasion.

Correction of “R. R. Garrison and P. C. Tobin. 2022. Development of Azalea Lace Bug, Stephanitis pyrioides, on Susceptible and Resistant Rhododendron species in Western Washington. J. Econ. Entomol.” DOI: 10.1093/jee/toab257 In the originally published version of this manuscript, the bottom panel of Figure 1 was erroneously duplicated. This has now been corrected online.

The invasive azalea lace bug, Stephanitis pyrioides (Scott), is one of the most damaging insect pests of the genus Rhododendron, especially azaleas. Feeding by nymphs and adults reduces the aesthetic value of infested plants. Rhododendron spp. (L.) and cultivars are a major component of public and private landscapes in the Pacific Northwest, as well as other parts of the U.S.. Variability in the susceptibility of Rhododendron to S. pyrioides has been previously examined but generally on a limited number of Rhododendron species and cultivars. We measured the susceptibility of 71 Rhododendron species, varieties, and cultivars over two years, selecting plants across the phylogenetic tree of Rhododendron, and quantified the proportion of leaf damage caused by S. pyrioides. We observed that trichome presence did not predict S. pyrioides damage. Plants from the subgenus Azaleastrum were the significantly most susceptible subgenus, and all sampled plants from this subgenus had measurable damage. In contrast, plants from the subgenus Hymenanthes were the significantly least susceptible, and most Hymenanthes plants had no measurable damage. This study provides a guideline for using host plant resistance to S. pyrioides in plant selection, and emphasizes the potential for S. pyrioides management if susceptible azaleas are to be used in the landscape. Species used in this study: Azalea lace bug, Stephanitis pyrioides, Rhododendron spp.

Some introduced species cause severe damage, although the majority have little impact. Robust predictions of which species are most likely to cause substantial impacts could focus efforts to mitigate those impacts or prevent certain invasions entirely. Introduced herbivorous insects can reduce crop yield, fundamentally alter natural and managed forest ecosystems, and are unique among invasive species in that they require certain host plants to succeed. Recent studies have demonstrated that understanding the evolutionary history of introduced herbivores and their host plants can provide robust predictions of impact. Specifically, divergence times between hosts in the native and introduced ranges of a nonnative insect can be used to predict the potential impact of the insect should it establish in a novel ecosystem. However, divergence time estimates vary among published phylogenetic datasets, making it crucial to understand if and how the choice of phylogeny affects prediction of impact. Here, we tested the robustness of impact prediction to variation in host phylogeny by using insects that feed on conifers and predicting the likelihood of high impact using four different published phylogenies. Our analyses ranked 62 insects that are not established in North America and 47 North American conifer species according to overall risk and vulnerability, respectively. We found that results were robust to the choice of phylogeny. Although published vascular plant phylogenies continue to be refined, our analysis indicates that those differences are not substantial enough to alter the predictions of invader impact. Our results can assist in focusing biosecurity programs for conifer pests and can be more generally applied to nonnative insects and their potential hosts by prioritizing surveillance for those insects most likely to be damaging invaders.

Geographical variation in the likelihood of biological invasions can be affected by propagule pressure and habitat suitability, which are driven by ecological and social processes. Past studies have empirically quantified the role of drivers by comparing geographical variation in numbers of invading species with variation in candidate factors; however, lack of data has limited empirical studies for individual species. Lymantria dispar (L.), a nonnative forest pest formerly known as gypsy moth, is an exemplar species for exploring invasion drivers because of extensive records on its spread. Since its establishment in eastern United States in 1869, it has been repeatedly introduced into outlying areas, prompting 325 eradication programs from 1972 to 2014. We used these eradication programs as proxies for new establishment events, with the assumption that populations would have established in the absence of eradication treatments. These proxy events were used to quantify the effects of socio-environmental factors on the probability of L. dispar arrival and establishment. Establishment probability was significantly affected by propagule pressure (distance to the previously invaded area, human population size, and the area of source outbreaks) and habitat suitability (climate and availability of host trees). The statistical model developed here can be used to predict invasions and inform surveillance strategies to more efficiently manage these invasions.

Pathogen host range and pathogen severity are dependent on interactions with their hosts and are hypothesized to have evolved as products of a coevolutionary arms race. An understanding of the factors that affect host range and pathogen severity is especially crucial in introduced pathogens that infect evolutionarily naïve hosts and cause substantial damage to ecosystems. Powdery mildews are detrimental pathogens found worldwide in managed and natural systems. Golovinomyces latisporus is a powdery mildew species that is especially damaging to plants within Asteraceae and to plants within the genus Helianthus in particular. In this study, we evaluated 126 species within Asteraceae to measure the role of host plant morphophysiological traits and evolutionary history on susceptibility to G. latisporus and disease severity. We observed phylogenetic signal in both susceptibility and severity within and among major clades of the Asteraceae. In general, there was a major phylogenetic structure of host severity to G. latisporus; however, there was some fine-scale phylogenetic variability. Phylogenetic statistical methods showed that chlorophyll content, biomass, stomatal index, and trichome density were not associated with disease severity, thus providing evidence that phylogenetic structure, rather than observed plant morphophysiological traits, is the most reliable predictor of pathogen severity. This work sheds light on the role that evolutionary history plays in plant susceptibility and severity to disease and underscores the relative unimportance of commonly assessed host plant traits in powdery mildew severity.