Climate suitability analyses compare the distributions of invasive knotweeds in Europe and North America with the source localities of their introduced biological control agents.

Climate suitability analyses based on ecological niche modeling provide a powerful tool for biological control practitioners to assess the likelihood of establishment of different candidate agents prior to their introduction in the field. These same analyses could also be performed to understand why some agents establish more easily than others. The release of three strains of Aphalara itadori (Shinji) (Hemiptera: Pysllidae), each from a different source locality in Japan, for the biological control of invasive knotweed species, Reynoutria spp. Houtt. (Caryophyllales: Polygonaceae), provides an important opportunity to compare the utility of climate suitability analyses for identifying potential climate-based limitations for successful biological control introductions. Here, we predict climate suitability envelopes for three target species of knotweed in Europe and two target species of knotweed in North America and compare these suitability estimates for each of these species to the source localities of each A. itadori strain. We find that source locality of one strain, the Kyushu strain, has little-to-no suitability compared to other locations in Japan based on knotweed records from Europe, supporting an earlier study based on North American Japanese knotweed records. The source locality of a second strain, the Murakami strain, was predicted to have medium-to-high suitability based on records of knotweeds from North America. In contrast, European records of Reynoutria × bohemica Chrtek & Chrtková and Reynoutria sachalinensis (F. Schmidt) Nakai predicted no suitability for this locality compared to other locations in Japan, while European records for Reynoutria japonica Houtt. predicted low suitability. The source locality of the final strain, the Hokkaido strain, was predicted as having medium-to-high suitability based on knotweed records of all examined species from both North America and Europe.

Establishment and postrelease recovery of Laricobius nigrinus and Laricobius osakensis (Coleoptera: Derodontidae), released for biological control of Adelges tsugae (Hemiptera: Adelgidae), in the Northeastern United States.

Hemlock woolly adelgid (HWA), Adelges tsugae Annand, is a major forest pest in the eastern United States responsible for killing millions of eastern hemlock, Tsuga canadensis (L.) Carrière and Carolina hemlock, T. caroliniana Engelmann. The US biological control program for HWA has largely invested in the rearing and release of Laricobius nigrinus Fender and more recently L. osakensis Montgomery and Shiyake. Though the establishment of L. nigrinus has been well-documented in the southern, mid-Atlantic, and coastal portions of the northeastern United States, documentation in interior areas of the northeastern United States is limited. Establishment of L. osakensis in the northeastern United States has not yet been documented. Release locations in the northeastern United States were surveyed for L. nigrinus and L. osakensis establishment to examine the relationship between establishment success and winter temperatures, as winter minimum temperatures likely limit the northern range of introduced Laricobius species. Our results suggest that L. nigrinus establishment is limited by winter minimum temperatures and that the probability of establishment declines as absolute minimum temperature declines. We found L. nigrinus established at sites in Maine, New York, and Pennsylvania, but did not recover any L. nigrinus in Massachusetts, New Hampshire, or Vermont. Similarly, we found L. osakensis established at sites in New York and Pennsylvania and recovered individuals in Maine, though further sampling is necessary to confirm presence of the F3 generation. We also report the first field observation of reproduction of silver flies, Leucotaraxis argenticollis (Diptera: Chamaemyiidae), released predator of HWA, in the eastern United States.

Seasonal differences in the timing of flight between the invasive winter moth and native Bruce spanworm promotes reproductive isolation.

The European winter moth, Operophtera brumata L. (Lepidoptera: Geometridae), was accidentally introduced to North America on at least 4 separate occasions, where it has been hybridizing with the native Bruce spanworm, O. bruceata Hulst, at rates up to 10% per year. Both species are known to respond to the same sex pheromones and to produce viable offspring, but whether they differ in the seasonal timing of their mating flights is unknown. Therefore, we collected adult male moths weekly along 2 transects in the northeastern United States and genotyped individuals using polymorphic microsatellite markers as males of these 2 species cannot be differentiated morphologically. Along each transect, we then estimated the cumulative proportions (i.e., the number of individuals out of the total collected) of each species on each calendar day. Our results indicate that there are significant differences between the species regarding their seasonal timing of flight, and these allochronic differences likely are acting to promote reproductive isolation between these 2 species. Lastly, our results suggest that the later flight observed by winter moth compared to Bruce spanworm may be limiting its inland spread in the northeastern United States because of increased exposure to extreme winter events.

Ecological network structure in response to community assembly processes over evolutionary time.

The dynamic structure of ecological communities results from interactions among taxa that change with shifts in species composition in space and time. However, our ability to study the interplay of ecological and evolutionary processes on community assembly remains relatively unexplored due to the difficulty of measuring community structure over long temporal scales. Here, we made use of a geological chronosequence across the Hawaiian Islands, representing 50 years to 4.15 million years of ecosystem development, to sample 11 communities of arthropods and their associated plant taxa using semiquantitative DNA metabarcoding. We then examined how ecological communities changed with community age by calculating quantitative network statistics for bipartite networks of arthropod-plant associations. The average number of interactions per species (linkage density), ratio of plant to arthropod species (vulnerability) and uniformity of energy flow (interaction evenness) increased significantly in concert with community age. The index of specialization H 2 ' has a curvilinear relationship with community age. Our analyses suggest that younger communities are characterized by fewer but stronger interactions, while biotic associations become more even and diverse as communities mature. These shifts in structure became especially prominent on East Maui (~0.5 million years old) and older volcanos, after enough time had elapsed for adaptation and specialization to act on populations in situ. Such natural progression of specialization during community assembly is probably impeded by the rapid infiltration of non-native species, with special risk to younger or more recently disturbed communities that are composed of fewer specialized relationships.

Richness and resilience in the Pacific: DNA metabarcoding enables parallelized evaluation of biogeographic patterns.

Islands make up a large proportion of Earth's biodiversity, yet are also some of the most sensitive systems to environmental perturbation. Biogeographic theory predicts that geologic age, area, and isolation typically drive islands' diversity patterns, and thus potentially impact non-native spread and community homogenization across island systems. One limitation in testing such predictions has been the difficulty of performing comprehensive inventories of island biotas and distinguishing native from introduced taxa. Here, we use DNA metabarcoding and statistical modelling as a high throughput method to survey community-wide arthropod richness, the proportion of native and non-native species, and the incursion of non-natives into primary habitats on three archipelagos in the Pacific - the Ryukyus, the Marianas and Hawaii - which vary in age, isolation and area. Diversity patterns largely match expectations based on island biogeography theory, with the oldest and most geographically connected archipelago, the Ryukyus, showing the highest taxonomic richness and lowest proportion of introduced species. Moreover, we find evidence that forest habitats are more resilient to incursions of non-natives in the Ryukyus than in the less taxonomically rich archipelagos. Surprisingly, we do not find evidence for biotic homogenization across these three archipelagos: the assemblage of non-native species on each island is highly distinct. Our study demonstrates the potential of DNA metabarcoding to facilitate rapid estimation of biogeographic patterns, the spread of non-native species, and the resilience of ecosystems.

Predation and Climate Limit Establishment Success of the Kyushu Strain of the Biological Control Agent Aphalara itadori (Hemiptera: Aphalaridae) in the Northeastern United States.

Species of knotweeds, Reynoutria spp. Houtt. (Caryophyllales: Polygonaceae), including Japanese knotweed (R. japonica Houtt.), are among the most invasive and ecologically destructive plant species introduced to North America and Europe. The Kyushu strain of the psyllid Aphalara itadori Shinji (Hemiptera: Aphalaridae) has been approved as a biological control agent for release against Japanese knotweed in the United Kingdom, Canada, and the United States. However, recent reports from Canada suggest that both biotic and abiotic factors may limit its establishment. Therefore, we examined the potential role of predation by comparing open- versus closed-sleeve treatments, and climate mis-matches by collecting temperature data from release sites and performing climate suitability analyses using MaxEnt. Our results indicated that populations of the Kyushu strain could only be maintained in the field in closed-sleeve treatments, suggesting that predation is likely limiting the establishment success of this strain. In addition, we noted that daily maximum temperatures at our field sites might exceed documented developmental thresholds for this strain, and that MaxEnt species distribution modeling indicates no climate similarities between locations in eastern North America and Kyushu. Combined with previous results, our study suggests that the establishment of the Kyushu strain of A. itadori as a biological control agent for Japanese knotweed may be limited in eastern North America. We suggest that one strategy to increase the probability of establishment of the Kyushu strain could be to increase the number of release sites in an effort to find a more optimal niche with predator-free space.

Real-time geographic settling of a hybrid zone between the invasive winter moth (Operophtera brumata L.) and the native Bruce spanworm (O. bruceata Hulst).

Hybridization plays an important and underappreciated role in shaping the evolutionary trajectories of species. Following the introduction of a non-native organism to a novel habitat, hybridization with a native congener may affect the probability of establishment of the introduced species. In most documented cases of hybridization between a native and a non-native species, a mosaic hybrid zone is formed, with hybridization occurring heterogeneously across the landscape. In contrast, most naturally occurring hybrid zones are clinal in structure. Here, we report on a long-term microsatellite data set that monitored hybridization between the invasive winter moth, Operophtera brumata (Lepidoptera: Geometridae), and the native Bruce spanworm, O. bruceata, over a 12-year period. Our results document one of the first examples of the real-time formation and geographic settling of a clinal hybrid zone. In addition, by comparing one transect in Massachusetts where extreme winter cold temperatures have been hypothesized to restrict the distribution of winter moth, and one in coastal Connecticut, where winter temperatures are moderated by Long Island Sound, we found that the location of the hybrid zone appeared to be independent of environmental variables and maintained under a tension model wherein the stability of the hybrid zone was constrained by population density, reduced hybrid fitness, and low dispersal rates. Documenting the formation of a contemporary clinal hybrid zone may provide important insights into the factors that shaped other well-established hybrid zones.

Parasite Prevalence May Drive the Biotic Impoverishment of New England (USA) Bumble Bee Communities.

Numerous studies have reported a diversity of stressors that may explain continental-scale declines in populations of native pollinators, particularly those in the genus Bombus. However, there has been little focus on the identification of the local-scale dynamics that may structure currently impoverished Bombus communities. For example, the historically diverse coastal-zone communities of New England (USA) now comprise only a few species and are primarily dominated by a single species, B. impatiens. To better understand the local-scale factors that might be influencing this change in community structure, we examined differences in the presence of parasites in different species of Bombus collected in coastal-zone communities. Our results indicate that Bombus species that are in decline in this region were more likely to harbor parasites than are B. impatiens populations, which were more likely to be parasite-free and to harbor fewer intense infections or co-infections. The contrasting parasite burden between co-occurring winners and losers in this community may impact the endgame of asymmetric contests among species competing for dwindling resources. We suggest that under changing climate and landscape conditions, increasing domination of communities by healthy, synanthropic Bombus species (such as B. impatiens) may be another factor hastening the further erosion of bumble bee diversity.

Four times out of Europe: Serial invasions of the winter moth, Operophtera brumata, to North America.

Reconstructing the geographic origins of non-native species is important for studying the factors that influence invasion success, however; these analyses can be constrained by the amount of diversity present in the native and invaded regions, and by changes in the genetic background of the invading population following bottlenecks and/or hybridization events. Here we explore the geographical origins of the invasive winter moth (Operopthera brumata L.) that has caused widespread defoliation to forests, orchards, and crops in Nova Scotia, British Columbia, Oregon, and the northeastern United States. It is not known whether these represent independent introductions to North America, or a "stepping stone" spread among regions. Using a combination of Bayesian assignment and approximate Bayesian computation methods, we analysed a population genetic data set of 24 microsatellite loci. We estimate that winter moth was introduced to North America on at least four occasions, with the Nova Scotian and British Columbian populations probably being introduced from France and Sweden, respectively; the Oregonian population probably being introduced from either the British Isles or northern Fennoscandia; and the population in the northeastern United States probably being introduced from somewhere in Central Europe. We discuss the impact of genetic bottlenecks on analyses meant to determine region of origin.

Validating Morphometrics with DNA Barcoding to Reliably Separate Three Cryptic Species of Bombus Cresson (Hymenoptera: Apidae).

Despite their large size and striking markings, the identification of bumble bees (Bombus spp.) is surprisingly difficult. This is particularly true for three North American sympatric species in the subgenus Pyrobombus that are often misidentified: B. sandersoni Franklin, B. vagans Smith B. perplexus Cresson. Traditionally, the identification of these cryptic species was based on observations of differences in hair coloration and pattern and qualitative comparisons of morphological characters including malar length. Unfortunately, these characteristics do not reliably separate these species. We present quantitative morphometric methods to separate these species based on the malar length to width ratio (MRL) and the ratios of the malar length to flagellar segments 1 (MR1) and 3 (MR3) for queens and workers, and validated our determinations based on DNA barcoding. All three measurements discriminated queens of B. sandersoni and B. vagans with 100% accuracy. For workers, we achieved 99% accuracy by combining both MR1 and MR3 measurements, and 100% accuracy differentiating workers using MRL. Moreover, measurements were highly repeatable within and among both experienced and inexperienced observers. Our results, validated by genetic evidence, demonstrate that malar measurements provide accurate identifications of B. vagans and B. sandersoni. There was considerable overlap in the measurements between B. perplexus and B. sandersoni. However, these species can usually be reliably separated by combining malar ratio measurements with other morphological features like hair color. The ability to identify bumble bees is key to monitoring the status and trends of their populations, and the methods we present here advance these efforts.

First Account of Phylogeographic Variation, Larval Characters, and Laboratory Rearing of the Endangered Cobblestone Tiger Beetle Cicindelidia marginipennis, Dejean, 1831 with Observations of Their Natural History.

The cobblestone tiger beetle, Cicindelidia marginipennis (Dejean, 1831) is a North American species specializing in riparian habitats from New Brunswick, Canada, to Alabama in the United States. In the United States, this species is state-listed as threatened or endangered range-wide and periodically receives consideration for federal listing, mostly due to habitat decline. Despite its conservation status, intraspecific genetic diversity for this species has not been explored and little is known about its natural history. To support further inquiry into the biology of C. marginipennis, this study provides the first look at range-wide genetic diversity using mitochondrial DNA (mtDNA), describes all three larval instars, and describes natural history characteristics from captive rearing and field observation. Based on mtDNA analyses, our results suggest that geographically based population structure may exist throughout the range, with individuals from Alabama possessing haplotypes not found elsewhere in our sampling. Further genetic analyses, particularly multi-locus analyses, are needed to determine whether the Alabama population represents a separate cryptic species. Our morphological analysis and descriptions of larval instars reveal a combination of characteristics that can be used to differentiate C. marginipennis from closely related and co-occurring species. Based on our field observations, we find that the larval "throw pile" of soil excavated from burrows is a key search image for locating larvae, and we provide descriptions and detailed photographs to aid surveys. Lastly, we find that this species can be successfully reared in captivity and provide guidelines to aid future recovery efforts.

The Reliability of Genitalia Morphology to Monitor the Spread of the Invasive Winter Moth (Lepidoptera: Geometridae) in Eastern North America.

Winter moth, Operophtera brumata L. (Lepidoptera: Geometridae), causes widespread defoliation in both its native and introduced distributions. Invasive populations of winter moth are currently established in the United States and Canada, and pheromone-baited traps have been widely used to track its spread. Unfortunately, a native species, the Bruce spanworm, O. bruceata (Hulst), and O. bruceata × brumata hybrids respond to the same pheromone, complicating efforts to detect novel winter moth populations. Previously, differences in measurements of a part of the male genitalia called the uncus have been utilized to differentiate the species; however, the accuracy of these measurements has not been quantified using independent data. To establish morphological cutoffs and estimate the accuracy of uncus-based identifications, we compared morphological measurements and molecular identifications based on microsatellite genotyping. We find that there are significant differences in some uncus measurements, and that in general, uncus measurements have low type I error rates (i.e., the probability of having false positives for the presence of winter moth). However, uncus measurements had high type II error rates (i.e., the probability of having false negatives for the presence of winter moth). Our results show that uncus measurements can be useful for performing preliminary identifications to monitor the spread of winter moth, though for accurate monitoring, molecular methods are still required. As such, efforts to study the spread of winter moth into interior portions of North America should utilize a combination of pheromone trapping and uncus measurements, while maintaining vouchers for molecular identification.

Rapid and cost-effective generation of single specimen multilocus barcoding data from whole arthropod communities by multiple levels of multiplexing.

In light of the current biodiversity crisis, molecular barcoding has developed into an irreplaceable tool. Barcoding has been considerably simplified by developments in high throughput sequencing technology, but still can be prohibitively expensive and laborious when community samples of thousands of specimens need to be processed. Here, we outline an Illumina amplicon sequencing approach to generate multilocus data from large collections of arthropods. We reduce cost and effort up to 50-fold, by combining multiplex PCRs and DNA extractions from pools of presorted and morphotyped specimens and using two levels of sample indexing. We test our protocol by generating a comprehensive, community wide dataset of barcode sequences for several thousand Hawaiian arthropods from 14 orders, which were collected across the archipelago using various trapping methods. We explore patterns of diversity across the Archipelago and compare the utility of different arthropod trapping methods for biodiversity explorations on Hawaii, highlighting undergrowth beating as highly efficient method. Moreover, we show the effects of barcode marker, taxonomy and relative biomass of the targeted specimens and sequencing coverage on taxon recovery. Our protocol enables rapid and inexpensive explorations of diversity patterns and the generation of multilocus barcode reference libraries across whole ecosystems.

Rise and Fall of an Oak Gall Wasp (Hymenoptera: Cynipidae) Outbreak in Massachusetts.

The recently described oak gall wasp Zapatella davisae Buffington & Melika (Hymenoptera: Cynipidae) has caused extensive damage and mortality to black oak trees, Quercus velutina L. (Fagales: Fagaceae), in coastal parts of New England, United States. Like many newly described and/or newly introduced species, it is unclear how long populations of Z. davisae have existed in this region. However, as this species forms galls on the woody-tissue of its host, it may be possible to obtain historical information about changes in its population size by examining the presence of galls in relation to annual growth nodes. Here, we explore the utility of this approach to determine population size changes in Z. davisae densities on Nantucket, Martha's Vineyard, and Cape Cod, Massachusetts, through dissection of black oak branches. In addition, we calculated parasitism rates during the years of study and obtained morphological and molecular identifications for the parasitoids associated with Z. davisae. Our results show significant changes in population sizes, with higher levels of parasitism at sites on Martha's Vineyard and Cape Cod compared to sites on Nantucket. In addition, morphological examinations, in combination with DNA sequencing, identified the associated parasitoids as five species in the genus Sycophila Walker (Hymenoptera: Eurytomidae). We comment that considerable morphological variation within several of these recovered species was observed, present the first record of males for a species from which only females have been described, and suggest that future work is required to clarify the species boundaries for this important parasitoid group.

Categorization of species as native or nonnative using DNA sequence signatures without a complete reference library.

New genetic diagnostic approaches have greatly aided efforts to document global biodiversity and improve biosecurity. This is especially true for organismal groups in which species diversity has been underestimated historically due to difficulties associated with sampling, the lack of clear morphological characteristics, and/or limited availability of taxonomic expertise. Among these methods, DNA sequence barcoding (also known as "DNA barcoding") and by extension, meta-barcoding for biological communities, has emerged as one of the most frequently utilized methods for DNA-based species identifications. Unfortunately, the use of DNA barcoding is limited by the availability of complete reference libraries (i.e., a collection of DNA sequences from morphologically identified species), and by the fact that the vast majority of species do not have sequences present in reference databases. Such conditions are critical especially in tropical locations that are simultaneously biodiversity rich and suffer from a lack of exploration and DNA characterization by trained taxonomic specialists. To facilitate efforts to document biodiversity in regions lacking complete reference libraries, we developed a novel statistical approach that categorizes unidentified species as being either likely native or likely nonnative based solely on measures of nucleotide diversity. We demonstrate the utility of this approach by categorizing a large sample of specimens of terrestrial insects and spiders (collected as part of the Moorea BioCode project) using a generalized linear mixed model (GLMM). Using a training data set of known endemic (n = 45) and known introduced species (n = 102), we then estimated the likely native/nonnative status for 4,663 specimens representing an estimated 1,288 species (412 identified species), including both those specimens that were either unidentified or whose endemic/introduced status was uncertain. Using this approach, we were able to increase the number of categorized specimens by a factor of 4.4 (from 794 to 3,497), and the number of categorized species by a factor of 4.8 from (147 to 707) at a rate much greater than chance (77.6% accuracy). The study identifies phylogenetic signatures of both native and nonnative species and suggests several practical applications for this approach including monitoring biodiversity and facilitating biosecurity.

Identification of the parasitoid community associated with an outbreaking gall wasp, Zapatella davisae, and their relative abundances in New England and Long Island, New York.

Gall wasps (Hymenoptera: Cynipidae) are phytophagous insects that often go unnoticed; however, when they are introduced to a new area or released from their natural enemies, they have the capacity to outbreak and cause extensive foliar damage. One such outbreaking pest, Zapatella davisae (Cynipidae: Cynipini), causes significant damage and mortality to black oak, Quercus velutina, in the northeastern United States. In this study, we aimed to identify the parasitoid community associated with Z. davisae, compare differences in percent parasitism of Z. davisae in Cape Cod and Long Island, and determine which parasitoid species contribute most to parasitism in each region. From both locations, we reared parasitoids, identified morphological groups, analyzed percent parasitism rates for each group, and used DNA barcoding to provide species-level identifications. On Long Island, there was nearly 100% parasitism in 2015 followed by a near total collapse of the population in 2016. In contrast, parasitism rates were lower and remained consistent on Cape Cod between 2015 and 2016, which may explain the greater canopy damage observed in that region. Species of Sycophila were the dominant parasitoids, with one species Sycophila nr. novascotiae representing ~65% of reared parasitoids from Long Island, and two species of Sycophila (S. nr. novascotiae and S. foliatae) with near equal representations on Cape Cod. In order to manage an insect pest, it is important to understand factors that influence its mortality and survival. An understanding of how these infestations progress overtime can help predict the impact that newer infestations in Nantucket, MA, and coastal Rhode Island will have on black oak populations and will aid in the management of this rapidly spreading gall wasp pest.

Using the SSU, ITS, and Ribosomal DNA Operon Arrangement to Characterize Two Microsporidia Infecting Bruce Spanworm, Operophtera bruceata (Lepidoptera: Geometridae).

Research pertaining to the two closely-related microsporidian genera Nosema and Vairimorpha is hindered by inconsistencies in species differentiation within and between the two clades. One proposal to better delimit these genera is to restructure the Nosema around a "True Nosema" clade, consisting of species that share a characteristic reversed ribosomal DNA operon arrangement and small subunit (SSU) ribosomal DNA sequences similar to that of the Nosema type species, N. bombycis. Using this framework, we assess two distinct microsporidia recovered from the forest insect Bruce spanworm (Operophtera bruceata) by sequencing their SSU and internal transcribed spacer regions. Phylogenetic analyses place one of our isolates within the proposed True Nosema clade close to N. furnacalis and place the other in the broader Nosema/Vairimorpha clade close to N. thomsoni. We found that 25% of Bruce spanworm cadavers collected over the four-year study period were infected with microsporidia, but no infections were detected in cadavers of the Bruce spanworm's invasive congener, the winter moth (O. brumata), collected over the same period. We comment on these findings as they relate to the population dynamics of the Bruce spanworm-winter moth system in this region, and more broadly, on the value of ribosomal DNA operon arrangement in Nosema systematics.

Identification of winter moth (Operophtera brumata) refugia in North Africa and the Italian Peninsula during the last glacial maximum.

Numerous studies have shown that the genetic diversity of species inhabiting temperate regions has been shaped by changes in their distributions during the Quaternary climatic oscillations. For some species, the genetic distinctness of isolated populations is maintained during secondary contact, while for others, admixture is frequently observed. For the winter moth (Operophtera brumata), an important defoliator of oak forests across Europe and northern Africa, we previously determined that contemporary populations correspond to genetic diversity obtained during the last glacial maximum (LGM) through the use of refugia in the Iberian and Aegean peninsulas, and to a lesser extent the Caucasus region. Missing from this sampling were populations from the Italian peninsula and from North Africa, both regions known to have played important roles as glacial refugia for other species. Therefore, we genotyped field-collected winter moth individuals from southern Italy and northwestern Tunisia-the latter a region where severe oak forest defoliation by winter moth has recently been reported-using polymorphic microsatellite. We reconstructed the genetic relationships of these populations in comparison to moths previously sampled from the Iberian and Aegean peninsulas, the Caucasus region, and western Europe using genetic distance, Bayesian clustering, and approximate Bayesian computation (ABC) methods. Our results indicate that both the southern Italian and the Tunisian populations are genetically distinct from other sampled populations, and likely originated in their respective refugium during the LGM after diverging from a population that eventually settled in the Iberian refugium. These suggest that winter moth populations persisted in at least five Mediterranean LGM refugia. Finally, we comment that outbreaks by winter moth in northwestern Tunisia are not the result of a recent introduction of a nonnative species, but rather are most likely due to land use or environmental changes.

Comparative genetics of invasive populations of walnut aphid, Chromaphis juglandicola, and its introduced parasitoid, Trioxys pallidus, in California.

Coevolution may be an important component of the sustainability of importation biological control, but how frequently introduced natural enemies coevolve with their target pests is unclear. Here we explore whether comparative population genetics of the invasive walnut aphid, Chromaphis juglandicola, and its introduced parasitoid, Trioxys pallidus, provide insights into the localized breakdown of biological control services in walnut orchards in California. We found that sampled populations of C. juglandicola exhibited higher estimates of genetic differentiation (FST) than co-occurring populations of T. pallidus. In contrast, estimates of both the inbreeding coefficient (GIS) and contemporary gene flow were higher for T. pallidus than for C. juglandicola. We also found evidence of reciprocal outlier loci in some locations, but none showed significant signatures of selection. Synthesis and applications. Understanding the importance of coevolutionary interactions for the sustainability of biological control remains an important and understudied component of biological control research. Given the observed differences in gene flow and genetic differentiation among populations of T. pallidus and C. juglandicola, we suspect that temporary local disruption of biological control services may occur more frequently than expected while remaining stable at broader regional scales. Further research that combines genomewide single nucleotide polymorphism genotyping with measurements of phenotypic traits is needed to provide more conclusive evidence of whether the occurrence of outlier loci that display significant signatures of selection can be interpreted as evidence of the presence of a geographic mosaic of coevolution in this system.

Postglacial recolonization shaped the genetic diversity of the winter moth (Operophtera brumata) in Europe.

Changes in climate conditions, particularly during the Quaternary climatic oscillations, have long been recognized to be important for shaping patterns of species diversity. For species residing in the western Palearctic, two commonly observed genetic patterns resulting from these cycles are as follows: (1) that the numbers and distributions of genetic lineages correspond with the use of geographically distinct glacial refugia and (2) that southern populations are generally more diverse than northern populations (the "southern richness, northern purity" paradigm). To determine whether these patterns hold true for the widespread pest species the winter moth (Operophtera brumata), we genotyped 699 individual winter moths collected from 15 Eurasian countries with 24 polymorphic microsatellite loci. We find strong evidence for the presence of two major genetic clusters that diverged ~18 to ~22 ka, with evidence that secondary contact (i.e., hybridization) resumed ~ 5 ka along a well-established hybrid zone in Central Europe. This pattern supports the hypothesis that contemporary populations descend from populations that resided in distinct glacial refugia. However, unlike many previous studies of postglacial recolonization, we found no evidence for the "southern richness, northern purity" paradigm. We also find evidence for ongoing gene flow between populations in adjacent Eurasian countries, suggesting that long-distance dispersal plays an important part in shaping winter moth genetic diversity. In addition, we find that this gene flow is predominantly in a west-to-east direction, suggesting that recently debated reports of cyclical outbreaks of winter moth spreading from east to west across Europe are not the result of dispersal.