Nathan P Havill

• Doctor of Philosophy
• Research Entomologist at US Forest Service

The Adelgidae form a small clade of insects within the Aphidoidea (Hemiptera) that includes some of the most destructive introduced pest species threatening North American forest ecosystems. Despite their importance, little is known about their evolutionary history and their taxonomy remains unresolved. Adelgids are cyclically parthenogenetic and e...

1. Induced plant responses can affect herbivores either directly, by reducing herbivore development, or indirectly, by affecting the performance of natural enemies. Both the direct and indirect impacts of induction on herbivore and parasitoid success were evaluated in a common experimental system, using clonal poplar trees Populus nigra (Salicales:...

Hemlock woolly adelgid, Adelges tsugae, is an invasive pest of hemlock trees (Tsuga) in eastern North America. We used 14 microsatellites and mitochondrial COI sequences to assess its worldwide genetic structure and reconstruct its colonization history. The resulting information about its life cycle, biogeography, and host specialization could help...

Southern pine beetle, Dendroctonus frontalis Zimmermann, is a major native pest of pine trees in the southeastern United States, Mexico, and Central America. The species’ range has recently expanded north for the first time in recorded history. Accordingly, information about the timing of population divergence and past geographic range occupancy ma...

The genome of the hemlock woolly adelgid ( Adelges tsugae ) is presented in 10 chromosomal pseudomolecules along with 132 unplaced scaffolds for a combined length of 216.56 Mb. The genome is highly contiguous, with a benchmarking universal single-copy orthologs (BUSCO) completion score of 98.25%, an N50 of 20.54 Mb, and the longest scaffold 37.41 M...

Hybridization between eastern and western lineages of the biological control agent, Leucotaraxis argenticollis (Zetterstedt) (Diptera: Chamaemyiidae), was demonstrated in the laboratory. The western lineage is abundant on hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae) in western North America while a genetically distinct easte...

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 and demonstrated that a partitioning of host bre...

A new subgenus and four new species of Adelges (Hemiptera: Adelgidae) are described from Bhutan. To support their taxonomic placement, we provide a phylogeny of Adelgidae reconstructed using mitochondrial and nuclear DNA sequence data. Cassiadelges subgen. nov is distinguished by the combination of feeding on Larix secondary hosts, having tergites...

Background Flight can drastically enhance dispersal capacity and is a key trait defining the potential of exotic insect species to spread and invade new habitats. The phytophagous European spongy moths (ESM, Lymantria dispar dispar) and Asian spongy moths (ASM; a multi–species group represented here by L. d. asiatica and L. d. japonica), are global...

Theodor Hartig’s aphid and scale insect type specimens have been presumed lost or destroyed for the last 140 years. Here we document their discovery at the Bavarian State Collection of Zoology (Zoologische Staatssammlung München, ZSM), in Munich, Germany. These specimens include primary types for 24 aphid, three adelgid, and two armored scale insec...

Adelges ( Cholodkovskya ) viridanus (Cholodkovsky 1896) (Hemiptera: Adelgidae) is found throughout Eurasia where it is understood to be anholocyclic, feeding on species of larch ( Larix ), without host alternation. For the first time, we report this species in North America, outside of its native range, from specimens collected in an arboretum in O...

The adelgids (Adelgidae) are a small family of sap-feeding insects, which together with true aphids (Aphididae) and phylloxerans (Phylloxeridae) make up the infraorder Aphidomorpha. Some adelgid species are highly destructive to forest ecosystems, such as Adelges tsugae, A. piceae, A. laricis, Pineus pini, and P. boerneri. Despite this, there are n...

The silver fly Leucopis hennigrata McAlpine is a predator of the silver fir wooly adelgid, Adelges nordmannianae (Eckstein), a pest in the European production of Christmas trees. While the fly is known to be a common native predator of the adelgid in Georgia, Turkey, and central Europe, it is absent from northern Europe, where the Christmas tree pr...

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 o...

The hemlock woolly adelgid (HWA, Adelges tsugae, Hemiptera: Adelgidae) is an invasive insect that threatens the ability to maintain eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana) as ecologically functional components of eastern North American forests. Since the early 1990s, a classical biological control program for HWA...

Sympatric host-associated genetic differentiation is a prominent pattern that could lead to speciation. In insects, there are numerous examples of host-associated differentiation among herbivores that prefer different plants, and parasitoids that prefer different hosts, but few examples for specialist predators. We developed new microsatellite loci...

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 for...

The hemlock woolly adelgid (Adelges tsugae (Annand)) is a serious invasive pest of hemlock trees in eastern North America. Multiple biological control agents have been the focus of research aimed at pest management and conserving hemlock communities. Three promising A. tsugae specialist predators are the beetle Laricobius nigrinus (Fender) (Coleopt...

Environmental DNA (eDNA) analysis can be a powerful tool for the early detection of invasive organisms. However, research on terrestrial eDNA detection from foliage surfaces has been limited. In this study, we developed methods to capture and detect eDNA using qPCR from an invasive forest pest, hemlock woolly adelgid (Adelges tsugae), and three of...

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...

Non-native organisms have invaded novel ecosystems for centuries, yet we have only a limited understanding of why their impacts vary widely from minor to severe. Predicting the impact of non-established or newly detected species could help focus biosecurity measures on species with the highest potential to cause widespread damage. However, predicti...

A new genus of Chamaemyiidae (Diptera: Lauxanioidea) is described, namely Leucotaraxis gen. nov. (type species Leucopis atrifacies Aldrich; other included species Leucotaraxis argenticollis (Zetterstedt), comb. nov., Leucotaraxis piniperda (Malloch), comb. nov., and Leucotaraxis sepiola sp. nov.). These species are predators of Adelgidae (Hemiptera...

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...

Many plant-sap-feeding insects have maintained a single, obligate, nutritional symbiont over the long history of their lineage. This senior symbiont may be joined by one or more junior symbionts that compensate for gaps in function incurred through genome-degradative forces. Adelgids are sap-sucking insects that feed solely on conifer trees and fol...

The southern pine beetle , Dendroctonus frontalis , is a native pest of pine trees that has recently expanded its range into the northeastern United States. Understanding its colonization, dispersal, and connectivity will be critical for mitigating negative economic and ecological impacts in the newly invaded areas. Characterization of spatial-gene...

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 hybridiza...

The root cause of the biological invasion problem is globalization, which has facilitated the planet-wide breakdown of biogeographic barriers to species migration (Mooney and Hobbs 2000). In order to understand and manage the problem, coordination on a global scale is essential, and international cooperation among affected countries as well as with...

Reconstructing the geographic origins of invasive species is critical for establishing effective management strategies. Frequently, molecular investigations are undertaken when the source population is not known, however; these analyses are constrained both by the amount of diversity present in the native region and by changes in the genetic backgr...

The Adelges (Dreyfusia) piceae (Ratzeburg) species complex is a taxonom-ically unstable group of six species. Three of the species are cyclically parthenogenetic [Ad. nordmannianae (Eckstein), Ad. prelli (Grossmann), and Ad. merkeri (Eichhorn)] and three are obligately asexual [Ad. piceae, Ad. schneideri (Börner), and Ad. nebro-densis (Binazzi & Co...

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...

Here we compare the environmental niche of a highly polyphagous forest Lepidoptera species, the winter moth ( Operophtera brumata ), in its native and invaded range. During the last 90 years, this European tree folivore has invaded North America in at least three regions and exhibited eruptive population behavior in both its native and invaded rang...

Two species of silver fly, Leucopis argenticollis (Zetterstedt) and Leucopis piniperda (Malloch) (Diptera: Chamaemyiidae), from the Pacific Northwest region of North America have been identified as potential biological control agents of hemlock woolly adelgid (Hemiptera: Adelgidae: Adelges tsugae Annand) in eastern North America. The two predators...

Assessing the ecological and economic impacts of non-native species is crucial to providing managers and policymakers with the information necessary to respond effectively. Most non-native species have minimal impacts on the environment in which they are introduced, but a small fraction are highly deleterious. The definition of ‘damaging’ or ‘high-...

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. F...

In North America the invasive winter moth (Operopthera brumata) has caused defoliation in forest and fruit crop systems in British Columbia, Nova Scotia, Oregon, and in the northeastern United States (the “Northeast”). In the Northeast, it was previously shown that hybridization is occurring with a native congener, Bruce spanworm (O. bruceata)—a sp...

A long‐standing goal of invasion biology is to identify factors driving highly variable impacts of non‐native species. Although hypotheses exist that emphasize the role of evolutionary history (e.g., enemy release hypothesis & defense‐free space hypothesis), predicting the impact of non‐native herbivorous insects has eluded scientists for over a ce...

The hemlock woolly adelgid (Hemiptera: Adelgidae: Adelges tsugae Annand) is an invasive insect, introduced from Japan to eastern North America, where it causes decline and death of hemlock trees. There is a closely related lineage of A. tsugae native to western North America. To inform classical biological control of A. tsugae in the eastern USA, t...

We collected data on mortality of late-instar gypsy moth, Lymantria dispar (L.), from outbreak populations over 4 wk in June 2017 at 10 sites in the New England region of the United States, along with estimated rainfall at these sites. Deposition of airborne conidia of the fungal pathogen, Entomophaga maimaiga Humber, Shimazu & R.S. Soper, was meas...

In eastern North America, the invasive hemlock woolly adelgid (Adelges tsugae Annand), has expanded northward at a pace that exceeds predictions from mechanistic models, suggesting successful long-distance dispersal despite the only viable dispersive phase being a flightless nymph, or “crawler.” We hypothesize that migrating birds may contribute to...

Sirexnoctilio is an invasive woodwasp that, along with its symbiotic fungus, has killed pine trees ( Pinus spp.) in North America and in numerous countries in the Southern Hemisphere. We tested a biological control agent in North America that has successfully controlled S.noctilio in Oceania, South Africa, and South America. Deladenussiricidicola n...

Populations of the recently described black oak gall wasp, Zapatella davisae Buffington (Hymenoptera: Cynipidae), have been identified as the cause of extensive tree damage and mortality to black oaks, Quercus velutina Lamarck (Fagales: Fagaceae), in the northeastern United States. Relatively little is known, however, about the distribution, phylog...

The pine bark adelgid, Pineus strobi (Hartig) (Hemiptera: Adelgidae), is an herbivore native to eastern North America that specialises on eastern white pine, Pinus strobus Linnaeus (Pinaceae). Little is known about P. strobi , especially in its southern range in the Appalachian Mountains, United States of America, and the composition of its predato...

The hemlock woolly adelgid (HWA), Adelges tsugae, is an invasive pest of Tsuga spp. in eastern North America. Scymnus coniferarum is a predaceous beetle that was collected from HWA in the western United States. Limited knowledge of this insect in its native habitat led to studies to evaluate its potential for biological control of HWA. Seasonal abu...

Nutritional bacterial symbionts enhance the diets of sap-feeding insects with amino acids and vitamins missing from their diets. In many lineages, an ancestral senior symbiont is joined by a younger junior symbiont. To date, an emergent pattern is that senior symbionts supply a majority of amino acids, and junior symbiont supply a minority. Similar...

Exploring genetic diversity within species of biological control agents can expose previously overlooked beneficial genotypes. This may be the case for two species of silver flies, Leucopis argenticollis and L. piniperda, predators of the hemlock woolly adelgid (Adelges tsugae) in the Pacific Northwest of North America. The same Leucopis species oc...

Forest invasive alien species are a major threat to ecosystem stability and can have enormous economic and social impacts. For this reason, preventing the introduction of Asian gypsy moths (AGM; Lymantria dispar asiatica and L. d. japonica) into North America has been identified as a top priority by North American authorities. The AGM is an importa...

Sap-sucking insects typically engage in obligate relationships with symbiotic bacteria that play nutritional roles in synthesizing nutrients unavailable or in scarce supply from the plant-sap diets of their hosts. Adelgids are sap-sucking insects with complex life cycles that involve alternation between conifer tree species. While all adelgid speci...

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 gen...

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 gen...

Leucopis argenticollis (Zetterstedt) and Leucopis piniperda (Malloch) are known to feed on the lineage of Adelges tsugae Annand that is native to western North America, but it is not known if they will survive on the lineage that was introduced from Japan to the eastern USA. In 2014, western Leucopis spp. larvae were brought to the laboratory and p...

Species delimitation in Pinaceae is often challenged by limited morphological differentiation and introgression. In Tsuga (hemlocks), species delimitation has been most challenging among northeastern Asian taxa, where the species are weakly marked morphologically and range in number from three to five in previous studies. Two low-copy nuclear four-...

The European winter moth, Operophtera brumata , is a non-native pest in the Northeastern USA causing defoliation of forest trees and crops such as apples and blueberries. This species is known to hybridize with O. bruceata , the Bruce spanworm, a native species across North America, although it is not known if there are hybrid generations beyond F1...

In 2003, Laricobius nigrinus Fender was introduced into the eastern United States as a biological control agent of the hemlock woolly adelgid (Adelges tsugae Annand). Following its release, it was discovered that L. nigrinus was hybridising and producing viable progeny with Laricobius rubidus LeConte, a species native to eastern North America. Rece...

A taxonomic and nomenclatural Catalogue of the adelgids (Hemiptera: Adelgidae) is presented. Six family group names are listed, five being synonyms of Adelgidae. Twenty-two genus-group names, of which nine are subjectively valid and in use, are presented with their type species, etymology, and grammatical gender. One hundred and six species-group n...

The predatory species Laricobius nigrinus (Fender) and Laricobius osakensis (Shiyake and Montgomery) (Coleoptera: Derodontidae) have been released for biological control of hemlock woolly adelgid (Adelges tsugae; Hemiptera: Adelgidae) in eastern North America. L. osakensis is native to Japan, whereas L. nigrinus is endemic to the Pacific Northwest...

An integrated management approach is needed to maintain eastern hemlock (Tsuga canadensis (L.) Carrière) in eastern North America and to minimize tree damage and mortality caused by the invasive hemlock woolly adelgid (Adelges tsugae Annand). This study examined the hypothesis that chemical control with low rates of insecticide and biological contr...

Two species of Leucopis have been found to be abundant and frequent associates of hemlock woolly adelgid in the Pacific Northwest. Current evidence suggests that these species are equally or more important to the population dynamics of the hemlock woolly adelgid in the Pacific Northwest than Laricobius nigrinus, a Pacific Northwest predator that ha...

Adelgids (Hemiptera: Sternorrhyncha: Adelgidae) are unusual among plant-sap-feeding hemipterans, in that all species appear to harbor two obligate bacterial endosymbionts. Moreover, multiple replacements of both endosymbionts have occurred over the history of the lineage. These changes appear to correlate with host-plant shifts, such that each adel...

Eastern hemlock, Tsuga canadensis (L.) Carriere, and Carolina hemlock, Tsuga caroliniana Engelmann, provide unique habitat that is threatened by the invasive hemlock woolly adelgid, Adelges tsugae Annand, which arrived in Georgia in 2003. In an attempt to conserve a portion of the mature hemlocks in north Georgia, the USDA Forest Service created ov...

Laricobius osakensis (Coleoptera: Derodontidae) was imported from Japan to the United States in 2006 for study in quarantine facilities as a potential biological control of Hemlock Woolly Adelgid. Laricobius osakensis was released from quarantine in 2010, but it was soon discovered that the colony also contained a cryptic species, Laricobius nagano...

The introduction of hemlock woolly adelgid, Adelges tsugae, into eastern forests has led to major losses of hemlock species, Tsuga spp., indigenous to the region. The primary tool available for managing hemlock woolly adelgid in forest settings is the use of biological control agents. Laricobius rubidus, a known predator of the pine bark adelgid, P...

The silver fir woolly adelgid, Dreyfusia nordmannianae, is the most severe pest occurring on Abies nordmanniana in Central and Northern Europe. The adelgid is particularly damaging to trees in Christmas tree plantations. Dreyfusia nordmannianae is native to the Caucasus region and alien to Europe, where its natural enemy complex is less diverse com...

Thirteen microsatellite loci for the threatened orange coral, Astroides calycularis have been designed. The polymorphism of these thirteen loci was tested in 24 polyps from different colonies. The results show that the allele numbers for each loci ranged from 2 to 14 (mean Na=5.1), with an average observed heterozygosity of 0.47 (He=0.45). These ne...

Knowledge of intraspecific variation in symbioses may aid in understanding the ecology of widespread insects in different parts of their range. We investigated bacterial symbionts of Adelges tsugae, a pest of hemlocks in eastern North America introduced from Asia. Amplification, cloning, and sequencing of bacterial 16S rDNA, in situ hybridizations,...

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