Browsing by Author "Havill, Nathan P."

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    Ancient and modern colonization of North America by hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae), an invasive insect from East Asia
    Havill, Nathan P.; Shiyake, Shigehiko; Galloway, Ashley Lamb; Foottit, Robert G.; Yu, Guoyue; Paradis, Annie; Elkinton, Joseph S.; Montgomery, Michael E.; Sano, Masakazu; Caccone, Adalgisa (2016-05)
    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 predict invasion by insect herbivores. We identified eight endemic lineages of hemlock adelgids in central China, western China, Ulleung Island (South Korea), western North America, and two each in Taiwan and Japan, with the Japanese lineages specializing on different Tsuga species. Adelgid life cycles varied at local and continental scales with different sexual, obligately asexual and facultatively asexual lineages. Adelgids in western North America exhibited very high microsatellite heterozygosity, which suggests ancient asexuality. The earliest lineages diverged in Asia during Pleistocene glacial periods, as estimated using approximate Bayesian computation. Colonization of western North America was estimated to have occurred prior to the last glacial period by adelgids directly ancestral to those in southern Japan, perhaps carried by birds. The modern invasion from southern Japan to eastern North America caused an extreme genetic bottleneck with just two closely related clones detected throughout the introduced range. Both colonization events to North America involved host shifts to unrelated hemlock species. These results suggest that genetic diversity, host specialization and host phylogeny are not predictive of adelgid invasion. Monitoring non-native sentinel host trees and focusing on invasion pathways might be more effective methods of preventing invasion than making predictions using species traits or evolutionary history.
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    Evaluation of hybridization among three Laricobius species, predators of hemlock woolly adelgid, (Adelgidae)
    Fischer, Melissa J. (Virginia Tech, 2013-10-02)
    Hybridization was evaluated among three Laricobius spp. involved in the biological control of hemlock woolly adelgid (Adelges tsugae Annand). Following lab mating studies, there was no evidence that Laricobius osakensis Montgomery and Yu could produce hybrid progeny with either Laricobius nigrinus Fender or Laricobius rubidus LeConte. Interaction between L. osakensis and L. nigrinus did not result in a lower production of progeny as a result of fitness costs associated with interspecific mating attempts. Laricobius nigrinus and L. rubidus hybrids were produced in the lab and collected in the field. Hybrid progeny showed very little evidence of decreased fitness. For example, there was no significant difference in the number of days it took for hybrids and pure parental species to develop from egg hatch to the prepupal stage, there was no difference among hybrids and pure parental species in the head capsule widths and larval lengths for the first through third instar, and there was evidence of an F2 generation from field collected specimens. Hybrids produced in the lab had intermediate shaped genital paramere angles compared with parental species, and had elytra coloration similar to that of L. rubidus. Hybrids showed no host preference in the lab, but a preference for Adelges tsugae in the field. Of 12 site factors examined, only the number of years that L. nigrinus was present at the site was found to be associated with percent hybrids. Contamination of the L. osakensis colony with Laricobius naganoensis Leschen resulted in the need to develop molecular methods to differentiate L. osakensis from L. naganoensis. Three restriction enzymes were found that correctly differentiated the two species.
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    Investigating the natural history and predator complex of the native pine bark adelgid (Pineus strobi) in southwestern Virginia
    Wantuch, Holly Anne (Virginia Tech, 2018-02-27)
    The pine bark adelgid, Pineus strobi (Hemiptera: Adelgidae) is a native herbivore of eastern white pine, Pinus strobus (Pinales: Pinaceae), in eastern North America. It is a sessile insect that settles on P. strobus and inserts its stylet bundle to feed on the tree’s phloem. Although P. strobi is not considered a serious pest, it shares its range with the invasive hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae). Predators introduced as biological control agents of A. tsugae interact with P. strobi and its native predators, including Laricobius rubidus LeConte (Coleoptera: Derodontidae). Prior to this study, little work had been done to document the phenology or predators of P. strobi, particularly in its southern range. In the present study, the phenology of P. strobi is reported in southwestern Virginia. Patterns in overwintering population dynamics varied notably from those described from this species’ northern range. The number of annual generations could not be measured due to overlap following two distinct spring generations. Adult body size varied seasonally and was greatest in the spring. Variation between observations from the northern and southern ranges of P. strobi indicate phenological plasticity that informs biological control efforts and offers insight into implication of climatic effects on population dynamics of this and related species. Arthropod predators associated with P. strobi in forests of southwest Virginia were collected during a two-year survey. Morphology and DNA barcoding were used for identification. Species of predators found included: Laricobius rubidus (Coleoptera: Derodontidae), a native adelgid specialist, and two species from the dipteran family Chamaemyiidae, Leucopis piniperda Malloch and L. argenticollis Zetterstedt, which are adelgid specialists. Members of the families Cecidomyiidae, Coccinellidae, Chrysopidae, Hemerobiidae, and Syrphidae were also recovered. Most diverse were the Cecidomyiidae, with 15 different species inferred from their DNA barcodes. Additional work was performed to quantify supercooling points of L. rubidus collected from November – December 2016. These will be compared to those of other Laricobius species in a parallel study. Knowledge of this predator complex is beneficial to describing P. strobi ecology, and also with regard to potential biological control of invasive adelgids in the same region.
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    Phenology and Synchrony of Scymnus coniferarum (Coleoptera: Coccinellidae) with Multiple Adelgid Species in the Puget Sound, WA, USA
    Darr, Molly N.; Brooks, Rachel K.; Havill, Nathan P.; Hoebeke, E. Richard; Salom, Scott M. (MDPI, 2018-09-11)
    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 abundance was sampled at six sites in Tacoma, WA, twice monthly, for one year on different host trees of potential adelgid prey. Tree species included Pseudotsuga menziesii, Pinus contorta, Pinus monticola, and Tsuga heterophylla. Scymnus coniferarum adults were found on all conifer species, except P. menziesii. Each conifer species supported a different adelgid species, suggesting S. coniferarum feeds on multiple adelgid species. More S. coniferarum were found on pine than hemlock. DNA barcoding of S. coniferarum found two distinct clusters that differed by 6% divergence. Beetles in each cluster were co-habiting the same conifer species, and they could not be distinguished morphologically. Further taxonomic studies are needed to understand the significance of DNA barcode sequence divergence. Because S. coniferarum was more frequently associated with pine adelgids than HWA, and because of remaining taxonomic uncertainty, S. coniferarum may not be suitable for HWA biological control.
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    Predators associated with the pine bark adelgid (Hemiptera: Adelgidae), a native insect in Appalachian forests, United States of America, in its southern range
    Wantuch, Holly A.; Havill, Nathan P.; Hoebeke, E. Richard; Kuhar, Thomas P.; Salom, Scott M. (Cambridge University Press, 2019-02-01)
    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 predator complex has not yet been documented in this region. The current study identifies arthropod predators associated with P. strobi in Appalachian forests of Virginia based on a two-year survey. Predators were identified using morphology and DNA barcoding. Predator species include: Laricobius rubidus LeConte (Coleoptera: Derodontidae), Leucopis piniperda Malloch (Diptera: Chamaemyiidae), and Leucopis argenticollis Zetterstedt (Diptera: Chamaemyiidae), that are known adelgid specialists. Also found were predators from the families Cecidomyiidae (Diptera), Coccinellidae (Coleoptera), Chrysopidae (Neuroptera), Hemerobiidae (Neuroptera), and Syrphidae (Diptera). The Cecidomyiidae were especially diverse, with 14 different species inferred from their DNA barcodes. Knowledge of this predator complex is particularly valuable for anticipation and detection of potential interactions between native predator species and those that are being considered for the introduction for biological control of invasive adelgid pests within the southern Appalachian ecosystem.