Effects of the emerald ash borer invasion on four species of birds

The emerald ash borer (EAB) Agrilus planipennis, first detected in 2002 in the vicinity of Detroit, Michigan, USA, is one of the most recent in a long list of introduced insect pests that have caused serious damage to North American forest trees, in this case ash trees in the genus Fraxinus. We used data from Project FeederWatch, a citizen science program focused on winter bird populations, to quantify the effects of EAB invasion on four species of resident, insectivorous birds known or likely to be EAB predators: three woodpecker species and the white-breasted nuthatch (Sitta canadensis). We compared relative numbers of birds within 50 km of the epicenter of the region where EAB was first detected, an area known to have suffered high ash tree mortality by 2008, to numbers 50–100 km from the epicenter and to control sites within 50 km of five comparable Midwestern cities where damage due to EAB has yet to be severe. We found evidence for significant effects on all four of the species in response to the EAB invasion in the highly impacted region, with red-bellied woodpeckers (Melanerpes carolinus) and white-breasted nuthatches showing numerical increases while downy woodpeckers (Picoides pubescens) and hairy woodpeckers (Picoides villosus) initially declined but exhibited at least temporary increases several years later. Temporal correlation analyses failed to provide support for immigration being a major cause of the elevated numbers in the highly impacted area, and thus these results are consistent with the hypothesis that increases were due to enhanced survival and/or reproduction associated with the EAB invasion within the highly impacted area. Results suggest that the continuing invasion of EAB into new areas is likely to significantly alter avian communities, although not always in ways that will be easy to predict.     

The effect of emerald ash borer-caused tree mortality on the invasive shrub Amur honeysuckle and their combined effects on tree and shrub seedlings

Invasive insects and plants are major threats to the health and viability of North American forests. Emerald ash borer (Agrilus planipennis) (EAB) may cause extensive changes to forest composition due to rapid ash (Fraxinus spp.) mortality. Invasive shrubs like Amur honeysuckle (Lonicera maackii) may benefit from EAB and have negative effects on woody seedlings. We predict that ash mortality has positive effects on seedling abundance, recruitment, and survival, but that these effects are influenced by L. maackii basal area and/or cover. We sampled 16 sites, representing a chronosequence of ash mortality throughout western Ohio. We tested whether L. maackii growth and fecundity varied in relation to ash decline. We also investigated effects of ash decline, stand basal area (BA), L. maackii BA and percent cover on woody seedling abundance, recruitment, and survival using linear mixed models evaluated with Akaike’s Information Criterion. These same responses were also investigated for four seedling groups: L. maackii, invasive plants (excluding L. maackii), shade tolerant natives, and shade intolerant natives. We found a significant positive relationship between ash decline and L. maackii BA growth. Lower seedling species richness corresponded with greater L. maackii BA and better ash condition. Greater L. maackii BA was also associated with lower seedling abundance and recruitment, as well as abundance and recruitment of shade-tolerant species, and recruitment of shade-intolerant species. Sites with poorer ash condition and greater L. maackii BA had more L. maackii seedlings. These findings indicate that the negative effects of L. maackii are more important to future forest composition than ash decline; however ash decline increases L. maackii growth, hence exacerbating the effects of this invasive shrub.     

Biogeography and phenology of oviposition preference and larval performance of <Emphasis Type="Italic">Pieris virginiensis</Emphasis> butterflies on native and invasive host plants

In invaded environments, formerly reliable cues might no longer be associated with adaptive outcomes and organisms can become trapped by their evolved responses. The invasion of Alliaria petiolata (garlic mustard) into the native habitat of Pieris virginiensis (West Virginia White) is one such example. Female butterflies oviposit on the invasive plant because it is related to their preferred native host plant Cardamine diphylla (toothwort), but larvae are unable to complete development. We have studied the impact of the A. petiolata invasion on P. virginiensis butterflies in the Southeastern USA by comparing oviposition preference and larval survival on both plants in North Carolina (NC) populations without A. petiolata and West Virginia (WV) populations where A. petiolata is present. Larval survival to the 3rd instar was equally low in both populations when raised on A. petiolata. Mean oviposition preference on the two plants also did not differ between populations. However, we found a seasonal effect on preference between early and late season flights within WV populations. Late season females laid 99% of total eggs on A. petiolata while early season females utilized both host plants. Late season females were also less likely to lay eggs than early season females. This change in preference toward A. petiolata could be driven by the early senescence of C. diphylla and suggests a seasonal component to the impact of A. petiolata. Therefore, the already short flight season of P. virginiensis could become further constrained in invaded populations.     

Factors influencing the dispersal of a native parasitoid, <Emphasis Type="Italic">Phasgonophora sulcata</Emphasis>, attacking the emerald ash borer: implications for biological control

High parasitism by a native parasitoid, Phasgonophora sulcata Westwood (Hymenoptera: Chalcididae), has been reported on emerald ash borer (hereafter EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), in North America. Use of this parasitoid in an augmentative biological control program has been proposed to slow the spread of EAB, yet information is lacking on key aspects of this parasitoid’s dispersal. We document the flight capacity and walking activity of P. sulcata, its potential fecundity, and describe how age, body size, temperature, and time of day affect these parameters. Wasp flight capacity, measured using flight mills, increased with temperature and decreased with age. Unexpectedly, age and body size did not affect wasp walking activity, and we saw no relationship between walking activity and flight capacity. Older wasps had lower potential fecundity than younger wasps. These results suggest that P. sulcata should be released as pupae near EAB-infested ash trees to improve efficacy and potential biological control success.     

Study of insectivorous mammals in North Vietnam

An inventory of the insectivorous mammal fauna of the Sa Pa area of Hoan Lien Son National Park (Lao Cai Province, North Vietnam) was conducted in 2005–2006. The high diversity of soricomorphs was found in primary and secondary forest habitats at altitudes from 1900 to 2200 m asl. The recorded species of insectivorous mammals are Neotetracus sinensis, Euroscaptor longirostris, Anourosorex squamipes, Blarinella griselda, C. cf. wuchinensis, C. cf. indochinensis, and Episoriculus leucops.     

Potential Species Replacements for Black Ash (<Emphasis Type="Italic">Fraxinus nigra</Emphasis>) at the Confluence of Two Threats: Emerald Ash Borer and a Changing Climate

The emerald ash borer (Agrilus planipennis; EAB) is causing widespread mortality of ash (Fraxinus spp.) and climate change is altering habitats of tree species throughout large portions of North America. Black ash (F. nigra), a moist-soil species common in the Northwoods of Minnesota, Wisconsin, and Michigan, USA, is under a double threat of losing habitat from climate change and near annihilation from EAB. Because black ash often occurs in nearly pure stands, planting non-ash species is a management strategy already underway or being planned for thousands of acres. Tools are needed to assist managers in prioritizing sites for early treatment and to select potential species to replace black ash. This study explores the implications of threats to black ash ecosystems using analyses of field data and models to assess both the threats to, and potential replacement species for, black ash in Minnesota. For our analysis we (1) assessed the status of ashes and co-occurring species in forest inventory plots throughout Minnesota; (2) modeled the risk of EAB attack for multiple years in Minnesota; (3) modeled potential impacts of climate change on tree species with current or potential future habitat in Minnesota; (4) evaluated species co-occurring with black ash in plots in Ohio and Michigan, southeast of Minnesota; and (5) synthesized these results to provide a classification for candidate replacement species, both from within Minnesota and from points farther south. Though this process is demonstrated for black ash in Minnesota, the elements to be considered and modeled would be similar for any other location with a pest or pathogen threat for a species which simultaneously faces a changing climate.     

Can enemy release explain the invasion success of the diploid <Emphasis Type="Italic">Leucanthemum vulgare</Emphasis> in North America?

Enemy release is a commonly accepted mechanism to explain plant invasions. Both the diploid Leucanthemum vulgare and the morphologically very similar tetraploid Leucanthemum ircutianum have been introduced into North America. To verify which species is more prevalent in North America we sampled 98 Leucanthemum populations and determined their ploidy level. Although polyploidy has repeatedly been proposed to be associated with increased invasiveness in plants, only two of the populations surveyed in North America were the tetraploid L. ircutianum. We tested the enemy release hypothesis by first comparing 20 populations of L. vulgare and 27 populations of L. ircutianum in their native range in Europe, and then comparing the European L. vulgare populations with 31 L. vulgare populations sampled in North America. Characteristics of the site and associated vegetation, plant performance and invertebrate herbivory were recorded. In Europe, plant height and density of the two species were similar but L. vulgare produced more flower heads than L. ircutianum. Leucanthemum vulgare in North America was 17 % taller, produced twice as many flower heads and grew much denser compared to L. vulgare in Europe. Attack rates by root- and leaf-feeding herbivores on L. vulgare in Europe (34 and 75 %) was comparable to that on L. ircutianum (26 and 71 %) but higher than that on L. vulgare in North America (10 and 3 %). However, herbivore load and leaf damage were low in Europe. Cover and height of the co-occurring vegetation was higher in L. vulgare populations in the native than in the introduced range, suggesting that a shift in plant competition may more easily explain the invasion success of L. vulgare than escape from herbivory.     

Quantifying the Impact of Woodpecker Predation on Population Dynamics of the Emerald Ash Borer (Agrilus planipennis)

The emerald ash borer (EAB), Agrilus planipennis, is an invasive beetle that has killed millions of ash trees (Fraxinus spp.) since it was accidentally introduced to North America in the 1990s. Understanding how predators such as woodpeckers (Picidae) affect the population dynamics of EAB should enable us to more effectively manage the spread of this beetle, and toward this end we combined two experimental approaches to elucidate the relative importance of woodpecker predation on EAB populations. First, we examined wild populations of EAB in ash trees in New York, with each tree having a section screened to exclude woodpeckers. Second, we established experimental cohorts of EAB in ash trees in Maryland, and the cohorts on half of these trees were caged to exclude woodpeckers. The following spring these trees were debarked and the fates of the EAB larvae were determined. We found that trees from which woodpeckers were excluded consistently had significantly lower levels of predation, and that woodpecker predation comprised a greater source of mortality at sites with a more established wild infestation of EAB. Additionally, there was a considerable difference between New York and Maryland in the effect that woodpecker predation had on EAB population growth, suggesting that predation alone may not be a substantial factor in controlling EAB. In our experimental cohorts we also observed that trees from which woodpeckers were excluded had a significantly higher level of parasitism. The lower level of parasitism on EAB larvae found when exposed to woodpeckers has implications for EAB biological control, suggesting that it might be prudent to exclude woodpeckers from trees when attempting to establish parasitoid populations. Future studies may include utilizing EAB larval cohorts with a range of densities to explore the functional response of woodpeckers.     

Genetic diversity and population structure identify the potential source of the invasive red clover casebearer moth, <Emphasis Type="Italic">Coleophora deauratella</Emphasis>, in North America

The red clover casebearer, Coleophora deauratella, is an invasive pest of red clover grown for seed in North America. In 2006, an outbreak in Alberta, Canada was discovered that resulted in significant seed losses, while further invasion threatens the world’s largest red clover forage seed production region in Oregon, USA. Prior to the recent outbreak, C. deauratella was thought to be restricted to eastern North America in its invasive range. We sequenced a 615-bp fragment of the mitochondrial cytochrome c oxidase subunit 1 gene, and developed three microsatellite markers to assess the genetic diversity and population structure of C. deauratella in North America and its native range in Europe. We observed signatures of a founder effect in North American populations and a further loss of genetic diversity within Alberta populations. Most genetic differentiation was found between continents, with no evidence of isolation-by-distance within each continent. From the limited number of European populations sampled, a single introduction from Switzerland is the most probable source of North American populations based on similar mitochondrial diversity and lack of population differentiation. Within North America, based on increased genetic diversity compared to the rest of the continent, the first North American record from Ithaca, NY, and the first documented outbreak in southern Ontario in 1989, the initial C. deauratella invasion most likely occurred in southern Ontario, Canada or adjacent states in the USA, followed by transport throughout the continent. This study provides insight into the phylogeographic history of C. deauratella in North America and Europe and may help to identify a regional source of future classical biological control agents.     

Pathogen invasion triggers an evolutionary trap for an endangered checkerspot butterfly dependent on an exotic host plant

Exotic pathogen invasions can change host eco-evolutionary interactions and possibly create an evolutionary trap when the pathogen generates mismatches between developmental phenology and reproductive cues. Taylor’s checkerspot butterfly (Euphydryas editha taylori), is an endangered species of western North America with 80 % of the extant populations dependent on an exotic host, Plantago lanceolata. Survey of occupied, recently extinct, and unsuccessful butterfly reintroduction sites spanning 4° of latitude revealed widespread disease on P. lanceolata caused by Pyrenopeziza plantaginis. This fungal pathogen, new to North America, reduces the standing crop of P. lanceolata foliage throughout the winter post-diapause larval feeding period. However, disease is absent when adult butterflies and pre-diapause larvae are active. Diseased plants were frequent in Taylor’s checkerspot populations with a history of persistence, but >90 % of the host plants in these populations had initiated new leaves within the first few weeks of post-diapause larval feeding. Conversely, host plants in recently extinct and unsuccessfully reintroduced populations were severely diseased, >66 % mean foliage necrosis/plant, and <23 % had initiated new leaves. Feeding choice trials with 25 larvae indicated that new leaves were strongly and consistently preferred by post-diapause larvae over all other available leaf types, both diseased and non-diseased. Because the influence of disease on post-diapause larval food resources is developmentally disassociated from oviposition, P. plantaginis invasion appears to have triggered an evolutionary trap for Plantago-dependent populations of Taylor’s checkerspot.     

Population expansion,current and past gene flow in Gould’s petrel: implications for conservation

Seabird life-history traits such as long generation time, low annual fecundity and delayed sexual maturation make them more prone to population loss and consequently to extinction; petrels are indeed amongst the most threatened birds. Based on coalescence and multiloci inference this study examines the extent of genetic differentiation of a vulnerable New Caledonia (caledonica) and Australia (leucoptera) subspecies of Pterodroma leucoptera (Gould’s Petrel), and whether the genetic relationship between them results from the influence of past events like variation in sea level, or is dominated by contemporary gene flow. Sequences of two mitochondrial genes and five nuclear introns were obtained from 86 individuals from both populations. Haplotype networks were used to infer relationships between the haplotypes of both populations. The demographic history of the P. leucoptera complex was studied using neutrality tests and Extended Bayesian Skyline Plots. A weak population differentiation was revealed. The Extended Bayesian Skyline plot suggested a population expansion approximately 80,000 years before present (bp) for caledonica and 30,000 years bp for leucoptera. The split was dated to 30,000 years bp by means of multilocus inference through *BEAST. Despite genetic similarity of the two taxa, we advocate to consider them as independent units for conservation management, given their strong ecological distinctiveness (foraging distribution, winter distribution, breeding phenology and breeding distribution).     

Seasonal dynamics of mesozooplankton in the Arctic Kongsfjord (Svalbard) during year-round observations from August 1998 to July 1999

We conducted a year-round mesozooplankton study in the Arctic Kongsfjord from August 1998 until July 1999 to investigate seasonal abundance and vertical as well as stage distributions of the prevalent taxa. It is the first investigation in Kongsfjord that covers the Arctic winter season and provides reasonable estimates also of small-sized copepod species. Abundant smaller copepods comprised Oithona similis, Pseudocalanus minutus, Microcalanus spp., Triconia borealis and Acartia longiremis. Among the larger copepods, Calanus finmarchicus, C. glacialis, C. hyperboreus and Metridia longa dominated. The thecosome pteropod Limacina helicina was also an important component. Abundance maxima occurred in November (988,669 ind. m^?2) with one to two orders of magnitude higher numbers as compared to all other months (39,832–200,067 ind. m^?2). The summers of 1998 and 1999 were characterized by intrusions of Atlantic water, but the community was not entirely dominated by advected boreal species. During winter, the majority of the mesozooplankton occurred below 100 m. Advection is the most likely reason for the accumulation of zooplankton at depth in winter, but local production may also contribute to high overwintering numbers. Much lower abundances of most species in spring suggest high winter mortality and emphasize the importance of sufficient reproductive success during the previous summer to ensure enough winter survivors as seed stock for the coming reproductive season. This study was conducted prior to the recent warming trend in the Arctic. Therefore, it provides valuable baseline data and allows comparing present and future states of the zooplankton community in Kongsfjord.     

Winter ecology of shallow lakes: strongest effect of fish on water clarity at high nutrient levels

While the structuring role of fish in lakes is well studied for the summer season in North temperate lakes, little is known about their role in winter when fish activity and light irradiance potentially are lower. This is unfortunate as the progressing climate change may have strong effects on lake winter temperature and possibly on trophic dynamics too. We conducted an enclosure experiment with and without the presence of fish throughout winter in two shallow lakes with contrasting phosphorus concentrations. In hypertrophic Lake Søbygård, absence of fish led to higher biomass of zooplankton, higher grazing potential (zooplankton:phytoplankton ratio) and, accordingly, lower biomass of phytoplankton and chlorophyll a (Chl a), while the concentrations of total nitrogen (TN), total phosphorus (TP), oxygen and pH decreased. The average size of egg-bearing Daphnia and Bosmina and the minimum size of egg-bearing specimens of the two genera rose. In the less eutrophic Lake Stigsholm, zooplankton and their grazing potential were also markedly affected by fish. However, the decrease in Chl a was slight, and phytoplankton biovolume, pH and the oxygen concentration were not affected. TN was higher when fish were absent. Our results indicate that: (i) there is a notable effect of fish on zooplankton community structure and size during winter in both eutrophic and hypertrophic North temperate lakes, (ii) Chl a can be high in winter in such lakes, despite low light irradiance, if fish are abundant, and (iii) the cascading effects on phytoplankton and nutrients in winter may be more pronounced in hypertrophic lakes. Climate warming supposedly leading to reduced winter mortality and dominance of small fish may enhance the risk of turbid state conditions in nutrient-enriched shallow lakes, not only during the summer season, but also during winter.     

Genetic diversity of the African poplar (<Emphasis Type="Italic">Populus ilicifolia</Emphasis>) populations in Kenya

We evaluated the genetic diversity of the African poplar (Populus ilicifolia) populations found in Kenya compared with reference samples of five poplar species from North America and one species introduced in Kenya from India (KEFRI-Kenya). Amplified fragment length polymorphism (AFLP) was used with the objective of providing important information for breeding and in situ/ex situ conservation of this species. Samples collected from three locations along the species’ natural range (Athi, Ewaso Nyiro, and Tana rivers) were compared with four samples of locally planted Populus deltoides stand introduced from India and ten reference samples from North America. Six AFLP primer combinations produced 521 clear bands for analysis. The percentage polymorphic loci were lowest in Tana (20.4 %) and highest in Athi (40.6 %). The average heterozygosity across the studied populations was between 0.07 and 0.3. AMOVA revealed more genetic variation partitioning within population (87 %; P?<?0.01) than among populations (13 %; P?<?0.01) suggesting significant genetic variation between populations. Further, UPGMA delineation showed two clusters of the Tana, Athi, and Ewaso Nyiro populations clustered together compared to the North America and India/KEFRI reference samples. Moreover, the study showed that the Athi population is more diverse than those of Tana and Ewaso Nyiro and may be important for conservation, domestication, and improvement studies. The genetic differentiation (F _ST ?=?0.134) among Kenyan P. ilicifolia populations suggests limited possibility of gene flow between these populations.     

Host genetic variation and microenvironment shape an emergent plant–antagonist interaction

Geographic mosaics of interspecific interactions can arise as a consequence of intrinsic and extrinsic deterministic factors. In this study, we took advantage of the recent discovery of a specialist leaf-miner (Caloptilia triadicae) on invasive Chinese tallow (Triadica sebifera) in the southeastern United States to examine deterministic drivers of variation in plant–animal antagonistic interactions. We conducted a common garden study to assess the influence of intrinsic host genetic variation and extrinsic microenvironment on Triadica traits as well as Caloptilia infestation and mortality. We found that tree size, branch leaf density, and leaf toughness differed according to multilocus estimates of genetic variation. Host genetic variation also influenced mortality of early instar Caloptilia, but had little effect on peak or late season infestation. Triadica from hyperinvasive populations were larger, exhibited reduced leaf density and tougher leaves, and had the lowest levels of peak season Caloptilia infestation, but also had the lowest levels of early instar mortality. Microhabitat variation associated with edge effects influenced tree size as well as late season infestation. These findings indicate that Caloptilia–Triadica interactions reflect seasonal shifts in the relative influence of intrinsic and extrinsic drivers, where peak season interactions largely reflect genetic variation in hosts, and late–season interactions reflect microenvironmental conditions. Further study of Caloptilia infestations could offer additional understanding of novel interactions that arise following species introductions.     

Pyramiding different aphid-resistance genes in elite soybean germplasm to combat dynamic aphid populations

The soybean aphid (Aphis glycines Matsumura), an invasive species, has posed a significant threat to soybean [Glycine max (L.) Merr.] production in North America since 2001. Use of resistant cultivars is an effective tactic to protect soybean yield. However, the variability and dynamics of aphid populations could limit the effectiveness of host-resistance gene(s). Gene pyramiding is a promising way to sustain host-plant resistance. The objectives of this study were to determine the prevalent aphid biotypes in Michigan and to assess the effectiveness of different combinations of aphid-resistance genes. A total of 11 soybean genotypes with known resistance gene(s) were used as indicator lines. Based on their responses, Biotype 3 was a major component of Michigan aphid populations during 2015–2016. The different performance of Rag-“Jackson” and Rag1-“Dowling” along with the breakdown of resistance in plant introductions (PIs) 567301B and 567324 may be explained by Biotype 3 or an unknown virulent biotype establishing in Michigan. With the assistance of flanking markers, 12 advanced breeding lines carrying different aphid-resistance gene(s) were developed and evaluated for effectiveness in five trials across 2015 to 2017. Lines with rag1c, Rag3d, Rag6, Rag3c?+?Rag6, rag1b?+?rag3, rag1c?+?rag4, rag1c?+?rag3?+?rag4, rag1c?+?Rag2?+?rag3?+?rag4, and rag1b?+?rag1c?+?rag3?+?rag4 demonstrated strong and consistent resistance. Due to the variability of virulent aphid populations, different combinations of Rag genes may perform differently across geographies. However, advanced breeding lines pyramided with three or four Rag genes likely will provide broader and more durable resistance to diverse and dynamic aphid populations.     

Contextualized niche shifts upon independent invasions by the dung beetle <Emphasis Type="Italic">Onthophagus taurus</Emphasis>

The historical contingencies of biological invasions may have important consequences for final invasion outcomes. Here, we characterize the variations in the realized niche during the invasions of the bull-headed dung beetle Onthophagus taurus (Coleoptera: Scarabaeidae) from its native Mediterranean range following accidental (Eastern North America) as well as deliberate (Western North America, Western Australia, and Eastern Australia) releases into novel, exotic ranges approximately 50 years ago. Specifically, we examined whether the climatic responses of exotic O. taurus have diverged from those characterizing their native range, and if so, to what degree and in what dimensions. We found that when compared to the native range, all exotic populations exhibited similar overlap proportions regardless of invasion history. However, more detailed analysis of climatic niche features showed that all three deliberately established populations were characterized by overall similar climatic niche features, whereas the accidentally-established Eastern North American populations have undergone significant changes in their climatic niche. Specifically, when analog climates were considered on the background of each pairwise range comparison, accidentally-established Eastern North American populations showed a different climatic niche expansion than their deliberately introduced Australian or Western North American counterparts, in particular towards colder and more humid climates. We discuss our results in the context of the widely divergent introduction histories of O. taurus in Australia and North America, and highlight the possible roles of contrasting propagule sizes, disparate genetic profiles and variances, adaptive processes and invadable landscapes in shaping invasion outcomes in the different exotic ranges.     

From species to individuals: combining barcoding and microsatellite analyses from non-invasive samples in plant ecology studies

By means of DNA barcoding and microsatellite analyses, we studied the species and individuals of legitimate seed dispersers of the Mediterranean shrub Pistacia lentiscus, a keystone species that represents the main source of food in winter for frugivorous birds. We collected dropping of birds containing seeds, and after DNA extraction we amplified and sequenced a fragment of the mitochondrial COI gene. Through BLASTN queries of the sequenced fragments against registered sequences in the GenBank database we identified the bird species that are currently dispersing P. lentiscus seeds. Further, through the amplification of specific nuclear microsatellite loci we calculated standard genetic diversity parameters of the population of birds from the genus Sylvia (the blackcap and Sardinian warbler), the most important dispersers of P. lentiscus. Five bird species were identified as seed dispersers through their barcode match. Further, we found that S. melanocephala displayed slightly lower levels of genetic diversity than S. atricapilla. In this study we show how the genetic analyses of environmental faecal samples can be a useful and convenient tool for the study of plant-frugivore interactions through the ascertainment of the identity of the species involved and through the analyses of genetic variability of their populations.     

The big chill: quantifying the effect of the 2014 North American cold wave on hemlock woolly adelgid populations in the central Appalachian Mountains

The ability to survive winter temperatures is a key determinant of insect distributional ranges and population dynamics in temperate ecosystems. Although many insects overwinter in a state of diapause, the hemlock woolly adelgid [Adelges tsugae (Annand)] is an exception and instead develops during winter. We studied a low density population of A. tsugae, which undergoes two generations per year, in a forested area in which its only available host plant, eastern hemlock (Tsuga canadensis), was patchy and scarce. In January 2014, this area also experienced an exceptionally cold winter due to a southward shift in the North Polar Vortex. We used 3 years of systematic sampling prior to the 2014 cold wave, and 1 year following, to quantify the effect of the 2014 cold wave on A. tsugae population dynamics. We observed a strong negative correlation between the number of days below sub-zero temperature thresholds and A. tsugae, and estimated that the 2014 cold wave resulted in at least a 238% decrease in its population growth rate. However, we also observed that the detrimental effect of the 2014 cold wave to A. tsugae was short-lived, as populations measured in the late summer of 2014 rebounded to pre-2014 cold wave densities. This study highlights the effect that cold winter weather events can have on a winter active insect species, and the speed at which populations can recover from stochastic mortality events.