Biology and evolution of adelgidae

Seasonality of forest insects: why diapause matters

Insects have major impacts on forest ecosystems, from herbivory and soil-nutrient cycling to killing trees at a large scale. Forest insects from temperate, tropical, and subtropical regions have evolved strategies to respond to seasonality; for example, by entering diapause, to mitigate adversity and to synchronize lifecycles with favorable periods. Here, we show that distinct functional groups of forest insects; that is, canopy dwellers, trunk-associated species, and soil/litter-inhabiting insects, express a variety of diapause strategies, but do not show systematic differences in diapause strategy depending on functional group. Due to the overall similarities in diapause strategies, we can better estimate the impacts of anthropogenic change on forest insect populations and, consequently, on key ecosystems.

Persistence and recovery of dinotefuran in eastern hemlock (Tsuga canadensis) foliage and twigs by UPLC-MS/MS and ELISA

BACKGROUND

Dinotefuran, a systemic neonicotinoid insecticide, is approved for control of hemlock woolly adelgid (HWA) (Adelges tsugae Annand), an invasive sap-feeding insect that can kill eastern hemlocks (Tsuga canadensis). Dinotefuran is highly water soluble, facilitating more rapid translocation and HWA control than other neonicotinoids, but its persistence is not well-known. Samples of needles and twigs were collected in spring 2021 from 50 hemlocks treated with a dinotefuran basal trunk spray in 2018 or 2019 (131-145 weeks and 85-93 weeks before sampling, respectively). Processed samples were analyzed with ultra-performance liquid chromatography-tandem mass spectrometer (UPLC-MS/MS) and enzyme-linked immunosorbent assays (ELISA).

RESULTS

Dinotefuran residues were 4.6-6.1 times higher in needles than in twigs collected from the same trees. Average (±SE) residues in foliage samples collected from trees treated in 2019 ranged from 0.663 ± 0.243 to 0.564 ± 0.119 mg kg-1 , compared with 0.213 ± 0.033 and 0.225 ± 0.132 mg kg-1 in foliage from trees treated in 2018. Foliage residues from UPLC-MS/MS were consistently lower but strongly related to those from ELISA. Matrix effects appeared to disrupt ELISA analysis of twigs. None of the 25 trees treated in 2019 had live HWA when samples were collected in 2021 while low densities of HWA were observed on 52% of trees treated in 2018.

CONCLUSIONS

Dinotefuran was recovered from hemlock foliage, and to a lesser extent twigs, >2 years post-treatment. This, along with its relatively rapid translocation, suggests dinotefuran is a viable option for protecting declining or heavily infested hemlocks from HWA. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Whole-genome sequence of the Cooley spruce gall adelgid, Adelges cooleyi (Hemiptera: Sternorrhyncha: Adelgidae)

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, Adelges piceae, Adelges laricis, Pineus pini, and Pineus boerneri. Despite this, there are no high-quality genomic resources for adelgids, hindering advanced genomic analyses within Adelgidae and among Aphidomorpha. Here, we used PacBio continuous long-read and Illumina RNA-sequencing to construct a high-quality draft genome assembly for the Cooley spruce gall adelgid, Adelges cooleyi (Gillette), a gall-forming species endemic to North America. The assembled genome is 270.2 Mb in total size and has scaffold and contig N50 statistics of 14.87 and 7.18 Mb, respectively. There are 24,967 predicted coding sequences, and the assembly completeness is estimated at 98.1 and 99.6% with core BUSCO gene sets of Arthropoda and Hemiptera, respectively. Phylogenomic analysis using the A. cooleyi genome, 3 publicly available adelgid transcriptomes, 4 phylloxera transcriptomes, the Daktulosphaira vitifoliae (grape phylloxera) genome, 4 aphid genomes, and 2 outgroup coccoid genomes fully resolves adelgids and phylloxerans as sister taxa. The mitochondrial genome is 24 kb, among the largest in insects sampled to date, with 39.4% composed of noncoding regions. This genome assembly is currently the only genome-scale, annotated assembly for adelgids and will be a valuable resource for understanding the ecology and evolution of Aphidomorpha.

Development of Novel Early Detection Technology for Hemlock Woolly Adelgid, Adelges tsugae (Hemiptera: Adelgidae)

Hemlock woolly adelgid (HWA), Adelges tsugae Annand, threatens hemlock forests throughout eastern North America. Management efforts focus on early detection of HWA to ensure rapid management responses to control and stop the spread of this pest. This study's goal was to identify an affordable, efficient trap to aid with airborne environmental DNA (eDNA) sampling approaches as an early monitoring tool for HWA. We initially compared HWA detection success between a standard sticky trap, commonly used for HWA monitoring, and trap designs potentially compatible with eDNA protocols (i.e., passive trap, funnel trap, and motorized trap). Passive, funnel, and motorized traps' estimated capture success probabilities compared to sticky traps were 0.87, 0.8, and 0.4, respectively. A secondary evaluation of a modified version of the motorized trap further assessed trap performance and determined the number of traps needed in a set area to efficiently detect HWA. By modifying the original motorized trap design, its estimated capture success probability increased to 0.67 compared to a sticky trap. Overall, the cumulative capture success over the 16-week sampling period for the motorized trap was 94% and 99% for the sticky trap. The number of traps did impact capture success, and trap elevation and distance to infested hemlocks influenced the number of adelgids captured per trap. As eDNA-based monitoring approaches continue to become incorporated into invasive species surveying, further refinement with these types of traps can be useful as an additional tool in the manager's toolbox.

Antimicrobial diterpene induced by two gall-inducing adelgids coexisting on Picea koraiensis

The mechanism by which closely related species can coexist is a central factor in the stability of ecological communities. The larch adelgid (Adelges laricis laricis) and the eastern spruce adelgid (Adelges (Sacchiphantes) abietis) have both been found on the branches of Picea koraiensis in China. These two adelgids exhibit strong infectivity and readily induce the formation of 'fish scale-like' and 'pineapple-like' galls with branch parasitism rates of between 75.01 ± 7.03 and 88.02 ± 4.39%. Interestingly, the gall tissues in which these two gall-inducing insects were found to be coexisting were discovered at a rate of ~0.2% in the studied populations. The weight and number of gall chambers as well as the number of adelgids in the 'fish scale-like' side were higher than those in the 'pineapple-like' side. Furthermore, compared with the normal branches, a diterpene neoabietic acid was found at elevated concentrations in the gall tissues, with especially high concentrations seen in the tissues of the co-occupied galls. Neoabietic acid exhibited strong antibacterial activities against Bacillus spp. isolated from the branches of P. koraiensis, as well as potent antifungal activity against the hyphal growth of Fusarium graminearum JMY-1, which was obtained from the gall tissues. Our result provides evidence that the coexistence of the two closely related species could be explained by alterations of the host tissues by the insects resulting in increased concentrations of the antimicrobial agent.

Transitional genomes and nutritional role reversals identified for dual symbionts of adelgids (Aphidoidea: Adelgidae)

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 follow complex life cycles in which the diet fluctuates in nutrient levels. Adelgids are unusual in that both senior and junior symbionts appear to have been replaced repeatedly over their evolutionary history. Genomes can provide clues to understanding symbiont replacements, but only the dual symbionts of hemlock adelgids have been examined thus far. Here, we sequence and compare genomes of four additional dual-symbiont pairs in adelgids. We show that these symbionts are nutritional partners originating from diverse bacterial lineages and exhibiting wide variation in general genome characteristics. Although dual symbionts cooperate to produce nutrients, the balance of contributions varies widely across pairs, and total genome contents reflect a range of ages and degrees of degradation. Most symbionts appear to be in transitional states of genome reduction. Our findings support a hypothesis of periodic symbiont turnover driven by fluctuating selection for nutritional provisioning related to gains and losses of complex life cycles in their hosts.

Evolutionarily recent dual obligatory symbiosis among adelgids indicates a transition between fungus- and insect-associated lifestyles

Adelgids (Insecta: Hemiptera: Adelgidae) form a small group of insects but harbor a surprisingly diverse set of bacteriocyte-associated endosymbionts, which suggest multiple replacement and acquisition of symbionts over evolutionary time. Specific pairs of symbionts have been associated with adelgid lineages specialized on different secondary host conifers. Using a metagenomic approach, we investigated the symbiosis of the Adelges laricis/Adelges tardus species complex containing betaproteobacterial ("Candidatus Vallotia tarda") and gammaproteobacterial ("Candidatus Profftia tarda") symbionts. Genomic characteristics and metabolic pathway reconstructions revealed that Vallotia and Profftia are evolutionary young endosymbionts, which complement each other's role in essential amino acid production. Phylogenomic analyses and a high level of genomic synteny indicate an origin of the betaproteobacterial symbiont from endosymbionts of Rhizopus fungi. This evolutionary transition was accompanied with substantial loss of functions related to transcription regulation, secondary metabolite production, bacterial defense mechanisms, host infection, and manipulation. The transition from fungus to insect endosymbionts extends our current framework about evolutionary trajectories of host-associated microbes.

Probing behavior of Adelges laricis Vallot (Hemiptera: Adelgidae) on Larix decidua Mill: Description and analysis of EPG waveforms

Adelgidae are a sister group of Aphididae and Phylloxeridae within Hemiptera, Aphidoidea and occur exclusively on Pinaceae. The piercing-sucking mouthparts of Adelgidae are similar to those of aphids and it is believed that adelgids ingest sap from both the non-vascular and vascular (phloem) tissues. The aim of the present study was to identify and characterize the adelgid stylet activities during their penetration in plant tissues. The probing behavior of Adelges laricis Vallot (Hemiptera: Adelgidae) on European larch Larix decidua Mill. and sucrose diets was monitored using the DC-EPG (Electrical Penetration Graph technique = electropenetrography). The EPG waveforms were described based on amplitude, frequency, voltage level, and electrical origin of the observed traces, and associated with putative behavioral activities based on analogy with aphid activities. Waveform frequency, duration, and sequence were analysed as well. A. laricis generated EPG signals at two clearly distinct voltage levels positive and negative, suggesting extracellular and intracellular stylet penetration, respectively. The adelgid EPG patterns were ascribed to four behavioral phases, which were non-probing, pathway, phloem, and xylem phases. Non-probing referred to the position of the stylets outside the plant tissues. Pathway phase was represented by three waveform patterns that visualized extracellular stylet penetration in non-vascular tissues without potential drops (AC1), with serial short (1.2–1.5 s) potential drops (AC2), and with ‘aphid-like’ (5–10 s) potential drops (AC3). Phloem phase comprised three waveform patterns at intracellular level, which in all probability represented phloem salivation (AE1), and phloem sap passive (AE2) and active ingestion (AE3). AE3 was a newly described waveform, previously unreported from Hemiptera. Waveform AG represented the ingestion of xylem sap. The comparative analysis demonstrated that the gymnosperm-associated adelgids show certain similarities in probing behavior typical of aphids and phylloxerids on angiosperm plants. The present work is the first detailed analysis of specific adelgid stylet activities on gymnosperms.

Historic Assessment and Analysis of the Mass Production of Laricobius spp. (Coleoptera: Derodontidae), Biological Control Agents for the Hemlock Woolly Adelgid, at Virginia Tech

Laricobius nigrinus (Coleoptera: Derodontidae) Fender and Laricobius osakensis (Coleoptera: Derodontidae) Montgomery and Shiyake have been mass produced by Virginia Tech as biological control agents for the hemlock woolly adelgid (HWA), Adelges tsugae (Hemiptera: Adelgidae) Annand, for the past 15 and 9 yr, respectively. Herein, we describe modifications of our rearing procedures, trends and analyses in the overall production of these agents, and the redistribution of these agents for release to local and federal land managers. Based on these data, we have highlighted three major challenges to the rearing program: 1) high mortality during the subterranean portion of its life cycle (averaging 37% annually) reducing beetle production, 2) asynchrony in estivation emergence relative to the availability of their host HWA minimizing food availability, and 3) unintended field collections of Laricobius spp. larvae on HWA provided to lab-reared larvae complicating rearing procedures. We further highlight corresponding avenues of research aimed at addressing each of these challenges to further improve Laricobius spp. production.

Ecological factors influencing the beneficial endosymbionts of the hemlock woolly adelgid (Hemiptera: Adelgidae)

Bacterial endosymbionts of sap-sucking insects provide their host with a number of beneficial qualities, including the supply of nutrition, defense against parasitoids, and protection from heat stress. Damage to these bacterial associates can therefore have a negative impact on the fitness of their insect host. We evaluated observational and experimental factors regarding the nonnative hemlock woolly adelgid (Adelges tsugae Annand) (Hemiptera: Adelgidae) to help understand the roles of its three recently identified symbionts, including under heat stress conditions. The prevalence of A. tsugae's facultative symbiont (Serratia symbiotica) was examined at different spatial scales to determine how variable infection rates are for this symbiont. There was no significant difference found in infection rates between adelgids on a tree, within a plot, or within a state. However, significantly more adelgids in Georgia (95%) had S. symbiotica compared to those in New York (68%). Microsatellite genotyping of the adelgids found that this difference was most likely not the result of a second introduction of A. tsugae into eastern North America. Comparison of S. symbiotica proportions between first and fourth instars showed that symbiont absence did not affect the ability of A. tsugae to survive aestivation. Evaluations of symbiont densities within each adelgid found that when S. symbiotica was absent, the density of obligate symbionts was significantly higher. Exposure to heat stress (32.5 °C) was not consistently correlated with changes in symbiont densities over a 4-d period. Overall, we have shown that symbiont prevalence and densities vary within the broad population of A. tsugae in eastern North America, with potentially significant effects upon the ecology of this important pest.

Partnering With a Pest: Genomes of Hemlock Woolly Adelgid Symbionts Reveal Atypical Nutritional Provisioning Patterns in Dual-Obligate Bacteria

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 symbionts supply a minority. Similar to other hemipterans, adelgids harbor obligate symbionts, but have higher diversity of bacterial associates, suggesting a history of symbiont turnover. The metabolic roles of dual symbionts in adelgids and their contributions to the consortium are largely unexplored. Here, we investigate the symbionts of Adelges tsugae, the hemlock woolly adelgid (HWA), an invasive species introduced from Japan to the eastern United States, where it kills hemlock trees. The response of hemlocks to HWA feeding has aspects of a defensive reaction against pathogens, and some have speculated that symbionts may be involved. We sequenced the genomes of "Ca. Annandia adelgestsuga" and "Ca. Pseudomonas adelgestsugas" symbionts to detail their metabolic capabilities, infer ages of relationship, and search for effectors of plant defenses. We also tested the relationship of "Ca. Annandia" to symbionts of other insects. We find that both symbionts provide nutrients, but in more balanced proportions than dual symbionts of other hemipterans. The lesser contributions of the senior "Ca. Annandia" support our hypothesis for symbiont replacements in adelgids. Phylogenomic results were ambiguous regarding the position of "Ca. Annandia". We found no obvious effectors of plant defenses related to insect virulence, but hypothetical proteins in symbionts are unknown players.

Phenology of the Pine Bark Adelgid, Pineus strobi (Hemiptera: Adelgidae), in White Pine Forests of Southwestern Virginia

The pine bark adelgid, Pineus strobi Hartig (Hemiptera: Adelgidae), is a native herbivore of eastern white pine, Pinus strobus L. (Pinales: Pinaceae), in eastern North America. P. strobi does not appear to have any dominant overwintering lifestage in southwest Virginia, as it does in its northern range. Eggs can be found consistently from late March through early December and may be produced sporadically later throughout the winter during warm periods. Two distinct generations were observed in the spring, after which life stage frequencies overlapped. Adult body size varied seasonally and was greatest in the spring. The present study constitutes the first recording of phenological details of the P. strobi in its southern range, informing biological control efforts aimed at closely related invasive pests. The phenological plasticity observed between northern and southern P. strobi populations provides insight into the potential effects of climate on the population dymanics of this and related species.

Dynamic Acquisition and Loss of Dual-Obligate Symbionts in the Plant-Sap-Feeding Adelgidae (Hemiptera: Sternorrhyncha: Aphidoidea)

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 species feed on spruce during the sexual phase of their life cycle, each adelgid species belongs to a major lineage that feeds on a distinct genus of conifers as their alternate host. Previous work on adelgid symbionts had discovered pairs of symbionts within each host species, and unusual diversity across the insect family, but left several open questions regarding the status of bacterial associates. Here, we explored the consistency of symbionts within and across adelgid lineages, and sought evidence for facultative vs. obligate symbiont status. Representative species were surveyed for symbionts using 16S ribosomal DNA gene sequencing, confirming that different symbiont pairs were consistently present within each major adelgid lineage. Several approaches were used to establish whether symbionts exhibited characteristics of long-term, obligate mutualists. Patterns of symbiont presence across adelgid species and diversification with host insects suggested obligate relationships. Fluorescent in situ hybridization and electron microscopy localized symbionts to bacteriocyte cells within the bacteriome of each species (with one previously known exception), and detection of symbionts in eggs indicated their vertical transmission. Common characteristics of long-term obligate symbionts, such as nucleotide compositional bias and pleomorphic symbiont cell shape were also observed. Superimposing microbial symbionts on the adelgid phylogeny revealed a dynamic pattern of symbiont gains and losses over a relatively short period of time compared to other symbionts associated with sap-sucking insects, with each adelgid species possessing an older, “senior” symbiont and a younger “junior” symbiont. A hypothesis relating adelgid life cycles to relaxed constraints on symbionts is proposed, with the degradation of senior symbionts and repeated acquisition of more junior symbionts creating opportunities for repeated colonization of new alternate-conifer hosts by adelgids.

Field-Cage Evaluation of Survival, Reproduction, and Feeding Behavior of Adult Scymnus coniferarum (Coleoptera: Coccinellidae), a Predator of Adelges tsugae (Hemiptera: Adelgidae)

The hemlock woolly adelgid, Adelges tsugae Annand, is an invasive pest of eastern (Tsuga canadensis (L.) Carrière) and Carolina hemlock (Tsuga caroliniana Engelmann) forests in the eastern United States. Scymnus (Pullus) coniferarum Crotch (Coleoptera: Coccinellidae) is a lady beetle that preys on A. tsugae in the western United States, where A. tsugae infestations on western hemlocks are not lethal. It is thought that S. coniferarum could be an important predator that helps keep A. tsugae populations from reaching damaging levels in this region. This study assesses the potential of this predator as a biological control agent for A. tsugae in the eastern United States. S. coniferarum predation, reproductive potential, and survival were evaluated in field-cages on adelgid-infested T. canadensis at two sites in southwestern Virginia. Sampling was conducted between December 2012 and June 2014 to evaluate the impact of S. coniferarum on both generations of A. tsuage (sistens and progrediens). Adult S. coniferarum fed on both generations and all life stages of A. tsugae during both field trials at rates comparable to other adelgid-specific predators. Evidence of S. coniferarum oviposition was minimal, and may be attributed to low temperatures and prey availability. S. coniferarum mortality was greatest when exposed to winter temperatures at the higher elevation site in 2013, and least throughout the 2014 spring sample period. S. coniferarum demonstrated a high predation rate on A. tsugae and survived for extended periods of time at sites in southwest Virginia, indicating that this species could be an effective predator of hemlock woolly adelgid in similar climates.

Fitness and physiology of Adelges tsugae (Hemiptera: Adelgidae) in relation to the health of the eastern hemlock

The hemlock woolly adelgid, Adelges tsugae Annand is an invasive insect that frequently causes hemlock (Tsuga spp.) mortality in the eastern United States. Studies have shown that once healthy hemlocks become infested by the adelgid, nutrients are depleted from the tree, leading to both tree decline and a reduction of the adelgid population. Since A. tsugae is dependent on hemlock for nutrients, feeding on trees in poor health may affect the ability of the insect to obtain necessary nutrients and may consequently affect their physiological and population health. Trees were categorized as lightly or moderately impacted by A. tsugae based on quantitative and qualitative tree health measurements. Population health of A. tsugae on each tree was determined by measuring insect density and peak mean fecundity; A. tsugae physiological health was determined by measuring insect biomass, total carbon, carbohydrate, total nitrogen, and amino nitrogen levels. Adelges tsugae from moderately impacted trees exhibited significantly greater fecundity than from lightly impacted trees. However, A. tsugae from lightly impacted hemlocks contained significantly greater levels of carbohydrates, total nitrogen, and amino nitrogen. While the results of the physiological analysis generally support our hypothesis that A. tsugae on lightly impacted trees are healthier than those on moderately impacted trees, this was not reflected in the population health measurements. Adelges tsugae egg health in response to tree health should be verified. This study provides the first examination of A. tsugae physiological health in relation to standard A. tsugae population health measures on hemlocks of different health levels.

Ancient and modern colonization of North America by hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae), an invasive insect from East Asia

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.

Host Range Specificity of Scymnus camptodromus (Coleoptera: Coccinellidae), A Predator of Hemlock Woolly Adelgid (Hemiptera: Adelgidae)

Scymnus (Neopullus) camptodromus Yu and Liu (Coleoptera: Coccinellidae) was brought to the United States from China as a potential biological control agent for hemlock woolly adelgid (Adelges tsugae Annand) (Hemiptera: Adelgidae). Scymnus camptodromus phenology is closely synchronized with that of A. tsugae and has several characteristics of a promising biological control agent. As a prerequisite to field release, S. camptodromus was evaluated for potential nontarget impacts. In host range studies, the predator was given the choice of sympatric adelgid and nonadelgid prey items. Nontarget testing showed that S. camptodromus will feed to some degree on other adelgid species, but highly prefers A. tsugae. We also evaluated larval development of S. camptodromus on pine bark adelgid (Pineus strobi (Hartig)) (Hemiptera: Adelgidae) and larch adelgid (Adelges laricis Vallot) (Hemiptera: Adelgidae); a small proportion of predator larvae was able to develop to adulthood on P. strobi or A. laricis alone. Scymnus camptodromus showed no interest in feeding on woolly alder aphid (Paraprociphilus tessellatus Fitch) (Hemiptera: Aphididae) or woolly apple aphid (Eriosoma lanigerum (Hausmann)) (Hemiptera: Aphididae), and minimal interest in cotton aphid (Aphis gossypii Glover) (Hemiptera: Aphididae) in choice and no-choice experiments. Scymnus camptodromus females did not oviposit on any host material other than A. tsugae-infested hemlock. Under the circumstances of the study, S. camptodromus appears to be a specific predator of A. tsugae, with minimal risk to nontarget species. Although the predator can develop on P. strobi, the likelihood that S. camptodromus would oviposit on pine hosts of this adelgid is small.

Catalog of the adelgids of the world (Hemiptera, Adelgidae)

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 names are listed, of which 70 are considered subjectively valid.

Convergent Reduction of Ovariole Number Associated with Subterranean Life in Beetles

BACKGROUND

Some species of obligate cavernicolous beetles are known to possess a unique feature-a contraction of the larval cycle. In contrast to many other subterranean beetles, life-cycle contraction in Trechini ground beetles (Carabidae) is correlated with a reduction in the number of eggs and a drastic reduction in the number of ovarioles. This remarkable peculiarity has only been reported for a small number of closely related species.

RESULTS

We give a description of the female internal reproductive system for six species of Trechini, including five subterranean species, with a particular focus on the western Pyrenean radiation of Aphaenops, a group for which nothing is known regarding the early life stages. We redescribe the internal female genitalia of A. crypticola Linder. Study of the ovarioles allowed us to infer the postembryonic development of the larvae for each species examined. We then used a phylogenetic framework to recognize two independent reductions in the number of ovarioles in the Pyrenean lineage. We discuss the multiple convergent evolutions in ovariole number and the potential link between a reduction of ovariole number and troglobiomorphism in a phylogenetic context.

CONCLUSIONS

There is an extreme reduction in ovariole number and size within the species studied; the eggs produced by small ovarioles have a remarkably large size. A reduction to one ovariole has occurred independently at least twice in this subterranean group. A reduction in the number of ovarioles in ground beetles is one of the striking consequences of subterranean specialization and it is correlated with another remarkable adaptation of subterranean beetles, a reduction in the number of larval instars.

Aphid polyphenisms: trans-generational developmental regulation through viviparity

Polyphenism, in which multiple discrete phenotypes develop from a single genotype, is considered to have contributed to the evolutionary success of aphids. Of the various polyphenisms observed in the complex life cycle of aphids, the reproductive and wing polyphenisms seen in most aphid species are conspicuous. In reproductive polyphenism, the reproductive modes can change between viviparous parthenogenesis and sexual reproduction in response to the photoperiod. Under short-day conditions in autumn, sexual morphs (males and oviparous females) are produced parthenogenetically. Winged polyphenism is observed in viviparous generations during summer, when winged or wingless (flightless) aphids are produced depending on a variety of environmental conditions (e.g., density, predators). Here, we review the physiological mechanisms underlying reproductive and wing polyphenism in aphids. In reproductive polyphenism, morph determination (male, oviparous or viviparous female) within mother aphids is regulated by juvenile hormone (JH) titers in the mothers. In wing polyphenism, although JH is considered to play an important role in phenotype determination (winged or wingless), the role is still controversial. In both cases, the acquisition of viviparity in Aphididae is considered to be the basis for maternal regulation of these polyphenisms, and through which environmental cues can be transferred to developing embryos through the physiological state of the mother. Although the mechanisms by which mothers alter the developmental programs of their progeny have not yet been clarified, continued developments in molecular biology will likely unravel these questions.

The pine bark Adelgid, Pineus strobi, contains two novel bacteriocyte-associated gammaproteobacterial symbionts

Bacterial endosymbionts of the pine bark adelgid, Pineus strobi (Insecta: Hemiptera: Adelgidae), were investigated using transmission electron microscopy, 16S and 23S rRNA-based phylogeny, and fluorescence in situ hybridization. Two morphologically different symbionts affiliated with the Gammaproteobacteria were present in distinct bacteriocytes. One of them ("Candidatus Annandia pinicola") is most closely related to an endosymbiont of Adelges tsugae, suggesting that they originate from a lineage already present in ancient adelgids before the hosts diversified into the two major clades, Adelges and Pineus. The other P. strobi symbiont ("Candidatus Hartigia pinicola") represents a novel symbiont lineage in members of the Adelgidae. Our findings lend further support for a complex evolutionary history of the association of adelgids with a phylogenetically diverse set of bacterial symbionts.

Endosymbiotic microorganisms in Adelges (Sacchiphantes) viridis (Insecta, Hemiptera, Adelgoidea: Adelgidae): Molecular characterization, ultrastructure and transovarial transmission

The aim of this paper was to identify endosymbiotic microorganisms living in the body cavity of a Polish population of an aphid, Adelges (Sacchiphantes) viridis, as well as to describe their ultrastructure and mode of transmission between generations. Molecular data (amplification and sequencing of 16S rRNA genes) indicated that endosymbionts of A. (S.) viridis are Betaproteobacteria of the species "Candidatus Vallotia virida". Endosymbiotic bacteria are rod-shaped and localized in the cytoplasm of specific cells, termed bacteriocytes, of host insects. Endosymbionts sharing the same bacteriocytes differ in the density of their cytoplasm. There are two morphotypes of endosymbiotic bacteria: with electron-dense cytoplasm and electron-translucent cytoplasm. Since only bacteria containing electron-dense cytoplasm were observed in the binary fusion stage, differences in density of the cytoplasm are probably due to changes in the cytoskeleton of bacteria during division. Endosymbionts of A. (S.) viridis are transovarially (i.e. via oocytes) transmitted from the mother to the offspring.

Hemlock woolly adelgid and elongate hemlock scale induce changes in foliar and twig volatiles of eastern hemlock

Eastern hemlock (Tsuga canadensis) is in rapid decline because of infestation by the invasive hemlock woolly adelgid (Adelges tsugae; 'HWA') and, to a lesser extent, the invasive elongate hemlock scale (Fiorinia externa; 'EHS'). For many conifers, induced oleoresin-based defenses play a central role in their response to herbivorous insects; however, it is unknown whether eastern hemlock mobilizes these inducible defenses. We conducted a study to determine if feeding by HWA or EHS induced changes in the volatile resin compounds of eastern hemlock. Young trees were experimentally infested for 3 years with HWA, EHS, or neither insect. Twig and needle resin volatiles were identified and quantified by gas chromatography/mass spectrometry. We observed a suite of changes in eastern hemlock's volatile profile markedly different from the largely terpenoid-based defense response of similar conifers. Overall, both insects produced a similar effect: most twig volatiles decreased slightly, while most needle volatiles increased slightly. Only HWA feeding led to elevated levels of methyl salicylate, a signal for systemic acquired resistance in many plants, and benzyl alcohol, a strong antimicrobial and aphid deterrent. Green leaf volatiles, often induced in wounded plants, were increased by both insects, but more strongly by EHS. The array of phytochemical changes we observed may reflect manipulation of the tree's biochemistry by HWA, or simply the absence of functional defenses against piercing-sucking insects due to the lack of evolutionary contact with these species. Our findings verify that HWA and EHS both induce changes in eastern hemlock's resin chemistry, and represent the first important step toward understanding the effects of inducible chemical defenses on hemlock susceptibility to these exotic pests.

DNA barcodes to identify species and explore diversity in the Adelgidae (Insecta: Hemiptera: Aphidoidea)

The Adelgidae are relatively small, cryptic insects, exhibiting complex life cycles with parthenogenetic reproduction. Due to these characteristics, the taxonomy of the group is problematic. Here, we test the effectiveness of the standard 658-bp barcode fragment from the 5'-end of the mitochondrial cytochrome c oxidase 1 gene (COI) in differentiating among 17 species of Adelgidae, in associating life-cycle stages, and in assessing patterns of geographical variation in selected species. Species of Adelgidae are well-differentiated by DNA barcodes, enabling the identification of different morphological forms, immature stages and individuals on different hosts and at different periods of the life cycle. DNA barcodes have uncovered cryptic diversity within taxa and, in other cases, a lack of sequence divergence in species pairs previously separated by life-cycle characteristics, indicating a need for further taxonomic analysis.

Diversity of proteobacterial endosymbionts in hemlock woolly adelgid (Adelges tsugae) (Hemiptera: Adelgidae) from its native and introduced range

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, and electron microscopy revealed that A. tsugae harbours up to five bacterial phylotypes, according to population. Three Gammaproteobacteria species are maternally transmitted. The first, designated 'Ca. Pseudomonas adelgestsugas' resides in the haemocoel, and was detected in all populations except Taiwan. The second phylotype, 'Ca. Serratia symbiotica', resides in bacteriocytes of populations on Tsuga sieboldii in Japan and in E. North America. The third phylotype, designated 'Ca. Annandia adelgestsuga', clustered within a lineage of several insect endosymbionts that included Buchnera aphidicola. It was detected in bacteriocytes in all populations, and in salivary glands of first instars. Two Betaproteobacteria phylotypes were detected in some Japanese T. sieboldii and eastern North America populations, and were observed only in salivary glands with no evidence of maternal transmission. Our results support the ideas that symbiont gain and loss has been volatile in adelgids, and that symbionts may help to trace the source of invasive species.

Exceptional plant penetration and feeding upon cortical parenchyma cells by the woolly poplar aphid

Forty percent of aphids live wholly or partly on trees, most species being associated with leaves or petioles. Species able to exploit woody parts have either specific adaptations, such as extra long stylets that allow them to reach the phloem, or the ability to induce galls. The woolly poplar aphid, Phloeomyzus passerinii (Signoret) (Hemiptera: Aphididae), colonizes the trunks and base of the lower branches of mature poplars and causes cortical necrosis leading to the death of trees where infestation is heavy. Very little is known about the mode of feeding of P. passerinii. This study looked at the feeding behavior of P. passerinii on stem-cuttings of Populus x canadensis Moench using: (i) histological analyses of the feeding site and stylet pathway and (ii) electrical penetration graphs (EPG, DC) based on parthenogenetic apterous females on woody tissues. The histological and EPG results showed that stylets of P. passerinii penetrated into the plant tissues following a straight unbranched extracellular and intracellular pathway to reach the cortical parenchyma. Compared to EPGs for phloem sap feeding aphids, there were differences in the waveforms A and C whereas a new waveform Icp was described. Based on histological analyses and previous descriptions of EPG waveforms, correlations with the stylet tip position and aphid activities within bark tissues are discussed. A pathway and a sustained intracellular phase were distinguished, both occurring in the cortical parenchyma cells. The bark aphid feeding mode is discussed in relation to the damage caused and in terms of changes in the aphid's diet.

Exotic herbivores on a shared native host: tissue quality after individual, simultaneous, and sequential attack

Plants in nature are often attacked by multiple enemies whose effect on the plant cannot always be predicted based on the outcome of individual attacks. We investigated how two invasive herbivores, the hemlock woolly adelgid (Adelges tsugae) (HWA) and the elongate hemlock scale (Fiorinia externa) (EHS), alter host plant quality (measured as amino acid concentration and composition) when feeding individually or jointly on eastern hemlock (Tsuga canadensis), an important long-lived forest tree that is in severe decline. The joint herbivore treatments included both simultaneous and sequential infestations by the two herbivores. We expected resource depletion over time, particularly in response to feeding by HWA. In contrast, HWA dramatically increased the concentration and altered the composition of individual free amino acids. Compared to control trees, HWA increased total amino acid concentration by 330% after 1 year of infestation. Conversely, EHS had a negligible effect when feeding individually. Interestingly, there was a marginally significant HWA × EHS interaction that suggests the potential for EHS presence to reduce the impact of HWA on foliage quality when the two species co-occur. We suggest indirect effects of water stress as a possible physiological mechanism for our results. Understanding how species interactions change the physiology of a shared host is crucial to making more accurate predictions about host mortality and subsequent changes in affected communities and ecosystems, and to help design appropriate management plans.

Macroevolutionary patterns in the Aphidini aphids (Hemiptera: Aphididae): diversification, host association, and biogeographic origins

Background

Due to its biogeographic origins and rapid diversification, understanding the tribe Aphidini is key to understanding aphid evolution. Major questions about aphid evolution include origins of host alternation as well as age and patterns of diversification in relation to host plants. To address these questions, we reconstructed the phylogeny of the Aphidini which contains Aphis, the most diverse genus in the family. We used a combined dataset of one nuclear and four mitochondrial DNA regions. A molecular dating approach, calibrated with fossil records, was used to estimate divergence times of these taxa.

Principal Findings

Most generic divergences in Aphidini occurred in the Middle Tertiary, and species-level divergences occurred between the Middle and Late Tertiary. The ancestral state of host use for Aphidini was equivocal with respect to three states: monoecy on trees, heteroecy, and monoecy on grasses. The ancestral state of Rhopalosiphina likely included both heteroecy and monoecy, whereas that of Aphidina was most likely monoecy. The divergence times of aphid lineages at the generic or subgeneric levels are close to those of their primary hosts. The species-level divergences in aphids are consistent with the diversification of the secondary hosts, as a few examples suggest. The biogeographic origin of Aphidini as a whole was equivocal, but the major lineages within Aphidina likely separated into Nearctic, Western Palearctic, and Eastern Palearctic regions.

Conclusions

Most generic divergences in Aphidini occurred in the Middle Tertiary when primary hosts, mainly in the Rosaceae, were diverging, whereas species-level divergences were contemporaneous with diversification of the secondary hosts such as Poaceae in the Middle to Late Tertiary. Our results suggest that evolution of host alternation within Aphidini may have occurred during the Middle Tertiary (Oligocene) when the secondary hosts emerged.

Bacteriocyte-associated gammaproteobacterial symbionts of the Adelges nordmannianae/piceae complex (Hemiptera: Adelgidae)

Adelgids (Insecta: Hemiptera: Adelgidae) are known as severe pests of various conifers in North America, Canada, Europe and Asia. Here, we present the first molecular identification of bacteriocyte-associated symbionts in these plant sap-sucking insects. Three geographically distant populations of members of the Adelges nordmannianae/piceae complex, identified based on coI and ef1alpha gene sequences, were investigated. Electron and light microscopy revealed two morphologically different endosymbionts, coccoid or polymorphic, which are located in distinct bacteriocytes. Phylogenetic analyses of their 16S and 23S rRNA gene sequences assigned both symbionts to novel lineages within the Gammaproteobacteria sharing <92% 16S rRNA sequence similarity with each other and showing no close relationship with known symbionts of insects. Their identity and intracellular location were confirmed by fluorescence in situ hybridization, and the names 'Candidatus Steffania adelgidicola' and 'Candidatus Ecksteinia adelgidicola' are proposed for tentative classification. Both symbionts were present in all individuals of all investigated populations and in different adelgid life stages including eggs, suggesting vertical transmission from mother to offspring. An 85 kb genome fragment of 'Candidatus S. adelgidicola' was reconstructed based on a metagenomic library created from purified symbionts. Genomic features including the frequency of pseudogenes, the average length of intergenic regions and the presence of several genes which are absent in other long-term obligate symbionts, suggested that 'Candidatus S. adelgidicola' is an evolutionarily young bacteriocyte-associated symbiont, which has been acquired after diversification of adelgids from their aphid sister group.

Lethal and sublethal effects of imidacloprid on hemlock woolly adelgid (Hemiptera: Adelgidae) and two introduced predator species

Eastern hemlock, Tsuga canadensis (L.) Carrière, branchlets were systemically treated with imidacloprid and bioassayed with hemlock woolly adelgid, Adelges tsugae (Annand) (Hemiptera: Adelgidae), and predators. After 10 d, two hemlock woolly adelgid predators, Laricobius nigrinus Fender (Coleoptera: Derodontidae) and Sasajiscymnus tsugae Sasaji & McClure (Coleoptera: Coccinellidae), were allowed to feed on remaining hemlock woolly adelgid for 20 d on branches systemically treated with 1, 10, or 100 ppm imidacloprid. Every 5 d, mortality, mobility (measured as flip time), number of hemlock woolly adelgid consumed, and degree of intoxication of each individual beetle were recorded. Liquid chromatography-mass spectrometry was used to quantify imidacloprid and some of its major metabolites in hemlock wood tissues and in the predator beetles postmortem. Probit analysis of hemlock woolly adelgid mortality and imidacloprid concentrations recovered from branch wood tissues determined the 30 d LC50 to be 242 ppb. A topical application of imidacloprid to the ventral abdomen of individual beetles resulted in a 6 d LD50 value of 1.8 and 0.71 ng imidacloprid per beetle for L. nigrinus and S. tsugae, respectively. In no-choice tests, L. nigrinus mortality was significantly higher on hemlock branchlets treated with 100 ppm imidacloprid than on controls, but S. tsugae mortality was not. S. tsugae consumed the same number of adelgids on treated branchlets as on controls, but L. nigrinus consumed fewer adelgids from the 100 ppm branchlets than on controls. In choice tests, beetle mortality and flip times were generally not significantly different from controls. At times, both beetle species displayed intoxication symptoms after feeding on adelgids from treated branchlets and imidacloprid was recovered from both beetle species postmortem. These results suggest that systemic imidacloprid displayed both lethal and sublethal effects on these two nontarget predators of the hemlock woolly adelgid.

Variation in winter survival of the invasive hemlock woolly adelgid (Hemiptera: Adelgidae) across the eastern United States

The hemlock woolly adelgid (Adelges tsugae Annand) is a small, aphid-like insect native to East Asia and western North America. First documented in the eastern United States in Richmond, VA, in 1951, it has spread to at least 17 states, where it causes increased mortality among both eastern and Carolina hemlocks (Tsuga canadensis Carrière and T. caroliniana Engelmann., respectively). Previous work has suggested low temperatures may limit northward spread of the adelgid. Using recent surveys of A. tsugae mortality across the infested latitudinal gradient of the eastern United States, we show there is a significant positive relationship between minimum winter temperatures and winter survival at the landscape scale. The strength and nature of this relationship, however, varies through time, with absolute minimum winter temperatures explaining almost one half of the tree-level variance in survival in the spring of 2004 but only 9% in 2003. Post hoc analyses of the data suggest the explanatory power of temperature can be improved in ongoing studies by examining seasonal temperature profiles. Previous studies have also suggested adelgid survival may be density dependent, and although these data support this observation, contemporary density is a poor predictor of adelgid survival at the landscape scale. Using landscape estimates of minimum winter temperature, we show two simple methods of estimating landscape-scale adelgid survival rates. Both methods suggest much of the range of T. canadensis in the eastern United States, and the entire range of T. caroliniana falls in areas where winter temperatures will not impose critical limits on A. tsugae populations.