Characterization of Emerging Xanthomonas campestris Isolates on the Nonnative Weed Garlic Mustard (Alliaria petiolata).

Nonnative plant infestations provide unique opportunities to investigate pathogen emergence with evolutionarily recent plant introduction events. The widespread distribution of invasive plants and their proximity to genetically related crops highlights the risks of nonnative plants acting as ancillary hosts and fostering microbial recombination and pathogen selection. Garlic mustard (Alliaria petiolata) is a widespread, nonnative cruciferous weed that grows throughout North America and along the forested edges of diverse agricultural fields. The recent identification of a novel Xanthomonas campestris pv. incanae strain isolated from a diseased A. petiolata population led to the current investigation of the distribution and diversity of X. campestris isolates from naturally infected A. petiolata. A total of 14 diseased A. petiolata sites were sampled across three states, leading to the identification of diverse X. campestris pathotypes and genotypes. Pathogenicity assays and multilocus sequence analyses identified pathogenic X. c. pv. incanae and X. c. pv. barbareae strains collected from disparate A. petiolata populations. Moreover, independently collected X. c. pv. incanae strains demonstrated a broad cruciferous host range by infecting cabbage (Brassica oleracea var. capitata), garden stock (Matthiola incana), and the cover crop yellow mustard (Guillenia flavescens). This study highlights the genetic variability and host potential of natural X. campestris populations and the potential risks to Brassica crops via widespread, dense garlic mustard reservoirs.

Glucosinolate profiles and phylogeny in Barbarea compared to other tribe Cardamineae (Brassicaceae) and Reseda (Resedaceae), based on a library of ion trap HPLC-MS/MS data of reference desulfoglucosinolates.

A library of ion trap MS2 spectra and HPLC retention times reported here allowed distinction in plants of at least 70 known glucosinolates (GSLs) and some additional proposed GSLs. We determined GSL profiles of selected members of the tribe Cardamineae (Brassicaceae) as well as Reseda (Resedaceae) used as outgroup in evolutionary studies. We included several accessions of each species and a range of organs, and paid attention to minor peaks and GSLs not detected. In this way, we obtained GSL profiles of Barbarea australis, Barbarea grayi, Planodes virginica selected for its apparent intermediacy between Barbarea and the remaining tribe and family, and Rorippa sylvestris and Nasturtium officinale, for which the presence of acyl derivatives of GSLs was previously untested. We also screened Armoracia rusticana, with a remarkably diverse GSL profile, the emerging model species Cardamine hirsuta, for which we discovered a GSL polymorphism, and Reseda luteola and Reseda odorata. The potential for aliphatic GSL biosynthesis in Barbarea vulgaris was of interest, and we subjected P-type and G-type B. vulgaris to several induction regimes in an attempt to induce aliphatic GSL. However, aliphatic GSLs were not detected in any of the B. vulgaris types. We characterized the investigated chemotypes phylogenetically, based on nuclear rDNA internal transcribed spacer (ITS) sequences, in order to understand their relation to the species B. vulgaris in general, and found them to be representative of the species as it occurs in Europe, as far as documented in available ITS-sequence repositories. In short, we provide GSL profiles of a wide variety of tribe Cardamineae plants and conclude aliphatic GSLs to be absent or below our limit of detection in two major evolutionary lines of B. vulgaris. Concerning analytical chemistry, we conclude that availability of authentic reference compounds or reference materials is critical for reliable GSL analysis and characterize two publicly available reference materials: seeds of P. virginica and N. officinale.

Comparison of glucosinolate diversity in the crucifer tribe Cardamineae and the remaining order Brassicales highlights repetitive evolutionary loss and gain of biosynthetic steps.

We review glucosinolate (GSL) diversity and analyze phylogeny in the crucifer tribe Cardamineae as well as selected species from Brassicaceae (tribe Brassiceae) and Resedaceae. Some GSLs occur widely, while there is a scattered distribution of many less common GSLs, tentatively sorted into three classes: ancient, intermediate and more recently evolved. The number of conclusively identified GSLs in the tribe (53 GSLs) constitute 60% of all GSLs known with certainty from any plant (89 GSLs) and apparently unique GSLs in the tribe constitute 10 of those GSLs conclusively identified (19%). Intraspecific, qualitative GSL polymorphism is known from at least four species in the tribe. The most ancient GSL biosynthesis in Brassicales probably involved biosynthesis from Phe, Val, Leu, Ile and possibly Trp, and hydroxylation at the ß-position. From a broad comparison of families in Brassicales and tribes in Brassicaceae, we estimate that a common ancestor of the tribe Cardamineae and the family Brassicaceae exhibited GSL biosynthesis from Phe, Val, Ile, Leu, possibly Tyr, Trp and homoPhe (ancient GSLs), as well as homologs of Met and possibly homoIle (intermediate age GSLs). From the comparison of phylogeny and GSL diversity, we also suggest that hydroxylation and subsequent methylation of indole GSLs and usual modifications of Met-derived GSLs (formation of sulfinyls, sulfonyls and alkenyls) occur due to conserved biochemical mechanisms and was present in a common ancestor of the family. Apparent loss of homologs of Met as biosynthetic precursors was deduced in the entire genus Barbarea and was frequent in Cardamine (e.g. C. pratensis, C. diphylla, C. concatenata, possibly C. amara). The loss was often associated with appearance of significant levels of unique or rare GSLs as well as recapitulation of ancient types of GSLs. Biosynthetic traits interpreted as de novo evolution included hydroxylation at rare positions, acylation at the thioglucose and use of dihomoIle and possibly homoIle as biosynthetic precursors. Biochemical aspects of the deduced evolution are discussed and testable hypotheses proposed. Biosyntheses from Val, Leu, Ile, Phe, Trp, homoPhe and homologs of Met are increasingly well understood, while GSL biosynthesis from mono- and dihomoIle is poorly understood. Overall, interpretation of known diversity suggests that evolution of GSL biosynthesis often seems to recapitulate ancient biosynthesis. In contrast, unprecedented GSL biosynthetic innovation seems to be rare.

Light Limitation Impacts Growth but Not Constitutive or Jasmonate Induced Defenses Relevant to Emerald Ash Borer (Agrilus planipennis) in White Fringetree (Chionanthus virginicus) or Black Ash (Fraxinus nigra).

White fringetree is a host for the invasive emerald ash borer (EAB) but is of lower quality than the related and highly susceptible black ash. Field observations suggest that host trees grown in full sun are more resistant to EAB than those in shade, however the impact of light limitation on chemical defenses has not been assessed. We quantified constitutive and jasmonate-induced phloem defenses and growth patterns of white fringetree and black ash under differential light conditions and related them to EAB larval performance. White fringetree had significantly lower constitutive and induced activities of peroxidase, polyphenol oxidase, ß-glucosidase, chitinase and lignin content, but significantly higher gallic acid equivalent soluble phenolic, soluble sugar, and oleuropein concentrations compared to black ash. Multivariate analyses based on tissue chemical attributes displayed clear separation of species and induced defense responses. Further, EAB performed significantly worse on white fringetree than black ash, consistent with previous studies. Light limitation did not impact measured defenses or EAB larval performance, but it did decrease current year growth and increase photosynthetic efficiency. Overall our results suggest that phenolic profiles, metabolite abundance, and growth traits are important in mediating white fringetree resistance to EAB, and that short-term light limitation does not influence phloem chemistry or larval success.

Ecological fitting: Chemical profiles of plant hosts provide insights on selection cues and preferences for a major buprestid pest.

Specific cues used by emerald ash borer (EAB, Agrilus planipennis) to select hosts are largely unknown. Attractants are likely general and the use of novel host plants provides an opportunity to investigate the commonality of these cues. We examined volatile profiles emitted by five plants that can host EAB and estimated their importance in explaining known oviposition preferences. Foliage volatiles were collected from potted black ash (Fraxinus nigra), Manchurian ash (F. mandshurica), blue ash (F. quadrangulata), white fringetree (Chionanthus virginicus), and olive (Olea europaea) and analyzed using GC-MS. Fifty-nine compounds were detected including eight green leaf volatiles (GLV), 12 monoterpenes, and 21 sesquiterpenes. Ordination plots show separation of species by full foliage profiles, monoterpenes, sesquiterpenes, and known antennally active compounds, but GLVs were similar across hosts. Random Forest (RF) analysis revealed eight compounds that separated plant species with an error rate of ~19%, consisting mostly of sesquiterpenes. Similarity of GLV profiles among known hosts suggests they serve as general cues for host selection. Manchurian ash, a resistant host, produced the highest quantities and variety of sesquiterpenes indicating that some of these chemicals may be antixenotic. All compounds identified by RF have been implicated as deterrents or attractants to woodborers in other studies and should be investigated for adult antennal activity and attraction.

Feeding, Survival, and Fecundity of Adult Emerald Ash Borer (Coleoptera: Buprestidae) on Foliage of Two Novel Hosts and Implications for Host Range Expansion.

Insect herbivores are more likely to successfully use a novel host if the plant is closely related to the ancestral host and the insect is polyphagous. Emerald ash borer (EAB), Agrilus planipennis (Fairmaire) (Coleoptera: Buprestidae), is a specialist wood borer of ash (Fraxinus spp., Lamiales: Oleaceae) trees and one of the most destructive forest pests in North American forests. Recent studies have found that larvae can develop in stems of two ash relatives; white fringetree (Chionanthus virginicus (L.) [Laminales: Oleaceae]) and cultivated olive (Olea europaea (L.) [Laminales: Oleaceae]). For EAB adults, the ability to consume, successfully mate, and lay viable eggs on foliage of these hosts is unknown. Thus, we conducted two no-choice assays with adult EAB on foliage of white fringetree and olive paired with positive controls of susceptible ash. Larval performance was also examined in a reciprocal study with cut stems of white fringetree and green ash (Fraxinus pennsylvanica Marshall) to determine whether adult diet impacted the success of progeny. Longevity, consumption rates, and fecundity of adults were similar on white fringetree and ash foliage. In contrast, adults consuming olive died quickly, consumed more over time, and females laid far fewer eggs compared to those on ash. Adult diet did not impact larval success, but larvae in white fringetree stems grew slower. These results indicate that white fringetree is a suitable host for EAB to complete its lifecycle, although larvae perform more poorly on this host than in susceptible ash species. In contrast, the more distantly related olive appears to be a poor host for adult EAB, although some viable eggs were produced by females.

Larval Performance of a Major Forest Pest on Novel Hosts and the Effect of Stressors.

Novel hosts lacking a coevolutionary history with herbivores can often support improved larval performance over historic hosts; e.g., emerald ash borer [Agrilus planipennis (Fairmaire) Coleoptera: Buprestidae] on North American ash (Fraxinus spp.) trees. Whether trees are novel or ancestral, stress on plants increases emerald ash borer preference and performance. White fringetree [Chionanthus virginicus (L.) Lamiales: Oleaceae] and olive [Olea europaea (L.) Lamiales: Oleaceae] are closely related non-ash hosts that support development of emerald ash borer to adulthood, but their relative suitability as hosts and the impact of plant stress on larval success has not been well studied. In a series of experiments, survival and growth of emerald ash borer larvae on these novel hosts were examined along with the impact of stress. In the first experiment, larvae grew more slowly in cut stems of olive than in green ash [Fraxinus pennsylvanica (Marshall) Lamiales: Oleaceae] and several adults successfully emerged from larger olive stems. In two experiments on young potted olive with photosynthesizing bark, larvae died within a week, but mechanical girdling increased the rate of gallery establishment. The final two experiments on field-grown fringetrees found increased larval survivorship and growth in previously emerald ash borer attacked and mechanically girdled plants than in healthy stems or stems treated with the defense hormone, methyl jasmonate. Our results demonstrate that these non-ash hosts are less suitable for emerald ash borer than preferred ash hosts, but previous emerald ash borer attack or girdling led to better survival and growth demonstrating the importance of stress for larval success. In potted olive, high mortality could be due to higher loads of toxic compounds or the presence of chlorophyllous tissue.

The potential for host switching via ecological fitting in the emerald ash borer-host plant system.

The traits used by phytophagous insects to find and utilize their ancestral hosts can lead to host range expansions, generally to closely related hosts that share visual and chemical features with ancestral hosts. Host range expansions often result from ecological fitting, which is the process whereby organisms colonize and persist in novel environments, use novel resources, or form novel associations with other species because of the suites of traits that they carry at the time they encounter the novel environment. Our objective in this review is to discuss the potential and constraints on host switching via ecological fitting in emerald ash borer, Agrilus planipennis, an ecologically and economically important invasive wood boring beetle. Once thought of as an ash (Fraxinus spp.) tree specialist, recent studies have revealed a broader potential host range than was expected for this insect. We discuss the demonstrated host-use capabilities of this beetle, as well as the potential for and barriers to the adoption of additional hosts by this beetle. We place our observations in the context of biochemical mechanisms that mediate the interaction of these beetles with their host plants and discuss whether evolutionary host shifts are a possible outcome of the interaction of this insect with novel hosts.

Variation in the Volatile Profiles of Black and Manchurian Ash in Relation to Emerald Ash Borer Oviposition Preferences.

Emerald ash borer (EAB; Agrilus planipennis) is a devastating pest of ash (Fraxinus spp.) in its invaded range in North America. Its coevolved Asian hosts are more resistant and less preferred for oviposition than susceptible North American species. We compared EAB oviposition preferences and bark and canopy volatile organic compound (VOC) emissions of resistant Manchurian ash and susceptible black ash, and examined relationships between VOC profiles and oviposition. In the field, black ash was highly preferred for oviposition while no eggs were laid on Manchurian ash, and we found clear differences in the VOC profiles of Manchurian and black ash. We detected 78 compounds emitted from these species, including 16 compounds that elicited EAB antennal activity in prior studies. Four compounds were unique to black and 11 to Manchurian ash. Emission rates of 14 canopy and 19 bark volatiles varied among the two species, including four previously reported as antennally active. Specifically, 7-epi-sesquithujene (bark) emissions were greater from black ash, while ß-caryophyllene (canopy), linalool (bark), and α-cubebene (bark) were emitted at higher rates by Manchurian ash. No relationships were found between the emission rate of any single compound or group of compounds (e.g. monoterpenes) suggesting that preference may be based on complex profile combinations. This is the first study to directly compare VOCs of black and Manchurian ash as well as the first to examine bark- and canopy-specific VOCs. The unique bark and canopy VOC profiles of these two species implicates potentially important variation in VOCs between a closely related resistant and susceptible species that provides a foundation for future studies of host preferences of EAB.

Feeding and Development of Emerald Ash Borer (Coleoptera: Buprestidae) on Cultivated Olive, Olea europaea.

We examined the suitability of cultivated olive, Olea europaea L., as a host for emerald ash borer, Agrilus planipennis Fairmaire. In a bioassay using cut stems from a field-grown olive tree (cv. 'Manzanilla') we found that 45% of larvae that had emerged from eggs used to inoculate stems, were recovered alive, many as larvae or prepupae, during periodic debarking of a subset of stems. Three intact stems that 19 larvae successfully entered were exposed to a simulated overwintering treatment. Four live adults emerged afterwards, and an additional pupa and several prepupae were discovered after debarking these stems. Cultivated olive joins white fringetree as one of the two species outside of the genus Fraxinus capable of supporting the development of emerald ash borer from neonate to adult.

Distribution, Predictors, and Impacts of Emerald Ash Borer (Agrilus planipennis) (Coleoptera: Buprestidae) Infestation of White Fringetree (Chionanthus virginicus).

Emerald ash borer, Agrilus planipennis (Fairmaire), is an invasive pest of ash trees (Fraxinus spp.) in North America that was recently found infesting white fringetree (Chionanthus virginicus L.). Initial reports of the infestation of white fringetree by emerald ash borer occurred in southwestern Ohio and Chicago, IL. We examined white fringetrees at additional sites in Illinois, Indiana, Ohio, and Pennsylvania in Summer and Fall 2015 and Winter 2016 for emerald ash borer infestation. Our aim was to examine white fringetrees at a limited number of sites with emerald ash borer infestation and to relate tree size, crown dieback, epicormic sprouting, tree sex, and adjacency to ash or white fringetrees with the likelihood of beetle infestation. A higher proportion of infested trees exhibited epicormic sprouting and the likelihood that a tree was infested increased with increasing crown dieback, variables that may be both predictors and responses to attack. The proportion of trees infested with emerald ash borer increased with increasing tree size. Signs consistent with emerald ash borer infestation were found in 26% of 178 white fringetrees, with at least one host infested at each site in all states. Infestation rates of white fringetrees increased with the density of white fringetrees at each site. The Chicago Botanic Garden site had a significantly lower infestation (3.7%) than other sites, which may be due to proactive management of ash. Overall, these data indicate white fringetree has been utilized by emerald ash borer throughout their overlapping ranges in the United States in ornamental settings likely due to ecological fitting.

Glucosinolate diversity within a phylogenetic framework of the tribe Cardamineae (Brassicaceae) unraveled with HPLC-MS/MS and NMR-based analytical distinction of 70 desulfoglucosinolates.

As a basis for future investigations of evolutionary trajectories and biosynthetic mechanisms underlying variations in glucosinolate structures, we screened members of the crucifer tribe Cardamineae by HPLC-MS/MS, isolated and identified glucosinolates by NMR, searched the literature for previous data for the tribe, and collected HPLC-MS/MS data for nearly all glucosinolates known from the tribe as well as some related structures (70 in total). This is a considerable proportion of the approximately 142 currently documented natural glucosinolates. Calibration with authentic references allowed distinction (or elucidation) of isomers in many cases, such as distinction of ß-hydroxyls, methylthios, methylsulfinyls and methylsulfonyls. A mechanism for fragmentation of secondary ß-hydroxyls in MS was elucidated, and two novel glucosinolates were discovered: 2-hydroxy-3-methylpentylglucosinolate in roots of Cardamine pratensis and 2-hydroxy-8-(methylsulfinyl)octylglucosinolate in seeds of Rorippa amphibia. A large number of glucosinolates (ca. 54 with high structural certainty and a further 28 or more suggested from tandem MS), representing a wide structural variation, is documented from the tribe. This included glucosinolates apparently derived from Met, Phe, Trp, Val/Leu, Ile and higher homologues. Normal side chain elongation and side chain decoration by oxidation or methylation was observed, as well as rare abnormal side chain decoration (hydroxylation of aliphatics at the δ rather than ß-position). Some species had diverse profiles, e.g. R. amphibia and C. pratensis (19 and 16 individual glucosinolates, respectively), comparable to total diversity in literature reports of Armoracia rusticana (17?), Barbarea vulgaris (20-24), and Rorippa indica (>20?). The ancestor or the tribe would appear to have used Trp, Met, and homoPhe as glucosinolate precursor amino acids, and to exhibit oxidation of thio to sulfinyl, formation of alkenyls, ß-hydroxylation of aliphatic chains and hydroxylation and methylation of indole glucosinolates. Two hotspots of apparent biochemical innovation and loss were identified: C. pratensis and the genus Barbarea. Diversity in other species mainly included structures also known from other crucifers. In addition to a role of gene duplication, two contrasting genetic/biochemical mechanisms for evolution of such combined diversity and redundancy are discussed: (i) involvement of widespread genes with expression varying during evolution, and (ii) mutational changes in substrate specificities of CYP79F and GS-OH enzymes.

Higher Activities of Defense-Associated Enzymes may Contribute to Greater Resistance of Manchurian Ash to Emerald Ash Borer Than A closely Related and Susceptible Congener.

Emerald ash borer (EAB) is an invasive beetle native to Asia that infests and kills ash (Fraxinus spp.) in North America. Previous experiments indicated that larvae feeding on co-evolved, resistant Manchurian ash (F. mandshurica) have increased antioxidant and quinone-protective enzyme activities compared to larvae feeding on susceptible North American species. Here, we examined mechanisms of host-generated oxidative and quinone-based stress and other putative defenses in Manchurian ash and the closely related and chemically similar, but susceptible, black ash (F. nigra), with and without exogenous application of methyl jasmonate (MeJA) to induce resistance mechanisms. Peroxidase activities were 4.6-13.3 times higher in Manchurian than black ash, although both species appeared to express the same three peroxidase isozymes. Additionally, peroxidase-mediated protein cross-linking activity was stronger in Manchurian ash. Polyphenol oxidase, ß-glucosidase, chitinase, and lipoxygenase activities also were greater in Manchurian ash, but only lipoxygenase activity increased with MeJA application. Phloem H2O2 levels were similar and were increased by MeJA application in both species. Lastly, trypsin inhibitor activity was detected in methanol and water extracts that were not allowed to oxidize, indicating the presence of phenolic-based trypsin inhibitors. However, no proteinaceous trypsin inhibitor activity was detected in either species. In response to MeJA application, Manchurian ash had higher trypsin inhibitor activity than black ash using the unoxidized water extracts, but no treatment effects were detected using methanol extracts. Based on these results we hypothesize that peroxidases, lignin polymerization, and quinone generation contribute to the greater resistance to EAB displayed by Manchurian ash.

The History of Attack and Success of Emerald Ash Borer (Coleoptera: Buprestidae) on White Fringetree in Southwestern Ohio.

Emerald ash borer, Agrilus planipennis Fairmaire, is an invasive insect that has caused widespread mortality of ash species in North America. The ability of emerald ash borer to utilize white fringetree as an alternate host was reported recently. We aimed to determine how long white fringetree has been under attack from emerald ash borer, the degree of attack, and the overall success of this beetle on this novel host. Stems from three of nine infested white fringetrees collected from the Dayton and Cincinnati, OH, areas in the winter of 2015 yielded four live adult emerald ash borers after being held in rearing containers, and numerous older exit holes were observed. Measurement and aging of feeding galleries on these stems indicated that emerald ash borer has been using this species since 2011, at least, with peak gallery densities reached in 2012 and 2013 on most of the harvested trees. On average, 32 galleries per square meter were found in these stems with about one-third of them being indicative of fourth-instar larvae. This supports the assertion that emerald ash borer has been using white fringetree as a host plant with moderate to good success for as long as ash species in these particular areas have been utilized.

Progress and gaps in understanding mechanisms of ash tree resistance to emerald ash borer, a model for wood-boring insects that kill angiosperms.

We review the literature on host resistance of ash to emerald ash borer (EAB, Agrilus planipennis), an invasive species that causes widespread mortality of ash. Manchurian ash (Fraxinus mandshurica), which coevolved with EAB, is more resistant than evolutionarily naïve North American and European congeners. Manchurian ash was less preferred for adult feeding and oviposition than susceptible hosts, more resistant to larval feeding, had higher constitutive concentrations of bark lignans, coumarins, proline, tyramine and defensive proteins, and was characterized by faster oxidation of phenolics. Consistent with EAB being a secondary colonizer of coevolved hosts, drought stress decreased the resistance of Manchurian ash, but had no effect on constitutive bark phenolics, suggesting that they do not contribute to increased susceptibility in response to drought stress. The induced resistance of North American species to EAB in response to the exogenous application of methyl jasmonate was associated with increased bark concentrations of verbascoside, lignin and/or trypsin inhibitors, which decreased larval survival and/or growth in bioassays. This finding suggests that these inherently susceptible species possess latent defenses that are not induced naturally by larval colonization, perhaps because they fail to recognize larval cues or respond quickly enough. Finally, we propose future research directions that would address some critical knowledge gaps.

Comparative Herbivory Rates and Secondary Metabolite Profiles in the Leaves of Native and Non-Native Lonicera Species.

Non-native plants introduced to new habitats can have significant ecological impact. In many cases, even though they interact with the same community of potential herbivores as their new native competitors, they regularly receive less damage. Plants produce secondary metabolites in their leaves that serve a range of defensive functions, including resistance to herbivores and pathogens. Abiotic factors such as nutrient availability can influence the expression of defensive traits, with some species exhibiting increased chemical defense in low-nutrient conditions. Plants in the genus Lonicera are known to produce a diverse array of these secondary metabolites, yet non-native Lonicera species sustain lower amounts of herbivore damage than co-occurring native Lonicera species in North America. In this study, we searched for evidence of biochemical novelty in non-native species, and quantified its association with resistance to herbivores. In order to achieve this, we evaluated the phenolic and iridoid glycoside profiles in leaves of native and non-native Lonicera species grown under high and low fertilization treatments in a common garden. We then related these profiles to naturally occurring herbivore damage on whole plants in the garden. Herbivore damage was greater on native Lonicera, and chemical profiles and concentrations of selected putative defense compounds varied by species. Geographic origin was an inconsistent predictor of chemical variation in detected phenolics and iridoid glycosides (IGs). Overall, fertilization did not affect herbivore damage or measures of phenolics or IGs, but there were some fertilization effects within species. While we cannot conclude that non-natives were more chemically novel than native Lonicera species, chemical defense profiles and concentrations of specific compounds varied by species. Reduced attraction or deterrence of oviposition, specific direct resistance traits, or a combination of both may contribute to reduced herbivory and competitive advantages for non-native Lonicera in North America.

White Fringetree as a Novel Larval Host for Emerald Ash Borer.

Emerald ash borer is an invasive Asian pest of ash species in North America. All North American species of ash tested so far are susceptible to it, but there are no published reports of this insect developing fully in non-ash hosts in the field in North America. I report here evidence that emerald ash borer can attack and complete development in white fringetree, Chionanthus virginicus L., a species native to the southeastern United States that is also planted ornamentally. Four of 20 mature ornamental white fringetrees examined in the Dayton, Ohio area showed external symptoms of emerald ash borer attack, including the presence of adult exit holes, canopy dieback, and bark splitting and other deformities. Removal of bark from one of these trees yielded evidence of at least three generations of usage by emerald ash borer larvae, several actively feeding live larvae, and a dead adult confirmed as emerald ash borer.

How Does Garlic Mustard Lure and Kill the West Virginia White Butterfly?

As it pertains to insect herbivores, the preference-performance hypothesis posits that females will choose oviposition sites that maximize their offspring's fitness. However, both genetic and environmental cues contribute to oviposition preference, and occasionally "oviposition mistakes" occur, where insects oviposit on hosts unsuitable for larval development. Pieris virginiensis is a pierine butterfly native to North America that regularly oviposits on an invasive plant, Alliaria petiolata, but the caterpillars are unable to survive. Alliaria petiolata has high concentrations of the glucosinolate sinigrin in its tissues, as well as a hydroxynitrile glucoside, alliarinoside. We investigated sinigrin as a possible cause of mistake oviposition, and sinigrin and alliarinoside as possible causes of larval mortality. We found that sinigrin applied to leaves of Cardamine diphylla, a major host of P. virginiensis that does not produce sinigrin, had no effect on oviposition rates. We tested the effect of sinigrin on larval performance using two host plants, one lacking sinigrin (C. diphylla) and one with sinigrin naturally present (Brassica juncea). We found no effect of sinigrin application on survival of caterpillars fed C. diphylla, but sinigrin delayed pupation and decreased pupal weight. On B. juncea, sinigrin decreased survival, consumption, and caterpillar growth. We also tested the response of P. virginiensis caterpillars to alliarinoside, a compound unique to A. petiolata, which was applied to B. oleracea. We found a significant reduction in survival, leaf consumption, and caterpillar size when alliarinoside was consumed. The 'novel weapon' alliarinoside likely is largely responsible for larval failure on the novel host A. petiolata. Sinigrin most likely contributes to the larval mortality observed, however, we did not observe any effect of sinigrin on oviposition by P. virginiensis females. Further research needs to be done on non-glucosinolate contact cues, and volatile signals that may induce P. virginiensis oviposition.

Incidence of Infestation and Larval Success of Emerald Ash Borer (Agrilus planipennis) on White Fringetree (Chionanthus virginicus), Chinese Fringetree (Chionanthus retusus), and Devilwood (Osmanthus americanus).

We compared the incidence of infestation by emerald ash borer (EAB) and lilac borer on white fringetree to that of its Asian congener, Chinese fringetree, Chionanthus retusus, and a North American relative, devilwood, Osmanthus americanus. We also conducted laboratory bioassays to determine the suitability of these hosts for EAB larvae. At Spring Grove Cemetery and Arboretum in Cincinnati, Ohio, 9 of 28 white fringetrees examined were infested by EAB. Most of the white fringetrees had lilac borer infestation, and most of the trees infested by EAB also had lilac borer infestation. None of the 11 Chinese fringetrees examined were infested by either EAB or lilac borer. Each of the five devilwood individuals examined was infested by lilac borer, but not EAB. At The Morton Arboretum in Lisle, Illinois, 7 of 16 white fringetrees examined were infested by EAB, while none of the seven Chinese fringetrees examined were infested by either insect. A 40-d bioassay confirmed that white fringetree was an acceptable host, producing fourth-instar larvae that were smaller than those produced on a highly susceptible cultivar of green ash, Fraxinus pennsylvanica. No larvae survived on Chinese fringetree, and neonates were largely incapable of feeding on it. Two larvae survived on devilwood, reaching the second instar and excavating extensive galleries. Future work should be aimed at biotic and abiotic factors influencing the susceptibility of white fringetree, as well as further examination of close relatives for their vulnerability to EAB.

Glucosinolate-related glucosides in Alliaria petiolata: sources of variation in the plant and different metabolism in an adapted specialist herbivore, Pieris rapae.

Specialized metabolites in plants influence their interactions with other species, including herbivorous insects, which may adapt to tolerate defensive phytochemicals. The chemical arsenal of Alliaria petiolata (garlic mustard, Brassicaceae) includes the glucosinolate sinigrin and alliarinoside, a hydroxynitrile glucoside with defensive properties to glucosinolate-adapted specialists. To further our understanding of the chemical ecology of A. petiolata, which is spreading invasively in North America, we investigated the metabolite profile and here report a novel natural product, petiolatamide, which is structurally related to sinigrin. In an extensive study of North American populations of A. petiolata, we demonstrate that genetic population differences as well as developmental regulation contribute to variation in the leaf content of petiolatamide, alliarinoside, sinigrin, and a related glycoside. We furthermore demonstrate widely different metabolic fates of these metabolites after ingestion in the glucosinolate-adapted herbivore Pieris rapae, ranging from simple passage over metabolic conversion to sequestration. The differences in metabolic fate were influenced by plant ß-glucosidases, insect-mediated degradation, and the specificity of the larval gut transport system mediating sequestration.