Lynne K. Rieske

Community Associates of an Exotic Gallmaker, Dryocosmus kuriphilus (Hymenoptera: Cynipidae), in Eastern North America

Abstract Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae) is a potentially devastating exotic invasive gall wasp that is rapidly spreading throughout the eastern United States, and infests all species of chestnut, Castanea spp. We investigated the community associates of D. kuriphilus in three geographic locations: Meadowview, VA, Bowling Green, KY, and Broadview Heights, OH. Dissection of galls and observation of chamber contents revealed that gall wasp larval mortality is approaching 47%, and parasitism accounts for nearly 70% of the mortality. Six parasitoid wasp species emerged from chestnut galls, including one introduced species and five of unknown origin. The life histories of each parasitoid and their potential roles within the D. kuriphilus community complex are discussed. Investigation of parasitoid interactions revealed a negative correlation between certain parasitoids, suggesting competition for resources, hyperparasitism, or both. The small chestnut weevil, Curculio sayi (Gyllenhal) (Coleoptera: Curculionidae), caused external damage to galls. Galls also were readily attacked by an unknown fungal pathogen resulting in gall wasp larval mortality. This study is the first to investigate the community associates of D. kuriphilus in North America. Our results have beneficial implications for commercial chestnut production, blight resistance breeding programs, and restoration of American chestnut.

Species-specific differences in oak foliage affect preference and performance of gypsy moth caterpillars

The gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), is an introduced defoliator that preferentially feeds on oaks, Quercus spp. (Fagaceae) in the north‐eastern USA. As the gypsy moth expands its geographic range, the extensive oak component in forests and urban environments of the USA assure its successful establishment. Given their economic and ecological importance, and the gypsy moths potential to cause mortality, we evaluated caterpillar preference and performance on various oaks prevalent in the central hardwoods region. Most of the physical and chemical characteristics we measured, from budbreak phenology to foliar chemistry, varied significantly among the oak species tested. Similarly, insect preference and performance varied significantly, though not always in predictable ways. Caterpillar preference was compared for black, Q. velutina Lamarck, burr, Q. macrocarpa Michaux, cherrybark, Q. pagoda Rafinesque, northern red, Q. rubra L., pin, Q. palustris Muenchhausen, swamp white, Q. bicolor Willdenow, white, Q. alba L., and willow, Q. phellos L., oaks. Gypsy moth preference was greatest for black and burr, and least for northern red, pin, and willow oaks. We assessed foliar characteristics and caterpillar performance on foliage from burr, cherrybark, northern red, pin, and willow oaks. Caterpillar preference did not always correlate with performance. Gypsy moth consumption and growth were highest, and development most rapid, on pin oak, which had high nitrogen and tannin levels, and was among the least preferred. Northern red and willow oaks were also among the least preferred and were the least suitable tested, producing caterpillars with moderate to low consumption and growth rates, as well as the longest development. Northern red oak contained the lowest foliar tannins; willow oak foliage was lowest in carbohydrates and nitrogen. Our results suggest that a combination of foliar characteristics may be responsible for gypsy moth preference and performance, and that an optimal combination of foliar components serves to maximize host suitability. These data will provide information useful for planning and managing urban forests in the presence of expanding gypsy moth populations.

Gall Structure Affects Ecological Associations of Dryocosmus kuriphilus (Hymenoptera: Cynipidae)

ABSTRACT Gall wasps (Hymenoptera: Cynipidae) induce structures (galls) on their host plants that house developing wasps and provide them with protection from natural enemies. The Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu, is an invasive pest that is destructive to chestnut (Castanea spp.). An improved understanding of the interactions among D. kuriphilus, its host, and its natural enemies is critical for the development of effective management strategies against this pest. The objective of our study was to evaluate the D. kuriphilus community interactions, and relate these interactions to variations among gall traits. Galls were collected from four locations throughout the eastern United States from May (gall initiation) through August (after gall wasp emergence), and January. Gall characteristics (volume, weight, and schlerenchyma layer thickness), gall inhabitants (D. kuriphilus, parasitoids, and chamber fungi), and other community associates (insect herbivores and lesions thought to be caused by endophytes) were evaluated and correlated using canonical correlation analyses. The primary mortality factors for D. kuriphilus were parasitism, gall chamber-invading fungi, and failure of adult gall wasps to emerge. Larger gall size and thicker schlerenchyma layers surrounding the larval chambers were negatively correlated with parasitoids and chamber fungi, indicating these gall traits are important defenses. External fungal lesions and insect herbivory were positively correlated with the absence of D. kuriphilus within galls. This study provides support for the protective role of cynipid galls for the gall inducer, identifies specific gall traits that influence gall wasp mortality, and improves our knowledge of D. kuriphilus ecology in North America.

Foliar Chemistry and Gypsy Moth, Lymantria dispar (L.), Herbivory on Pure American Chestnut, Castanea dentata (Fam: Fagaceae), and a Disease-Resistant Hybrid

Abstract We investigated herbivore suitability, foliar chemistry, and seedling growth of blight-susceptible pure American chestnut, Castanea dentata (Marsh.) Borkh., and a blight-resistant Chinese chestnut, Castanea mollisima Blume × American chestnut hybrid, using supplemental fertilizer and ectomycorrhizal inoculation to affect nutrient availability and nutrient uptake, and the gypsy moth, Lymantria dispar (L.), to measure herbivore suitability. Gypsy moth performance was best on fertilized hybrid seedlings, and was lowest on untreated American chestnut seedlings. Foliar carbohydrates were greatest, and tannin levels were lowest, in mycorrhizae-inoculated American chestnut. Foliar nitrogen was also high in mycorrhizal American chestnut, and was equivalent to that found in fertilized seedlings of both species. American chestnut seedlings had greater height and diameter growth than hybrids, regardless of soil amendments. Our results suggest that blight resistance may exact a cost in plant growth and productivity for this chestnut hybrid, and may enhance plant suitability for a generalist herbivore. Additionally, enhanced gypsy moth performance on blight-resistant chestnut hybrids has implications with respect to the restoration of chestnut to eastern deciduous forests, because intense herbivore pressure could compromise seedling growth and survival, and play a role in sustaining potentially damaging gypsy moth populations. The implications of this work within the context of current theories addressing herbivore–plant relations are discussed.

Interactions Among Insect Herbivore Guilds: Influence of Thrips Bud Injury on Foliar Chemistry and Suitability to Gypsy Moths

This study investigated the consequences of early season bud herbivory on host-plant phytochemistry and subsequent effects on a later mid-season leaf-feeding herbivore, to test the hypothesis that temporally segregated interguild interactions could affect herbivore success through plant-mediated responses. Our system consisted of American bass wood, Tilia americana, a bud-feeding thrips species, Thrips calcaratus, and the folivorous gypsy moth, Lymantria dispar. The impact of thrips bud-feeding on American basswood foliar chemistry and subsequent effects on gypsy moth larval preference and performance were measured. Foliar total nonstructural carbohydrates increased and phenolic levels decreased in response to bud injury, which affected larval feeding preference. In a two-choice test, gypsy moth larvae preferred leaf discs with high carbohydrate and low phenolic levels. The effects on larval performance depended on the extent of prior bud injury and were correlated with carbohydrate concentrations. In an early season assay, larval performance was lowest on moderately bud-damaged tissue, which also had the lowest total nonstructural carbohydrates. In a mid-season assay, larval performance and carbohydrate concentrations were highest in severely bud-damaged foliage. Foliar phenolics were highest in severely bud-damaged tissue in the early season assay, and in moderately damaged tissue in the mid-season assay. Gypsy moth performance was not correlated with foliar phenolic levels. Secondary (reflushed) foliage had higher carbohydrate levels than did primary (original) foliage, which correlated with increased larval performance. This study illustrates that bud-feeding herbivores can alter the phytochemistry and subsequent suitability of host-plant foliage for later folivores. The implications of these results to interactions between feeding guilds, community structure, and forest health are discussed.

Wildfire alters oak growth, foliar chemistry, and herbivory

Fire is a major disturbance factor influencing the formation and maintenance of oak (Quercus)-dominated forests of eastern North America. Fire suppression practices have resulted in declining oak dominance, and caused the loss of oak seedlings due to poor light regimes and vegetative competition. Both wildfires and prescribed fires can alter forest stand composition and influence succession. Fire can also cause physiological changes in plants, potentially influencing growth, competition, and susceptibility to herbivory. Fire may impact herbivore populations directly by altering habitat and abundance, or indirectly through alterations in food supply. The objective of my study was to assess the effects of a naturally occurring wildfire on chestnut oak (Q. prinus L.) seedling growth, foliar chemistry, and suitability to a generalist herbivore, the gypsy moth (Lymantria dispar L.). I sampled chestnut oak seedlings four times for phytochemical analysis throughout the post-fire growing season, and sampled once to assess suitability for caterpillar performance and to measure seedling growth. Chestnut oak seedlings sampled from burned sites had significantly higher foliar nitrogen and water content than seedlings sampled from non-burned sites. Seedlings from burned sites had transient declines in foliar carbohydrate concentrations, and also had higher initial tannin levels. Although seedlings from burned sites were smaller with respect to stem diameter and height, they grew more with respect to absolute growth rate, leaf area, and biomass, than their non-burned counterparts. In spite of the differences in leaf chemistry, there were no significant differences in the growth or development of gypsy moth caterpillars fed foliage from burned versus non-burned seedlings.

Influence of Site on Diversity and Abundance of Ground- and Litter-Dwelling Coleoptera in Appalachian Oak-Hickory Forests

Abstract We evaluated the family-level richness, diversity, evenness, and abundance of ground- and litter-dwelling beetles in two forested areas of southeastern Kentucky for 2 yr, and related beetle diversity to habitat characteristics in these deciduous forests. Using pitfall traps and leaf litter samples, we collected over 13,420 beetle specimens in 42 families during this 2-yr study. Carabidae, Scolytidae, and Staphylinidae were the most abundant families in pitfall traps, and Nitidulidae, Staphylinidae, and Pselaphidae were most common in litter samples. Pitfall traps captured the widest array, with 41 beetle families, whereas litter samples produced 25 families. Plots from Robinson Forest had a higher family richness but lower evenness than Kentucky Ridge Forest plots in both 1997 and 1998. The greater evenness of the families at Kentucky Ridge contributed to a higher Shannon index at Kentucky Ridge than at Robinson Forest, though these differences were significant only in 1998. Kentucky Ridge plots tended to be less rocky, with greater amounts of coarse woody debris, less dense herbaceous cover, a smaller mid-canopy component, and less deciduous cover than Robinson Forest. Family richness, diversity, evenness and abundance varied with site, plot, and sample interval, but the site variables we measured were inconsistent in their ability to predict our response variables, as was the multivariate cluster analysis. The effects of site characteristics and habitat complexity on beetle family diversity are discussed.

Stem galls affect oak foliage with potential consequences for herbivory

Abstract.   1. On two dates, foliar characteristics of pin oak, Quercus palustris, infested with stem galls caused by the horned oak gall, Callirhytis cornigera, were investigated, and the consequences for subsequent herbivory assessed.

Identification of prey of Myotis septentrionalis using DNA-based techniques

Abstract Identifying and characterizing trophic linkages is fundamental to understanding how prey availability affects predator behavior, distribution, and density, and to elucidating the extent to which predators regulate prey populations. Vertebrate insectivores, such as bats, are a pervasive top-down force on insect populations in forest ecosystems. Bats are predators sensitive to habitat perturbations, whose prey selection behavior warrants further study. We identified trophic connections between a forest bat (Myotis septentrionalis) and its prey by isolating and sequencing cytochrome c oxidase subunit I gene (COI) fragments of insect prey obtained from bat fecal samples. Prey identities were inferred using GenBank and the Barcode of Life Data System (BOLD). We also identified prey remains morphologically from the same fecal samples, allowing comparisons across novel (GenBank and BOLD) and traditional (morphological) techniques. Lepidopterans were the most frequently detected prey in all approaches. Detection of common insect orders varied across procedures (P < 0.001), suggesting methodological bias at coarse taxonomic resolutions. Of the DNA-based approaches, GenBank provided the more diverse assessment of prey. We reveal trophic linkages for northern bats by identifying 20 prey genera and species using BOLD, more than one-half of which were smaller lepidopterans. The disproportionate number of smaller lepidopteran prey (mean [±SE] wingspan 24.2 ± 2.05 mm) exceeded expectations based on field-based assessments. M. septentrionalis is known to use both aerial-hawking and gleaning behaviors. Lepidopteran prey consumed by M. septentrionalis were smaller than reported for conspecfic genera, suggesting this species differentiates itself from sympatric insectivorous bats with the prey it selects.

Effects of prescribed fire on canopy foliar chemistry and suitability for an insect herbivore

We assessed the effects of a prescribed fire on the phytochemical characteristics and vigor of overstory chestnut oak, scarlet oak, and red maple, and measured the impact of potential changes on herbivore fitness. We compared foliar carbohydrates, tannins, nutrients, and fiber concentrations in foliage from burned and non-burned forest canopies. There were significant differences in most foliar characteristics between tree species. Total non-structural carbohydrate concentrations in scarlet oak and red maple foliage, and calcium levels in red maple foliage, were significantly lower in burned plots, but other phytochemical characteristics were largely unaffected by burning. Tree growth also varied with species. Burning increased chestnut oak relative growth, decreased scarlet oak growth, and had no affect on red maple growth. Scarlet oak and red maple foliage from burned and non-burned forest canopies were assayed for gypsy moth performance. Caterpillars fed foliage from scarlet oak, the preferred host, grew larger and developed more rapidly than did those fed red maple foliage. There were no significant burn treatment differences in caterpillar development within either tree species, suggesting that managers using prescribed fire to promote oak regeneration need not worry about enhancing forest stand susceptibility to gypsy moth. However, the fire in this study was of low to moderate intensity; more intense fires may alter foliar palatability.