Jerome F. Grant

Molecular and genomic basis of volatile‐mediated indirect defense against insects in rice

Rice plants fed on by fall armyworm (Spodoptera frugiperda, FAW) caterpillars emit a blend of volatiles dominated by terpenoids. These volatiles were highly attractive to females of the parasitoid Cotesia marginiventris. Microarray analysis identified 196 rice genes whose expression was significantly upregulated by FAW feeding, 18 of which encode metabolic enzymes potentially involved in volatile biosynthesis. Significant induction of expression of seven of the 11 terpene synthase (TPS) genes identified through the microarray experiments was confirmd using real-time RT-PCR. Enzymes encoded by three TPS genes, Os02g02930, Os08g07100 and Os08g04500, were biochemically characterized. Os02g02930 was found to encode a monoterpene synthase producing the single product S-linalool, which is the most abundant volatile emitted from FAW-damaged rice plants. Both Os08g07100 and Os08g04500 were found to encode sesquiterpene synthases, each producing multiple products. These three enzymes are responsible for production of the majority of the terpenes released from FAW-damaged rice plants. In addition to TPS genes, several key genes in the upstream terpenoid pathways were also found to be upregulated by FAW feeding. This paper provides a comprehensive analysis of FAW-induced volatiles and the corresponding volatile biosynthetic genes potentially involved in indirect defense in rice. Evolution of the genetic basis governing volatile terpenoid biosynthesis for indirect defense is discussed.

Insect Guild Structure Associated with Eastern Hemlock in the Southern Appalachians

Abstract An assessment of the insect guild structure associated with immature and mature eastern hemlock, Tsuga canadensis (L.) Carrière, at high and low elevations was made before the invasion by the hemlock woolly adelgid, Adelges tsugae (Annand), and elongate hemlock scale, Fiorinia externa Ferris. Guild dynamics were determined among 243 insect species associated with eastern hemlock in the southern Appalachians. Detritivore, hematophage, herbivore, fungivore, parasitoid, predator, scavenger, and transient guild assignments were made. The herbivore and transient guilds were subdivided into chewers, sapsuckers, flower feeders, pollen feeders, pollen/nectar/sap feeders, and seed feeders. A significant association was found between guilds on immature and mature hemlocks at low elevations, but no significant association was found at high elevations. There was also a strong association of phytophagous insects on immature hemlocks and scavengers on mature hemlocks. The observed transient, scavenger, and predator guilds had a significantly lower co-occurrence among species indicating segregation of the species within these guilds. The herbivore guild had a significantly higher co-occurrence among species than the simulated index indicating aggregation of species within this guild across sites. Detritivore, hematophage, and parasitoid guilds did not differ significantly from the simulated community. These results document a diverse and dynamic insect community on eastern hemlock before invasion by hemlock woolly adelgid and elongate hemlock scale.

Community Response of Insects Associated with Eastern Hemlock to Imidacloprid and Horticultural Oil Treatments

ABSTRACT The hemlock woolly adelgid, Adelges tsugae Annand, is an invasive species reducing the populations of eastern hemlock, Tsuga canadensis L. Carrière, throughout the eastern United States. Systemic imidacloprid and horticultural oil are the primary chemicals used to control infestations of this invasive pest; however, the impact of these two chemicals on nontarget canopy insects is unknown. This study was initiated in November 2005 to assess the effects of (1) imidacloprid soil drench, (2) imidacloprid soil injection, (3) imidacloprid tree injections, and (4) horticultural oil applications on multiple levels of organization (composition, overall specimen abundance and species richness, guild specimen abundance and species richness, and individual species) within the phytophagous and transient canopy insect community. Community composition differed significantly among treatments based on analysis of similarity. Mean species richness and specimen abundance were significantly reduced by one or more treatments. Soil drench applications significantly reduced species richness for the detritivore and phytophaga guilds. Furthermore, specimen abundance for species in the detritivore, fungivore, phytophaga, scavenger, and transient phytophaga guilds was significantly lower in the soil drench treatment. This trend was consistent in all insect guilds examined, with the exception of the hematophaga guild that was not significantly lower than for species on the control trees. Of the 293 species documented to be associated with eastern hemlocks, 33 species were found to be directly effected by one or more of the chemical treatments.

Spatial and temporal distribution of imidacloprid in eastern hemlock in the southern Appalachians.

ABSTRACT The hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), is an exotic insect species dramatically reducing populations of eastern hemlock, Tsuga canadensis (L.) Carrieré, throughout the eastern United States, Systemic imidacloprid is one of the primary chemicals used to successfully control infestations of the hemlock woolly adelgid, The concentration levels for this systemic insecticide present in the sap of eastern hemlocks were evaluated from three strata within the canopy over a two year time span, Enzyme-linked immunosorbent assays were conducted every three months posttreatment to assess imidacloprid concentration within the sap. The effect of application timing (fall versus spring) and application method (soil drench, soil injection, and tree injection) on the translocation of imidacloprid throughout the canopy, and the quantity of imidacloprid translocated in the sap of eastern hemlock branches and the terminal twig and needle tissue was determined. Concentration levels progressively declined from the bottom strata to the top strata of the canopy. This trend was consistent in all chemically treated trees. Tree injections provided the lowest concentration and the most nonuniform distribution of imidacloprid throughout the canopy. The highest insecticide concentrations within the tree across all strata over the two year period were consistently associated with the soil drench method followed by the soil injection method. Imidacloprid concentrations peaked between month 9 and 12 posttreatment, and then declined; however, at two years posttreatment, soil drench and soil injected trees contained concentrations reported as being effective for control of the hemlock woolly adelgid.

Infestation levels of dogwood borer (Lepidoptera: Sesiidae) larvae on dogwood trees in selected habitats in Tennessee.

Infestation levels of dogwood borer [Synanthedon scitula (Harris)] on flowering dogwood (Cornus florida L.) in commercial nursery, urban, and forest habitats in eastern and middle Tennessee were measured during 1987 and 1988. The highest average infestation level (ca. 60%) was found in the urban habitat, where mechanical injury, e.g., damage caused by lawn mowers or string trimmers, may have provided oviposition or larval entry sites. Dogwood borer larvae were found in all nursery blocks examined, with ca. 7% of the trees infested/block. Infested trees are not marketable; thus, economic losses averaged ca.

Distribution and seasonal phenology of cereal leaf beetle (Coleoptera: Chrysomelidae) on wheat in Tennessee

l,800/block (x = 1,770 trees/block) of dogwoods. Infestation levels were lowest (ca. 1%) in the forest habitat, where dogwoods grow as a natural component of the forest understory.

Associations Between Causal Agents of the Beech Bark Disease Complex [Cryptococcus fagisuga (Homoptera: Cryptococcidae) and Nectria spp.] in the Great Smoky Mountains National Park

A three-year study was conducted to assess the distribution and seasonal incidence of cereal leaf beetle, Oulema melanopus (L.), on wheat, Triticum aestivum L., in Tennessee. Cereal leaf beetle was distributed across the state with populations most frequently encountered in eastern and middle Tennessee. Cereal leaf beetle adults were active in wheat fields during late March to early April; eggs were found from late March to early May; and larvae were found from early April to early June, peaking during mid May. In our experimental plots, larval densities exceeded the suggested economic threshold during each year. F1 adults emerged from late May to late June and fed approximately 2 wks on corn and other available Graminae plants. Adult activity then ceased; adults, eggs, and larvae were not encountered again until the following March and April.

Spatial and temporal distribution of residues of imidacloprid and its insecticidal 5-hydroxy and olefin and metabolites in eastern hemlock (Pinales: Pinaceae) in the southern Appalachians.

Abstract American beech, Fagus grandifolia Ehrhart, is currently threatened by the insect-mediated disease complex known as beech bark disease. The organisms (beech scale, Cryptococcus fagisuga Lindinger, and two pathogenic fungi, Nectria galligena Bresadola and Nectria coccinea variety faginata Lohman, Watson, and Ayers) associated with beech bark disease were assessed using a qualitative rating system and correlated with other biotic and abiotic factors in 10 permanent plots in the Great Smoky Mountains National Park from spring 1994 through spring 1997. Tree mortality, as well as the presence of another scale species [Xylococculus betulae (Pergande)], also were documented and analyzed. During this study, incidence of C. fagisuga and overall tree mortality increased (55.6–87.9 and 16.0–26.8%, respectively). A forward stepwise logistic regression model selected average overall ratings of C. fagisuga, sum of presence of X. betulae, average presence of. X. betulae, average overall ratings of Nectria spp., maximum presence of X. betulae, sum of south ratings of C. fagisuga, average south ratings of C. fagisuga, and diameter at breast height (dbh) of the tree as significant variables that best explained mortality of American beech. Pearson correlation analysis showed significant associations between ratings of Nectria spp. and C. fagisuga from both the previous season and previous year during fall 1996 and spring 1997. Moderate correlations between elevation, as well as aspect, and north, south, and overall ratings of C. fagisuga from fall 1995 to spring 1997 were documented. The significant association between presence of C. fagisuga and infection by Nectria spp. suggests that control of C. fagisuga could decrease occurrence and slow the spread of beech bark disease. Unless appropriate control and/or management of the disease complex is identified and implemented, mortality of American beech is expected to increase throughout most areas in the Great Smoky Mountains.

Assessment of Imidacloprid and Its Metabolites in Foliage of Eastern Hemlock Multiple Years Following Treatment for Hemlock Woolly Adelgid, Adelges tsugae (Hemiptera: Adelgidae), in Forested Conditions

ABSTRACT Widespread mortality of eastern hemlock, Tsuga canadensis (L.) Carrière, resulting from infestation by hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), has occurred throughout the native range of eastern hemlock within the eastern United States. Imida-cloprid, a systemic insecticide, is one of the primary chemical compounds used to control hemlock woolly adelgid in both urban and, in a limited manner, in natural forest environments. The metabolism of imidacloprid in eastern hemlock produces 12 metabolites; two of these, imidacloprid 5-hydroxy and imidacloprid olefin, are considered toxicologically important metabolites. However, little is known about the persistence of these metabolites in eastern hemlock in the southern Appalachians. Concentrations of imidacloprid, olefin, and 5-hydroxy were quantified by using HPLC/MS/MS techniques. Over the 3-yr study, concentrations of imidacloprid and consequent 5-hydroxy and olefin were highest in trees treated with a soil injection in the spring. Imidacloprid and 5-hydroxy concentrations in sap were highest at 12 mo posttreatment and in tissue at 15 mo posttreatment. Imidacloprid was detected through 36 mo posttreatment and 5-hydroxy was detected through 15 mo posttreatment. Olefin concentrations in both sap and tissue were highest at 36 mo posttreatment and were detected in high concentrations through 36 mo posttreatment. Concentrations of imidacloprid were highest in the bottom stratum of the canopy and lowest in the top stratum. Concentrations of olefin and 5-hydroxy were highest in the top stratum and lowest in the bottom stratum.

Establishment and coexistence of two predators, Laricobius nigrinus and Sasajiscymnus tsugae, introduced against hemlock woolly adelgid on eastern hemlock

ABSTRACT Widespread decline and mortality of eastern hemlock, Tsuga canadensis (L.) Carrie` re, have been caused by hemlock woolly adelgid, Adelges tsugae (Annand) (HWA) (Hemiptera: Adelgidae). The current study is a retrospective analysis conducted in collaboration with Great Smoky Mountains National Park (GRSM) to determine longevity of imidacloprid and its insecticidal metabolites (imidacloprid olefin, 5-hydroxy, and dihydroxy) in GRSMs HWA integrated pest management (IPM) program. Foliage samples were collected from three canopy strata of hemlocks that were given imidacloprid basal drench treatments 4–7 yr prior to sampling. Foliage was analyzed to assess concentrations in parts per billion (ppb) of imidacloprid and its metabolites. Imidacloprid and its olefin metabolite were present in most, 95 and 65%, respectively, branchlets 4–7 yr post-treatment, but the 5-hydroxy and dihydroxy metabolites were present in only 1.3 and 11.7%, respectively, of the branchlets. Imidacloprid and olefin concentrations significantly decreased between 4 and 7 yr post-treatment. Concentrations of both imidacloprid and olefin were below the LC50 for HWA 5–7 yr post-treatment. Knowledge of the longevity of imidacloprid treatments and its metabolite olefin can help maximize the use of imidacloprid in HWA IPM programs.