Red Oak Borer Research Articles

Current and Future Insect Threats to Oaks of the Midwest, Great Lakes, and Northeastern United States and Canada

Increasing temperatures, prolonged drought, the increased severity and intensity of storms, and other effects of climate change are being felt globally, and long-lived forest tree species may struggle in their current ranges. Oaks (Quercus spp.) have evolved a range of adaptations to dry and hot conditions and are believed to be a “climate change winner” by increasing their suitable habitat. However, a mixture of life history traits and increasing susceptibility to herbivores and xylovores as well as secondary pathogen infections still put oaks at risk of decline. Oak species found in the Midwestern, Great Lakes, and Northeastern United States and Canada are important keystone species with high ecological and economical importance. They are also vulnerable to existing, new, and emerging threats that have the potential to cause mortality across entire stands quickly. Current examples of insect threats include the Lymantria dispar (spongy moth), Agrilus bilineatus (twolined chestnut borer), and Nitidulidae (sap beetles) as disease vectors. Examples of emerging insects of concern include Cynipidae (oak gall wasps) and Enaphalodes rufulus (red oak borer). This study describes these insects, explains their mechanisms of action and the effects on oaks, and explores mitigation strategies for each.

Indirect effects mediate direct effects of climate warming on insect disturbance regimes of temperate broadleaf forests in the central U.S.

Abstract Climate warming directly affects insect disturbance regimes by altering temperature‐dependent population development. Indirect effects of climate change on insect disturbance may mediate or accelerate direct effects via vegetation feedback (e.g. host tree demographic dynamics). However, such indirect effects have rarely been incorporated in predicting insect disturbance regimes. We included both direct and indirect effects in a forest landscape modelling framework to simulate red oak borer [ROB, Enaphalodes rufulus (Coleoptera: Cerambycidae)] disturbance regimes under a warming climate from 2000 to 2150 in the Central Hardwood Forests, U.S. We quantified effect sizes and relative importance of direct effects and indirect effects of warming climate on the ROB disturbance using a factorial experimental design and two‐way ANOVA. Both direct and indirect effects acted positively in the short and medium term (e.g. 0–100 years) while the effect size of indirect effects changed over time from positive (+30.9 kha) to negative (−17.3 kha) and mediated the positive direct effects in the long term (e.g. 100–150 years). Direct effects had greater influence than indirect effects on ROB disturbed areas in the short term (e.g. <50 years), whereas indirect effects were more important (ω2 = 0.38 vs. 0.26) in the long term. This was because the host tree abundance significantly declined over time under warming climates, which decreased the forest susceptibility to ROB and thus overrode the outbreak‐promoting effects of warming climates in the long term. Synthesis and applications. This study reveals indirect effects of warming climates mediate direct effects on insect disturbance regimes by altering primary host tree demographic dynamics. We highlight that indirect effects are important in understanding insect disturbance regimes under warming climates as they may mediate or even reverse the expectation of increased insect disturbance. Long‐term predictions of insect disturbance without considering indirect effects may overestimate its impacts under warming climates. Our findings also indicate that different management interventions are required at different time‐scales to maintain oak forests' health and sustainability in the U.S. central temperate broadleaf forests.

Spatial patterns of within-treeEnaphalodes rufulus(Coleoptera: Cerambycidae) attacks during outbreak conditions in the Ozark National Forest in Arkansas, United States of America

AbstractEnaphalodes rufulus(Haldeman) (red oak borer; Coleoptera: Cerambycidae) is a native wood borer that colonises and develops in oaks (QuercusLinnaeus; Fagaceae) across southeastern Canada and the eastern United States of America. It is rarely considered a pest because it normally occurs at low population density levels in stressed or dying oak trees. In the late 1990s and early 2000s there was a large, historically unique outbreak ofE.rufulusin the Ozark mountains of Arkansas and Missouri, United States of America. This outbreak provided an opportunity to investigate within-tree spatial distribution of attacks during unusually high insect population levels. Fifty trees from northern Arkansas were felled and destructively sampled. The locations of attack sites by femaleE.rufuluswere standardised across varying heights and diameters for comparison across trees. Attack sites showed a significant clustered pattern within trees. Attack sites were aggregated towards the lower and middle bole, and on the south-facing side of trees. This pattern has been seen in other insects, including wood borers, and is potentially related to differences in temperature. These patterns of ovipositional behaviour in outbreak situations have implications forE.rufulusresource partitioning and facultative intraguild predation among larvae.

Near Absence ofAgrilus bilineatusfrom an Oak Decline Event in the Ozark Mountains of Arkansas

It was unknown whether twolined chestnut borer, Agrilus bilineatus (Coleoptera: Buprestidae), a common secondary agent of tree decline in eastern US oak forests, contributed to tree mortality during a recent (1999–2003) episode of oak decline in the Ozark Mountains. Adult beetle flight was monitored by trapping in 2001, 2003, and 2004 and oak branches and trunks were visually examined for exit holes and dissected to examine larval galleries. Very few A. bilineatus adults were found each year by trapping (< 10 as opposed to > 100 red oak borers [Enaphalodes rufulus; Coleoptera: Cerambycidae]), and no evidence of A. bilineatus was found in 70 dissected tree boles or in upper crown material, although other buprestids (Chrysobothris femorata) were noted.

Monitoring oak-hickory forest change during an unprecedented red oak borer outbreak in the Ozark Mountains: 1990 to 2006

Upland oak-hickory forests in Arkansas, Missouri, and Oklahoma experienced oak decline in the late 1990s and early 2000s during an unprecedented outbreak of a native beetle, the red oak borer (ROB), Enaphalodes rufulus (Haldeman). Although remote sensing supports frequent monitoring of continuously changing forests, comparable in situ observations are critical for developing an understanding of past and potential ROB damage in the Ozark Mountains. We categorized forest change using a normalized difference water index (NDWI) applied to multitemporal Landsat TM and ETM+ imagery (1990, 2001, and 2006). Levels of decline or growth were categorized using simple statistical thresholds of change in the NDWI over time. Corresponding decline and growth areas were then observed in situ where tree diameter, age, crown condition, and species composition were measured within variable radius plots. Using a machine learning decision tree classifier, remote sensing-derived decline and growth was characterized in terms of in situ observation. Plots with tree quadratic mean diameter at breast height ≥21.5 cm were categorized remotely as in severe decline. Landsat TM/ETM+-based NDWI derivatives reveal forest decline and regrowth in post-ROB outbreak surveys. Historical and future Landsat-based canopy change detection should be incorporated with existing landscape-based prediction of ROB hazard.

Laboratory and field bioassays on the effects of Beauveria bassiana Vuillemin (Hypocreales: Cordycipitaceae) on red oak borer, Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae)

An unexpected outbreak of a native longhorned beetle, the red oak borer (Enaphalodes rufulus (Haldeman)), occurred in upland oak forests of Arkansas, Missouri and Oklahoma ca. 1999–2005. Few management tools exist for reducing E. rufulus populations. Laboratory bioassays were conducted to determine susceptibility of all E. rufulus life stages to the fungal pathogen Beauveria bassiana Vuillemin. Egg, neonate, early-instar, pupal, and adult stages of E. rufulus were all susceptible to a natural isolate of B. bassiana collected from E. rufulus (ARSEF 7404) or a commercial B. bassiana product, BotaniGard®. In July 2003, 10 living, E. rufulus-infested northern red oak (Quercus rubra L.) boles were sprayed with a 2 L BotaniGard®B. bassiana suspension of 1.3×1011 viable conidia per 2m of each bole at a forested site in the Ozark National Forest, Franklin County, Arkansas. The following spring, trees were removed and sampled for E. rufulus larvae that had survived or died during the winter. Live E. rufulus larval density in untreated Q. rubra log samples was significantly greater than in treated log samples with means of 16.4±1.8 (SE) and 4.4±2.0 larvae per m2 of bark for untreated and treated logs, respectively. Application of B. bassiana spray against early-instar E. rufulus would be most effective in mid-summer of odd-numbered years to target vulnerable early E. rufulus life stages and to reduce structural damage to trees caused by E. rufulus feeding.

Partial Life Tables From Three Generations of &lt;I&gt;Enaphalodes rufulus&lt;/I&gt; (Coleoptera: Cerambycidae)

We used life table analyses to investigate age specific mortality and to better understand the population dynamics of the red oak borer, Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae). We continually sampled populations within 177 trees at primarily two sites in the Ozark National Forest in Arkansas throughout three (2-yr) generations. The first cohort (adults emerged in 2003) was sampled during a severe population outbreak, whereas the second and third (2005 and 2007) were sampled during the population crash that followed. Generation mortality was 94% in 2003 and 99% in both 2005 and 2007. Estimates of apparent mortality indicated that the E. rufulus population crash likely occurred during or before the first overwintering period (2003-2004) of the generation that emerged as adults in 2005. We found limited evidence for density dependent mortality, which suggest that intraspecific competition after the first active feeding period was apparently not an important mortality factor during E. rufulus development. Life tables revealed that E. rufulus larvae generally experienced the greatest apparent mortality during the second summer of active feeding (80-94%) when larvae were feeding in, and moving between phloem and sapwood. The least apparent mortality was incurred during the following spring and early summer (26-67%) when late stage larvae and pupae were deepest and most protected within sapwood or heartwood tunnels. We found very little evidence for mortality from associated species. Scarring of vascular tissue in response to E. rufulus feeding occurred during early life stages and may be an important tree resistance mechanism and E. rufulus mortality factor.

Oak decline and red oak borer outbreak: impact in upland oak-hickory forests of Arkansas, USA

Summary Oak-hickory forests in the Ozark and Ouachita Mountains of Arkansas recently experienced an episode of oak mortality in concert with an outbreak of the red oak borer (Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae)). We utilized data from the Forest Inventory and Analysis (FIA) program of the USDA Forest Service to explore changes in percent red oak (Quercus subgenus Erythrobalanus) mortality as a function of standing trees, basal area and stem density during and after the recent borer outbreak throughout the state of Arkansas. Mean red oak mortality levels in Arkansas FIA oak-hickory plots that were sampled both during and after the borer outbreak increased from 19 ± 3 to 34 ± 4 per cent of standing red oaks, resulting in significantly reduced red oak basal area and stem density in these stands. Mean size of red oaks did not change significantly during this time period, implying that all size classes experienced mortality. After red oak borer populations subsided, oak-hickory survey plots experienced increases in red oak mortality levels during a drought year (2006) and after an ice storm (2009), which suggests that these stress events, in addition to prior red oak borer infestation, could have had some influence on tree mortality.

Phloem and xylem nitrogen variability in Quercus rubra attacked by Enaphalodes rufulus

AbstractWe analyzed nitrogen (N) content in phloem and xylem of 75 northern red oak, Quercus rubra L. (Fagaceae), removed in 2002–2007 from three sites within the Ozark National Forest, Arkansas, to investigate the relationship between vascular tissue N status and wood borer infestation. Populations of native red oak borer, Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae), experienced an outbreak and population crash during the sampling period. Vascular tissue N was not correlated with borer infestation density (exit holes/m−2/bark surface), which suggests variation in N status of vascular tissue was not influenced by or did not influence borer success. Vascular tissue N was greater in trees sampled during winter months than in trees sampled in spring and summer months.

Temporal aspects ofQuercus rubradecline and relationship to climate in the Ozark and Ouachita Mountains, Arkansas

Extreme climate events are frequently important factors associated with episodes of forest decline. A recent oak decline event and concurrent outbreak of a native wood-boring beetle, the red oak borer ( Enaphalodes rufulus (Haldeman)), occurred throughout Arkansas Ozark and Ouachita Mountains. To investigate the role of drought and stand maturity on northern red oak ( Quercus rubra L.) decline, we analyzed tree-ring growth patterns and their relationships to climate from 815 live and 161 recently dead Q. rubra. While younger Q. rubra exhibited faster growth rates and stronger climate relationships than older Q. rubra, some individuals within all stands that originated &gt;60 years ago were susceptible to growth decline or mortality. A significant growth interaction occurred among the three age classes identified where currently healthy Q. rubra were initially growing at slower decadal rates than currently declining or recently dead Q. rubra and later transitioned to higher growth rates than the others. These differences appear to be related to carbon allocation patterns towards rapid aboveground and (or) belowground growth early in development that led to later decline and (or) mortality. Decline in growth and weakening tree growth – climate relationships appeared to be initiated by an unusually severe and sustained drought in the early 1950s.

Factors that affect compartmentalization and wound closure of Quercus rubra infested with Enaphalodes rufulus

The mechanisms by which hardwood trees resist invasion by native wood borers are still poorly understood. 2 We examined the importance of several host, herbivore and environmental variables in relation to Quercus rubra L., northern red oak, resistance to a native cerambycid, Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae), the red oak borer. 3 We employed tree-ring techniques to date and measure two indicators of host tree physical resistance, vertical lesion size and wound closure of scars left by larval galleries, within 107 Q. rubra hosts from eight sites within the Ozark and Ouachita National Forests of Arkansas. 4H ostQ. rubra decline status proved a valuable predictor of resistance, wherein healthy trees exhibited better compartmentalization capacity, as indicated by shorter lesions and faster wound closure, than declining trees and those that died during a recent E. rufulus outbreak. 5 Only healthy Q. rubra exhibited a significant declining lesion length trend from 1988 to 2006 and were likely able to re-allocate resources in favour of maintaining resistance as the feeding pressure from borers increased and then relaxed post- outbreak. 6 Variables related to borer feeding pressure consistently explained more variation in lesion length than host or environmental variables. Hosts were better able to compartmentalize injury from small, unsuccessful E. rufulus galleries than large, successful galleries from which larvae survived to adulthood. 7 Healthy Q. rubra, as survivors of the recent outbreak, were able to effectively tolerate feeding pressure from borers at the same time as sustaining growth and maintenance. Tolerance may be an important resistance mechanism for hardwood hosts against the native wood borers that attack them.

Optimal Cross-Sectional Sampling Strategy for Red Oak Borer (Coleoptera: Cerambycidae) Scars within Northern Red Oaks

Abstract We used dendrochronological techniques to develop an optimal sampling strategy for the purpose of investigating the history of red oak borer (Enaphalodes rufulus [Haldeman]) population patterns within northern red oaks (Quercus rubra L.). We cut the entire length of three northern red oak tree boles into cross-sections, sanded top and bottom surfaces of each cross-section, and dated all scars within each bole. Our goal was to devise a strategy to reduce the amount of bole sampled without compromising the data necessary to accurately estimate historical population patterns of red oak borer. When we tested four possible sampling strategies and compared them with the entire-tree data sets from which they originated, we found no statistical differences in the distribution of scar counts by year. We also assessed processing time and found that compared with sampling an entire host bole, sampling strategies that include the lower 20% or 30% of boles would reduce labor efforts by 55–63%. We suggest that development of similar sampling methods for other bark or wood-boring species may be possible if the relationship between insect life history and annual tree-ring formation, as well as the general spatial and temporal distribution of insect evidence within trees, is known.

Factors Affecting Suitability ofQuercus rubraas Hosts forEnaphalodes rufulus(Coleoptera: Cerambycidae)

Epidemic populations of Enaphalodes rufulus (Haldeman), red oak borer, a native longhorned wood boring beetle, were implicated as a major contributor to a recent widespread oak mortality event in the Ozark National Forest of Arkansas. We assessed potential factors affecting suitability of a primary host Quercus rubra L., northern red oak, which experienced dieback and mortality throughout two successive borer cohorts. We sampled trees with various E. rufulus infestation levels during 2001-2003 when populations were at outbreak levels and 2003-2005 when borer numbers were declining. We measured phloem thickness and calculated a vigor index; the ratio of the past 5-yr basal area increment to sapwood area. We also counted established first year larval feeding galleries and outer-bark adult emergence holes and measured surface area of feeding galleries on a subset of Q. rubra to assess the importance of host susceptibility versus suitability. Phloem thickness did not exhibit any patterns among hosts of varying infestation levels and was therefore not likely an important factor limiting larval success. Less vigorous Q. rubra appeared to be the most suitable hosts, although it is unclear whether reduced vigor was initially caused by stress of E. rufulus infestation or environmental factors. Host suitability seems to be more important than host susceptibility, as numbers of initiated galleries were not consistently different among host infestation classes and between both cohorts, whereas numbers of emerging adults did differ predictably among host infestation classes.

Dendroentomological evidence associated with an outbreak of the native wood-boring beetleEnaphalodes rufulus

An outbreak of Enaphalodes rufulus Haldeman, a North American wood-boring cerambycid beetle, appears to be a major contributing factor to a recent Quercus rubra L. mortality event. The objectives of this research were to investigate the historical activity and within-tree distributions of E. rufulus by using scars formed by larval feeding in the cambium and xylem. Scars were counted and dated in fifteen 63- to 88-year-old northern red oaks; five in each of three infestation classes (low, moderate, and high). There were significantly fewer scars noted in low infestation trees than in trees with high infestations, and moderately infested trees showed intermediate scarring. There were significant differences in the date of the first xylem scar with initial scars occurring in 1980 in low infestation trees, 1952 in moderate, and 1940 in high. The number of xylem scars present varied significantly at different heights on the tree bole, but no differences were found based on tree aspect. This research provides evidence that an outbreak of red oak borer has not occurred before in these trees, beetles have not undergone recent population oscillations, trees that are currently highly infested have been infested over a longer period of time and at higher densities than low infestation trees, and there are distinctive within-tree larval distributions.

Stand and individual tree characteristics associated with Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae) infestations within the Ozark and Ouachita National Forests

Many oak decline events have been reported within the past century in the eastern U.S., and important causal factors often differ among them. Coincident with a recent decline event in upland oak-dominant forests of Arkansas, Missouri, and Oklahoma was an unexpected outbreak of a native cerambycid beetle, Enaphalodes rufulus (Haldeman), the red oak borer. A large range in estimates of oak mortality throughout affected forests was presumably due to variation in species composition, where oak-dominant areas experienced the greatest mortality. We chose eight sites across the Ozark and Ouachita National Forests of Arkansas, similar both topographically and by oak dominance, to determine if other stand or tree characteristics were important factors in variation of E. rufulus infestations across these forests. At each site, we sampled ∼125 dead, declining or healthy host Quercus rubra L., northern red oak. We created an estimate of the E. rufulus population level at each site during the recent outbreak using counts of dated larval gallery scars within a subset ( n = 120) of all Q. rubra sampled ( n = 976). We used classification tree partitioning to determine host tree characteristics that differed among dead, declining, and healthy Q. rubra. We also used classification tree partitioning, followed by logistic regression to determine stand characteristics that varied significantly among high, moderate and low infestation stands as well as between forests. Models indicated that trees which died were smallest, grew the least during the borer outbreak, and were apparently suppressed. These dying trees were likely poor competitors for resources, allowing neighboring survivors to experience a growth release during the E. rufulus outbreak. Larval survivorship was higher in trees which died, though larval densities were not greatest within these trees, which suggests that resistance in these individuals was compromised. At the stand level, differences between forests were apparently more important than those due to borer infestation. E. rufulus populations were higher at sites with lower Q. rubra basal area. This reduced basal area was likely a result of greater Q. rubra mortality at these sites during the borer outbreak in the early 2000s.

Identification and distribution of Armillaria species associated with an oak decline event in the Arkansas Ozarks

SummaryForests in the Ozark Mountains of northern Arkansas recently experienced a widespread oak decline event. Armillaria, a root rot fungus, has been associated with other oak decline events and may have been an important contributing factor to tree mortality in this event. Although Armillaria has been identified from the Ozark Mountains in Missouri, it has never been investigated in the Arkansas Ozarks. Molecular diagnostic techniques were used in this study to identify species of Armillaria present on roots removed from dead trees of two common oak species, northern red oak, Quercus rubra L., and white oak, Q. alba L., from three geographic areas and on three topographic positions – ridges, south‐ and west‐facing benches. Armillaria(A. mellea, A. gallica or A. tabescens) was identified from 31% of root samples taken from 102 trees in seven of nine sample plots. Armillaria mellea, occurred most often (20 samples, both oak species on seven plots) followed by A. gallica (10 samples, northern red oak only on four plots), and A. tabescens occurred twice (on northern red oak in a single plot). Thus, all three Armillaria species occurred on northern red oaks while A. mellea was the only species recovered from white oaks. Results varied by topographic position with samples from tree roots on ridges having the fewest positive identifications, one of 29. West‐facing benches had the highest positive samples with 20 of 41 testing positive and trees on south‐facing benches were intermediate with 11 of 32 samples from infected trees. This study documents the occurrence of three species of Armillaria in the Arkansas Ozarks and their association with oak mortality resulting from an oak decline event coupled with a red oak borer, Enaphalodes rufulus, outbreak. Further, it documents some potential variation in host/pathogen combinations and forest site conditions.

Segmenting Landowners Based on Their Information-Seeking Behavior: A Look at Landowner Education on the Red Oak Borer

Abstract This study uses a segmentation technique to classify landowners into four relevant groups to explore their information-seeking behavior about the red oak borer—an insect pest found primarily in the Ozark and Ouachita regions of Arkansas. Cluster Analysis technique was used to classify landowners into four groups—amenity focused rural, amenity focused urban, passive rural, and passive urban landowners—based on ownership objectives and rural and urban residence of the landowner. A relatively higher proportion (58%) of amenity focused rural landowners were familiar with red oak borer problems while the level of familiarity was more or less similar among passive rural (35%), amenity focused urban (36%), and passive urban (33%) landowners. Urban residents primarily received information about the red oak borer through mass media whereas rural residents relied on personal communication. Those that had taken some steps to reduce red oak borer impacts ranged from 14 to 19% among amenity focused urban, passive rural, and amenity focused rural landowners while none of the passive urban landowners had taken any action. The results from our study also suggest that targeting landowners based on their ownership objectives may be useful to stimulate forest management. If suitably targeted to amenity focused landowners, personal communication, although expensive and time-consuming, can be fruitful and a more efficient way to optimize resources.

Rise and Fall of Red Oak Borer (Coleoptera: Cerambycidae) in the Ozark Mountains of Arkansas, USA

Oak-hickory forests of the Arkansas Ozarks recently incurred extensive tree mortality due in part to a native wood-boring beetle, the red oak borer Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae). Historically, red oak borer has existed throughout southeastern U.S. forests at relatively low population levels, but Arkansas infestation estimates in 2001 and 2003 reported much higher populations. Red oak borer has a two-year generation with adult emergence occurring synchronously only in odd numbered years. We report here results of whole-tree estimates of pre-emergent red oak borer population numbers from 7 stands in 2005 and 3 stands in 2003 and 2007 in the Ozark National Forest. Trees were felled at each sampling site, cut into 0.5 m sections, split on site with hydraulic log splitters, and a count of live red oak borers was recorded for each tree. In 2001 and 2003, red oak borer population estimates indicated emerging populations much higher than any previously reported. An exponential decrease during a single cohort between 2003 and 2005, and even lower populations in 2007 suggest that red oak borer populations have returned to historic densities. Los bosques de roble-nogal de las montañas Ozark del estado de Arkansas recientemente sufrió una mortalidad de árboles extensiva debido en parte a un escarabajo nativo barrenador de madera, el barrenador de roble rojo Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae). Históricamente, el barrenador de roble rojo ha existido por todos los bosques del sureste de los Estados Unidos con niveles de población relativamente bajos, pero los informes del nivel de infestación en Arkansas en el 2001 y 2003 indica una población mucho más alta. El barrenador de roble rojo cumple una generación en dos años con la emergencia de los adultos, ocurriendo sincrónicamente durante los años de número impar. Reportamos los resultados de los números aproximados de la población pre-emergente del barrenador de roble rojo de los árboles totales de 7 grupos de árboles en 2005 y 3 grupos de árboles en 2003 y 2007 del Bosque Nacional de Ozark. Los árboles en cada uno de los sitios de muestreo fueron tumbados, cortados en secciones del tamaño 0.5 m, partidos con un rajador hidráulico de troncos y se noto el numero de barrenadores de roble rojo vivos encontrados por cada árbol. En el 2001 y 2003, los aproximados de la población del barrenador de roble rojo indicaron la emergencia de poblaciones mucho mas altas que las reportadas anteriormente. Una disminución exponencial durante un solo cohorte entre el 2003 y 2005, y aun poblaciones mas bajas en el 2007 sugerieron que la población del barrenador de roble rojo ha vuelto a las densidades históricas.

Occurrence ofCamponotus pennsylvanicus(Hymenoptera: Formicidae) in Trees Previously Infested withEnaphalodes rufulus(Coleoptera: Cerambycidae) in the Ozark Mountains of Arkansas

ABSTRACT Black carpenter ants, Camponotus pennsylvanicus (DeGeer), are nearly ubiquitous in North American forests. These ants are documented as predators of red oak borer, Enaphalodes rufulus (Haldeman), a native longhorn beetle that experienced an unprecedented population increase synonymous with an oak decline event in the oak hickory forests of the Ozark Mountains of Arkansas from the late 1990s until 2005. We examined previous red oak borer emergence holes, tree crown conditions, and site aspects in 13 pre-established vegetation monitoring plots and correlated these forest and tree attributes with the presence or absence of black carpenter ants. At each site, all red oaks >10 cm diameter at breast height were baited for black carpenter ants with a mixture of tuna and honey. Black carpenter ants were more frequently found on trees with low levels of previous red oak borer infestation versus those trees with previously high infestations. These data suggest a potential role for black carpenter ants in t...

Protein digestion in larvae of the red oak borer Enaphalodes rufulus

Abstract In the Ozark Mountains of the U.S.A., the red oak borer Enaphalodes rufulus contributes to the destruction of red oaks. To understand nutrient digestion in E. rufulus larvae, digestive proteinases are compared in both larvae fed heartwood phloem and those transferred to artificial diet. The pH of gut extracts is approximately 6.3 in the midgut and foregut and decreases to 5.5 in the hindgut region. The hydrolysis of casein by midgut extracts from E. rufulus larvae fed either artificial diet or phloem from tree sections increases in buffers greater than pH 6.19, with maximum hydrolysis being observed at pH 10.1. Casein zymogram analysis reveals two major proteinase activities in larval midgut extracts of diet‐fed larvae, with molecular masses of approximately 25 and 40–60 kDa, whereas phloem‐fed larvae have proteinase activities corresponding to 40, 45, 60, 80 and &gt;100 kDa. Substrate analysis indicates at least one major trypsin‐like activity in both gut extracts with a molecular mass of &gt;100 kDa, but two chymotrypsin‐like activities of approximately 25 and &gt;200 kDa are found only in diet‐fed larvae. Inhibitors of serine proteinases are most effective in reducing the general proteolytic activity of midgut extracts from larvae fed either food source. The data indicate that serine proteinase inhibitors have the potential to reduce E. rufulus larval damage to oaks. In particular, transgenic technologies incoporating trypsin inhibitors may be effective in reducing protein digestion in phloem‐feeding larvae.