Red Oak Borer - Forest Entomology, Fred Stephen's Lab

Development and Comparison of Intensive and Extensive Sampling Methods and Preliminary Within-Tree Population Estimates of Red Oak Borer (Coleoptera: Cerambycidae) in the Ozark Mountains of Arkansas
M. K. Fierke; D. L. Kinney; V. B. Salisbury; D. J. Crook; F. M. Stephen
Abstract
Populations of red oak borer, Enaphalodes rufulus (Haldeman), a native wood-boring beetle, seem to be at unprecedented levels that are coinciding with extensive oak mortality occurring in the Ozark Mountains of Arkansas, Oklahoma, and Missouri. To quantify population levels, we developed intensive and extensive sampling methods with respect to the seasonal phenology of active and quiescent stages of the borer's synchronous 2-yr life cycle. Intensive whole-tree sampling yields data for the entire infested tree bole and provides baseline data for development of less time-consuming sampling methods. Extensive partial-tree sampling uses a nine-sample proportional sampling scheme to estimate densities, which are extrapolated to the whole tree. Data comparison reveals extensive estimates and intensive data are not significantly different, thus verifying extensive sampling as a relatively accurate and acceptable sampling method. Preliminary data from 58 trees confirm epidemic population levels in three areas of the Ozark National Forest in northern Arkansas. Mean number of phloem galleries initiated by current generation larvae on 38 trees was 599 ± 50 (SE) per tree, average number of live red oak borer found in 57 trees was 77 ± 15 per tree, and mean number of previous generation heartwood galleries present in 38 trees was 185 ± 30. Data generated through this research will permit detailed studies of red oak borer biology and mortality, facilitate development of less time-consuming field sampling techniques, and set the stage for further study of factors contributing to the current outbreak and associated tree mortality.

"Red Oak Borer (Coleoptera: Cerambycidae) Larval Mortality Resulting from Intraguild Predation." ESA Poster. 2004. Vanessa Ware.

Abstract
Historically considered innocuous, red oak borer, Enapholodes rufulus (Haldeman), is currently experiencing an outbreak of epidemic proportions in the Ozark National Forests of Arkansas which is resulting in widespread tree mortality. The cause of this outbreak is currently unknown. Insect populations increase when they escape natural controls, e.g. limited food resources, predators, etc. Some larval mortality has been accounted for by woodpeckers and nitidulids but the majority of mortality is from unknown factors. Larvae of E. rufulus feed in the phloem of living oak trees so phloem sandwiches were used to observe inter- and intra-specific predation of E. rufulus. Our investigations reveal that E. rufulus is cannibalistic with one larvae consuming up to 3 other larvae placed in close proximity. One of the potential benefits of this behavior, weight gain, is examined. Observations are also made on the contribution to larval mortality of some intraguild insects, e.g.
carpenterworm and elaterid larvae. This research has important implications in red oak borer population dynamics and may potentially help to explain the recent shift in population levels.

“A Remarkable and Unprecedented Red Oak Borer Outbreak in the Ozark Mountains of
Arkansas” Ecological Society of America, Portland, Oregon. 2004. Melissa Fierke. Also presented modified versions of this talk at the Arkansas Chapter of the Wildlife Society annual meeting in Fayetteville, Arkansas and at the UofA Ecomunch Biology seminar series. 2004.

Abstract: The Ozark National Forest in Arkansas, Missouri and Oklahoma is experiencing widespread oak mortality coinciding with increased populations of red oak borer, Enaphalodes rufulus (Haldeman)(Coleoptera: Cerambycidae), a native long horned wood-boring beetle. Red oak borer has an unusual two-year life cycle with synchronous emergence in odd numbered years and though it is endemic to areas throughout the northeastern U.S., it has not been indicted as a causal organism in other oak decline mortality events. Intensive sampling of 24 northern red oak, Quercus rubra L., ranging from apparently healthy to recently dead trees reveal populations that are deviating extraordinarily from normal levels of 1 or 2 insects per tree to an average of 98 live larvae per tree (range 0-577). Insect populations are kept at endemic population levels by either biotic or abiotic variables. Biotic variables include limited food resources, predators, parasites or disease organisms while abiotic include environmental variables, e.g. climate. At this point in time, we have not conclusively determined why this normally innocuous beetle has escaped from historic populations levels. Some stand and site variables that appear to be associated are percent northern red oak and stand aspect. Other variables that are being investigated are presence/importance of Armillaria root-rot species, tree-insect interactions and tree defense mechanisms. We are studying the biology and ecology of red oak borer in an attempt to understand mortality and survival as well as adult behavior. This research should help us understand better the causes of and the repercussions of this outbreak and subsequent tree mortality, which is changing tree species composition, increasing fuel loads and decreasing biomass and carbon sequestration in this forest system.

Stand Aspect as an Estimator of Tree Susceptibility to Red Oak Borer, Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae) Induced Mortality
Brent Kelley, Melissa K. Fierke, Dana Kinney, and Fred M. Stephen. University of Arkansas, Entomology Department, 319 Agriculture Building, Fayetteville, AR
Study stands were located in the Ozark-St. Francis National Forest, Arkansas, U.S.A. Three general areas were located exhibiting high oak mortality attributed to red oak borer, Enaphalodes rufulus (Haldeman). Five stands were chosen in each area on north, south, east, west, and ridge aspects. At each site, species and dbh was deteremined for all live and standing dead trees > 10cm dbh within a 30 X 100m plot (0.33 ha). A rapid estimation procedure was also used to determine infestation history at the tree level.
Data from this research indicated that ridge plots experience significantly higher tree mortality compared to all other plots and also have a higher incidence of long-term infestation. One explanation for this is that red oak borer outbreaks may occur on ridges first, providing a source area from which red oak borers disperse to adjacent areas. Another explanation is that there may be other stand variables associated with ridges which when coupled with other environmental stressors allow for increased fecundity or survival of red oak borers.

Does a landscape determine the fate of its trees? Predicting outbreaks of red oak borer using geographic information systems
Leah D. Lucio1, Fred M. Stephen1, and C. Fred Limp2. (1) University of Arkansas, Department of Entomology, 319 Agriculture Building, Fayetteville, AR, (2) University of Arkansas, Center for Advanced Spatial Technologies, Ozark Hall, Fayetteville, AR
The Red Oak Borer, Enaphalodes rufulus (Haldeman) has been wreaking havoc on the forests in the Ozark Mountains of Arkansas, Missouri and Oklahoma in recent years. A model predicting when and to what extent certain areas of the forest will be affected is being created using several landscape attributes. These attributes were chosen for importance to tree or stand health or for facilitation of insect movement. It is expected that certain variables will prove to be more important than others in determining the overall susceptibility of forest acreage to the insect.

Food digestion in different larval stages of the red oak borer, Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae)
Sheila Prabhakar1, Brenda Oppert2, Damon R. Crook3, and Fred M. Stephen3. (1) Kansas State University, Department of Entomology, Waters Hall, Manhattan, KS, (2) USDA-ARS-GMPRC, 1515 College Avenue, Manhattan, KS, (3) University of Arkansas, Department of Entomology, 319 Agricultural Building, Fayetteville, AR
Biochemical analyses were used to characterize the digestive physiology of larval red oak borer Enaphalodes rufulus (Haldeman). In second-year hardwood feeders, the pH of gut extracts from the hindgut region was 5.4 to 5.6, and increased to 6.2-6.4 in mid and foregut extracts. The hydrolysis of casein by gut extracts from larval E. rufulus increased steadily from pH 7.2 -11.7. Zymogram analysis with casein demonstrated two major proteinase activities, approximately 25 and 45 kDa. A 25 kDa proteinase hydrolyzed substrates with phenylalanine and leucine in the active site, characteristic of chymotrypsin-like proteinases. A proteinase with a molecular mass greater than 100 kDa hydrolyzed L-BapNA, a substrate for trypsin-like proteinases. Results show that, similar to reports in other Cerambycids, these larvae use serine proteinases to digest food. We are currently analyzing the digestive proteinases of first-year phloem feeders for a comparison of digestive capability.

Flight and landing behavior of red oak borer, Enaphalodes rufulus (Haldeman), (Coleoptera: Cerambycidae)
Melissa K. Fierke, Damon R. Crook, Stephen W. Wingard, Vaughn B. Salisbury, and Fred M. Stephen. University of Arkansas, Entomology Department, AGRI 319, Fayetteville, AR
Field tests were conducted within the Ozark-St Francis National Forest to evaluate flight and landing behavior of red oak borer, Enaphalodes rufulus (Haldeman). Passive flight intercept traps were hung at various levels up to the canopy to determine preferred flight height of adult red oak borers. Clear plexi-glass passive traps were attached to tree boles to assess landing preferences on different tree species and on a single tree species. Preferential landing on suitable host trees indicate an attractant, either chemical or visual, while landing on non-host trees indicates a random flight and landing pattern with host evaluation occurring tactilely after landing. Northern red oak, Quercus rubra L., the tree species currently experiencing elevated mortality, was further assessed based on different red oak borer infestation levels. Results will be discussed and we believe these findings will give insight into the biology and behavior of Cerambycid species as well as facilitating the development of successful trapping methods.

Intensive, extensive and rapid sampling techniques for estimating within-tree population densities of red oak borer, Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae)
Dana L Kinney, Vaughn B. Salisbury, Damon R. Crook, Melissa K. Fierke, and Fred M. Stephen. University of Arkansas, Department of Entomology, A 321, Fayetteville, AR
We are currently developing methods for sampling red oak borer populations. These methods include intensive, extensive and rapid sampling procedures. Intensive sampling requires the examination of the entire infested surface of the tree and provides a very precise estimate of within-tree red oak borer population densities. Extensive sampling procedures examine a proportion of the infested bole, require less time, but are less accurate than intensive techniques. Rapid estimation is a visual, non-destructive method that provides within tree red oak borer population estimates very quickly and economically. The method most appropriate for any sampling program is dependent on the precision required and the resources available to the researcher.

Pathogens of red oak borers, Enapholodes rufulus (Coleoptera: Cerambycidae), in Arkansas
J. M. Meyers, Donald Steinkraus, Fred M. Stephen, and Damon R. Crook. University of Arkansas, 319 Agriculture Building, Fayetteville, AR
Surveys were made of entomopathogens of the red oak borer, Enaphalodes rufulus (Haldeman), in northern red oak, Quercus rubra in northwest Arkansas. Natural isolates of Beauvaria bassiana were discovered, isolated and used in laboratory and field assays.

Food digestion in different larval stages of the red oak borer, Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae)

Sheila Prabhakar¹, Brenda Oppert2, Damon Crook3 & Fred Stephen3
1Department of Entomology, Kansas State University, Manhattan, KS 66506, 2USDA ARS Grain Marketing and Production Research Center, 1515, College Avenue, Manhattan, KS 66502, and 3Department of Entomology, University of Arkansas, Fayetteville, AR 72701

Biochemical analyses were used to characterize the digestive physiology of larval red oak borer Enaphalodes rufulus (Haldeman). In second-year hardwood feeders, the pH of gut extracts from the hindgut region was 5.4 to 5.6, and increased to 6.2-6.4 in mid and foregut extracts. The hydrolysis of casein by gut extracts from larval E. rufulus increased steadily from pH 7.2 -11.7. Zymogram analysis with casein demonstrated two major proteinase activities, approximately 25 and 45 kDa. A 25 kDa proteinase hydrolyzed substrates with phenylalanine and leucine in the active site, characteristic of chymotrypsin-like proteinases. A proteinase with a molecular mass greater than 100 kDa hydrolyzed L-BapNA, a substrate for trypsin-like proteinases. Results show that, similar to reports in other Cerambycids, these larvae use serine proteinases to digest food. We are currently analyzing the digestive proteinases of FIRST-year phloem feeders for a comparison of digestive capability.

Life table analysis of the Red Oak Borer, Enaphalodes rufulus (Coleoptera: Cerambycidae).

Damon Crook, Dana Kinney, Vaughn Salisbury and Fred Stephen.
University of Arkansas, Entomology, A 321, Fayetteville, AR.

The recent epidemic of northern red oak, Quercus rubra L., mortality within the Ozark-St. Francis National Forests appears to result from a population explosion of a normally innocuous, native species of long-horned wood boring beetle, the Red Oak Borer, Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae).
Constructing life tables of the various life stages with the objective of comparing the histories of populations inhabiting individual trees will be discussed. We present here a summary of the red oak borer’s biology from when larvae first attack the bark surface up to when adults emerge two years later from a hardwood gallery. The following ‘within-tree’ population densities were assessed: attack density, emergence hole density, first year gallery density and previous generation gallery density. Data on stage-specific within-tree population densities will be presented and survivorship of these life stages will be discussed in relation to factors such as site aspect and tree species composition.

Flight and host selection studies on the red oak borer Enaphalodes rufulus (Coleoptera: Cerambycidae)

Melissa Fierke, Stephen Wingard, Damon Crook & Fred Stephen. University of Arkansas, Entomology, A 321, Fayetteville, AR

Field tests were conducted within the Ozark-St Francis National Forest to evaluate the flight and landing behavior of the red oak borer, Enaphalodes rufulus (Haldeman). Clear plexi-glass ‘passive’ traps were used to assess landing rates on the following tree species: black gum, hickory, maple, black oak, northern red oak and white oak.
Northern red oaks which are currently suffering the highest red oak borer mortality were further assessed based on infestation history. Passive traps were placed on trees rated as having a low, medium and high history of red oak borer infestation to determine differential landing preferences.
Corrugated plastic passive traps (IPM technologies, Portland) were also positioned at various levels up to the canopy to determine the preferred flight height of adult beetles.
We will discuss host tree attractiveness by the red oak borer with regards to tree species and tree health. It is hoped that these findings will help develop a more successful trapping method along with the possible identification of tree ‘stress’ released chemical lures.

Spatial distribution of within tree populations of red oak borer (Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae)
V.B. Salisbury, D. J. Crook, D.L. Kinney and F.M. Stephen. University of Arkansas, Entomology, A 321, Fayetteville, AR
Infested Northern Red Oak (Quercus rubra) trees were felled and cut into 0.5m sections. Whole trees and systematically selected sections of trees were examined and dissected in the laboratory. Red oak borer entrance and exit holes on the bark surface were recorded and mapped using a coordinate/degree system. The bark was then removed from each tree section so that positions of early and late larval galleries could be mapped. Two-dimensional maps were developed which depict red oak borer populations at various life stages. Mapped data was then divided into four quadrants, each centered on a cardinal direction. The spatial distribution of the various life stages of the red oak borer will be presented for a total of ------ partial/whole trees. Effects of site and stand factors in relation to how beetle populations are distributed within the tree will be discussed.

Red Oak Borer, Enaphalodes rufulus (Coleoptera: Cerambycidae): A Remarkable Epidemic of Oak Mortality in the Interior Highland Forests
Fred Stephen, Vaughn Salisbury, Fred Limp, and Damon Crook
Eric Heitzman and Lynne Thompson
Forests of the Ozark Mountain in Arkansas and Missouri (USA) currently are experiencing a remarkable outbreak of a native, normally endemic insect species, the red oak borer, Enaphalodes rufulus (Coleoptera: Cerambycidae). Estimates predicted that by the end of 2001 greater than 450,000 ha of forest in the Ozark Mountains would be impacted. We do not know whether this epidemic is increasing or what its duration will be. We present here a brief description of the affected forests; the symptoms of oak decline; the biology of the insect; a synopsis of preliminary lab and field data that confirm the remarkable nature of this population outbreak in contrast to the limited published literature; and a brief description of a possible coordinated response to the present crisis.

Biology and Sampling of Red Oak Borer Populations in the Ozark Mountains of Arkansas
Damon Crook, Fred Stephen, Melissa Fierke, Dana Kinney, and Vaughn Salisbury
A complex interaction of multiple factors has resulted in >75 percent mortality/decline of more than 1 million acres of red oak (Quercus, subgenus Erythrobalanus) on the Ozark-St. Francis National Forests. The most striking feature of this oak decline event is an unprecedented outbreak of red oak borer. A visual stand assessment method was devised for categorizing red oak borer infestation based on crown condition and number of adult emergence holes in the tree bark. An intensive sampling method was also developed to study borer populations at the within-tree level. Complete tree dissections revealed that red oak borer colonizes the entire tree bole. Emergence holes are the highest ever reported in the literature averaging 19.97/m2 of bark despite high mortality during larval stages.