Fred M. Stephen

Red Oak Borer, Enaphalodes rufulus (Coleoptera: Cerambycidae), in the Ozark Mountains of Arkansas, U.S.A.: An Unexpected and Remarkable Forest Disturbance

A complex interaction of multiple factors has resulted in an oak decline event in oak-hickory forests of the Ozark Mountains of Arkansas and Missouri, U.S.A. The most striking feature of this situation is an unprecedented population explosion of red oak borer, a species of cerambycid beetle, Enaphalodes rufulus (Haldeman), which appears to be causing extensive mortality to mature red oaks (Quercus, subgenus Erythrobalanus). The insect is a native species, historically a minor pest of oaks, found throughout the eastern United States. Beetles normally reproduce in living oaks, as larvae initially feed in phloem tissue and subsequently bore into xylem where pupation occurs. The life cycle is two years in length and synchronous adult emergence occurs in odd-numbered years. Data from previous research indicate average attack densities of less than four per tree with a high of 71 on a single tree. Historical emergence densities are similarly low and the highest reported was 15 adults from one tree. Our research is concerned with understanding factors contributing to this outbreak; developing sampling methods for red oak borer; assessing oak mortality; and evaluating site and stand conditions associated with the current outbreak. Results of our initial sampling reveal dramatically higher average attack densities of 244 per m2 and emergence densities of 18 per m2 of bark surface area. We confirm a three-week period of adult emergence and activity during mid-June to early July. We also report on possible management responses by federal and state agencies to this remarkable epidemic and oak mortality crisis.

Per-segment Aboveground Forest Biomass Estimation Using LIDAR-Derived Height Percentile Statistics

An outbreak of red oak borer, an insect infesting red oak trees, prompted the need for a biomass model of closed-canopy oak-hickory forests in the rugged terrain of the Arkansas Ozarks. Multiple height percentiles were calculated from small-footprint aerial LIDAR data, and image segmentation was employed to partition the LIDAR-derived surface into structurally homogeneous modeling units. In situ reference data were incorporated into a machine-learning algorithm that produced a regression-tree model for predicting aboveground woody biomass per segment. Model results on training data appear adequate for prediction purposes (mean error 2.38 kg/m2, R 2 = 0.83). Model performance on withheld test data reveals slightly lower accuracy (2.77 kg/m2, R 2 = 0.72).

Ant predation on red oak borer confirmed by field observation and molecular gut-content analysis

1 Populations of an indigenous longhorn beetle, the red oak borer Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae), recently reached epidemic levels in the Ozark National Forests of Arkansas and Missouri, resulting in extensive tree mortality.

RED OAK BORER (COLEOPTERA: CERAMBYCIDAE) FLIGHT TRAPPING IN THE OZARK NATIONAL FOREST, ARKANSAS

Abstract High population densities of red oak borer, Enaphalodes rufulus (Haldeman), are believed to be a major contributor to recent widespread oak mortality in the Ozark Mountains of Arkansas. The intent of this research was to expand our knowledge on specific aspects of this insects biology, life history, and distribution by trapping flying adults in the Ozark National Forest during emergence of 2001, 2003, and 2005 cohorts. Passive flight intercept trap catches revealed that preferred flight height and thus optimal trap placement for monitoring populations was close to the base of the dominant/co-dominant northern red oak, Quercus rubra L., canopy. Flight periods and peak flight were different in 2001 and 2003. Emergence occurred a week earlier in 2001 vs. 2003. Peak flight occurred over a 3-week period from mid Jun to early Jul in 2001 in contrast to 2003 peak flight, which occurred the first week of Jul. Male to female ratios were 1.9:1 and 1.4:1 for 2001 and 2003, respectively. In 2003, sex ratios varied significantly among 5 topographic positions evaluated, north, south, east, and west-facing benches and ridges. Total numbers of red oak borers caught varied both spatially and temporally from cohort to cohort in traps placed in 3 different areas on 5 topographic positions. This research should facilitate efficient future monitoring of adult red oak borer and form a basis for investigating stand and landscape-level factors affecting population densities throughout the forest.

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

ABSTRACT 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. RESUMEN 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.

Callus formation and bark moisture as potential physical defenses of northern red oak, Quercus rubra , against red oak borer, Enaphalodes rufulus (Coleoptera: Cerambycidae)

The red oak borer, Enaphalodes rufulus (Haldeman), is a native wood-boring beetle implicated as a major contributor to recent high levels of oak mortality in northern Arkansas. Northern red oaks, Quercus rubra L. (Fagaceae), were grouped into three classes of red oak borer infestation history based on crown condition and basal red oak borer emergence holes: class I (low infestation), class II (moderate infestation), and class III (high infestation). In 2004 and 2005, trees from each class were mechanically wounded and callus formation was measured after one year. Class I trees exhibited significantly greater callus formation than class III trees in both years. Monthly measurements in spring and summer of 2006 indicated significant differences in callus formation among classes, with class I trees healing over significantly earlier. Moisture was measured in bark samples removed 1 week and 4 weeks after initiation of three treatments: control, mechanical wounding, and artificial insertion of larvae. Moisture...

Height Distribution of Adult Parasitoids of the Southern Pine Beetle Complex

Abstract The height distribution of adult parasitoids of the Dendroctonus frontalis Zimmermann complex trapped on the boles of Pinus taeda L. trees was examined. The study was conducted within two active D. frontalis infestations in the Talladega National Forest in Alabama in July 1998. Stickem Special-coated 15 × 20 cm wire mesh (6 mm2) traps were placed on pines with late instar to adult D. frontalis and Ips spp. at 2 m intervals to a height of 16 m on 12 trees and at 4-m intervals to a height of 16 m on 6 trees. Traps were changed on alternate days for 14 d, and all adult parasitoids of the D. frontalis complex were identified and counted. There was a positive correlation between height and number of parasitoids. This is most likely due to the high proportion of Roptrocerus xylophagorum Ratzeburg and Heydenia unica Cook and Davis collected, because both of these species preferred the upper bole. Each parasitoid species had different height distributions. R. xylophagorum, H. unica and Dendrosoter sulcatus Muesebeck all preferred the upper bole, with a peak trap catch between 12 and 16 m. In contrast, Coeloides pissodis (Ashmead) and Dinotiscus dendroctoni (Ashmead) both preferred the midbole, with a peak catch at 6 m. Only Spathius pallidus Ashmead showed no height preference; however, this species also had the lowest trap catch. Although each parasitoid species had its height preferences, all species were distributed throughout the length of the infested bole.

Adult parasitoids of the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), feed on artificial diet on pine boles, pine canopy foliage and understory hardwood foliage

Abstract This study examined adult parasitoids of Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae) utilizing an artificial parasitoid food on locations with and without hosts. Eliminade™ was applied to bark on boles of infested pines, to pine canopy foliage and to understory hardwood foliage. Adult parasitoids were collected, identified and dissected to determine the presence of Eliminade™ within their guts. Individuals from eight parasitoid species were collected on pine boles within D. frontalis infestations in the Talladega National Forest (Alabama) in the summer of 1999 and 2000. Mean percentage of parasitoids feeding on Eliminade™ was 62±10% during both summers. Percentage of parasitoids feeding was the same 24 h after Eliminade™ application, regardless of food location or parasitoid species. Seven days later, level of parasitoid feeding on Eliminade™ was insignificant in the pine canopy and hardwood understory. In contrast, percent of parasitoid feeding on Eliminade™ applied to pine boles remained the same between 1 and 7 days of the application. Therefore, not only will adult parasitoids visit and feed on artificial food on pine boles with hosts, but also non-host locations such as pine canopy and understory hardwood foliage. These results have implications for potential sources of adult nutrition for parasitoids of D. frontalis.

Emergence of adult female Sirex nigricornis F. and Sirex noctilio F. (Hymenoptera: Siricidae) coincides with a decrease in daily minimum and maximum temperature

The establishment and spread of Sirex noctilio F. (Hymenoptera: Siricidae), in northeastern North America necessitates reliable monitoring methods for this alien woodwasp pest of Pinus. The native congener, Sirex nigricornis F., is common across the eastern U.S.A. and has been studied as a proxy for S. noctilio. Predicting the emergence of S. noctilio is important for guiding monitoring efforts. Degree‐day models have been developed to predict flight phenology of S. noctilio and S. nigricornis across eastern North America. These model parameters were tested against three years of S. nigricornis collections from two locations in Arkansas. Neither of the proposed models accurately predicted emergence. The emergence of females for both S. noctilio and S. nigricornis was significantly negatively correlated with minimum and maximum temperature, indicating that emergence increases when minimum and maximum temperatures decrease. These results suggest that, as S. noctilio spreads south, where higher mean temperatures are present, it will emerge later in the season as the temperatures decline compared with the current northeastern population. We propose that monitoring for the spread of S. noctilio in the southeastern U.S.A. should begin slightly before daily temperatures are expected to decline (i.e. mid‐September).

Monochamus species from different continents can be effectively detected with the same trapping protocol

Pine wilt disease is one of the most serious introduced threats to coniferous forests worldwide. Its causal agent, the pinewood nematode (PWN), Bursaphelenchus xylophilus, is vectored primarily by cerambycids of the genus Monochamus Dejean throughout its native (North America) and introduced (Japan, China, Korea, Taiwan, Portugal) ranges. Despite strict import regulations and phytosanitary measures, interception records indicate that PWN and Monochamus species continue to be moved worldwide. Following its introduction in Portugal in the late 1990s, extensive monitoring programs for PWN and its vectors have been conducted throughout the European Union, using locally developed and tested lures and traps. The trapping system developed in Europe and used in this study is composed of a Crosstrap® and Galloprotect Pack® lures. These trapping systems were deployed in two locations in the USA, two locations in Canada, and one location in China in order to test their capacity to detect Monochamus species exotic to Europe. Large numbers of M. carolinensis, M. mutator, M. notatus, M. s. scutellatus, M. clamator, and M. titillator were trapped in North America, while large numbers of M. alternatus were trapped in China. The trapping systems developed in Europe for monitoring the European Monochamus species are also effective for the detection of many exotic Monochamus species and could thus be used as an early detection tool in ports and other high-risk sites.