Project Aims and Current Work

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Tree mortality is normally not associated with red oak borer infestation although damage to oak lumber may be economically important throughout its range (Hay 1969, Donley and Acciavatti 1980). Little is known on factors influencing population dynamics, particularly in relation to how epidemics develop and collapse. We are currently, from sites and stands of a variable nature, collecting data on red oak borer densities and their distribution. These data will permit comparison with previous life history parameters and enable estimation of overwintering mortality to immatures and prediction of trends in population growth.


The main aims of our current project are:

1. Learn more about the borer’s biology and raise public awareness.
2. Examine how various factors may influence growth and decline of borer populations. Discover why this once minor pest has reached such high population levels as to become an overwhelming epidemic?
3. Assess the current outbreak and predict future outbreaks using satellite images and GIS based software.
   

Developing sampling methods for this insect is complicated by the two-year life cycle of this cryptic species and synchronous adult emergence only in odd-numbered years. Despite this, we have developed methods for sampling within-tree populations of red oak borer over the past four years. We have also investigated multiple factors affecting red oak borer populations and their interactions with tree mortality.

Intensive or whole-tree dissection (Fig. 3) yields accurate red oak borer within-tree population data. It was the first step in method development but is time-consuming, ~130 hours/tree, and required large amounts of storage space (Fierke et al. 2005b).(Click graphic for more details)

Extensive dissection uses nine sub-samples taken systematically up the tree bole and data are extrapolated to the whole-tree. Statistical analysis revealed that extensive estimates are acceptably accurate and further analysis indicated that seven sub-samples was the optimal number of samples to dissect considering both accuracy and efficiency.
Future research includes investigating environmental contributors to tree mortality and interactions of silvicultural treatments on tree health and red oak borer populations, e.g. controlled burns, removal of “brood trees”. Research toward elucidating biological and mortality factors associated with changes in red oak borer populations continue as does development of an interactive prediction model of stand hazard and efforts continue toward making it available to the public.
Graph below shows typical attack hole densities for a whole tree (in blue). Extensive sub-samples are shown in red.

A Rapid Estimation Procedure was developed after making extensive field observations and intensively sampling whole trees in the lab. This survey method takes less than 5 minutes using 2 tree variables: basal emergence holes and tree crown condition based on dieback and transparency. Quantification of these data allow classification of trees into three general infestation histories; high, moderate and low. Analysis of sampling data show significant differences between classes and data yield acceptable estimates of within-tree populations (Fierke et al. 2005a).

We examined the literature and noted that Hay (1974) examined 480 trees over 3 red oak borer generations and reported 2.5 to 3.7 average attacks per tree (with the single highest being 71). In our preliminary studies we recorded an average attack density of 245 attacks per square meter of bark. Hay (1974) also reported that the greatest number of surviving adults to emerge from one tree (of 480) was 15.Our study showed an average emergence of 19 adults emerging per square meter of bark area. These densities of attacks, and emerging adults are so dramatically higher than any published records that they suggest the most serious and visible problems from this insect outbreak are yet to be experienced.

Sampling has added to our knowledge of red oak borer biology, including flight period, male/female ratios and mortality agents, e.g. intra/interguild predation (Ware and Stephen 2006), pathogens, parasitoids. Adult flight has been investigated with results indicating that optimum trap placement for monitoring is near the canopy. Investigations of host selection, e.g. preferential landing, tree volatiles and beetle pheromones have not been conclusive, but baseline data are available and will be used for further research. Other potential mortality influences/agents include stand and tree data associated with differentially infested trees, Armillaria root rot, two-lined chestnut borer presence and abundance and tree defenses.

Since ROB populations have gone down, we have started sampling whole trees again to study population changes and maybe determine an efficient sampling plan for low populations of ROB.

Following life stages/galleries have been assessed (using sampling methods)-

• Attacks on bark (From 2001 summer)
• 1st year gallery larvae (Quiescent 1 Period)
• 2nd year surviving larvae entering hardwood (Active 2 Period)
• 2nd year hardwood gallery larvae (Quiescent 2 Period)
• Late hardwood larvae, pupae and adults (Active 3 Period)

©Diagram by Dana Kinney

Despite fairly high mortality early on in the life cycle surviving numbers of larvae are still high. Once the larvae burrow deep into the heartwood mortality drops dramatically (See Survival Curve Below).

This ongoing data collection will enable us to predict trends in population growth.. These data will be linked to spatially explicit stand and site data, thereby allowing a prediction of ROB population growth to be made. Tree mortality factors contributing to the existing ROB outbreak can also be potentially isolated.

To date we have three main study areas. One is at the ‘Fly Gap’ area of the Ozark National Forest, one is at the ‘White Rock’ area and one is in the ‘Oark’ area. We have field plots on north facing, east facing, south facing and west facing benches so that we can compare borer population levels and mortality from different sites/aspects..

Lab Rearing of Red Oak Borer

During the short adult flight seasons we have kept adults alive in the lab for assays, egg and neonate production. We also developed lab-rearing methods. Adults are maintained in cages with northern red oak bolts and supplied with sugar water. After mating, females oviposit on bolts wrapped with medical gauze. Eggs are collected and kept on damp filter paper until eclosion. Seven to ten days later, neonates hatch and are inserted into an agar based diet (cerambycid diet, Bioserv Ltd) bulked out with extra cellulose to provide a firmer medium. Trays of diet and larvae are kept in the dark at room temperature. Fresh diet is supplied every 3-4 weeks.

Basal Cookies

The goal of basal cookie research is to correlate tree and stand variables with red oak borer population density variables that we measure through intensive and intensive sampling. Stand variables include topographic position (north, south, west, or east-facing bench or ridge) and geographic area that sampled trees were taken from. Tree data taken in the field include diameter at breast height, crown condition, basal red oak borer emergence holes (from 2 m to the ground). Additional tree data are measured from basal cross-sections taken at 0.5 m from the base of the tree. Data includes basal dbh, tree age, phloem width, functional xylem width, number of functional xylem rings, last five year growth rate, 10 year growth rates back to tree initiation, and relative drought response in signature drought years. These variables will be correlated with red oak borer population densities to evaluate tree and stand variables that may be linked to the population increase or increased densities in trees.

Population History Cookies

The goal of population history cookie research is to gain a general idea of red oak borer population densities through time. Methods used were originally developed by Rose-Marie Muzika and Richard Guyette (2001)(PDF). As red oak borer larvae injure the cambial tissue layer as they chew out of their first year galleries in even-numbered years and start excavating pupal galleries in the heartwood. These injuries are a long-term record that can be a proxy to compare red oak borer population densities from cohort to cohort as they leave a permanent scar in the xylem rings and so can be accurately dated back to when the injury occurred. Additional data being gathered include vertical distribution of scars, injury occurrence on directional aspects (N,S,E and W) and cross-sectional heartwood galleries holes.

CAST (Center for Advanced Spatial Technologies)

We are working with CAST at U of A to develop a Query-Based Data Management System for multiple parameters and measurements we are taking for all of the work we have done the past 5 years. We can also add future work and results to the data base. Dr. Jason Tullis, his grad student, Jason Defibaugh, are working with us on this project: “Development of Geospatial Techniques for the Prediction and Assessment of Red Oak Decline Due to Red Oak Borer”.