Speaker: Dr. Karla Addesso, Associate Professor of Entomology and Center Director, Tennessee State University Nursery Research Center, McMinnville, TN
Webinar Date: July 18, 2024
Moderator: Dr. Shimat Joseph, UGA Extension Entomologist
Duration: 53:37
NARRATIVE SUMMARY
Dr. Karla Addesso presented a comprehensive overview of flathead borer identification and management for southeastern landscapes, focusing specifically on the genus Chrysobothris. These native beetles represent a significant challenge for nursery and landscape professionals because approximately 750 flathead borer species exist in North America, with over 140 Chrysobothris species distributed from Canada to Mexico. Dr. Addesso explained that while emerald ash borer receives considerable attention as an invasive species, native Chrysobothris borers cause substantial economic damage to woody ornamentals, particularly newly transplanted and drought-stressed trees. The presentation emphasized that what has historically been called “flathead apple tree borer” and attributed to a single species (Chrysobothris femorata) actually represents a complex of closely related species that are extremely difficult to differentiate, even for expert entomologists.
The webinar detailed the typical life cycle of Chrysobothris beetles, with adults emerging in May-June in Tennessee, laying eggs on tree trunks, and larvae developing under the bark throughout summer and fall. Dr. Addesso emphasized that damage remains invisible until October-November when bark begins breaking and powdery frass becomes visible, often mistaken for frost damage. She presented innovative research on species identification using morphological dissection, genetic analysis, chemical profiling of cuticular waxes, and spectral analysis of beetle coloration. A particularly noteworthy finding involved Chrysobothris larvae discovered in pear fruit in California orchards, representing a potential host shift from woody tissue to fruit tissue, possibly driven by drought conditions.
Dr. Addesso discussed monitoring strategies using purple sticky traps designed as trunk mimics rather than panel traps, explaining that these beetles respond to visual cues resembling small tree trunks. The presentation covered growing degree day models for predicting emergence, with first adults appearing around 580-600 growing degree days (base 50°F) in Tennessee, typically mid-May. Management recommendations emphasized cultural practices as the primary defense, with irrigation proving remarkably effective at preventing attacks. Research demonstrated that properly irrigated transplants experienced very low beetle damage, and even the presence of weeds or cover crops around tree bases provided significant protection by shading trunks and reducing stress-induced chemical signals that attract beetles. Chemical control options were thoroughly reviewed, with imidaclopride systemic drenches remaining the most effective treatment, providing up to three years of protection when applied at transplant. Alternative products including Acelepryn and Mainspring showed variable results, while trunk spray applications with bark penetrants required monthly applications throughout the beetle flight period. Dr. Addesso also discussed non-chemical options including white latex paint for orchard trees and the importance of preserving parasitic wasp populations that provide natural biological control. The presentation concluded with practical recommendations for reducing drought stress, avoiding herbicide drift that stimulates attacks, and implementing integrated management strategies appropriate for both nursery production and landscape installations.
YOUTUBE TIMESTAMPS
0:00 Introduction and Welcome
1:22 Dr. Karla Addesso Introduction
1:49 Tennessee State University Nursery Research Center Overview
2:42 Research Philosophy: Focus Areas for Woody Ornamentals
4:09 Introduction to Flathead Borers
4:46 Larvae Morphology: Why Called “Flathead”
5:05 Emerald Ash Borer and Invasive Species Context
5:22 Focus on Genus Chrysobothris
5:52 Species Diversity and Distribution in North America
6:10 Flathead Apple Tree Borer: The “Problematic” Common Name
6:41 Life Cycle Overview: Adult Emergence and Egg Laying
7:31 Seasonal Timing Adjustments for Different Regions
8:06 Larval Development Under Bark
8:52 When Damage Becomes Visible: October-November
9:08 Frass and Bark Breaking Symptoms
10:04 Exit Holes and Spring Emergence
10:39 Feeding Location: Phloem and Cambium vs. Heartwood
11:05 Most Susceptible Trees: Newly Transplanted and Drought-Stressed
11:34 Suckering, Premature Fall Color, and Other Symptoms
12:29 Species Identification Challenges Begin
13:06 The Flathead Apple Tree Borer Complex
13:34 Why Accurate Species ID Matters: Host Specificity
14:06 Chrysobothris femorata vs. quadriimpressa: Maple vs. Oak
14:42 Morphological Identification: Nine Similar-Looking Species
15:06 Traditional Beetle Identification Methods
15:30 Male Genitalia Dissection for Species ID
16:03 Female Identification Challenges
17:10 Genetics: University of Tennessee Research Team
17:42 Genetic Challenges with Closely Related Species
18:04 Interbreeding and True Species Questions
19:09 Chihuahua vs. German Shepherd Analogy
19:36 Larval Identification Using Genetics
20:12 Raising Larvae to Adult Stage: Time-Consuming Process
20:33 California Pear Fruit Infestation Discovery
21:12 Chrysobothris in Fruit: An Unprecedented Finding
21:52 Pacific Flathead Borer Confirmed in Fruit
22:23 Potential Host Shift from Wood to Fruit Tissue
23:01 Why Beetles May Seek Moisture in Fruit During Drought
23:37 Can Larvae Complete Development in Fruit?
24:01 Adults Successfully Emerged from Dried Fruit
24:27 Chemistry and Insect Communication
25:05 Cuticular Waxes and Chemical Profiling
26:02 Wax Profiles Can Distinguish Species
26:22 External Appearance: Boring vs. Spectacular Under Wings
27:09 Spectral Analysis: What Beetles See That We Don’t
27:46 Dorsal vs. Ventral Abdomen Color Differences
28:09 Museum Specimen Analysis Using Color Spectroscopy
28:22 Scouting Challenges: You Won’t Find Eggs or Adults
29:00 Egg Appearance and Placement
29:46 Purple Sticky Traps for Monitoring
30:08 Color Vision: Blue and Red Regions
30:27 Work with Chrysobothris femorata in Southeast
30:44 Trunk Mimic Traps vs. Panel Traps
31:26 Visual Cues: Small Tree Trunks Attract Beetles
32:08 Trap Effectiveness in Different Systems
32:52 Growing Degree Day Models for Emergence Prediction
33:18 Base Temperature: 50°F Starting January 1
33:31 Pupation Timing: Late March to Early April
34:01 First Adults Inside Tree: Around May 6th at 580 GDD
34:20 Sclerotization: Hardening Before Emergence
35:02 Mid-May Emergence: Consistent Timing
35:18 Shimat’s Participation in Multi-State Data Collection
35:47 Species Emergence Variation
36:02 How Small of a Tree Will They Attack? Very Small
36:41 Smaller Trees May Establish Better Despite Attack Risk
37:32 Scouting Tips: Southwest Side of Trees
37:44 Herbicide Drift Stimulates Attacks
38:22 Management Practices Begin
38:30 Horticultural Practices: Focus on Irrigation
39:01 Drought Stress as Red Flag for Attacks
39:08 Systemic Drenches: Imidacloprid at Transplant
39:22 Three Years Protection from Single Application
39:54 Neonicotinoid Concerns and Label Compliance
40:08 Application Rate Tables in Extension Publications
40:53 Half the Low Rate Still Effective
41:00 Acelepryn and Mainspring: Inconsistent Results
41:36 Mainspring Shows More Promise
41:48 Trunk Sprays: Challenges and Requirements
42:26 Southeastern U.S. Pest Control Guide Resource
43:07 Mainspring as Trunk Spray with Bark Penetrant
43:29 Monthly Applications: Mid-May Through Mid-July
44:14 White Latex Paint for Orchard Trees
44:39 Surround Kaolin Clay: Not Effective
45:00 Weeds Protect Trees from Borers: Surprising Finding
45:21 Imidacloprid and Herbicide Treatment Study Results
45:59 Cover Crops Provide Protection
46:42 Companion Plantings in Landscape Design
47:18 Foot-Tall Plants Needed to Shade Trunk
47:32 Irrigation Research: Unexpected Results
47:55 No Cover Crop + Irrigation = Very Low Attacks
48:23 Container Production: Less Borer Problems Due to Irrigation
48:42 Natural Enemies: Parasitic Wasps
49:21 Wasps Lay Eggs in Beetle Larvae Under Bark
49:47 Judicious Insecticide Use Preserves Biocontrol
50:06 Summary: Native Borers Impact Landscape Trees
50:36 Parking Lot Plantings: Perfect Borer Habitat
50:40 Chemical and Non-Chemical Options Available
51:04 Importance of Judicious Pesticide Use
51:17 Funding Acknowledgment: USDA NIFA and Southern SARE
51:39 QR Code for Publications and Extension Materials
51:54 Closing and Transition to Q&A
52:05 Question: Imidacloprid Availability
52:36 Answer: Generic Products Available, Check Concentrations
53:19 Final Thanks and Contact Information
QUESTIONS & ANSWERS
Q: What makes flathead borers difficult to identify to species level?
A: There are over 140 Chrysobothris species in North America that are extremely similar in appearance. Even expert entomologists have difficulty distinguishing species, requiring dissection of male genitalia for identification. Female beetles are often indistinguishable morphologically. The species historically called “flathead apple tree borer” (Chrysobothris femorata) actually represents a complex of closely related species that may still be interbreeding.
Q: Why is accurate species identification important for management recommendations?
A: Different Chrysobothris species are often host-specific and emerge at different times. For example, Chrysobothris quadriimpressa prefers oaks while C. femorata prefers maples. Some species emerge earlier or later in the season. Knowing which species is present allows professionals to target management efforts appropriately and determine which trees in a landscape are at risk.
Q: What new research tools are being developed to identify these beetles?
A: Researchers are exploring multiple approaches including genetic analysis (DNA sequencing), chemical profiling of cuticular waxes on beetle surfaces, and spectral analysis of coloration at wavelengths humans cannot see. The genetics tools have successfully enabled identification of larvae without raising them to adult stage, which previously took many months. Chemical wax profiles can distinguish females that look identical under microscopy.
Q: What was the significance of finding Chrysobothris larvae in California pear fruit?
A: This was unprecedented—Chrysobothris beetles feed under tree bark, never previously in fruit. Genetic analysis confirmed the larvae were Pacific flathead borer, a common western species, not an invasive pest. Researchers successfully reared adults from dried fruit, proving larvae can complete development. This suggests a possible host shift from woody tissue to fruit tissue, potentially driven by drought stress, which could transform these from ornamental pests into direct crop pests.
Q: When do flathead borers typically emerge in the Southeast?
A: Adults emerge in mid-May in Tennessee, around 590-600 growing degree days (base 50°F from January 1). In Georgia and areas further south, emergence likely occurs in early May, while northern areas may see emergence one to two weeks later. Pupation begins in late March to early April. Using growing degree days provides more reliable timing than calendar dates because seasonal temperatures vary year to year.
Q: What type of traps work best for monitoring Chrysobothris beetles?
A: Purple sticky traps designed as trunk mimics work much better than panel traps for Chrysobothris. These beetles appear to use visual cues resembling small tree trunks or branches when seeking host plants. Panel traps (like those used for emerald ash borer) are less effective. Trunk mimics work best in full sun nursery settings; they’re less effective in mature orchards with heavy canopy shade.
Q: What trees are most susceptible to flathead borer attack?
A: Newly transplanted trees and drought-stressed trees are most vulnerable. Trees with mechanical injuries or graft unions are particularly attractive because these represent weakened tissue. Beetles can successfully infest very small trees—research shows trees as small as a quarter-inch diameter can be attacked. Southwest-facing sides of trunks receive the most attacks because beetles need heat for larval development.
Q: What is the most effective chemical treatment for flathead borers?
A: Imidacloprid applied as a systemic drench at transplant remains the most effective treatment, providing approximately three years of protection for young trees. Research shows that even half the lowest labeled rate is effective. Alternative products like Acelepryn and Mainspring have shown inconsistent results, though Mainspring applied as a trunk spray with bark penetrant shows promise in recent trials.
Q: Are there effective non-chemical management options?
A: Yes. Irrigation is remarkably effective—research found that irrigated transplants had very low beetle attacks even without insecticides. Cover crops and even weeds around tree bases provide protection by shading trunks. In orchards, painting trunks with white latex paint reduces attacks, likely by disrupting visual cues beetles use. Maintaining plant health through proper horticultural practices is the primary defense.
Q: How does irrigation protect trees from flathead borers?
A: Drought-stressed trees emit chemical signals that attract beetles. Properly irrigated trees don’t produce these stress signals. Field research showed that new transplants with irrigation but no cover crops had basically very low beetle attack numbers. This explains why container production sees fewer borer problems—containers require consistent watering, eliminating the drought stress that makes field-grown trees vulnerable. Irrigation is especially critical during the first year of establishment.
Q: Does herbicide application affect flathead borer attacks?
A: Yes, herbicide drift significantly stimulates attacks. Research demonstrated that accidental trunk contact with herbicides like glyphosate (Roundup) makes trees much more attractive to beetles—they can actually smell the difference between herbicide-treated and untreated trees. You don’t need to hit the foliage; just overspray on the trunk is sufficient to trigger attacks. Professionals should be very careful with herbicide applications around valued trees.
Q: Are there natural enemies that control flathead borer populations?
A: Yes, several species of tiny parasitic wasps attack Chrysobothris larvae. These micro-wasps run along tree trunks and can hear and smell beetle larvae underneath the bark. They pierce through the bark to lay their eggs, and their larvae feed on the beetle larvae. Research found multiple species including some previously unreported. Judicious insecticide use helps preserve these beneficial insects that provide natural biological control.
ADDITIONAL RESOURCES
Dr. Karla Addesso Contact:
Tennessee State University Nursery Research Center
McMinnville, Tennessee
Email: Available through TSU Extension
Extension Publications Referenced:
- Southeastern U.S. Pest Control Guide (NC State Extension website)
- TSU Flathead Borer Management Guide (includes imidacloprid application rate tables)
Research Collaborators:
- University of Tennessee genetics team
- Multi-institutional team led by Dr. Addesso and Dr. Shimat Joseph (UGA)
- California colleagues (Pacific flathead borer research)
Funding:
- USDA NIFA (National Institute of Food and Agriculture)
- Southern SARE (Sustainable Agriculture Research and Education)
Website: QR code provided in presentation links to updated publications and extension materials on flathead borer management.
For questions about flathead borer identification and management in nursery and landscape systems, contact Dr. Karla Addesso at Tennessee State University or Dr. Shimat Joseph at UGA Extension.