1. 1 Mississippi State University 2 University of South Alabama, Mobile
Impacts of Laurel Wilt Disease on Insect Herbivores of North American Lauraceae
Natalie A. Dearing1, John P. Formby1, Adam D. Chupp2, Hannah M. Bares1, Richard L. Brown1 and John J. Riggins1
1 Mississippi State University
2 University of South Alabama, Mobile
MSU
Forest Entomology
Abstract:
The redbay ambrosia beetle (Xyleborus glabratus) is an invasive wood-boring insect originating from southeast Asia, and carries the fungus responsible for laurel wilt disease (Raffaelea lauricola). Laurel wilt is causing widespread mortality in redbay (Persea borbonia), swampbay (Persea palustris), and sassafras (Sassafras albidum), and has potential to decimate at least 8 other North American trees and shrubs within Lauraceae. Lauraceous trees under attack by laurel wilt provide a vital food source and habitat for many native insect herbivores. The purpose of this study is to determine the risks native North American forests insects face from the mass die-off of their lauraceous hosts. A preliminary literature review is ongoing, and all insects reported associated with North American laurels were assigned a risk rating based on their level of specialization on laurel hosts. We found that ~9% of all insects associated with Lauraceae are specialist herbivores of laureaceous hosts. Laurel wilt could have dramatic impacts on native forest insects as this disturbance continues to radiate outwards through time, space, and trophic levels.
Methods:
An exhaustive literature search was performed on the 11 susceptible Lauraceous tree and shrub species to determine which herbivores are associated with those plants. A database of all arthropod herbivores of susceptible lauraceous species from North America north of Mexico was created, excluding non-native insects. Each insect was categorized by feeding guild, and all known host plants were recorded. An endangerment risk rating of 1-5 (1=highest risk, 5=lowest risk) was then assigned based on the number of non-lauraceous hosts and degree of specialization to LWD susceptible host species. Risk rating assignment criteria is as follows:
1= Redbay/Swampbay specialists
4 = triphagous, eating 2 non-Lauraceous host species
2 = monphagous on lauraceous species
5 = polyphagous eating 3 or more non-Lauraceous host species, or specialist on non Lauraceae
3 = biphagous, eating one non-Lauraceous host species
Introduction:
Laurel wilt disease (LWD) is a deadly disease of redbay (Persea borbonia) (Fig. 1) and other Lauraceae
Discovered near Savannah, GA in 2004
Spread across the southeast as far as Texas
Males are flightless and sexually dimorphic
Females are highly attracted to redbay trees, which can be killed after inoculation by a single beetle (Fig. 2)
LWD is decimating redbay (Persea borbonia) populations and rapidly spreading across the southern coastal plain
Loss of susceptible hosts may lead to the decline and possible endangerment of specialists like the palamedes swallowtail (Fig. 3)
Could lead to multi-trophic cascade effects across the southeastern Coastal Plain, recently listed as the World’s 37th biodiversity hotspot A B
Figure 1: After attack by the redbay ambrosia beetle (A), inoculated redbay trees quickly exhibit characteristic wilted foliage (B) and vascular streaking (C) caused by the pathogen it carries. C
Preliminary Results and Discussion:
~200 arthropod herbivores of laurel wilt hosts were identified from North America north of Mexico
~170 additional arthropod herbivores were recorded from Mexico and Central/South America (not included in subsequent analyses)
~9% of species recorded specialize on laurels only (risk ratings 1-2, Fig 4A) and have the greatest risk of strong effects from host mortality from laurel wilt disease
Lepidoptera and Coleoptera comprise the largest percentages of arthropod herbivores potentially affected by laurel wilt disease (Fig. 4B)
Most common feeding guilds (risk ratings 1-3) of arthropods at greatest risk from LWD are Phyllophages (leaf feeders, 78%), Xylophages (wood feeders, 13%), Carpophages (fruit feeders, 5%), and sap suckers (4%) (Fig. 4C)
Impacts of LWD are not limited to these first-level trophic effects and will continue to radiate throughout ecosystems of the Southeastern Coastal Plain
Although currently not as well vetted, our data from Mexico, Central, and South America indicate impacts may continue into forests there that are global hotspots for diversity and endemism of Lauraceae A
Hosts:
avocado (Persea americana)
California laurel (Umbellularia californica)
camphor tree (Cinnamomum camphora)
lancewood (Ocotea coriacea)
pondberry (Lindera melissifolia)
pondspice (Litsea aestivalis)
redbay (Persea borbonia)
sassafras (Sassafras albidum)
silk bay (Persea borbonia var. humilis)
spicebush (Lindera benzoin)
swamp bay (Persea palustris) B
Figure 2: Laurel wilt disease cycle. C
Figure 3: The endemic Papilio palamedes swallowtail butterfly is an obligate herbivore of redbay/swampbay. It is also the primary pollinator of the yellow-fringed orchid
Causative Agents:
- Xyleborus glabratus, non-native insect vector (Fig. 2A)
- Raffaelea lauricola, exotic fungus
Acknowledgements:
Funding provided by Region 8 FHP, Mississippi Forestry Commission, and the Mississippi Agricultural and Forestry Experiment Station.
Contact:
Natalie A. Dearing
Undergraduate Research Assistant
Box 9775
Mississippi State, MS 39762
(662)
Figure 4: The percentage of Laurel Herbivores within each endangerment risk category (A). Percentage of herbivores with risk ratings 1-3 within each order (B). Number of herbivores with risk ratings 1-3 in each feeding guild separated by order.
Photo: A. Chupp
Palamedes Swallowtail Larva and Eggs on Redbay