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REDBAY AMBROSIA BEETLE

 Redbay Ambrosia Beetle, Photo by Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org, CC BY 3.0 US

Florida’s $100 million avocado industry faces grave danger from the redbay ambrosia beetle and related insects, which transmit the pathogen responsible for laurel wilt, a fungal disease that kills avocado trees.

Estimated losses: $4.2 million in lost trees, $450,000 per year in lost future avocado sales from those trees. 

The redbay ambrosia beetle is a tiny insect that colonizes the sapwood of trees in the Laurel Family, which includes native trees such as redbay and swampbay and the fruit crop avocado. The beetle transmits a pathogenic fungus to host trees, causing a disease known as laurel wilt. Currently, it is believed that laurel wilt disease is also spread by several additional ambrosia beetle species in South Florida. The disease has been documented to kill 98 percent of infected native host trees.

The redbay ambrosia beetle was first reported in the U.S. in 2002, in Savannah, Ga., on the Atlantic coast. In 2003-2004, scientists recognized the connection between the beetle and laurel wilt disease. By then, the beetle had begun expanding its initial range, spreading north and south along the coast, as well as moving inland. Laurel wilt disease killed millions of native redbay trees in Georgia and South Carolina within two to three years of its establishment. In Florida, the laurel wilt was first reported in Jacksonville in 2005, and the nation’s first confirmed avocado tree death from laurel wilt occurred in Jacksonville in 2007.

In 2011, a redbay ambrosia beetle was captured in Miami-Dade County, home of the state’s avocado industry, which has a total economic impact of about $100 million annually. The first reports of laurel wilt disease in commercial avocado trees occurred in 2012. As of May 2016, the disease has killed about 12,000 commercial avocado trees, or 1.5 percent of the state’s inventory. Recent UF/IFAS research has implicated not only the redbay ambrosia beetle, but other ambrosia beetles as capable of transmitting the laurel wilt pathogen in Florida avocado groves. Growers are taking steps to discourage fungal infections and reduce populations of the ambrosia beetles. However, there is no cost-effective cure for laurel wilt disease and its impact on the industry may increase in years to come.

BASICS

Common Name: Redbay ambrosia beetle

Scientific Name: Xyleborus glabratus

Good Bug or Bad Bug? Bad Bug

What It Is: A small beetle that’s part of the insect order Coleoptera, as are all beetles. Within the Coleoptera order, the redbay ambrosia beetle is part of the family Curculionidae, the true weevils. Furthermore, within the Curculionidae family, this pest is one of about 3,400 species of weevil that comprise a highly specialized sub-family, commonly known as ambrosia beetles. The term “ambrosia” originated in Greek mythology, it was a divine (and fictitious) food that sustained the gods. In entomological lore, “ambrosia” is a reasonable adjective to use in describing these beetles because they cultivate their own food – something so rare among insects that it seems almost miraculous.

To produce food, ambrosia beetles carry fungal spores everywhere they go, and grow fungal “gardens” inside galleries excavated in the trees they colonize. The redbay ambrosia beetle is associated with a fungus known scientifically as Raffaelea lauricola, the pathogen responsible for laurel wilt disease. Scientists once believed that each ambrosia beetle species was associated with only one species of fungus, but recent studies have shown that some ambrosia beetle species associate with more than one fungus, sometimes carrying spores from multiple fungal species at the same time.

What It Does: All ambrosia beetle species can carry fungal spores on their exoskeletons and in specialized fungal carrying pouches called mycangia. When adult ambrosia beetles colonize a host tree they first bore holes in the trunk to gain entry, then excavate tunnels known as galleries through the sapwood. There, the beetles begin cultivating fungus in some galleries, by depositing spores they keep stored in their mycangia. The beetles farm the fungus and use it as their only food source.

The redbay ambrosia beetle colonizes trees in the Laurel Family. Unlike many ambrosia beetles, this species will readily colonize healthy trees, as UF/IFAS research has demonstrated. It carries and cultivates a fungus that’s deadly to host trees, Raffaelea lauricola. As the fungal gardens grow, they cause the host tree to weaken and potentially die, apparently because the tree reacts to the fungal infection by reducing the activity of its xylem, the equivalent of the tree’s circulatory system. In a worst-case scenario, laurel wilt disease can kill a tree within four to eight weeks after the initial infection.

Who Is Affected: The most obvious stakeholder group affected is the Florida avocado industry, which involves about 7,000 acres and 500 growers, almost all in Miami-Dade County. Florida is the nation’s second-largest avocado producer, after California, and avocado represents the state’s second-largest fruit tree industry, after citrus. Florida growers produce primarily green-skinned avocados, which represent about 12 percent of U.S. avocado production and generate about $100 million in total output contribution. Because laurel wilt disease has begun killing commercial avocado trees, the growers’ livelihood is in jeopardy.

In addition, some Florida residents are affected because laurel wilt disease has killed an unknown number of the state’s estimated 250,000 dooryard avocado trees, including the first confirmed avocado tree death caused by laurel wilt disease, in Jacksonville in 2007.

Finally, in both landscaped and natural environments, laurel wilt disease is believed to have killed millions of redbay trees since it was first reported in the Savannah, Ga. area in 2002 and the beetle began spreading. Experts have cautioned that continued loss of laurel-family trees in natural ecosystems could have a cascading effect that harms other species, similar to the consequences that followed the mass tree die-offs caused by U.S. outbreaks of Dutch elm disease and chestnut blight in the 20th century.

Where It’s Found in Florida: As of May 2016, laurel wilt disease has been reported in 61 of Florida’s 67 counties – presumably, the redbay ambrosia beetle is present in those counties as well. The only counties that have not yet reported laurel wilt disease are located in the Panhandle – Escambia, Franklin, Gulf, Okaloosa, Santa Rosa and Wakulla counties. The location of these apparently unaffected counties is perhaps unsurprising, considering that the redbay ambrosia beetle was first detected in the U.S. along the Atlantic coast, and may have spread north and south more quickly than it spread west.

The redbay ambrosia beetle’s progression into peninsular Florida was tracked by scientists who were concerned about the possibility of laurel wilt disease devastating the avocado industry if the beetle reached Miami-Dade County, at the southeastern tip of the state. Experts believe that the redbay ambrosia beetle expanded its range steadily through its own efforts, partly because the insect was able to colonize wild redbay, swampbay and sassafras trees, as well as dooryard avocados. Furthermore, experts believe that the beetle was sometimes introduced to new areas inadvertently when people transported firewood and other untreated wood items that harbored the beetle.

Scientists have relatively little data on the presence of laurel wilt disease in the state’s interior, particularly in natural environments. Avocados do not grow wild in Florida but many trees in the laurel family are found in natural ecosystems, notably redbay, swampbay and sassafras, as well as silkbay, pondspice, and the endangered pondberry. Improved management methods are urgently needed by avocado growers, but ultimately the state may face a greater challenge in trying to protect wild Laurel-Family trees from laurel wilt disease.

How It’s Currently Addressed: Management strategies for the redbay ambrosia beetle fall into three categories – monitoring efforts that indicate laurel wilt and, by implication, ambrosia beetles are present, strategies for protecting trees from the laurel wilt pathogen and ambrosia beetles, and outreach efforts aimed at the public to discourage activities that might establish the beetle and disease in new areas.

Monitoring has proven useful but has also revealed that Florida’s commercial avocado groves are inhabited by numerous species of ambrosia beetle, raising the possibility that more than one beetle species transmits the pathogen responsible for laurel wilt disease.

Strategies for protecting trees include supportive care such as providing appropriate irrigation and fertilization, and promptly destroying laurel wilt affected trees. Some growers have begun applying fungicides and/or insecticides to their groves, as precautions intended to reduce fungal presence and ambrosia beetle populations. However, the effectiveness of these measures depends upon the economic cost, timely implementation and consistent application. There is one systemic fungicide available for commercial avocado producers and native trees in the Laurel Family. There are several contact chemical and biological insecticides registered to control ambrosia beetles but their efficacy, cost and application frequency varies. Also, it can be difficult to ensure that insecticides reach redbay ambrosia beetles, because the insects spend much of their time in the galleries they excavate in host trees.

Outreach efforts are aimed at raising public awareness of laurel wilt disease, educating property owners about tell-tales symptoms exhibited by infected trees, and urging Florida residents and visitors to avoid transporting firewood and similar untreated wood items that could harbor ambrosia beetles.

BACKGROUND

Native to Florida? No. The redbay ambrosia beetle is native to Southeast Asia. It was first reported in the United States in the Savannah, Ga. area in 2002 and is believed to have arrived unnoticed in pallets, packing materials or wood products shipped from overseas. In 2003-2004, scientists recognized the connection between the beetle and laurel wilt disease. Laurel wilt was first reported in Florida in 2005, in the Jacksonville area. In 2007, the first known U.S. avocado death attributable to laurel wilt disease occurred, also in Jacksonville. Since 2007, the disease and redbay ambrosia beetle has spread southward down Florida’s east coast to Miami-Dade County, and simultaneously spread westward across the peninsula and into some parts of the Panhandle. Laurel wilt disease has been reported in 61 of Florida’s 67 counties, and the beetle is present in habitats where the disease is found. Laurel wilt and the redbay ambrosia beetle has also been reported in nine states: North Carolina, South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, Texas, and Arkansas.

Big Money Associates: About 30 species of ambrosia beetles are established in Florida, several of them non-native. They all live in symbiosis with fungi that they cultivate and consume. Apart from the redbay ambrosia beetle, it’s uncertain how many other species found in South Florida pose a serious threat to avocado. However, laboratory studies by UF/IFAS researchers have demonstrated that several ambrosia beetles found in Miami-Dade County are capable of carrying and transmitting the fungus responsible for laurel wilt disease.

Interesting Fact: One ambrosia beetle species found in Australia, Austroplatypus incompertus, exhibits social behavior. When a fertilized female nests, she is attended by a small group of unfertilized females that protect and nurture her. It’s rare to find social behavior in insects, apart from members of the orders Hymenoptera (ants, bees and wasps) and Isoptera (termites). This is the first reported example of social behavior in the order Coleoptera (beetles). For more information on insect orders, see the blog post on our Bug Week website, “What Are Arthropods, Anyway?”

IMPACTS

Estimated Losses: As of May 2016, the Florida avocado industry had lost 12,000 mature, productive trees, valued at $350 each. They represented about 1.5 percent of the state’s commercial avocado tree inventory. The lost trees had a total value of $4.2 million, and the resulting losses in future production will equal about $450,000 per year in farmgate revenue.

Estimated Management Costs: Growers are encouraged to scout their groves for laurel wilt infestations regularly. The average cost for professional scouting is $30 per acre per visit, with a minimum of about 12 visits needed per year. Total cost: $360 per acre per year.

It should be kept in mind that Florida’s avocado industry had historically enjoyed a large degree of freedom from pests and diseases. Until laurel wilt disease emerged, the primary disease threat to the industry was phytophthora root rot, which typically appeared in the wake of heavy rains that resulted in flooding. Therefore, growers were not accustomed to investing the amount of money on crop protection that laurel wilt disease demands.

RESPONSE

What Is UF/IFAS Doing About It? UF/IFAS personnel have led the effort to investigate the biology and control of ambrosia beetles and the laurel wilt pathogen in commercial avocado groves,  develop early detection technology of laurel wilt through spectral photography and analysis, develop methods to combat laurel wilt disease, and advise growers on management practices. The UF/IFAS personnel most heavily involved in addressing laurel wilt disease include two plant pathologists, several entomologists, a tropical fruit Extension specialist, a food and resource economist, all based at the UF/IFAS Tropical Research and Education Center in Homestead, in the heart of the state’s commercial avocado industry.

Among their accomplishments, UF/IFAS researchers and Extension personnel have achieved the following:

  • Carried out experiments and monitoring that demonstrated other ambrosia beetles besides the redbay ambrosia beetle pose a threat of spreading laurel wilt in commercial avocado groves.
  • Evaluated numerous fungicides and insecticides for effectiveness and cost, and advised growers of their findings.
  • Investigated possible repellents and attractants that could be used to keep repel ambrosia beetle away from commercial avocado groves, or lure them to traps.
  • Evaluated almost 30 avocado varieties grown in Florida, to assess their tolerance to laurel wilt disease, and advised growers of their findings.
  • Developed a diagnostic test that can detect the fungus that causes laurel wilt disease and delivers results in less than 24 hours.
  • Designed a data-analysis algorithm that can be used to evaluate aerial photos of avocado groves, and identify trees infected with laurel wilt disease before symptoms are visible to the naked eye.
  • Searched for resistance factors in avocado trees that might enable breeders to develop resistant avocado varieties.
  • Made numerous live presentations and generated many scientific papers, technical documents, photographs, videos, PowerPoint presentations, web pages and other outreach materials aimed at reaching audiences that included laypeople, growers, industry personnel, scientists, lawmakers and agency employees.

What Can YOU Do About It? As with many of Florida’s challenges involving invasive species, residents and visitors are in a position to help. In this case, there’s a web page on the Florida Department of Agriculture and Consumer Services’ website, “Save the Guac,” which is designed for laypeople and contains background information on laurel wilt disease and steps that can help discourage its spread. http://www.freshfromflorida.com/Divisions-Offices/Plant-Industry/Save-the-Guac

Perhaps the most important contribution the average Floridian can make is to avoid purchasing non-local and/or non-certified firewood, or transporting any unprocessed local wood to other destinations in Florida, or destinations outside Florida. These actions could lead to accidental establishment of ambrosia beetle colonies (or other invasive pests) to previously unaffected areas. In fact, it’s believed that the beetle was introduced to Central Florida via infested wood in 2007, an event that accelerated the beetle’s progress toward Miami-Dade County, home to Florida’s commercial avocado industry.

Finally, if you’re thinking about adding any laurel-family trees to your property, it’s prudent to buy trees only from registered nurseries. These businesses are typically operated by individuals with longtime interest in horticulture, who will do their best to ensure they offer only pest-free, disease-free stock.

FURTHER INFORMATION

Read more about the redbay ambrosia beetle in this “Featured Creatures” document produced by the UF Entomology and Nematology Department. http://entnemdept.ufl.edu/creatures/trees/beetles/redbay_ambrosia_beetle.htm

Read more about laurel wilt disease in this document from the EDIS online Extension library.

https://edis.ifas.ufl.edu/hs379

To learn more about Florida’s common ambrosia beetles, visit this UF/IFAS document. http://edis.ifas.ufl.edu/pdffiles/FR/FR38900.pdf

Photo by Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org, CC BY 3.0 US

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