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News Article

A new repellent could deter pest from Avocado trees


The redbay ambrosia beetle is a vector of the laurel wilt fungus which can kill Avocado trees

Avocados grown in Florida bring around $100 million a year into its economy.  They are primarily grown in southern Miami-Dade County, but growers have been battling the laurel wilt fungus (Raffaelea lauricola) a lethal vascular wilt disease, which can kill avocado and redbay trees, since it was first detected in monitoring traps in Savannah, Georgia in 2003.  However, researchers from the University of Florida Institute of Food and Agricultural Sciences have discovered an effective repellent that is less expensive than current insecticides.

The invasive redbay ambrosia beetle (Xyleborus glabratus) which is native to Asia, first arrived in the United States in 2002, most likely through solid wood packing material.  They have a symbiotic relationship with the laurel wilt fungus, carrying the fungal spores on their bodies.  When the beetles bore into the sapwood of the host tree, the galleries that are formed become inoculated with the spores, which then germinate and infect the tissue of the host tree.  This disrupts the flow of water and nutrients and the trees wilt within weeks.  The fungus can spread to other trees because the roots of avocado trees connect to each other underground over time. So if one tree becomes infected, the disease can spread through the roots to the adjoining trees.

Over 12,000 avocado trees have already been lost in Florida, due to the pathogen, which, last year was recorded in 61 out of 67 Florida counties.  Given its rapid spread, the fungus represents a significant threat to the commercial avocado growers of the region.

During the study, the researchers found that when infected with the laurel wilt fungus, redbay trees, which are closely related to the avocado, produce methyl salicylate to repel the insects which gave the tree the fungus in the first place.  The team compared the number of beetles captured on sticky traps that were disposed on redbay tree logs.  Ten weeks later, they examined the holes dug by the beetles into the logs, because that is when the beetles transmit the fungus. 

Three different blends of repellents were then tested, and they found that verbenone and verbenone plus methyl salicylate, which is produced by the infected redbay tree, were the most efficient.  When the researchers applied the repellents onto the redbay logs, the number of beetles captured on sticky traps was reduced by 95% and the number for boring holes by 90 percent.

“We believe that these repellents could be used in a larger context, if associated with bug lures to have a push-pull system,” said Marc Hughes, a former postdoctoral researcher in the Forest Pathology Laboratory in UF/IFAS School of Forest Resources and Conservation.  The repellents drive the beetles away, while the lures, or “attractants”, pull them towards traps, where they are killed.  “Attractants would be placed outside the avocado groves, while avocado trees will be treated with repellent.”

As well as being an effective repellent, methyl salicylate is about 80 percent cheaper than verbenone.  While there are some fungicides available for avocado growers, they are expensive.  Insecticides are not very efficient at repelling the insects, as they spend most of their time within the wood.  The new repellents are insecticide free, which is a sustainable way to protect the trees, said co-author Xavier Martini. 

Further information on redbay ambrosia beetles, the laurel wilt fungus and avocado trees is available to subscribers of the Forest Science database.  Using the search string ("redbay ambrosia beetles" OR "Xyleborus glabratus") AND "Persea americana" yields 40 records.  ("Raffaelea lauricola" OR "Laurel wilt") AND "Persea americana" yields 51 records and "Xyleborus glabratus" AND "forest pests" yields 26 results. 

Further information on the distribution of the redbay ambrosia beetle (Xyleborus glabratus) is available on the open access CABI Invasive Species Compendium

Subscribers of the Forestry Compendium can access further information on the Avocado Tree (Persea Americana)

Journal Reference

M. A. Hughes, X. Martini, E. Kuhns, J. Colee, A. Mafra-Neto, L. L. Stelinski, J. A. Smith. Evaluation of repellents for the redbay ambrosia beetle, Xyleborus glabratus, vector of the laurel wilt pathogenJournal of Applied Entomology, 2017; DOI: 10.1111/jen.12387

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 07 March 2017
  • Source
  • Institute of Food and Agricultural Sciences
  • Subject(s)
  • Forest trees