New invasive beetle-fungus complex discovered in Riverside and San Diego Counties

December 6th, 2013 by Iqbal Pittalwala in Biology / Ecology
A box elder (Acer negundo) tree that has been attacked by the polyphagous shot hole borer. The beetle burrows into the tree, leaving holes. Credit: Eskalen Lab, UC Riverside


A box elder (Acer negundo) tree that has been attacked by the polyphagous shot hole borer. The beetle burrows into the tree, leaving holes. Credit: Eskalen Lab, UC Riverside

(Phys.org) —A recently discovered beetle-fungus complex that has been causing dieback and mortality to numerous agricultural and landscape ornamental trees in Los Angeles County has been detected in Riverside and San Diego counties.

The fungus Fusarium euwallaceae forms a symbiotic relationship with the beetle that is known as the polyphagous shot hole borer (PSHB, Euwallacea sp.). Together, they cause the disease Fusarium dieback (FD).

"This beetle has also been found in Israel, and since 2009, the beetle-fungus combination has caused severe damage to avocado and landscape there," said Akif Eskalen, an extension plant pathologist at the University of California, Riverside.

Eskalen first discovered the beetle-fungus complex in 2012 on backyard avocado trees in Los Angeles County. Since then, his lab has conducted ongoing monitoring efforts in Southern California to address the problem.

"Our survey efforts show that this pest/disease complex is actively spreading in Los Angeles, Orange and recently San Bernardino, Riverside and San Diego counties," Eskalen said.

When the beetle burrows into the tree, it inoculates the host plant with the fungus, which is carried in its mouthparts in a structure called mycangia. The fungus attacks the vascular tissue of the tree, blocking the transport of water and nutrients from the roots to the rest of the tree, and eventually causing FD and tree mortality. The beetle larvae live in galleries within the tree and feed on the fungus.

When the polyphagous shot hole borer burrows into a tree, it inoculates the tree with a fungus, which, in turn, attacks the vascular tissue of the tree, blocking the transport of water and nutrients from the roots to the rest of the tree. Credit: Eskalen Lab, UC Riverside

FD has been observed on more than 117 different plant species in Southern California, including many species commonly found in urban landscapes. Preferred trees include about one third of the street trees in Southern California, avocado, and nine tree species native to California.

The following is a selective list of host trees:

What to do if you suspect a tree has FD:

Photo shows a polyphagous shot hole borer. The female beetle is about 0.1 inches long. Credit: Eskalen Lab, UC Riverside.

Whom to contact if you find the problem:

If you suspect that this beetle/fungus complex is on your tree, please contact either your local farm advisor, pest control advisor, county Ag Commissioner Office. You may also contact Eskalen at 951-827-3499 or akif.eskalen@ucr.edu.

More information: For more information, see eskalenlab.ucr.edu/

Provided by University of California - Riverside

"New invasive beetle-fungus complex discovered in Riverside and San Diego Counties." December 6th, 2013. http://phys.org/news/2013-12-invasive-beetle-fungus-complex-riverside-san.html