Deadly Beetle Threatens Palm Trees

The South American palm weevil has destroyed hundreds of Canary Island date palms, says UC Riverside entomologist

Photo shows Rhynchophorus palmarum, commonly known as the South American palm weevil.Photo credit: CISR, UC Riverside.

RIVERSIDE, Calif. – A palm tree-killing insect that is already established in southern San Diego County in California could spread elsewhere, warns an entomologist at the University of California, Riverside.

The beetle, called the South American palm weevil, threatens California’s Canary Island date palms – these are palms that have the top region pruned to look like a pineapple – and date-growing gardens in the desert.

“It has already killed hundreds of Canary Island date palms in Tijuana and parts of San Diego County,” said Mark Hoddle, the director of the Center for Invasive Species Research at UC Riverside.  “We are on the verge of a major crisis for California’s palms.”

The South American weevil (R. palmarum) is native to parts of Mexico, Central and South America and the Caribbean. It has invaded Southern California most likely by flying into urban areas from infested palms in Tijuana. These distances are only about 3 miles, and lab studies suggest this weevil can fly 15 miles in a day.

Weevil larvae feed inside the crown and this damage kills palms within months. Weevils are vulnerable to properly applied pesticides. Another palm weevil from Indonesia, a close cousin of the South American weevil, was found in Laguna Beach in Orange County in October 2010. It was eradicated by Hoddle and others in January 2015.

A dead Canary Island date palm killed by the South American palm weevil in San Ysidro, San Diego County, Calif. Note the “halo” of fronds around the trunk apex. Photo credit: CISR, UC Riverside.

“Besides ornamental Canary Island date palms, the South American palm weevil poses a significant threat to date growers in California and Arizona,” said Hoddle, an extension specialist in the Department of Entomology.

The threat posed by South American palm weevil could be greatly increased if a palm-killing nematode, the red ring nematode, is found in California. So far, the red ring nematode – which is spread from palm-to-palm by the weevils – has not been detected. But it is known to be in Mexico.

Adult South America weevils are large beetles, 30 to 40 mm long when measured from the tip of the snout to the back of the abdomen. The female uses the long, slender snout to penetrate palm tissue and create access wounds in which eggs are deposited. Adult weevils are predominately black in the most typical form.

“We don’t know how far the weevil has spread in California,” Hoddle said. “We are relying on the public to be our eyes and to report suspicious looking palms.”

The Center for Invasive Species Research at UC Riverside has set up a website where suspect palms can be reported.

Besides San Diego County, Canary Island date palms are found throughout California.

“They are truly one of the most iconic trees in the urban landscape,” Hoddle said.

More information on the South American palm weevil invasion into California is available here: http://cisr.ucr.edu/palmarum.html.

 

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Mark Hoddle
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