Asian beetle destroying Wetland Preserve trees

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Gardena’s newest resident, a small beetle, has been causing big problems for the city’s Willows Preserve. Tens of thousands of the bugs, called Ambrosia Beetles, have invaded the Gardena Willows Wetland Preserve, leaving a path of damaged and destroyed trees in its wake.

Kelley Dawdy, a certified arborist and Gardena Willows Wetland Preserve board member, estimated that swarms of the beetles have infected and destroyed between 200 and 300 trees in the preserve.

Gardena’s newest resident, a small beetle, has been causing big problems for the city’s Willows Preserve. Tens of thousands of the bugs, called Ambrosia Beetles, have invaded the Gardena Willows Wetland Preserve, leaving a path of damaged and destroyed trees in its wake.

Kelley Dawdy, a certified arborist and Gardena Willows Wetland Preserve board member, estimated that swarms of the beetles have infected and destroyed between 200 and 300 trees in the preserve.

While most people would consider a small beetle a minor annoyance, when it comes to the preservation of the trees, pest control is an extremely serious matter, especially considering the beetle’s impact on the trees themselves, Willows officials say.

Dawdy said that a pregnant female beetle will find a tree that she likes [trees that the beetles like are called host trees] and then she will dig a hole into the tree and then dig around in the hardwood inside the middle of the tree to make what are called galleries.

At the end of each gallery, the beetle will deposit an egg. The beetle then grows fungus under her chin called ambrosia, which she will leave in the galleries for the larvae to eat once they hatch. Then the beetle will die.

When the eggs hatch, the young beetles will go through their different metamorphic stages within the tree. Sisters and brothers will mate with each other and then the pregnant females will leave and find another tree or another hole in the same tree.

According to Dawdy, the list of host trees includes almost every California-native tree that grows in southern California including the Western Sycamore, Boxelder, Fremont Cottonwood, Scrub Oak, Black Willow and Arroyo Willow. Unfortunately, this list describes every tree in the Gardena Preserve.

Cheral Sherman, vice president of the Friends of the Gardena Willows Wetland Preserve, said that the beetles, which originated in Thailand and Vietnam, arrived in the United States thanks to plants that were brought here from those two countries.

Originally discovered in San Diego, Sherman estimated that the time frame between when the beetles were discovered and their eventual arrival in Gardena was about nine months.

Once the beetles infect the trees, both Sherman and Dawdy admitted that there was not much that could be done to rid the area of the destructive pests since there is no chemical that can kill them, and no natural predators to eat them.

“The problem with invasive pests is that whatever was keeping its population in check in its home country or place of origin, usually doesn’t come with it,” said Dawdy. “So all of a sudden it has unlimited amounts of food, it has weather that it loves, and there’s nothing eating it or getting it sick, or anything. It’s just the perfect environment for it.”

However, just because the beetles can’t be controlled through traditional means doesn’t mean that there are no possible solutions.

Sherman said that one possible solution is to solarize the trees, meaning that the infected trees would be cut down and wrapped in a clear, thick plastic and stored away for two years, hopefully suffocating the beetles living with each tree. While it sounds good, the problem is that the process requires rolls of plastic that are $150 per 100 yards. For more the almost 300 trees affected, that is an expensive proposition.

Another potential solution is to place the infected trees in a woodchipper which would blow the chips in 40-yard roll offs into a net screen to catch any escaping beetles. The chipped wood is then transported to an STA (Seal of Testing Assurance)-approved composting facility where it will be baked for three days at 150 degrees. Once the load cools, it would then be sold as a biodegradable product.

Gardena is not the only affected area. Sherman said that the beetle has already infected 600 trees at UC Irvine and several trees at the Madrona Marsh in Torrance.

Currently, scientists at UC Riverside are working on the development of a bacteria that will at the very least cut down the number of beetles in the affected cities.

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