Invasive new beetle threatens tree crops

KIA'I MOKU

Adult Queensland longhorned beetles are attracted to house lights at night. They can be identified by the size — up to 4 inches — and spine-like bumps on either side of their head. -- Hawaii Department of Agriculture photo

In 2009, a resident of Orchidland subdivision in Puna on Hawaii island found a strange beetle with extremely long antennae on the screen door. This report marked the first detection of a new species of longhorned beetle — Acalolepta aesthetica, in Hawaii and in the United States. Lacking an official common name, the beetle is called the Queensland longhorn beetle, reflecting its native home in Australia.

Despite survey efforts by the Hawaii Department of Agriculture, the beetle wasn’t detected again for years, but that first incursion wasn’t a one-off and its population continued to grow. Four years later it was seen again. Sightings increased as the beetles spread across Puna. Over the last three months, the Big Island Invasive Species Committee has received over a dozen reports.

The arrival of this new insect has officials with the DOA concerned. According to DOA entomologist Darcy Oishi, the Queensland longhorned beetle could cause significant damage to citrus and other trees. The larvae tunnel through living wood creating big galleries, similar to termites, but on a much bigger scale, Oishi says, “They make these giant weeping wounds in branches or the trunk of a tree. The damage can cause dieback in a limb or the death of a tree.”

Not much is known about this beetle, perhaps because it’s not a pest elsewhere. Its arrival in Hawaii marks the first time this beetle has acted invasively with potential impacts only now being realized. The list of trees damaged by beetle larvae continues to grow. It’s been found tunneling through lemons, limes and other citrus; Polynesian-introduced trees such as ulu (breadfruit) and kukui; favorite food crops like cacao (chocolate) and possibly avocado; and introduced species such as gunpowder trees and sago palm. As the current world expert on the beetle, the DOA has not identified any natural enemies in Hawaii nor any effective controls methods.

Complicating research on control options is the presence of native longhorned beetles in our state. Important both as wood decomposers and food for native birds, our Cerambycid beetles are one of the many native insects that show amazing rates of adaptive radiation. From what entomologist estimate were three distinct arrivals, over 120 species evolved. One of the largest native insects in Hawaii is a Cerambycid beetle. Measuring 2 inches from tip to tail with sweeping antennae as long as its body, Megopis reflexa is closest in appearance to the invasive Acalolepta aesthetica.

An indication of the presence of the Queensland longhorned beetle is large pinky-sized holes that the larvae leave behind as they exit the tree. The beetle has been found on citrus, breadfruit, kukui and cacao. -- Hawaii Department of Agriculture photo

The new wood-boring pest is not yet known to be on Maui or any of the other Hawaiian islands, but farmers and residents can take steps to prevent its arrival. The best way to keep it from moving interisland is to not bring green woody material between islands, particularly if the vegetation shows signs of damage, such as weeping wounds where a beetle may have laid its eggs and larvae entered the tree.

Be alert to sightings of the beetle, often attracted to houselights at night. The adult measures from 0.75 to 1.75 inches in length. The antennae on the male are twice as long as the body — giving rise to the moniker “longhorned.” Antennae on the female are shorter. On either side of the thorax (the body part behind the head) are two thorn-like spines. The abdomen is dimpled and looks as though covered in peach fuzz. In contrast, the native Megopis beetle has ridges running down the abdomen, giving it a striped appearance.

Oishi also suggests looking for wounding on trees. The beetle larvae can be even larger than the adults, and as they leave the tree to mature they leave behind large holes, up to 0.5 inch in diameter, as big around as a pinky. Other indications are sawdust-like frass being pushed out of holes on the trunk, girdling on trunk, sap oozing from where the adult laid eggs, and branch dieback and drop. Find more details and the official pest advisory on the DOA website: hdoa.hawaii.gov/pi/ppc/new-pest-advisories/.

On Maui, report any suspected sightings. Collect the beetle and contain it in a secure container. Take clear digital photos of the beetle and record the location, type of plant or tree, date and how you found it. If you see damage on a tree, take photos. Use an object (coin or ruler) for reference. Email the photos and the information to: hdoa.ppc@hawaii.gov or report it online through 643PEST.org.

* Lissa Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. “Kia’i Moku,” “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy and quality of life.