Asian longhorned beetle: A threat to hardwood trees in Georgia

The Asian longhorned beetle (Anoplophora glabripennis, ALB; Fig. 1) is an invasive insect pest native to China and North and South Korea that threatens many hardwood trees in forests and landscapes in the USA. The pest is also referred to as the roundheaded borer because the segment below the head is round-shaped. The larval stages of ALB feed on the vascular bundles, and affected trees succumb to death over years of repeated infestations. In addition, larval feeding compromises the structure of tree trunks. With extensive boring activity, those infested trees are vulnerable to falling during storms, endangering lives and property, and saddling homeowners and local governments with tree removal expenses.

Fig. 1. Adult Asian Longhorn beetle. Photo credit: Kenneth R. Law, USDA APHIS PPQ, Bugwood.org

ALB was accidentally introduced to the USA via global trade, possibly in packing materials, such as pallets and crates. It was first positively identified in 1996 in New York. This pest is now reported in Massachusetts, New York, Ohio, Illinois, and South Carolina. Georgia has not reported it to date. Although ALB is not reported in Georgia, it could pose a serious threat to hardwood trees in the state. Because ALB is challenging to manage, it is important to identify, report, and develop plans to eradicate it upon detection.

Description

The adults of ALB are about 1-1.5 inches long, black, with small white spots on their body (Fig. 1). The antennae are distinctly long with black and white. The females of ALB chew on the bark of young branches, creating depressions (also referred to as “oviposition pits”) in the bark (Fig. 2). This feeding, especially by newly emerged adults, is referred to as maturation feeding, as adults obtain much-needed nutrition through sugar-rich tissue to mature their eggs. A female lays white, rice-grain-sized eggs singly on those depressions (Fig. 3). A female can lay up to 90 eggs in her lifetime. In about 14 days, the eggs hatch, and the emerging larvae bore into the bark. They feed on the tree’s cambium layer under the bark that transports water. Once the larvae increase in size, they move to the heartwood. All the larval stages of the ALB feed on wood tissue and slowly develop inside the tree trunk (Fig. 4). They undergo 13 growth stages, and their feeding creates tunnels and galleries within the tree trunk (Fig. 5).

Fig. 2. Oviposition pit or depression in the bark. Photo credit: Dennis Haugen, USDA Forest Service,
Bugwood.org

Fig. 3. Rice-grain sized egg laid on the bar. Photo credit:, Larry R. Barber, USDA Forest Service,
Bugwood.org

Fig. 4. Larvae of Asian longhorn beetle. Photo credit: Thomas B. Denholm, New Jersey Department of Agriculture, Bugwood.org

Fig. 5. Extensive tunneling from Asian longhorn beetle larval feeding. Photo credit: Dennis Haugen, USDA Forest Service, Bugwood.org

Along with feeding, they excrete the waste (frass), filling the infested galleries (Fig. 6). They pupate inside the tree for 13 to 24 days (Fig. 7). The eggs, larval stages, or pupae overwinter inside the tree, and ALB adults do not survive the freezing temperatures in the winter. New emerged adults inside the tree trunk chew on the wood to create a tunnel to exit the tree (Fig. 8). The exit holes on the bark are round and 3/8^th of an inch in diameter (Fig. 9).

Fig. 6. Frass accumulated from larvae of Asian longhorn beetle larval feeding. Photo credit: Pennsylvania Department of Conservation and Natural Resources – Forestry

Fig. 7. Pupa of Asian longhorn beetle inside the gallery. Photo credit: Kenneth R. Law, USDA APHIS PPQ, Bugwood.org

Fig. 8. Newly emerged adult Asian longhorn beetle chewing exit hole. Photo credit: Michael Bohne, USDA Forest Service

Fig. 9. Newly emerged adult Asian longhorn beetle chewing exit hole. Photo credit: Dennis Haugen, USDA Forest Service, Bugwood.org (left) and Leslie J. Mehrhoff, University of Connecticut, Bugwood.org (right)

It is common to find various stages of ALB larvae overwintering inside the tree trunk. These larvae pupate, and adults emerge at different times of the year – from April to December. The peak emergences of adults are noticed in the summer and fall. The adults typically fly only a short distance from their emergence site before settling and beginning to feed. The newly emerged adults feed on leaves and bark for two weeks before mating and egg-laying.

Host range

Common reported hosts for ALB are ash (Fraxinus), birch (Betula), Elm (Ulmus), golden raintree (Koelreuteria), London planetree/sycamore (Platanus), maple (Acer), horsechestnut/buckeye (Aesculus), katsura (Cercidiphyllum), mimosa (Albizia), mountain ash (Sorbus), poplar (Populus), and willow (Salix).

Damage and symptoms

ALB larvae feed on the vascular bundles, especially the xylem tissue, which affects water transportation from the roots to the tree crown. Persistent feeding from larvae blocks the xylem vessels. The tree branches weaken and begin to show die-back symptoms (Fig. 10). Later, season-long feeding affects the entire tree, leading to death. The xylem-feeding habit of roundheaded borers reduces the tree’s structural stability as they are likely to break during storms (Fig. 11). The exit holes are deep because the larvae feed on the xylem tissue. The presence of depressions or oviposition pits on bark and sawdust from the galleries at the base of the tree indicates roundheaded borer activity. Because ALB adults tend to fly only short distances after emerging, reinfestation of the tree is common. Branch damage and crown thinning appear within 3-4 years of initial infestation, and the trees die within 10-15 years.

Fig. 10. Die-back symptoms after Asian longhorn beetle infestation. Photo credit: Dennis Haugen, USDA Forest Service

Fig. 11. Asian longhorn beetle infestation reduces the structural stability of trees. Photo credit: USDA ARS, Agricultural Research Service, Bugwood.org (right); and Michael T. Smith, Bugwood.org (left).

Stop the spread

Quarantine areas have been established to restrict the movement of ALBs. If a tree has been identified positive for ALB, it should be removed. Live or dead wood, such as firewood or branches, should not be moved out of the quarantine areas. Because this pest threatens hardwood trees and disrupts diversity in forest, residential, and recreational ecosystems, it is critical to report any new detections to stop the spread and save many trees in any region.