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The end of beech trees: How beeswax pests cause devastating disease?
A disease called beech dieback is causing severe tree mortality and defects in beech forests across East America, Canada, and Europe. The main causes of the disease are the beeswax borer (Cryptococcus fagisuga) and another pest, Xylococcus betulae. Infestations by these pests cause two fungi—Neonectria faginata and Neonectria ditissima—to form deadly lesions on the bark, eventually withering the entire crown of the tree.
"Overfeeding by the wax beeswax pest activated the growth of the fungus, and although we did not fully understand the process at first, the disastrous consequences were already apparent."
History and Distribution
The disease was first recorded in Europe in 1849, while the wax beeworm was observed in North America in 1890, with Neonectria first discovered around 1900. Initially, it was believed that the wax borer was the main cause of the disease, but it was not until 1914 that a causative fungus was identified as being closely associated with the disease. The first outbreak of Fagus dieback occurred in 1920 in American beech trees in Nova Scotia, and the disease subsequently spread southward and westward. The first case in the United States was reported in Massachusetts in 1929, and by 2004 the disease had spread to Michigan and western North Carolina.
Infection Mechanism
Beeswax pests
The beeswax beetle is a native North American pest that feeds exclusively on beech trees. Adult bees can be found on tree trunks and branches, forming a fuzzy white fuzz. The larvae of these pests hatch in the summer and establish habitats in tiny cracks in the bark, feeding with piercing-sucking mouthparts, which eventually damage the bark and create pathways for the fungus to invade.
Fungi
In North America, the main fungi that cause beech dieback are Neonectria faginata and Neonectria ditissima. These fungi enter the tree through wounds left by beeswax pests and form capsules on the bark, releasing spores each year that can be spread by the wind to other beech trees. Although the cysts are found primarily on dead bark, they can still produce viable spores the following year.
Signs and symptoms
The first sign of a beeswax bug infestation is the appearance of a fuzzy, white, waxy substance on the tree trunk. As the disease progresses, a reddish-brown fluid oozes out of the trunk, a phenomenon known as "bleeding" of the beech tree, accompanied by the formation of cystic fruit, which is characteristic of the disease. These symptoms not only appear on the trunk, but also affect the leaves, causing them to become sparse, yellow, and may even cause the tree to die.
"When the crowns of trees are weakened, the trees will eventually die even when they appear healthy."
Management Strategy
There are few strategies for controlling beech tree dieback, but preventing the transportation of seedlings and timber with beeswax pests is an important measure. Furthermore, although insecticide use is mainly targeted at high-value ornamental plants, its effectiveness is limited in forest settings. Natural enemies, such as ladybugs and other organisms that parasitize the fungus, are also thought to be potentially helpful in controlling the disease, but their role has not been fully evaluated. In the woods, the cost of controlling this disease is high, so it has become a wise choice to take timely logging actions to reduce economic losses.
In the face of the spread of beech tree diseases, how to find effective and sustainable management solutions to protect our tree resources is a question that every ecologist and forester needs to think about?
