Thousands of trees around the world are killed each year due to beetles. With climate change and the rising of winter temperatures, infestations of beetles seem to be worsening.
Are you wondering what is killing the tree in your yard? Are you curious if the beetle you found on one of your trees could cause damage? Continue reading below to find out more.
Why Do Some Beetles Kill Trees?
Due to inadequate rain and a higher number of dead trees, dense tree groups are susceptible to beetle attacks. This is due to stress, which is a result of competition for limited resources.
The beetles are simply trying to complete their lifecycle, which may involve laying eggs under the tree bark or on leaves.
How Do Beetles Kill Trees
There are a number of ways in which beetles kill trees. Some bore into the trunk, roots, and limbs of the tree, causing extensive damage. Others attack woody plants, such as ornamental and fruit trees.
There are other beetles that lay eggs, that hatch and feed under the bark, on the tree root system. Beetles can kill a tree within weeks in warmer weather.
13 Examples of Beetles That Kill Trees
The 13 examples of beetles that kill trees include:
1. Boll Weevil
Scientific name: Anthonomus grandis.
Common name: Boll weevil.
The boll weevil is a beetle that feeds on cotton buds and flowers. It is native to Central Mexico and migrated into the United States, infesting all US cotton-growing areas. This beetle became a pest in South America in the 20th century.
They have a long snout and are gray in color, growing to less than 6mm in length. The female lays her eggs inside the buds and ripens fruit on cotton plants. This causes damage to the exterior of the flower bud.
The boll weevil remains the most destructive cotton pest in North America today, costing cotton producers in excess of $300 million each year.
2. Mountain Pine Beetle
Scientific name: Dendroctonus ponderosae.
Common name: Mountain pine beetle.
Mountain pine beetles are bark beetle species. They are native to forests in western North America, all the way from British Columbia to Mexico.
These black beetles grow to 5mm in body length and have a hard exoskeleton. Outbreaks of the mountain pine beetle have affected large areas of lodgepole pine forests, along with more than forty million acres of forests in British Columbia.
The mountain pine beetle inhabits white bark, lodgepole, jack, limber, ponderosa, and Scots pine trees. They do play a role in forest life, where they attack older and weakened trees. This speeds the development of younger trees.
This beetle lays eggs under the bark of the tree, which introduces a blue stain fungus into the sap, preventing the tree from killing the beetle. The fungus blocks water and nutrient transport inside the tree.
The tree starts to develop popcorn-looking masses, where the beetles have entered. The fungal colonization and the larvae feeding will kill the host tree within weeks. Trees remain green when first attacked but the needles will turn red after about a year.
When the needles turn red, it is a sign that the tree is dying or is already dead and the beetles have moved on to another tree. Trees turn gray with very little foliage after around four years.
As the mountain pine beetle populations grow, more trees become stressed and populations can increase and spread. This is when even the healthiest of trees are attacked.
3. Elm-leaf Beetle
Scientific name: Xanthogaleruca luteola.
Common name: Elm-leaf Beetle.
The elm leaf beetle is native to Europe, invading other parts of the world. The adult beetle can grow to 8mm in length. They range from yellow to green with a spot on the head.
There is an hourglass marking and two spots on the pronotum and a dark stripe along each elytron. These beetles can be found from Portugal to Central Asia. They were introduced to Australia and North America.
The elm leaf beetle is a serious pest to elm trees. Adults and larvae feed on the leaves of the tree. A heavy infestation will not kill the tree right away, rather weaken it and make it vulnerable to disease.
The first signs of the final stage of decomposition are the outer edge and vein of the leaf are intact, while the foliage has a net-like appearance. Anywhere where the beetle eats, dries up, and dies. This results in the leaf dropping prematurely.
Any tree that loses its leaves often due to infestation will develop another set of leaves, which are then consumed by the next generation.
4. Lemon Tree Borer
Scientific name: Oemona hirta.
Common name: Lemon Tree Borer.
Lemon tree borers are also referred to as whistling beetle and are endemic to New Zealand. The larvae bore into the wood of a variety of trees. When disturbed, this beetle creates a squeak.
They are medium to large-sized beetle, around 25mm in length as adults. They have a slender body and long antennae. They vary from black to red-brown with pale yellow hairs on the head and scutellum.
Females are larger than males and have shorter antennae. She will lay single eggs that hatch in a few days. The larvae start tunneling into the wood, first into sapwood and then into the hardwood.
There are usually only two larvae per tree. They create long tunnels, eating the wood as they go. They move into the stems, going in the direction of the main branch or stem.
The first symptom of infestation of the lemon tree borer is the wilting of foliage. The trees have excretion holes up to 3mm in diameter. The stems and branches will weaken, eventually drying up and breaking.
5. Asian Long-horned Beetle
Scientific name: Anoplophora glabripennis.
Common name: Asian long-horned beetle, starry sky, sky beetle, ALB.
Asian long-horned beetles, also referred to as sky beetles are native to eastern China and Korea. They were accidentally introduced in the United States, Canada, and some European countries.
These are large beetles, growing up to 3.9cm in length with long antennae. They are shiny black with lots of white spots on their wing covers. The long antennae are banded in black and white.
While they can fly, they can only travel short distances. Adult females chew a small pit through the bark of trees and lay one egg under the bark in the pit. The larvae create a feeding gallery, while mature larvae tunnel through the hardwood.
A single larva can eat up to one thousand cubic centimeters of wood in its lifetime. Pupation takes place when the larvae reach the end of the sapwood tunnel and chew out of the tree. As adults, they feed on the petioles of leaves and can chew through small bark on branches.
The larvae do feed outside their native range, which has changed forests and urban ecosystems. In the United States alone, these beetles can potentially destroy up to thirty percent of urban trees, causing more than $600 billion in economic loss.
6. European Spruce Bark Beetle
Scientific name: Ips typographus.
Common name: European Spruce Bark Beetle.
European spruce bark beetles belong to the weevil subfamily Scolytinae and are common from Europe to Asia and parts of Africa. These beetles are black to brown/black in color and can grow to 5.5mm.
They are cylindrical, long, and robust beetles that reproduce in the inner bark of living and dead trees. Adults will hibernate in litter and host trees and will travel up to half a mile to find the right host tree.
Once they find a suitable host, the adult burrows through weakened bark, building tunnels where they mate and lay their eggs. After a few weeks, they move to another host and repeat the process.
The larvae hatch, feed, and pupate under the bark. These beetles infest the middle to lower part of the tree trunks. Trees that have been attacked can be identified for the brown dust at the basal areas of trunks and stems.
The red to brown colored dust can also be found between the bark, round exit holes, and patches of red foliage.
7. Walnut Twig Beetle
Scientific name: Pityophthorus juglandis.
Common name: walnut twig beetle.
Walnut twig beetles are known for feeding on a number of walnut tree species. These are small beetles, growing to 1.9mm in body length. The beetles gather in galleries inside the walnut tree with a small entrance hole visible from the exterior.
These beetles are associated with the Geosmithia morbida fungus, causing damage from discoloration to the mortality of walnut trees. In most cases, the trees only last a few years after the beetle starts feeding.
8. New Zealand Pinhole Boring Beetle
Scientific name: Platypus apicalis.
Common name: New Zealand pinhole boring beetle.
The New Zealand pinhole boring beetle is a wood-boring beetle. It is endemic to New Zealand and common in the North and sound Island. They can be found in a range of environments.
These dark brown beetles have a yellow basal joint on the antennae. Their cylindrical body is elongated. They grow to 5.8mm in length.
They have downward orientated mandibles. They are more common in natural beech wood forests and exotic plantations, such as eucalyptus. The beetles can be found in the dead tissues surrounding trees.
They are not partial to any type of wood and will reside inside soft and hardwood trees. They are a threat to healthy trees and are pests in native forests. They produce fungi that develop in the wood, altering the color.
They create deep tunnels, which creates an imperfection in finished timber, weakening it.
9. Douglas-fir Beetle
Scientific name: Dendroctonus pseudotsugae.
Common name: Douglas-fir beetle.
The Douglas fir beetle is a bark beetle from western North America. These beetles infest Larch trees that have been downed. Infestations occur when there is a drought, the tree has root rot disease, and environmental disturbances.
These are light brown beetles, that darken with age, turning black or dark brown with red wing covers. They are hairy and can grow to 7mm in length.
Infestations can be identified by the red to brown colored boring dust in the bark and at the base of the tree. Egg galleries run parallel with the grain inside the bark. Eggs are laid on both sides of the gallery with larvae tunneling perpendicular once hatched.
10. Colorado Potato Beetle
Scientific name: Leptinotarsa decemlineata.
Common name: Colorado potato beetle, Colorado beetle, ten-striped spearman, ten-lined potato beetle, potato bug.
The Colorado potato beetle is a major potato crop pest. They grow to 10mm in length and are bright yellow or orange with five brown stripes down each elytra. They are native to the Rocky mountains and have spread quickly into potato crops in America and Europe.
Females can lay up to five hundred eggs in five weeks. The 1mm eggs are deposited in large batches on the underside of leaves on the host plant. Eggs hatch and feed on the leaves of the host.
11. Coconut Hispine Beetle
Scientific name: Brontispa longissima.
Common name: coconut leaf beetle, two-coloured coconut leaf beetle, coconut hispine beetle.
The coconut hispine beetle feeds on the young leaves of mature coconut palms, damaging the seedlings. They have become a serious pest specifically in the Pacific.
In 2007 Philippines Metro Manila and twenty-six provinces were quarantined due to coconut hispine beetle infestations, in order to save the $800 million coconut industry in the Philippines.
12. Eucalyptus Snout Beetle
Scientific name: Gonipterus scutellatus.
Common name: eucalyptus snout beetle, eucalyptus weevil, gum tree weevil.
The eucalyptus snout beetle is a species of weevil, endemic to Australia. This beetle is a gray/brown color with a light-colored band. They grow to 13mm in length.
These beetles only infest eucalyptus trees. They are endemic to Australia but have spread to China, Africa Brazil, and the United States. They are also found in Europe.
The eucalyptus snout beetle female lays approximately two-hundred eggs in batches of ten. They are attached to both the upper and lower side of the leaves, hatching in a week. The larvae then feed on the young shoots and leaves of the plant.
They pupate below the surface, after crawling and falling to the ground.
13. Great Spruce Bark Beetle
Scientific name: Dendroctonus micans.
Common name: Great spruce bark beetle.
The great spruce bark beetle is native to the coniferous forests in Asia and Europe. They burrow into the bark of trees, laying eggs. Once the larvae hatch, they feed on the wood under the bark.
These beetles are found in the coniferous forests of Asia and Europe and are extending their range into Europe. These beetles infest spruce trees, along with Scots pine, silver fir, Douglas fir, and more.
Females create tunnels in the bark to create a brood chamber. The waste which is pushed out of the tunnel is purple-brown, known as resin tubes. They lay more than one hundred eggs in a brood chamber.
She then moves on and does the same near the first tunnel or she creates a tunnel in a new tree. The hatched larvae chew their way to the broad front. Once the larvae are fully developed, they create their own pupate chambers.
While it is a natural part of nature, beetles that kill trees can cost farmers and the economy millions each year. From those that runnel through the trees to those that eat the leaves, the damage they cause can be serious.
If you have seen holes in your trees and suspect you have a tree-killing beetle infestation, you can try insecticides or call in the professionals.