Dogwood bark beetles are one of the most common insect pests of trees. They cause damage to many species of trees, including oaks, ash, birch, elm and maple. Bark beetle infestations can be severe and even fatal to some species. Bark beetles feed on the woody parts of trees such as branches or trunks. They lay eggs inside dead or dying leaves or needles (or both) from other plants and animals such as moths and butterflies. When the egg hatches, it develops into a larva which feeds on the host plant or animal. After several weeks, the pupa emerges and grows into a fully grown adult beetle.

The bark beetle larvae are very small and resemble tiny maggots. These little bugs can survive for only two days without water before they die of dehydration. Bark beetles live in moist places such as under logs, rocks or soil where there is moisture but not enough air to keep them dry. Bark beetles are also found near human habitation such as houses, barns, sheds and garages. Bark beetles usually do not attack people unless they have been bitten by a tick or flea bite.

However, bark beetle larvae may be carried indoors when someone touches infected areas with their hands or clothing. If the person then breathes indoor dust containing the larvae, it can spread infection to others.

Bark beetle larvae normally feed on dead animals or plants. Some species also feed on dying or recently dead trees, especially if there is a food shortage. Bark beetles can thrive in both hot and cold temperatures and do not need to hibernate. They have four stages of life: egg, larva, pupa and adult. The eggs are oval-shaped and measure between 0.2mm and 1.2mm in length.

The average bark beetle egg is less than 0.5mm long. The eggs are smooth and white when first laid but turn light brown before they hatch. The larvae are legless and have a yellowish-white, creamy or pink body. The head capsule is darker in colour than the rest of the body. The larval stage lasts between 9 and 28 days, during which time the larvae will shed their skin (molt) several times until they reach maturity.

Bark beetles will attack a wide range of plants, including humans. Bark beetles can be a serious problem when they attack trees and shrubs in urban, residential and recreational areas because they leave the tree or shrub weakened or dead. Dead trees and shrubs increase the risk of fire in urban areas.

The most effective way to get rid of bark beetles is to make sure the affected tree or shrub receives as much water and nutrients as it can so it remains healthy. Fertilizer or compost can be spread around the base of the tree.

If the infestation is small, hand picking and disposing of the affected tree or shrub in the trash can also help.

The insecticide carbaryl also known as Sevin is effective against bark beetles. In larger trees, a systemic insecticide such as imidacloprid can be injected into the soil around the tree’s roots to stop the bark beetle from reaching the foliage.

Bark beetles leave telltale evidence of their presence in wood by the small round holes they chew in it. These holes can be found on both standing and felled trees. The exit holes are perfectly round because the beetles bore straight through the wood. These exit holes can be found in clusters because the adult bark beetles emerge from those areas. Dead trees and dying branches are other signs of bark beetle activity.

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Look for clusters of small, oval-shaped holes in the wood. The colour of these holes is beige or white as the bark beetles naturally favour this material when constructing their cocoons.

Beetles normally attack sick, dying or dead trees and shrubs, although they can cause damage to healthy plants as well. The bark beetle can be found in every province and territory in Canada. They have been known to infest entire forests made up of a single species of tree.

Bark beetles typically attack trees and shrubs in the mountains, coastal and inland forests. They have been known to attack various species of birch, spruce and pine trees.

Some of the most common bark beetles in British Columbia are the montane, black, white mountain, ponderosa and Douglas-fir beetles. Each one prefers a different species of tree. The black mountain bark beetle is a serious pest of ponderosa pines. The montane and ponderosa bark beetles are most likely to be found in lodgepole pines. The white mountain bark beetle infests subalpine fir.

The ponderosa and the Douglas-fir bark beetles attack both lodgepole and ponderosa pines.

Bark beetles have five developmental stages: egg, larva or caterpillar, pupa, adult and spent or dead adult. The female beetle bores into the inner bark of a tree or shrub and lays between 12 and 40 eggs in a mass. The eggs hatch after one to three months, depending on the temperature.

The eggs hatch into beetles known as larvae or caterpillars. The larvae are white, C-shaped grub-like insects which grow up to 1cm long. They feed on the inner tissue of the bark and tunnel through it while they develop and mature. It takes between three to five highly active months for the larvae to grow.

The larvae then make their way to the outside of the tree where they spin protective covers or cocoons for themselves out of silk. They remain in this pupal state for one to two months while they complete the transformation from larva to adult. The pupa is inactive and non-feeding during this stage.

The newly formed adult beetle then chews its way out of the bark and makes its way to the outside of the tree to begin the cycle again. The entire process takes one to two years and is dependent on climate, species of tree and other factors.

As the bark beetle’s name suggests, it bores into the bark of trees and feeds on them. This insect has a narrow head which allows it to bore into the tiniest cracks in the bark. It prefers trees that are already dead or dying.

The bark beetle typically attacks the most valuable trees in a forest first, such as those that are tall, straight and mature. As it feeds on the trees, it attracts other insects and diseases which further weaken the tree.

The amount of feeding damage the bark beetle causes is directly related to its numbers. If there are very few beetles attacking a tree, they may only eat shallowly into the bark. Large numbers of beetles, however, can completely girdle or encircle a tree trunk.

Not all the bark beetles in an attack will actually feed on trees. Some may be more intent on mating and laying eggs in the bark. The females lay their eggs in bark crevasses or tunnels. Each female lays 12 to 40 eggs in one egg mass.

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Many types of insects prey on bark beetles. One of the most effective is a tiny wasp known as a trank. The females sting the bark beetles and lay their eggs in the bodies of their prey. When the wasp eggs hatch, the larvae feed on the living bark beetles as they slowly die.

The Douglas-fir tussock moth has also been known to prey on bark beetles. The female moth lays its eggs among those of the bark beetle in tree bark crevasses or tunnels. When the eggs hatch, the larvae feed on the bark beetle eggs and larvae.

In order to protect trees against bark beetles, you can apply a solution of one part diesel fuel to 16 parts water. This destroys the protective wax coating of the insect and causes it to dehydrate.

Other natural predators include velvet ants, shrews and certain types of spiders.

When choosing trees for a forest it is important to know which trees are most susceptible to attack by bark beetles. Certain types of trees, such as aspen, alder, willow and pine are particularly prone to attacks.

Other trees such as spruce, hemlock and fir are resistant to bark beetles. These three types of trees can also help reduce the impact of an infestation in other parts of the forest by attracting the bark beetles away from other trees.

The Dendroctonus bark beetle has been labeled as one of the most destructive pests to forestry in the world. In North America, this insect is known to have destroyed millions of acres of forest land.

It is thought that the bark beetle has a range of hosts from at least 550 types of trees including conifers and deciduous. It has also been known to attack some types of plant that are not trees, such as Cacti.

The name bark beetle is a little misleading, as many of these insects do not actually bore into tree trunks. Most adult bark beetles live in the foliage of trees and shrubs and only attack the trunks and branches when laying eggs.

Although most bark beetles are specific to one type of tree, there are some types which will attack several species of trees. The Dendroctonus bark beetle is one of these general attackers.

The adult bark beetles lay their eggs in crevasses in the bark or in small holes made by other insects. The grubs develop in the bark for up to a year before they emerge as adult beetles to continue the cycle.

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When the bark of an attacked tree is peeled back it reveals thin tunnels bored into the wood by larvae. The tunnels are packed with coarse sawdust-like material which is the waste excrement of the grubs.

These tunnels are also packed with the bodies of other insects that got caught and eaten by the grubs. The most common prey consists of various kinds of sawfly larvae.

The number of eggs laid by a female bark beetle depends on the species, as some will lay only a few while others may lay several dozen. Some eggs are laid directly on the tree, while others are transported from elsewhere and laid under the bark.

Most eggs hatch after about one month, however some eggs may take up to a year to hatch.

Sources & references used in this article:

Evaluation of pheromone-based management strategies for dogwood borer (Lepidoptera: Sesiidae) in commercial apple orchards by TC Leskey, J Christopher Bergh… – Journal of economic …, 2009 – academic.oup.com

Controlling clearwing moths with entomopathogenic nematodes: The dogwood borer case study by JA Davidson, SA Gill, MJ Raupp – Journal of Arboriculture, 1992 – academia.edu

Flight Phenology of the Dogwood Borer (Lepidoptera: Sesiidae) and Implications for Control in Cornus florida L. by DA Potter, GM Timmons – Journal of economic entomology, 1983 – academic.oup.com

Infestation levels of dogwood borer (Lepidoptera: Sesiidae) larvae on dogwood trees in selected habitats in Tennessee by LE Rogers, JF Grant – Journal of Entomological Science, 1990 – meridian.allenpress.com

Dogwood borer (Lepidoptera: Sesiidae) flight activity and an attempt to control damage in ‘Gala’apples using mating disruption by DG Pfeiffer, JC Killian – Journal of Entomological Science, 1999 – meridian.allenpress.com

Incidence and control of dogwood borer (Lepidoptera: Sesiidae) and American plum borer (Lepidoptera: Pyralidae) infesting burrknots on clonal apple rootstocks in … by DP Kain, RW Straub, AM Agnello – Journal of economic …, 2004 – academic.oup.com

Factors promoting infestation of newly planted, nonbearing apple orchards by dogwood borer (Lepidoptera: Sesiidae) by TC Leskey, JC Bergh – Journal of economic entomology, 2005 – academic.oup.com

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