Bark beetles are one of the 220 varieties of beetles, with around 6,000 species belonging to the subfamily of Scolytinae. While the southern pine beetle (Dendroctonus frontalis) and the mountain pine beetle (Dendroctonus ponderosae) pose major threats to the conifer forests in North America, the Spruce lps (Dendroctonus rufipennis ) is the most dreadful bark beetle species in Europe.
Utility of the WoodThe wood of the bark beetle-infested tree remains unaffected for the first year after infestation, and hence, can be utilized for domestic purposes.
Of all the bark beetle species, the mountain pine beetle has greatly impacted a large area of forests in Colorado, Wyoming, Nebraska, and South Dakota. This beetle species has affected almost 4 million acres of forests in southeastern Wyoming and northern Colorado, since their first signs of outbreak in 1996. Considering its voracious appetite, it is natural for environmentalists and farmers to remain wary about this tiny, yet destructive creature. We at Buzzle have put together some interesting facts about this beetle, along with information about its life cycle, habitat, and predators.
Mountain pine beetle
Southern pine beetle
» The name 'Bark Beetle' is given to these species because they reproduce in the inner bark of the tree. Furthermore, the word beetle is derived from the Old English word bitela (little biter).
» One of the typical traits that makes bark beetle identification easier, are their hardened forewings. These wings act as a protective shield for the delicate flight wings as well as the soft abdomen.
» Also, the species of trees that are attacked, and the location of the attack helps determine the type of beetle species. For instance, an engraver beetle attacks large pines at the top, whereas, the red turpentines attack the lower portion of the trunk.
» Usually, bark beetles attack those trees that are weakened by diseases, drought, smog, or physical damage. However, during outbreak conditions, they can infest even healthy trees.
» The spruce beetle attacks and breeds only in spruce trees. Hence, if other tree varieties like cottonwood, birch, hemlock, aspen, etc., are planted along with these trees, they are probably not at risk.
» During the breeding season, sometimes, one male bark beetle is accompanied by sixty female bark beetles.
» 10 out of the 20 invasive bark beetle species in California have been found since 2002, and the rest are yet to be discovered.
» Bark beetles are black, brown, or dark red, and cylindrical-shaped insects with tough bodies.
» They are about the size of a rice grain, and measure around 3 to 8 mm in length.
» Like other insects, the bodies of bark beetles are divided into three segments: the head, the thorax, and the abdomen. The head boasts of two compound eyes, and a pair of antennae. The thorax comprises two pairs of wings, and three pairs of legs. The abdominal region bears the reproductive and digestive organs.
» They also possess chewing jaws, known as mandibles, that move like scissors, for cutting through the bark and the phloem.
» Pine bark beetle species fly to the nearest host tree for colonization. They avoid flying long distances; their longest flight has been recorded at approximately 2 miles.
» Bark beetles have a unique feature which helps them detect a susceptible host tree. Diseased or damaged trees release certain volatile compounds called turpenes. Bark beetles have the ability to detect these compounds, and identify a suitable host tree.
» Bark beetles live in the inner bark of conifer trees, which have evergreen needle-like and scale-like leaves.
» Females of the mountain pine beetles usually look for trees with a large diameter and evergreen leaves. They attack the tree by tunneling it under the bark.
» However, when epidemic levels are high, bark beetles tend to attack and infest trees even with smaller diameters.
» After successful infestation, each beetle pair of the colony mates and forms a vertical tunnel, which becomes the gallery for laying eggs.
» All bark beetles undergo four stages in their life cycle: egg, larva, pupa, and adult.
» Adult male and female beetles bore galleries or tubes between the inner bark and outer sapwood of the host tree, and the female then lays small, whitish, oval-shaped eggs in those galleries. The average number of eggs that the female beetle lays is around 75.
» The eggs then hatch and become larvae. These larvae feed on the phloem and other nutritious fluids of the tree, until they reach the pupal stage. The larvae mines, which are narrow initially, increase in diameter as the larvae grow.
» Pupation happens in or beneath the chambers at the end of the larval tunnels. The larvae form a hardened outer casing around themselves, and transform into pupae. These pupae are plump and whitish in color.
» The pupae then develop into adult bark beetles inside the casing, and are ready to emerge. Although adult beetles may emerge anytime during the year, they prefer emerging during late summer.
» Adult beetles may re-infest the same tree, or even look for another susceptible tree for further colonization. Usually, bark beetles develop two or more generations within one year, depending on the temperatures. At warmer locations, they have more generations than cooler, coastal, or high-elevation locations.
Birds- Amongst birds, various species of the woodpecker family are well-known enemies of bark beetles. Species such as the lesser spotted woodpecker, black woodpecker, and especially the three-toed woodpecker, disrupt the natural population growth of bark beetles.
Beetle Species - Surprisingly, even certain beetle species are also in the list of predators of bark beetles. Out of them, the checkered beetle is the most commonly known bark beetle predator.
Parasites - Parasitic wasps, especially the ones from the Hymenoptera family, are an important link in the forest ecosystems, and help regulate the bark beetle population, and maintain the natural balance. These are not only parasites, but also act as parasitoids, who survive on their hosts, and eventually kill them.
As mentioned earlier, bark beetles usually attack diseased and damaged trees. However, to protect the trees from bark beetles, it is important to maintain their good health, take special care by using fertilizers, remove dead or dying trees as early as possible, and destroy their remains properly.