Bark beetles bore through the protective bark of a tree to lay their eggs in the moist, living tissues. These beetles and the larvae they produce feed on this living tissue, cutting off the tree’s ability to transport water and nutrients. The shape of the tunnels created by adult beetles and their larvae as they feed are unique for each species of beetle. The principle gallery is created by the female who lays eggs along the gallery walls (egg gallery). The eggs hatch and the larva create ‘larval galleries’ that tend to increase in width as the larva increases in size.
Consecutive years of drought have stressed pine trees throughout California, making them more susceptible to attack from pine bark beetles. When a pine is healthy, it can successfully fight off attacks from pine bark beetles by successfully drowning and flushing out the beetles that attempt to enter (pitching out). During a drought, pine trees are too water-stressed and can’t produce that defensive response to prevent bark beetles from attacking. Yet, when beetle populations are high, even a healthy tree may not be able to produce enough pitch to ward off hundreds of simultaneous attacks (a mass attack)
Bark beetle adults are small, cylindrical, hard-bodied insects about the size of a grain of rice. Most species are dark red, brown, or black. When viewed under magnification, their antennae are visibly elbowed with the outer segments enlarged and clublike. When viewed from above, the head is partly or completely hidden by the pronotum (the top of the body part behind the head). Bark beetles have strong mandibles (jaws) for chewing. A buckshot pattern of holes is apparent on the bark surface of infested branches or trunks where the new adults have emerged. Larvae of most species are off-white, robust, grub like, and may have a dark brown head.
Identifying Bark Beetles by their Damage and Signs
Bark beetles mine the inner bark (the phloem-cambial region) on twigs, branches, or trunks of trees and shrubs. This activity often starts a flow of tree sap in conifers, but sometimes even in hardwoods like elm and walnut. The sap flow (pitch tube) is accompanied by the sawdust like frass created by the beetles. Frass accumulates in bark crevices or may drop and be visible on the ground or in spider webs. Small emergence holes in the bark are a good indication that bark beetles were present. Removal of the bark with the emergence holes often reveals dead and degraded inner bark and sometimes new adult beetles that have not yet emerged. Bark beetles frequently attack trees weakened by drought, disease, injuries, or other factors that may stress the tree. Bark beetles can contribute to the decline and eventual death of trees; however only a few aggressive species are known to be the sole cause of tree mortality.
Except for general cultural practices that improve tree vigor, little can be done to control most bark beetles once trees have been attacked. Because the beetles live in the protected habitat beneath the bark, it is difficult to control them with insecticides. While some trees do survive bark beetle attack, the vast majority are killed once infested.
If trees or shrubs are infested, prune and dispose of bark beetle-infested limbs. If the main trunk is extensively attacked by bark beetles, the entire tree or shrub should be removed. Unless infested trees are cut and infested materials are quickly removed, burned, or chipped on site, large numbers of beetles can emerge and kill nearby host trees, especially if live, unattacked trees nearby are weakened or stressed by other factors. Never pile infested material adjacent to a live tree or shrub.
Prevention is the most effective method of managing bark beetles and related wood-boring insects; in most instances it is the only available control. Avoid injuries to roots and trunks, damage and soil compaction during construction activities, and protect trees from sunburn (sunscald) and other abiotic disorders. Irrigation may be important during dry summer months in drought years, especially with tree species that are native to regions where summer rain is common.
Irrigate when appropriate around the outer canopy, not near the trunk. Avoid the frequent, shallow type of watering that is often used for lawns. A general recommendation is to irrigate trees infrequently, such as twice a month during drought periods. However, a sufficient amount of water must be used so that the water penetrates deeply into the soil (about 1 foot below the surface). The specific amount and frequency of water needed varies greatly depending on the site, size of the tree, and whether the tree species is adapted to summer drought or regular rainfall.
Properly prune pine trees during mid-October to February and remove and dispose of dying trees so that bark- and wood-boring insects do not emerge and attack other nearby trees. Timing of pruning is important; avoid creating fresh pruning wounds during the adult beetles’ flight season. Do not pile unseasoned, freshly cut wood near woody landscape plants. Freshly cut wood and trees that are dying or have recently died provide an abundant breeding source for some wood-boring beetles.
Red Turpentine beetle
This beetle is very common on Monterey pines planted in urban landscapes and highway corridors within about 100 miles of the California coast. It is also prevalent on most pines that grow in the Sierra Nevada, particularly on pines damaged by wildfire. Otherwise healthy pines often survive attacks by a few individuals of the red turpentine beetle. Prominent pitch tubes on the lower trunk of standing trees or stumps of recently cut trees nearly always indicate the beetle’s presence. A red turpentine beetle attack likely indicates that pines are stressed from an unfavorable growing environment, drought, injuries, inappropriate cultural care, or that pines are declining from old age. Ensure that planted trees receive proper care and a good growing environment to enhance tree survival.
Symptoms of Red Turpentine Beetle Injury
The most obvious sign of RTB attack is large (up to 2 inches across) reddish globules of pitch (pitch tubes) at the point of entry. These are located on the lower part of the tree trunk and on the root crown. Very weak trees may not produce much pitch in response to the beetle attack and pitch tubes may be missing. However, accumulations of reddish-brown boring dust will be present at the base of the tree and in bark crevices. Piles of coarse, granular pitch are often present with the boring dust. Internal evidence is the distinctive gallery patterns left by the feeding larvae. The beetles also introduce the blue stain fungus into the tree. The fungus grows in the live wood tissue clogging the water transporting vessels and staining the wood blue. The fungus may also reduce the flow of pitch, reducing the tree's protective mechanism.
Ips is a genus of beetles in the family Curculionidae, the true weevils. They are small (1/8 to 3/8 inch long), reddish-brown to black beetles. They have a pronounced cavity at the rear end, which is lined with three to six pairs of tooth-like spines, distinguishing them from other bark beetles. They are commonly known as engraver beetles and members of the subfamily Scolytinae. Many species are pests of forest trees, especially pines and spruces.
Ips beetles are generally not considered as destructive or aggressive as bark beetle species. Normally ips beetles limit their attacks to trees that are in decline due to root injuries, wounding, or other stresses. However, under widespread conditions which allow improved survival and large population build-ups, ips beetles are a considerable threat to living trees. The main factor that recently contributed to ips beetle problems in California is the prolonged drought stress.
Symptoms of Ips Beetle Injury
As adult ips beetles enter trees and tunnel, a yellowish- or reddish-brown boring dust is produced and accumulates in bark crevices or around the base of the tree. When the larval tunnel, affected parts of the tree discolor (“fade”) and die. These symptoms may be limited to parts of the tree, such as a single branch or the top. However unlike mountain pine beetle, infestation by ips beetles does not necessarily mean the whole tree will die, but over time, attacks may progress as later generations “fill” the tree and then ultimately the host can die.
Small round holes in the bark of infested trees indicate the beetles have completed development in that part of the tree and the adults have exited. The presence of these holes peppering the bark show the beetles have moved to another part of the same tree or to neighboring trees.
In 1972, Kerry Ray started his journey in tree trimming by pruning the trees at his rental house in Reseda, California. He then volunteered to help his LAPD motor officer partner, Randy, trim his parents Ash tree. So, they went out and bought a Homelite chainsaw, climbing gear and a black/orange trucker's rope...