Sunday, August 18, 2013

More on wood borers

As promised, here is some useful information about wood-boring insects. There are a lot of these insects that we encounter through our work around Chicagoland. I've covered quite a few here, but yet there are even more! This list is lengthy,  but doesn't even cover all the different wood borers out there. A least my hope is this will give you some insight on what to look for in and around your yard. Remember, for questions, treatment or removal of these pests, contact your local tree service and/or arborist. Trees "R" Us, Inc. for the readers in the Chicagoland area will provide you with the expertise of a certified arborist in order to help you with your tree care issues. First up is...

Long-horned beetles or round-headed borers (Coleoptera: Cerambycidae) 

Adults are called long-horned beetles because their antennae are unusually longer than their bodies. Larvae tunnel underneath bark and into the heartwood. The tunnels are oval to almost round in cross section because of the round shape of the larvae. Larvae of some species are legless, but most have three pairs of small legs on the first three segments behind the head capsule. While tunneling, larvae continually pack their tunnels with excrement (frass), which looks like compressed wood fibers, or push frass out of the holes they produce. This excrement, along with the sap exuded by the plant in response to the damage, is often visible on the outside of infested trunks or branches. Many species of beetles belong to this group, but most are secondary invaders. Some examples of long-horned beetles are described below.

Locust borer (Megacyllene robiniae) adults are medium-sized (3/4 inch long) long-horned beetles frequently found feeding on goldenrod or other flowers in the fall. They are dark brown to black with distinctive gold-yellow markings. Larvae hatch from eggs laid in bark crevices. Visible symptoms of infestation are wet spots and frass on the bark of black locusts. Later, larvae tunnel into the inner bark and construct cells in which they spend the winter months. In a year the larvae are fully grown and about an inch in length.

Cottonwood borer (Plectrodera scalator) is frequently found on cottonwood, poplar or willow trees. Adult beetles are large (1 1/4 inches long) with an attractive black and whitish-yellow pattern. They are active from May through August. The larvae (1.75 to 2 inches long) tunnel at the base of the trunk or below ground level. They require about 2 years to develop.

Red-headed ash borer (Neoclytus acuminatus) is one of the most common wood-boring beetles. It has a narrow body with a reddish thorax and light brown wing covers marked with four yellow lines on each. The yellow lines are slanted downward toward the middle, giving the appearance of a “V” across the back. The antennae are rather short and the long legs are thin and fragile. Red-headed ash borers feed in many species of wood including ash, oak, elm and even grapes. Adults can be found on dead log piles and frequently emerge from firewood. 

Red oak borer (Enaphalodes rufulus) attacks oak and maple trees and can be a serious pest in nurseries. The reddish-brown adults (5/8 to 1 1/8 inches long) lay eggs individually in bark crevices during July and August. Larvae tunnel under the bark and into the heartwood. Infested sites can be recognized by the frass around the buckled bark near the gallery entrance. Larvae often tunnel completely around the trunk or branches they infest, producing noticeable scars or girdling. Red oak borers feed for more than a year before pupating in chambers tunnelled into the heartwood. Damage kills limbs or terminals and increases the risk from secondary invaders and diseases.

Twig girdler (Oncideres species) damage occurs primarily from egg laying. This insect attacks pecan, mimosa, chinaberry and huisache. The grayish-brown adults (1 1/16 inch long) girdle limbs during the fall (late August through mid-November) by chewing a V-shaped groove entirely around twigs, branches or terminals. Eggs are inserted into the bark on the girdled part of the branch away from the tree. Girdled limbs eventually break and fall to the ground, particularly during high winds and storms. Damage can disfigure a young tree and leads to secondary branching, particularly if the terminal is attacked. Larvae reach up to 7/8 inch long and are unable to develop in healthy sapwood. Removing the girdled twigs and branches from the ground during winter and spring and destroying them can reduce the population of these insects.

Twig and branch pruners (Elaphidionoides and Agrilus species) produce damage superficially similar to that of twig girdlers on elm, hackberry, hickory, maple, oak, pecan, persimmon, redbud, sweetgum and other trees. In these species, however, it is the larvae that girdle twigs and branches underneath the bark. The surface of the severed end of the twig is smooth. The insect usually severs branches where small twigs branch from the main, girdled branch.

Metallic wood-boring beetles (or flatheaded borers) (Coleoptera: Buprestidae)

Adult beetles are flattened, hard-bodied and boat-shaped with short antennae. These are beautiful beetles with distinctive metallic colors (green, blue, bronze, copper). Larvae are cream-colored and legless with widened, flattened body segments just behind the heads. Consequently, when these larvae tunnel beneath bark or into the sapwood they produce oval or flattened tunnels in cross section. Galleries are often winding and packed with frass. Tunneling can girdle trunks and branches. Many species of flat-headed borers occur in the state. Most are secondary invaders.

Bark beetles (Coleoptera: Scolytidae)

Beetles in this group tunnel below the bark of trees and/or into the wood. Adult beetles are small and reddish-brown to black. Larvae are cream colored grubs without legs. One member of this group, the European elm bark beetle (Scolytus multistriatus), is the carrier of Dutch elm disease. Other members of this group are described below.

Southern pine beetle (Dendroctonus frontalis) is a primary pest of southern pine forests. Adult beetles are active during warmer months (when temperatures are above 58 degrees F), and disperse widely to injured, weakened or stressed trees in the spring. Seven or more generations may be completed within a year. When abundant, they can attack healthy trees. Larvae tunnel beneath the bark producing tunnels or galleries in patterns resembling the letter “S”. This tunnelling quickly disrupts the cambium layer, girdling the tree. Infested trees can have numerous masses of resin called "pitch tubes" on the tree trunk. Needles of newly attacked trees turn reddish-brown 1 to 2 months after infestation during the summer, and up to 3 months afterward in the winter. Removal and destruction of infested trees may prevent healthy trees in the vicinity from being attacked.

Ips engravers (Ips. spp.) are often mistaken for the southern pine bark beetle because their appearance and damage are similar. Their gallery patterns tend to be more parallel to each other, however. Ips usually attack weakened trees only. Recently felled wood should be covered with plastic to prevent Ips beetle infestation.

The black turpentine beetle, Dendroctonus tenebrans, is another species attacking pines.

Shothole borers (Scolytus rugulosus) are secondary pests of common fruit trees (peach and plum), wild plums and occasionally ash, elms and hawthorne. Beetles tunnel through the bark and make small holes in the bark crevices.

Asian ambrosia beetle (Xylosandrus crassiusculus) is a newly introduced species that attacks healthy, stressed or freshly cut elm, pecan, peach, Prunus species, oak, sweetgum and other trees. Tiny (2 to 3 millimeters long), dark reddish-brown adult female beetles tunnel into twigs, branches or small tree trunks, excavating a system of tunnels in the wood or pith in which they lay eggs. They also introduce a fungus on which the larvae feed. Visible damage includes wilted leaves on infested branches and protrusions of compressed wood dust from numerous small holes, resembling toothpicks pointing outward. Dead and dying areas of bark (cankers) can form at the damage site, eventually
girdling the tree and killing it. There are several generations per year. Chemical control of this species has been generally unsuccessful. Native ambrosia beetles are also called shot-hole or pine-hole borers. These species have similar biologies but rarely attack healthy, vigorous trees. 

Weevils (Coleoptera: Curculionidae)

Adult weevils have a characteristic snout that bears the chewing mouthparts. Larvae are legless and cream-colored, and generally feed in cells or hollowed out cavities underneath the bark rather than in galleries or tunnels as do bark beetles. Weevils attack the trunks during the winter, where young trees are in poor planting sites. Several weevil species attack the bases and roots of woody ornamental plants, cottonwood, Chinese tallow and fruit trees such as pear and cherry. These larvae develop over 2 or 3 years, initially feeding underneath the bark but later tunnelling into the heartwood. Outward signs of attack include piles of sawdust and excrement, particularly in cracks and crevices. Carpenter worms may enter and exit the trunk of the tree several times during their development. Adult moths, which emerge in the spring, are rather large with spotted wings.

Peach tree borer (Synanthedon exitiosa) is one of the most important insect pests of peach and plum. Adult peach tree borer moths mate and lay their eggs on the trunks of peach and plum (Prunus species) trees during August and September. These daytime fliers are one of several species often called clear-wing moths, and they look superficially like wasps. Larvae hatch from eggs in about 10 days and tunnel beneath the bark for 10 to 11 months before emerging from the base of the trunk. Infected trees exhibit dieback, yellowing of leaves, stunted growth and possible death if larvae girdle the trunk near the soil line - from 10 inches above the ground to 3 inches below the ground. After emerging, they drop to the soil to pupate at the base of the tree. Affected trees can be identified by masses of sap around damage sites at the base of the trunk. Infestations can kill scaffolding limbs or entire trees.

Other species of clear-wing moths are: 1) the lilac or ash borer (Podosesia syringae), which has its adult flight period during the spring and early summer; 2) the dogwood borer (Synanthedon scitula); and 3) the lesser peach tree borer (Synanthedon pictipes).

Other caterpillar pests include: the southern pine coneworm (Dioryctria amatella), which tunnels around the bases of Virginia pine trunks; Euzophera ostricolorella, a root collar borer that infests potted magnolia; and the American plum borer (Euzophera semifuneralis), which invades damaged or improperly pruned branches on a wide variety of woody ornamentals.

If you are concerned about the bugs lurking in your yard and munching on your trees, then stay tuned for my next post on managing wood boring insects.

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