Ips engraver beetles

Common engraver: how the bark beetle lives and develops

Pine bark beetles are frequent pests of stressed pines, Pinus spp., in the southern United States. The five most common southern pine bark beetle species include three in the genus Ips: the sixspined ips, Ips calligraphus (Germar); the eastern fivespined ips, Ips grandicollis (Eichhoff); and the small southern pine engraver, Ips avulsus (Eichhoff); and two species of Dendroctonus: the southern pine beetle, Dendroctonus frontalis Zimmermann, and the black turpentine beetle, Dendroctonus terebrans (Olivier).

Like other pine bark beetles, Ips pine engravers live predominantly in the inner bark, where they breed and feed on phloem tissue. Pines successfully colonized by Ips engravers, if not already dead, are killed by adult and larval feeding in the phloem (which can girdle the tree) and by colonization of the sapwood with blue-stain fungi that the beetles introduce. The blue-stain fungi spread into the xylem and block water flow, serving to hasten tree mortality (Connor and Wilkinson 1983, Kopper et al. 2004).

Ips beetles usually colonize only those trees that are already stressed, declining, or fallen due to other environmental or biotic factors. Ips also readily colonize cut logs and slash, and are attracted to fresh pine odors. Infestations may occur in response to drought, root injury or disease, timber management activities, lightning strikes, or other stresses, and sometimes occur in association with attacks by Dendroctonus frontalis or Dendroctonus terebrans (Anderson and Anderson 1968, Lovelady et al. 1991, Miller 1983). When populations of Ips beetles are sufficiently high, they can overcome the defenses of apparently healthy trees by attacking in large numbers. However, Ips outbreaks are greatly limited in duration and spatial scale compared to outbreaks of the more aggressive Dendroctonus frontalis (Anderson 1977).

Distribution (Back to Top)

All three Ips species can be found throughout Florida in areas where pines occur. Ips calligraphus has two recognized subspecies, Ips calligraphus, found throughout much of the eastern US, north to southern Ontario, Canada, and Ips ponderosae, a western US subspecies.

The distributions of both Ips calligraphus and Ips grandicollis north of the southern pines coincide with the range of pitch pine (Pinus rigida Mill), although they will affect any pine species within that range. Ips avulsus is restricted to the southeastern states, from southern Pennsylvania to Florida and Texas (USDA Forest Service 1985).

Description (Back to Top)

Adults: Adults are small (approx. 2 to 6 mm in length), cylindrical, reddish-brown to black, with the head generally concealed by the pronotum when viewed from above. The posterior portion of the elytra (wing covers) is distinctively hollowed-out, coarsely punctured, and bordered with multiple spines.

The three southern species can be distinguished by body length and number of spines along each side of the elytral declivity:

Sixspined ips, Ips calligraphus, 3.5 to 6.5 mm long, six spines per side.

Figure 1. Adult sixspined ips, Ips calligraphus (Germar). Photograph by David T. Almquist, University of Florida.

Figure 2. Dorsal view of the elytral apices of an adult sixspined ips, Ips calligraphus (Germar). Photograph by David T. Almquist, University of Florida.

Eastern fivespined ips, Ips grandicollis, 2.8 to 4.7 mm long, five spines per side.

Figure 3. Adult eastern fivespined ips, Ips grandicollis (Eichhoff). Photograph by David T. Almquist, University of Florida.

Figure 4. Dorsal view of the elytral apices of an adult eastern fivespined ips, Ips grandicollis (Eichhoff). Photograph by David T. Almquist, University of Florida.

Small southern pine engraver, Ips avulsus, 2.3 to 2.8 mm long, four spines per side.

Figure 5. Adult small southern pine engraver, Ips avulsus (Eichhoff). Photograph by David T. Almquist, University of Florida.

Figure 6. Dorsal view of the elytral apices of an adult small southern pine engraver, Ips avulsus (Eichhoff). Photograph by David T. Almquist, University of Florida.

Dorsal comparisons of the elytral apices under magnification may also aid in distinguishing species.

Eggs: Eggs are oblong (ca. 1.0 mm × 0.5 mm) and pearly white.

Larvae: Larvae are small, whitish, legless, and grublike with reddish colored heads that are <1 mm wide.

Pupae: Pupae are waxy-white and similar in size to adults

(All descriptions from USDA Forest Service 1985, Connor and Wilkinson 1983).

Biology (Back to Top)

Adult male Ips beetles are responsible for host selection, principally attacking trees that are stressed, damaged, or recently killed (Coulson and Witter 1984). Males release two primary types of aggregation pheromones, one produced when successfully feeding and the other in response to the presence of defensive resin produced by the tree. These pheromones attract both females and males in numbers that can overwhelm a tree’s defense mechanisms. The highest rates of aggregation occur when both pheromone types are produced, indicating that the tree is susceptible to colonization yet still capable of activating its defenses (Vité et al. 1972).

The adult male bores into the phloem and excavates a nuptial chamber, where it mates with one to five (commonly three) females. After mating, each female excavates an egg gallery that extends away from the nuptial chamber and usually parallel to the wood grain, resulting in an overall I-, H- or Y-shaped gallery pattern.

Figure 7. Inner bark gallery characteristic of the sixspined ips, Ips calligraphus (Germar). Photograph by Ronald F. Billings, Texas Forest Service; http://www.forestryimages.org.

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Figure 8. Inner bark gallery characteristic of the eastern fivespined ips, Ips grandicollis (Eichhoff). Photograph by Jeffrey M. Eickwort, FDACS.

Figure 9. Inner bark gallery characteristic of Ips avulsus (Eichhoff). Photograph by Ronald F. Billings, Texas Forest Service; http://www.forestryimages.org.

Eggs are deposited in niches along the sides of the egg galleries. Larvae tunnel in the phloem perpendicular to the egg galleries and eventually pupate in individual cells excavated in the inner bark. After pupation, the adult will feed for a short time in the phloem before emerging through the bark, leaving small scattered emergence holes (USDA Forest Service 1985). Newly-emerged adults can fly as far as four miles in their first dispersal flight to find a new host tree (Kinn 1986).

Development is slower in cool temperatures and the time required to complete the life cycle varies from a few weeks in the summer to several months through the winter. Ips calligraphus and Ips grandicollis can complete their life cycles within 25 days during the summer and can produce eight generations per year in Florida (Dixon 1984), while the Ips avulsus life cycle can take as little as 18 days, producing 10 generations per year. Generations commonly overlap and all life stages may overwinter in the tree (Connor and Wilkinson 1983).

The three species of Ips tend to colonize different parts of the tree, although there is considerable overlap between these territories (Coulson and Witter 1984). Ips calligraphus usually attacks the lower bole or portions of stumps, trunks, and large limbs greater than 10 cm (4 in) in diameter (Connor and Wilkinson 1983). Ips grandicollis prefers to infest recently felled trees and slash, but also can be found infesting weakened living trees, most heavily on large limbs and the mid to upper bole of the host. Ips avulsus prefers small-diameter slash, but will attack groups of young trees and the crowns of large trees (USDA Forest Service 1985). Ips avulsus shows a higher degree of aggregation behavior than some other Ips species (Mason 1970).

Hosts (Back to Top)

All three southern Ips species can infest any pine species within their range, and occasionally other conifers such as spruce, hemlock, and fir. Common hosts in Florida include loblolly pine (Pinus taeda L.), longleaf pine (Pinus palustris Mill.), pond pine (Pinus serotina Michx.), sand pine (Pinus clausa (Chapm. ex Engelm.) Vasey ex Sarg.), shortleaf pine (Pinus echinata Mill.), slash pine (Pinus elliottii Engelm.), and spruce pine (Pinus glabra Walt.).

Detection (Back to Top)

Often the first noticeable indication of an Ips infestation is the fading of foliage from green to yellow to reddish brown as the host tree wilts due to plugging of the xylem by blue-stain fungi.

Figure 10. Fading crown, a possible sign of an Ips engraver beetle infestation. Photograph by John L. Foltz, University of Florida.

Figure 11. Blue-stain fungi in the sapwood, emanating from an Ips gallery in the phloem, a possible sign of an Ips engraver beetle infestation. Photograph by John L. Foltz, University of Florida.

These color changes can occur in two to four weeks in warm weather, but may take several months in the winter. In cooler weather, the beetles have frequently vacated the tree by the time the needles fade. Early signs of attack include the accumulation of reddish-brown boring dust on the bark, nearby cobwebs, or understory foliage.

Figure 12. Boring dust, a possible sign of an Ips engraver beetle infestation. Photograph by Albert E. Mayfield III, FDACS.

If there is sufficient resin pressure within the host, attacked trees will exhibit dime-sized, whitish or reddish-brown globs of resin and boring dust called «pitch tubes» on the bark at each point of beetle attack.

Figure 13. Pitch tube, a possible sign of an Ips engraver beetle infestation. Photograph by Wayne N. Dixon, FDACS.

Unlike those of the southern pine beetle, Ips pitch tubes are more commonly seen on the surface of bark plates than in bark crevices. After beetles emerge from the tree, scattered circular emergence holes (1 to 3 mm diameter) can be observed on the outer bark. By removing a section of the outer bark, the characteristic Y-, I- or H-shaped galleries may be observed in the phloem or engraved on the outer sapwood (Connor and Wilkinson 1983).

These gallery patterns are sometimes obscured by larval galleries of other phloem borers in the families Cerambycidae (roundheaded borers) and Buprestidae (flatheaded borers) that readily colonize dead pines.

Prevention and Management (Back to Top)

The strategies for preventing damage and controlling the spread of Ips beetles essentially involve promoting tree vigor and reducing the amount of vulnerable host material within the stand.

Preventative strategies in forest stands include:

  • planting species that are appropriate to the site,
  • thinning dense, overstocked stands,
  • conducting prescribed burns or other treatments to control competing understory vegetation,
  • removing and/or salvaging damaged, declining, or recently-dead trees,
  • avoiding damage to residual stand when conducting management operations, and
  • lopping and scattering or removing logging slash.

(From Connor and Wilkinson 1983, Dixon 1984, Thatcher and Barry 1982)

As for control, when Ips infestations are small and/or sparsely scattered throughout a stand, the best course of action is often to let them die out on their own. Cutting and removal of isolated infested trees or small «spot» infestations with buffer strips (as is done to control D. frontalis infestations) is not recommended. Observations in Florida suggest that such selective removals may increase the likelihood of Ips problems by producing fresh host odors, logging slash, and additional stress or injury to the residual stand. If scattered mortality is progressing to unacceptable levels, a stand-level clearcut or a contiguous block removal of a generally infested area may be preferable to selection harvests.

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For urban and residential landscape trees, preventative strategies include the following:

  • avoiding compaction of, physical damage to, or pavement over the root zones of pines,
  • providing adequate spacing (15 to 20 feet) between trees,
  • minimizing competing vegetation beneath pines,
  • maintaining proper soil nutrient and pH status by employing an acidic needle or pine bark mulch over the root zone in place of turf grasses that require frequent irrigation, and
  • providing supplemental deep watering during extended drought periods.

In some cases, the application of an approved insecticide that coats the entire tree bole may be warranted to protect high-value landscape trees from infestation; contact your local county Cooperative Extension Service office for current insecticide recommendations.

When infested trees are removed, care should be taken to avoid injury to surrounding pines. There is no effective way to save an individual tree once it has been successfully colonized by Ips beetles (Connor and Wilkinson 1983, Dixon 1984, Thatcher et al. 1978).

Selected References (Back to Top)

  • Anderson NH, Anderson DB. 1968. Ips bark beetle attacks and brood development on a lightning-struck pine in relationship to its physical decline. Florida Entomologist 51: 23-30.
  • Anderson RF. 1948. Host selection by the pine engraver. Journal of Economic Entomology 41: 596-602.
  • Anderson RF. 1977. Dispersal and attack behavior of the southern pine engraver Ips grandicollis Eichh., Coleoptera, Scolytidae. Pg. 17-23 In Technical Bulletin 310. Technical Bulletin of the Agricultural Experiment Station, University of Minnesota.
  • Connor MD, Wilkinson RC. 1983. Ips bark beetles in the South. USDA Forest Service, Washington, D.C. Forest Insect & Disease Leaflet 129. 8 p.
  • Coulson RN, Witter JA. 1984. Forest Entomology: Ecology and Management. John Wiley & Sons, Inc. 315-318.
  • Dixon WN. 1984. Ips engraver beetles. FDACS, Division of Forestry. Forest and Shade Tree Pests Leaflet No. 2. 2 p.
  • Kinn DN. 1986. Studies on the flight capabilities of Dendroctonus frontalis and Ips calligraphus: preliminary findings using tethered beetles. USDA Forest Service Research Note SO-324. 3 p.
  • Kopper BJ, Klepzig KD, Raffa KF. 2004. Components of antagonism and mutualism in Ips pini-fungal interactions: relationship to a life history of colonizing highly stressed and dead trees. Environmental Entomology 33: 28-34.
  • Lovelady CN, Pulley PE, Coulson RN, Flamm RO. 1991. Relation of lightning to herbivory by the southern pine bark beetle guild (Coleoptera: Scolytidae). Environmental Entomology 20: 1279-1284.
  • Mason RR. 1970. Comparison of flight aggregation in two species of southern Ips (Coleoptera: Scolytidae). Canadian Entomologist 102: 1036-1041.
  • Miller MC. 1983. Lightning strike simulation for studying southern pine bark and engraver beetle attacks. USDA Forest Service Research Note SO-296. 4 p.
  • Thatcher RC, Barry PG. 1982. Southern pine beetle. USDA Forest Service, Washington, D.C. Forest and Disease Leaflet No.49. 7 p.
  • Thatcher RC, Coster JE, Payne TL. 1978. Southern pine beetles can kill your ornamental pine. USDA Forest Service, Combined Forest Pest Research Development Program, Washington, D.C. Home and Garden Bulletin 226. 15 p.
  • USDA Forest Service. 1985. Insects of Eastern Forests. Miscellaneous Publication No. 1426. Washington, DC. 358-359.
  • Vité JP, Bakke A, Renwick JAA. 1972. Pheromones in Ips (Coleoptera: Scolytidae): occurrence and production. Canadian Entomologist 104: 1967-1975.

Authors: Jeffrey M. Eickwort and Albert E. Mayfield III, Florida Department of Agriculture and Consumer Services ( FDACS ) — Division of Forestry; and John L. Foltz, University of Florida
Originally published as DPI Entomology Circular 417.
Photographs: David T. Almquist and John L. Foltz, University of Florida; Jeffrey M. Eickwort, Albert E. Mayfield III, and Wayne N. Dixon, Florida FDACS; Ronald F. Billings, Texas Forest Service.
Web Design: Don Wasik, Jane Medley
Publication Number: EENY-388
Publication Date: September 2006. Reviewed: October 2018.

An Equal Opportunity Institution
Featured Creatures Editor and Coordinator: Jennifer L. Gillett-Kaufman, University of Florida

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Bark Beetles in Trees and Firewood

Description of bark beetles

Bark beetles feed and develops within the cambium layer just under the bark of trees. They are widespread, common and frequently abundant. Bark beetles are found in trees that are under stress or are in the process of dying. They are also common in firewood cut from recently-dead or cut trees. There are hundreds of species of bark beetles. Most are host plant specific and will attack only one species of group of related trees.


Bark beetle emergence holes. Photo by DR Lewis.

Life cycle of Bark beetles

Bark beetles are small (1/16 to 1/8-inch in length) cylindrical, brown to black beetles. Adults typically appear in the spring and females deposit eggs in galleries just under the bark. The eggs hatch into small white legless larvae with brown heads. The larvae tunnel under the bark as they eat and grow, producing winding tunnels between the bark and the sapwood of the tree. New adults emerge through small round exit holes in the bark. There may be 2 or 3 generations of beetles produced each season and dying trees, logs or firewood may contain hundreds of individuals.

Damage caused by bark beetles

Bark beetle attack of trees, logs or firewood is recognized by powdery, sawdust-like frass created as the beetles chew and tunnel under the bark. Small, buckshot-sized emergence holes indicate past bark beetle activity as most of the holes are made when the beetles emerge from infested wood. Small winding tunnels or galleries (less than one-eighth inch wide) under the loose bark show where bark beetles were feeding.

Bark beetles are usually a secondary problem in the landscape. Most bark beetle species attack trees that are severely stressed or dying. They do not cause trees to decline or die but rather are taking advantage of a tree weakened by previous events or circumstance (even though the tree may not outwardly appear compromised). Newly transplanted trees are particularly susceptible to attack. Healthy, well-established trees are rarely successfully attacked by bark beetles.

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Management of bark beetles


Bark beetle galleries. Photo by Pennsylvania
Department of Conservation
and Natural Resources via Bugwood.org.

Control of bark beetles is usually not practical after they are established inside a tree (as evidenced by numerous emergence holes or loose bark). Prune and discarded bark beetle-infested limbs and trees. Prevent bark beetle problems by promoting tree vigor through proper site selection, planting, mulching, watering, pruning, and avoidance of injury. Insecticide sprays are not effective when applied to trees that are already heavily infested.

Bark beetles attack green logs and firewood for one or two seasons following cutting but do not attack cured wood or lumber. Bark beetles that emerge inside the house can be annoying and a source of anxiety. However, they are never a threat to people, furniture or the house structure. Spraying infested firewood is of no practical benefit and is not advised.

Do you live in Iowa and have an insect you would like identified?

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them. Please see our website for current forms, fees, and instructions on preserving and mailing insects.

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Pests & Diseases of Pine Trees

Healthy pine trees can better resist diseases or insect infestations.

Related Articles

Pine trees and shrubs are members of the conifer family, a diverse group that grows in a variety of climates. They like full sun and well-drained soil and, once established, don’t require a lot of water. They vary widely in size, from the tiny 4-foot dwarf mugo pines (Pinus mugo), to the stately 100-foot white pine (Pinus strobes). Pines are generally easy to care for, but can be plagued by pests and diseases. Some of the more common include cankers, rusts, bark beetles and soft scales.

Cankers

If your pine tree develops an area of dead, sunken tissue on its stems or branches, it could be afflicted with a canker disease. Foliage on infected limbs can turn yellow or brown and wilt, while infected bark can become discolored and ooze resin. Pines infected with canker diseases are also vulnerable to fungal diseases. Untreated canker diseases can spread, killing limbs or the entire tree. The best defense against canker diseases is to choose disease-resistant cultivars that are suited to your soil and climate. If existing pines become infected, prune out infected areas by cutting into healthy wood past the infection. Once the trunk is infected, pruning is of limited effect. Do not fertilize pines with cankers, as this can promote the spread of disease.

Rusts

Rusts on pine trees look just like what their name implies: Infected areas develop dry red, orange or yellow pustules or spore masses. Some rusts cause cankers on bark, spots on foliage, and orange, gelatinous masses. Rusts can cause limbs and branches to die back, and, if untreated, can spread and kill the entire pine. “Witches brooms,” leaves and foliage that become dwarfed, distorted and discolored, can also be the result of rust infections. To combat rusts, don’t water pine shrubs from above, as this can cause spores to germinate. Clean up and dispose of infected needles, remove and dispose of infected branches as soon as you see them. Fungicides applied in the spring can reduce rust infections but frequent applications are required, which can be difficult.

Bark Beetles

Bark beetles are common pine pests, with more than 600 species of bark beetles in North America and 200 species in California alone. The most common species are western pine beetles, engraver beetles and red turpentine beetles. If you suspect bark beetle infestation, peeling back the bark to expose beetle tunnels can help identify which beetle you’re dealing with. Western pine beetles attack pines mid-trunk then work their way up and down the tree in a spaghetti-like pattern. Red turpentine beetles attack the lowest parts of the trunk and the roots and tunnel out cave-like galleries then move downward. Engraver beetles attack pines near the top and make wishbone-shaped tunnels. Because beetles live under bark, insecticides are usually not effective against them. Cultural practices, such as selecting healthy trees that are suited to your environment, avoiding injuring pines which can allow beetles access through wounds, and thinning dense stands of trees are the best defenses.

Soft Scale Insects

Although scale insects don’t typically harm pines, they are a nuisance because they secrete honeydew, a sticky liquid that provides a place for black sooty mold to grow. Scales don’t always look like typical insects — adult females and immature nymphs don’t have recognizable body parts, don’t move and look like rounded, flat lumps. Adult males are tiny and only live for a few hours, so you will probably never see them. Irregular pine scale insects typically infect Monterey pines (Pinus radiata) but are also found on other pine species. Heavy scale infestation can cause foliage to yellow and drop but the major concern is the abundant production of honeydew. They rarely kill trees although they do reduce trees’ health and vigor. Scale insects are usually controlled by natural predators, unless ants, attracted to the honeydew, interfere. Applications of pesticides and narrow-range oils can control scales, but these also kill natural predators. Controlling ants is usually enough to allow natural predators to return and, in turn, control the scales.

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