Ips beetles, Ips spp.
Order: Coleoptera
Family: Curculionidae
Description
There are 11 species of Ips spp. inhabiting Colorado: Ips hunteri, Ips pilifrons, Ips pini, Ips knausi, Ips calligraphus, Ips confusus, Ips latidens, Ips borealis, Ips integer, Ips woodi, and Ips mexicanus. Adults are typically dark red or brown to black, 3-9.5 mm (1/8-3/8 inches) long and have a pronounced rear lined with three to six pairs of spines, depending on the species. Larvae of Ips beetles are white or gray, legless, have dark heads, and measure about 6.5 mm (1/4 inch) long. The larvae develop and feed under the bark of pine (Pinus spp.) and spruce (Picea spp.) trees. These beetles tend to target trees in declining health with root injuries, wounds, or other stresses. Ips beetles rarely attack healthy trees and are not as destructive as beetles in the genus Dendroctonus which also attack coniferous trees in Colorado. Prolonged drought stress and the abundance of freshly cut wood have contributed to the recent escalation of the Ips beetle infestations in the state.
Blue spruce engraver
Along the front range of Colorado and southeastern Wyoming, the blue spruce engraver (Ips hunteri) is a common pest of Colorado blue spruce (Picea pungens). Adults of this species are about 3-4 mm (1/8-1/4 inch) long and have four spines along the tip of the abdomen. The larvae are legless and C-shaped.
Ips confusus
This species of Ips beetle can kill more pinyon (Pinus edulis) trees than any other pest. While pinyon pines are the preferred host, I. confusus can also attack other pine species. The light brown beetles are cylindrical and measure 3-6 mm (1/8-1/4 inch) in length and have five spines along the tip of the abdomen.
Quick Facts
- The genus Ips includes several species of small beetle that attack stressed or unhealthy pine and spruce trees. Management is typically not required.
- Trees infested with Ips beetles tend to accumulate yellow or red fine sawdust around the base that is pushed out of the trees by adults as they form galleries under the bark.
- Newly transplanted trees, trees in poor health, and trees surrounded by infested wood are susceptible to Ips beetle attack. In these cases, preventative insecticide applications should be considered.
Adult of Ips sp. Note the brown coloration and spines at the rear. Image credit: Ladd Livingston, Idaho Department of Lands, Bugwood.org
Ips beetle with black coloration. Note the spines at the end of the abdomen. Image credit: USDA Forest Service, USDA Forest Service, Bugwood.org
Southern pine beetle (Dendroctonus frontalis). Note the gradual curvature of the wings and lack of spines at the end of the abdomen, which is a distinguishing feature of Dendroctonus spp. Image credit: Gerald J. Lenhard, Louisiana State University, Bugwood.org
Larva of the blue spruce engraver. Note the C-shape. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Nuptial chamber and galleries produced by Ips beetle. Image credit: G. Keith Douce, University of Georgia, Bugwood.org
Galleries produced by Ips confusus. Note the absence of dust in the network of tunnels. This photo was captured near Cannon City, CO. Image credit: William M. Ciesla, Forest Health Management International, Bugwood.org
Pitch tube due to boring of Ips spp. Pitch tubes are not always present on trees infested with Ips beetles and are also observed on trees infested with other bark-boring beetles in the genus Dendroctonus. Image credit: G. Keith Douce, University of Georgia, Bugwood.org
Red pine (Pinus resinosa) with exit holes produced by Ips pini. Image credit: Steven Katovich, Bugwood.org
Sawdust excavated by Ips beetles. Image credit: Jeffrey Eickwort, FL Department of Agriculture and Consumer Services, Bugwood.org
An example of top kill due to infestation of spruce engraver beetle. This photo of Colorado blue spruce was captured in Fort Collins, CO. Image credit: William M. Ciesla, Forest Health Management International, Bugwood.org
Life history and habits
Adults overwinter under bark or in litter at the tree base. Males construct a nuptial chamber under the bark of weakened trees in the spring and are attracted to the volatile compounds in tree resin. Pheromones secreted by the male attract females to the chamber for mating, after which galleries for egg laying are excavated from the central chamber and appear as a “Y” or “H” shape, depending on the species. Adults push dust out of the entrance holes as they expand the galleries, resulting in clear galleries that appear different than the frass-filled galleries produced by Dendroctonus spp. Upon hatching, young larvae tunnel small lateral galleries. There are two to four generations produced each year in Colorado.
Blue spruce engraver
Ips beetles associated with spruce, such as the blue spruce engraver, produce two or more generations each year. Flights tend to occur in April and late July, and sometimes a third flight occurs in October during periods of warm fall weather. The blue spruce engraver produces two egg galleries that radiate in opposite directions away from the central nuptial chamber. In the summer of 2022, Fort Collins experienced an alarming increase in spruce tree deaths caused by the blue spruce engraver.
Ips confusus
This species is attracted to pinyon trees with compromised defenses due to root injuries, wounding, compacted soil, winter damage, overwatering, or underwatering. However, even healthy trees are susceptible to infestation during times of drought stress. Ips confusus activity begins and ends when daytime temperatures are consistently above or below 50 °F (10 °C), respectively. The first generation of Ips confusus tend to infest stressed trees, green branches removed during tree cuttings, or freshly cut green logs or firewood. Ips confusus produces up to four generations per year.
Populations of I. confusus are usually sparce, but they can increase rapidly when large numbers of stressed host trees are available. During outbreaks, populations can spread from susceptible stands to adjacent, unsusceptible stands. Large numbers of host trees can be killed during such outbreaks, and many acres of pinyon trees can be affected. For example, in 2002 to 2004 an outbreak of I. confusus killed millions of pinyon trees across six southwestern states.
Injury
Trees can tolerate a certain amount of Ips beetle infestation. However, repeated infestations of Ips beetles can increase the stress on a tree and decrease its likelihood of survival. Trees infested with Ips beetles will have yellow or red to brown dust accumulate at the base, which is produced by adults as they excavate tunnels beneath the bark. Portions of the tree affected by tunneling larvae will be discolored and can die. Small round exit holes in bark are a common symptom of Ips beetle infestation and indicate that adults have completed their development and exited an infested tree. Another indicator of an Ips beetle infestation is patches of tree bark removed by woodpeckers in search of larvae. In addition, Ips beetles can introduce blue-stain fungi to infested trees, which can quicken tree mortality.
Spruce engraver beetle
Outbreaks of spruce engraver beetle in healthy trees are uncommon and tend to be short-lived. Feeding injuries produced by the spruce engraver beetle include top kill of infested trees and the presence of pitch tubes. However, pitch tubes may not always be present and can also be caused by other bark-boring beetles such as the red turpentine beetle (Dendroctonus valens). The spruce engraver beetle tends to kill the top of infested trees and gradually moves downward.
Ips confusus
When under attack, the needles of pinyon trees fade from green to rust or straw in color. In infested trees, needles will continue fading to brown and die. When pinyon trees are showing visible signs of death, it is likely that the beetles have already exited and spread to other susceptible trees. However, dry conditions can cause needles to begin fading weeks after an infestation, or even several months after an infestation in years with adequate precipitation.
Scouting
When external indicators of an infestation are present, removing small sections of bark can reveal galleries created by Ips beetles. One important feature is that the galleries of Ips spp. will be free of dust, unlike galleries produced by Dendroctonus spp. who often have overlapping hosts.
Prevention
Practices that promote vigorous tree growth, such as optimally positioning trees within landscapes, can help prevent attacks. Adequately watering trees and avoiding injuries to root systems through compaction, mechanical damage, or disease, is also recommended. Freshly cut trees should not be placed near valuable trees, and green or infested coniferous wood should not be stacked near living coniferous trees. Woody materials can be chipped to destroy any remaining larvae. Cut wood can also be scattered (rather than piled) or slashed to facilitate drying. Newly transplanted trees, trees in poor health, and trees surrounded by infested wood are susceptible to infestations of Ips beetles. In such cases, trees may benefit from preventative insecticide applications.
Spruce engraver beetle
Spruce engraver beetle can be particularly problematic in high-use recreation areas due to the increased stress from soil compaction and wounding from human activity. Removing infested trees is typically sufficient to prevent the spread of spruce engraver beetle. In Fort Collins, it is also recommended that about 10 gallons of water per diameter inch be applied to trees weekly from May through October when temperatures remain over 40 °F (4.5 °C). Water can also be applied from November through April under suitable environmental conditions. In some situations, preventative insecticide applications may be warranted on ornamentals in urban settings.
Ips confusus
Watering pine trees in winter and in summer during periods of drought can help improve tree health and protect against stress. In winter, favored trees can be watered monthly when temperatures are above 40 °F (4.5 °C) and no snow is present. Water can be applied to the edge of the drip line, which includes the root zone where rain would naturally drip off the canopy. Trees infested with I. confusus should be removed as soon as they are identified. Dead trees should be removed to reduce wildfire risks and for aesthetic purposes.
Chemical control
There are no chemical treatments available for cut wood infested with Ips beetles. For live trees, insecticides should be applied as sprays on trunks and larger branches prior to infestation of adult beetles. Insecticide concentrations for bark beetles are typically greater than those used to target insects on foliage. For this reason, it is recommended that applications be limited to bark. Active ingredients effective against Ips beetles include carbaryl, bifenthrin, and permethrin. To protect ornamentals from spruce engraver beetle, preventative insecticides should be applied prior to beetle flight. It is important to note that insecticide applications are ineffective against Ips beetles once a tree is already infested.
Depending on the insecticide, preventative spraying for I. confusus typically requires at least two applications per year when beetle populations are high.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
City of Fort Collins. (n.d.). Tree Diseases and insect Pests. City of Fort Collins – Forestry. Available https://www.fcgov.com/forestry/diseases-insects
City of Louisville. (n.d.). Ips Beetle. City of Louisville. Available https://www.louisvilleco.gov/local-government/government/departments/parks-recreation-and-open-space/forestry-program/ips-beetle
Cranshaw, W. 2016. Ips hunter Swaine. Bugwood Wiki – High Plains Integrated Pest Management. Available https://wiki.bugwood.org/HPIPM:Spruce_Ips
CSFS. (n.d.). Pinon Ips Bark Beetle. CSFS – Quick Guide Series. Available https://csfs.colostate.edu/wp-content/uploads/2020/06/2020_Pinon_Ips_CSFS_Quick_Guide_Web.pdf
USDA. 2011. Pinyon Ips. USDA – Forest Service. Available https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5306142.pdf
West, A. 2023. Ips beetles. University of Idaho – Extension. Available https://www.uidaho.edu/extension/ipm/urban-pests/arthropods/ips-beetles