Northern Spruce Engraver & Other Ips spp.

Ips perturbatus (Eichhoff),
I. tridens (Mannerheim), I. borealis Swaine,
I. pini (Say), Pseudips concinnus (Mannerheim),
P. mexicanus (LeConte)

Host(s) of Ips perturbatus in Alaska:

White spruce (Piceae glauca), black spruce (P. mariana), Lutz spruce (P. glauca x sitchensis), and Sitka spruce (P. sitchensis)

Habitat(s): phloem, inner bark, and bark

Damage: Beetle larvae feeding in phloem tissue can girdle trees, resulting in tree mortality.

Current Status (2023 Update)

Northern spruce engraver activity was observed on about 124 acres in 2023, down considerably from the 840 acres mapped in 2022. The northern spruce engraver damage observed this year was almost entirely in the Interior. A few additional scattered pockets of activity were observed in the Copper River valley. Damage from northern spruce engraver is typically mapped in Interior Alaska along streams and rivers and in areas of natural disturbances such as fire and wind, though it occurs throughout Alaska’s boreal forest.

The main areas of northern spruce engraver activity in 2023 are noted below. All acreages should be considered the total of several scattered small areas of damage unless otherwise noted.

Newman Creek drainage near its confluence with Dry Creek (one polygon, 25 acres)
North Fork of the Kuskokwim River from its source downstream to around Haystack Mountain (20 acres)
North Fork of the Kuskokwim River from Chleca Lakes downstream about 7 miles to near Bellen Lakes (30 acres)

Historic Activity

Northern spruce engraver activity was observed on about 840 acres in 2022, primarily in small pockets throughout Interior Alaska, a marked increase in activity with less than 10 acres of damage mapped statewide in 2021. Damage from northern spruce engraver is typically mapped in the Interior along streams and rivers and in areas of natural disturbances such as fire and wind, though it occurs throughout Alaska’s boreal forest.

High populations of engraver beetles caused white spruce mortality on 43,000 acres along the south side of the Brooks Range, and in the McGrath area, in 2008. High populations are common in river-bottom spruce stands of interior Alaska, particularly those periodically flooded along the Yukon, Porcupine, Chandalar, and Tanana Rivers.

Symptoms, Biology, & Impacts

Adult engraver beetles are small (3.0 to 4.9 mm long), cylindrical, reddish-brown to black beetles who have a distinct declivity (concave area) on their posterior end with 3 to 4 pairs of tooth-like spines along the outer margins. Species of engraver beetle are differentiated mainly by those spines. Engraver beetles normally completes its life cycle in one year throughout its range, although some observations suggested that the adult stage may last nearly two years while some species can have two generations per year. Adults overwinter as adults primarily in forest litter beneath their brood trees, though occasionally under the bark of the host material in which they developed depending on species. In Alaska, adults begin flying from overwintering sites in late April to late May and continue to mid-July, with peak flight in early to mid-June. The exact timing of emergence depends on temperature. Dispersing beetles attack fresh host materials soon after emergence. Galleries are initiated in the phloem by males, which are later joined by and mate with up to four females in a central nuptial chamber. Mated females extend egg galleries (the arms of the “tuning fork”) that radiate from the central nuptial chamber and deposit eggs in individual niches along the gallery walls. Eggs are oblong, pearly white, and less than 1.5 mm long. Larvae hatch from eggs in 7 to 10 days and feed on phloem tissue. These larvae are stout, cylindrical, legless grubs that pass through four instars (stages) and reach a length of about 3.3 mm at maturity. They develop into pupae after 4 to 5 weeks. Pupae are opaque white, inactive, and somewhat similar in size and shape to adults. The pupal stage lasts approximately 10 days. Pupae transform to new adults and usually exit the host material before the onset of winter. In most cases new adults remain under the bark of the infested tree for a few weeks before moving to their overwinter location. In Alaska, adults have been observed to only establish a single gallery system in a brood tree; adults do not re-emerge and reattack the same or neighboring trees or host logs. Large diameter infested spruce can produce enormous quantities of new adults.

These beetles are known for their opportunistic use of trees damaged by fire, drought, flooding, and human development activities that alter forest stands. The first evidence of engraver beetle attack is the presence of fine, yellow-red boring dust in bark crevices. Preferred host material includes freshly cut logs, and tops of weakened trees. Trees with dead and dying tops are evidence of engraver beetle damage and mortality.

At first glance, engraver beetles may be confused with spruce beetle (Dendroctonus rufipennis). However, spruce beetles are larger (about 4.4 to 7.0 mm long) with its head visible when viewed from above and elytra (wing covers) that are evenly rounded, without spines along the elytral declivity. Engraver egg galleries are also kept free of frass by parent adults unlike spruce beetle galleries that can be partially blocked with frass. Unlike spruce beetle damage and injury, pitch-tubes are rarely formed in response to engraver beetle infestations.

Guidelines for Reducing Damage

Direct control operations generally are not used against Ips as outbreaks develop and disappear rapidly, usually within three years. To reduce engraver beetle population buildup and damage, maintain healthy spruce stands. This can be accomplished by removal of over-mature, densely grown, diseased, and dying trees. Damaged and windthrown trees should be removed or used or destroyed by cutting, burning, chipping, or burying. Partially burned trees in the fringe area of a wildfire should be harvested immediately after the fire if the fire occurs in early spring; otherwise, harvest during the late summer, fall or winter. Timber harvests should be scheduled after July and before February. This ensures that all breeding material produced during the harvest is at least three months old by the time of the beetles flight, rendering it less suitable then fresh material. Infested wood should not be stacked or stored in areas surrounded by live trees. Freshly cut spruce should have the bark removed and/ or be spilt for rapid drying as soon as possible following harvest. Cull logs, tops, and slash greater than 4 inches in diameter should be limbed and cut into short lengths. The material should then be processed or stacked. Insecticides can be used to protect high-value trees from beetle attack.

Western Ips spp. with Host, Distribution & Impacts

Species Name	Hosts	Common Name	Distribution	Impacts
Ips perturbatus (Eichhoff)	Picea glauca, P. engelmannii, P. lutzii (P. glauca x sitchensis) Rarely: P. mariana, P. sitchensis	Northern spruce engraver	Throughout Interior, SC, and SE Alaska	Breeds in logged, slashed, and windthrown trees; overwinters as adults in leaf litter underneath their brood trees
I. tridens (Mannerheim)	Picea engelmannii, P. glauca, P. sitchensis	-	Interior, SC, and SE AK, including the Kenai Peninsula.	Attacks weakened and downed trees
I. borealis Swaine	P. glauca, P. x lutzii, P. engelmannii	-	Interior & SC, AK, including the Kenai Peninsula.	Associated with I. perturbatus in white spruce, with narrower egg galleries
I. pini (Say)	Pinus ponderosa, P. contorta, P. flexilis, P. jeffreyi, other Pinus spp.; also Piceae	Pine engraver	SE AK (Douglas Is., Ketchikan)	Attacks windfallen trees, recently cut logs, and slash; 1-5 generations per year, depending on locality and season length
Pseudips (=Ips) concinnus (Mannerheim)	P. sitchensis, P. × lutzii	Sitka spruce “Ips”	SC & SE AK, Kodiak Is.	Attacks injured, dying, and downed Sitka spruce
Pseudips (=Ips) mexicanus (Hopkins)	Pinus contorta, P. radiata, P. albicaulis, P. attenuata, P. flexilis, P. muricata, other Pinus spp.	Monterey pine “Ips”	SE AK (Juneau, Douglas Is.)	Commonly associated with other bark beetle species; attacks living, injured, dying, and downed pines
Table References: Burnside et al. 2011, Furniss et al. 2002, Graves et al. 2008 https://www.barkbeetles.org/ips/Westips.html

Resources and Publications

Burnside, R. E., Holsten, E. H., Fettig, C. J., Kruse, J. J. Schultz, M. E., Hayes, C. J., Graves, A. D., and S. J. Seybold. 2011. Northern Spruce Engraver Forest Insect and Disease Leaflet. FIDL-180. Available here.

Furniss, M. M., Holsten, E. H., Schultz, M. E. 2002. Species of Alaska Scolytidae: Distribution, hosts, and historical review. Entomological Society of British Columbia, 99: 83-92.

Graves, A. D., Holsten, E. H., Ascerno, M. E., Zogas, K. P., Hard, J. S., Huber, D. P., ... & Seybold, S. J. 2008. Protection of spruce from colonization by the bark beetle, Ips perturbatus, in Alaska. Forest ecology and management, 256(11): 1825-1839.

Holsten, E. H. 2013. Engraver Beetles in Alaska. USDA Forest Service, Alaska Region, State and Private Forestry. Leaflet R10-TP-155. Available here or here.

Holsten, E. H., Hennon, P., Trummer, L., Kruse, J., Schultz, M., & Lundquist, J. 2008. Insects and Diseases of Alaskan Forests. USDA Forest Service, Alaska Region, State and Private Forestry, Forest Health Protection. Publication R10-TP-140, 55. Available here.

Content adapted from Insects and Diseases of Alaskan Forests (2008) p.78-80 (available here) and Engraver Beetles in Alaska Forest Health Leaflet (available here or here).

For more information about this agent, contact Entomologist Dr. Sydney Brannoch at sydney.brannoch@usda.gov.

https://www.fs.usda.gov/detailfull/r10/forest-grasslandhealth/?cid=FSEPRD691404