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How to identify it
- Adults average about 5 mm long (the Idaho guide gives 3.6 to 5.0 mm), are light tan when newly transformed and darken through reddish brown to jet black, and are thinly clothed in fine short hairs. Each wing cover carries three tooth-like projections along the outer margin of the rear slope, with the middle one standing out; in the Idaho guide's key the third spine is large, cylindrical and knob-tipped, unlike the smaller, more pointed third spine of Ips latidens.[1][2]
- The gallery is distinctive. A rounded central nuptial chamber, two to three times the width of the egg tunnels, has one or two strongly curved egg tunnels running from it, often forming an incurved or S-shaped pattern that deeply etches the sapwood. Egg niches sit evenly spaced along the outer side of the curves, and two to four frass-filled larval tunnels fan out from each niche, running 5 or more inches and ending in an oval pupal chamber.[1][2]
- Eggs are off-white, glossy and ovoid, about three-quarters of a millimeter long, laid usually four to a pocket and plugged with borings. Larvae are off-white, deeply wrinkled and legless with a light tan to reddish-brown head, and pupae are off-white and glossy in cells cut by the full-grown larva.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| California fivespined ips (Ips paraconfusus) | Shares the same slash and sometimes the same trees; it carries five spines on each side of the rear slope rather than three.[1] |
| Pine engraver (Ips pini) | Another western Ips of pine slash and weakened trees; the Monterey pine ips is told by its three-spined declivity with a large knob-tipped third spine and its strongly curved, S-shaped egg galleries.[1][2] |
| Red turpentine beetle (Dendroctonus valens) | Attacks the lower trunk and is listed as one of the stresses that make a maturing pine susceptible to Monterey pine ips attack higher up.[1] |
Where it lives
Recorded from British Columbia and Alberta, Alaska, and Washington, Idaho, Montana, Wyoming, Utah, Oregon and California, at elevations from sea level to over 9,000 feet; in Idaho it is known from Blaine, Kootenai, Payette and Valley counties among others. Its best-known damage is in the native Monterey pine forests from the San Francisco Bay area and the Monterey Peninsula south to Cambria in San Luis Obispo County, California, with scattered records elsewhere in California from Sequoia National Park, Lake Tahoe, the Lassen National Forest and other sites.[1][2]
Biology and life cycle
The male starts the attack. He bores through the bark, excavates the central nuptial chamber, and is joined by two and sometimes three females; he stays in the chamber to mate and to clear borings while the females extend the egg tunnels. Each female lays about 90 eggs, and one female has been recorded laying more than 170.[1]
Development is fastest in summer and fall: eggs hatch in 4 to 8 days, larvae finish in 6 to 7 weeks, pupal cells are built at the end of the sixth and during the seventh week, pupation follows in the eighth week and adults appear in the ninth. Very few mature before winter sets in, and the beetle overwinters mainly as adults and larvae, with all stages sometimes present and considerable brood overlap.[1]
Under optimum conditions up to three generations are produced in a year, the number varying with temperatures within the stand; a single life record from lodgepole pine at Lake Tenaya showed just one generation that year, and the Idaho guide gives probably one generation a year in Idaho.[1][2]
Hosts are pines: Monterey pine above all, plus lodgepole, knobcone, whitebark, Jeffrey, limber and bishop pine, and in the Northern Rockies lodgepole and ponderosa pine. The beetle breeds abundantly in fresh slash, in stems from 3 to more than 20 inches in diameter with bark a quarter inch to an inch thick, and in recently felled trees.[1][2]
Damage and signs
- Attacks kill branches, tops and sometimes entire trees, hitting scattered individual trees or groups in both natural and planted stands. Infestations usually go undetected until a limb, a top or much of the crown fades, and dying trees mostly appear in late fall, winter and spring, marking fall attacks. Where summer logging or clearing has left slash, reddened limbs or tops may show in nearby trees that fall.[1]
- Maturing stands are attacked when trees are weakened by competition, drought, mistletoe infection, basal red turpentine beetle infestation or Peridermium rust, and outbreaks are most likely where such weakened trees stand near abundant broods in slash. Woodpecker workings or their holes along the main stem can give away an infestation before the crown fades.[1]
- Blue-stain fungi carried in by attacking beetles stain the sapwood and cambium deeply, though they are not believed to kill the brood.[1]
Health risk
A forest and landscape tree pest; the leaflet describes damage to pines only.[1]
Control
Prevention
Keep stands vigorous: spacing that gives trees light and moisture, minimizing insect-infested, fungus-infected and mistletoe-ridden trees, and avoiding root damage from fills or excavations all reduce the supply of weakened hosts.[1]
Sanitation
Keep fresh pine slash from accumulating. The 1970 leaflet advises removing winter storm breakage from the woods before the end of spring, not leaving thinning, clearing or logging slash with stems over 3 inches in diameter in the woods longer than four weeks between mid-February and mid-November, and utilizing each felled tree to as small a top diameter as is practical. Appraising damage soon after severe winter storms shows how much potential breeding material is on the ground.[1]
Traps and physical control
Outbreak populations in living stands can be suppressed by felling infested trees and destroying the broods, by milling the logs promptly or running remaining material through a chipper. Logs taken to a nearby mill and processed at once have their broods destroyed in the milling.[1]
Biological control
Several predators attack the beetle in the bark: the green trogositid Temnochila virescens chlorodia, the black-bellied and red-bellied clerids, the flattened red beetle Cucujus clavipes, and a small grayish mite that preys on eggs and larvae. Braconid wasps in the genus Coeloides are believed to be important parasites, and molds in the galleries are thought to kill some brood.[1]
When to call a professional
The leaflet's own insecticide recipes date from 1970 and it warns that pesticide recommendations are reviewed regularly; check current guidance with a county agricultural agent, state agricultural experiment station or local forester before any chemical treatment of slash or trees.[1]
Common questions
- Why is the name different everywhere?
- The beetle has been published as Ips radiatae and as Ips mexicanus, and Cognato transferred it to the new genus Pseudips in 2000, so older Forest Service and extension material uses the older names.[2][1]
- My Monterey pine lost its top this winter. Could this beetle be why?
- It is a known pattern. Attacks kill branches and tops as well as whole trees, and dying trees mostly show up in late fall, winter and spring after fall attacks, especially where fresh slash was nearby.[1]
- What is the single most useful thing to do?
- Deal with the slash. Fresh pine slash over 3 inches in diameter is where the big broods come from, so removing, milling or chipping it promptly, and not leaving storm breakage through spring, is what keeps populations down.[1]
Sources
- USDA Forest Service, Pacific Southwest Forest and Range Experiment Station, “Forest Pest Leaflet 56: Monterey Pine Ips (G. R. Struble, revised August 1970; as Ips radiatae).” www.fs.usda.gov/foresthealth/docs/fidls/FIDL-56-MontereyPineIps.pdf (accessed 2026-11-10)
- University of Idaho, Idaho Forest, Wildlife and Range Experiment Station, “Furniss and Johnson. Field Guide to the Bark Beetles of Idaho and Adjacent Regions, Station Bulletin 74 (2002).” objects.lib.uidaho.edu/fwres/fwres201.pdf (accessed 2026-11-10)
- iNaturalist, “Pseudips mexicanus taxon page (order and family).” www.inaturalist.org/taxa/456040 (accessed 2026-11-10)