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Poplar borer

Saperda calcarata[5]

The poplar borer is a longhorned beetle whose larvae tunnel through the sapwood and heartwood of aspen, cottonwood, poplar and willow. Utah State calls it a major pest of aspen in landscapes and forests: the tunnels weaken trunks and limbs, and smaller trees can be killed.[1][2][3]

Group
Insect
Order
Coleoptera
Family
Cerambycidae
US records
31 states
Sources
5 cited
Updated
2026-11-08
Adult poplar borer, a gray longhorned beetle speckled with orange-brown spots, with long antennae, on a white sheet
Adult poplar borer, a gray longhorned beetle speckled with orange-brown spots, with long antennae, on a white sheet. (c) Louis Imbeau, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0
On this page
  1. Identification
  2. Where it lives
  3. Biology
  4. Damage and signs
  5. Health risk
  6. Control
  7. Related profiles
  8. Common questions
  9. Sources

How to identify it

  • Adults are longhorned beetles about 1 inch long, sometimes more, gray to gray-blue or gray-tan with small dark, brown or orange spots on the wing covers and antennae about as long as the body.[1][2][4]
  • The larvae are legless, elongate, cream to yellow-white grubs that grow to about 1 1/4 to 1 1/2 inches.[1][2][3]
  • Infested trunks and larger limbs ooze sap mixed with fine frass from the borer holes, with rust-colored stains on the bark and piles of coarse frass at tunnel entrances; heavily infested trees may show a blackish stain below the attack.[2][1][3]

Where it lives

Utah State describes it as a major pest of aspen in Utah's landscapes and forests, Montana State covers it on aspen, cottonwood and poplar in Montana, and Nebraska Extension lists it among the borers of shade trees there.[1][3][4]

US map: public records from 31 states since 1990 (GBIF).

Biology and life cycle

Hosts are aspen, cottonwood, poplar and willow. Females favor older trees, stressed trees and trees growing in full sun.[1][2][3][4]

Adults are out from about mid-June through August. Females feed on leaves and shoots for a couple of weeks, then chew slits in the bark and lay one to three eggs in each.[1][2][3]

The larvae bore into the sapwood and heartwood, mostly in trunks and limbs 3 inches or more across, though branches as small as 1 1/2 inches can be attacked. They spend the winter in the wood and pupate under the bark in late spring.[2][1][3]

One generation takes up to about three years.[1][3]

Woodpeckers, parasitic wasps and nematodes attack the larvae; Utah State notes woodpeckers can eat up to 65 percent of them in some regions.[2]

Damage and signs

  • The tunnels weaken trunks and branches, which can snap in high winds, and the wounds let wood rot and other pathogens in.[1][3]
  • Larvae can girdle a tree, and smaller-diameter trees can be killed.[3][1]

Health risk

It is a wood-boring beetle of trees; Utah State and Montana State mention no risk to people.[1][3]

Control

Prevention

Keep trees healthy and well watered. Utah State advises against planting aspen at low-elevation valley sites, and Montana State suggests planting aspen in groups so their trunks are shaded.[1][3]

Sanitation

Remove heavily infested trees, chipping or burning them, since they can affect other trees in the area.[1][3]

Biological control

Insect-attacking (Steinernema) nematodes can be sprayed or injected into active larval galleries.[1][3]

Pesticides

To prevent new attacks, a pyrethroid or carbaryl insecticide labeled for borers can be applied to the bark of the trunk and large branches before egg laying, around early June, concentrating on areas already attacked. Systemic insecticides have given poor control of larvae already in the wood.[2][1][3]

Common questions

What is the rusty, oozing sap and sawdust on my aspen trunk?
Those match the signs Utah State lists for poplar borer: holes oozing sap mixed with frass, rust-colored stains on the bark, and coarse frass at the tunnel openings.[2][1]
Can a heavily infested aspen be saved?
Utah State and Montana State both recommend removing heavily infested trees, which can affect other trees in the area.[1][3]
Will a systemic insecticide kill the borers inside my tree?
Not reliably. Systemics such as acephate or neonicotinoids have not given satisfactory control of the larvae; bark sprays before egg laying are aimed at preventing new attacks.[2][3]

Sources

  1. Utah State University Extension, Integrated Pest Management, “Poplar Borer (Ornamental Pest Guide).” extension.usu.edu/planthealth/ipm/ornamental-pest-guide/arthopods/wood-borers/poplar-borer (accessed 2026-11-08)
  2. Utah State University Extension, Integrated Pest Management, “Poplar Borer (IPM fact sheet, trees and shrubs).” extension.usu.edu/planthealth/ipm/notes_orn/list-treeshrubs/polar-borer (accessed 2026-11-08)
  3. Montana State University Extension, Urban and Horticulture IPM, “Poplar Borer (Saperda calcarata) (Urban Entomology Fact Sheets).” urbanipm.montana.edu/entomology/resources/fact-sheets/poplar-borer.html (accessed 2026-11-08)
  4. University of Nebraska-Lincoln Extension, “Insect Borers of Shade Trees and Woody Ornamentals, EC1580 (J. A. Kalisch and F. P. Baxendale, 2010).” extensionpubs.unl.edu/publication/ec1580/2010/pdf/view/ec1580-2010.pdf (accessed 2026-11-08)
  5. iNaturalist, “Saperda calcarata taxon page (order and family).” www.inaturalist.org/taxa/230386 (accessed 2026-11-08)

Updated 2026-11-08. Built from sourced records. Spot an error? Tell us.