Pest profile

Poplar and Willow Borer

Cryptorhynchus lapathi · Coleoptera: Curculionidae[2]

The poplar and willow borer is a weevil whose larvae girdle and tunnel in willow, poplar, alder and birch stems, killing small limbs.[1]

Poplar and willow borer, a bumpy black weevil with a bright white rear third, seen from the side
Poplar and willow borer, a bumpy black weevil with a bright white rear third, seen from the side. (c) Cosimo Costanzia di Costigliole, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Adults are 1/5 to 1/3 inch, mottled whitish with black or brown, with the rear third of the wing covers bright white.[1]
  • The body is hard and bumpy, and the small head extends into a slender beak.[1]
  • Larvae are white, legless, C-shaped grubs with a reddish-brown head, up to 1/4 inch.[1]

Where it lives

It prefers willow and also attacks alder, birch and poplar.[1]

US map: public records from 23 states since 1990 (GBIF).

Biology and life cycle

Adults emerge from spring to early fall, feed lightly on young bark, and play dead when disturbed.[1]

Females chew holes in bark, lay eggs at the bottom and pack them with frass; egg laying peaks March–April and July–September.[1]

Development takes one to three years.[1]

Damage and signs

  • Larvae girdle and kill small stems; survivors turn bushy and crooked, and weakened stems break.[1]
  • Bark splits and holes ooze sap mixed with reddish-brown and white frass.[1]

Health risk

It feeds on trees only; UC IPM mentions no risk to people.[1]

Control

Traps and physical control

Prune off and destroy infested stems; adults seldom fly, so this reduces local populations.[1]

When to call a professional

Where damage is intolerable, pyrethroid bark sprays in March and July are available only through professional applicators.[1]

Common questions

What is the black weevil with a white rear on my willow?
It's likely the poplar and willow borer.[1]
Why are my willow shoots bushy and crooked?
Larvae killing stem tips cause lateral shoots that look bushy and crooked.[1]

Sources

  1. University of California Statewide IPM Program, “Poplar and Willow Borer (Pests in Gardens and Landscapes).” ipm.ucanr.edu/PMG/GARDEN/PLANTS/INVERT/poplrwilborer.html (accessed 2026-10-06)
  2. iNaturalist, “Cryptorhynchus lapathi taxon page (order and family).” www.inaturalist.org/taxa/217843 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.