Pest profile

Western Raspberry Fruitworm

Byturus unicolor · Coleoptera: Byturidae[2]

The western raspberry fruitworm, or raspberry beetle, is a small beetle that feeds on raspberry buds and blossoms; its larvae feed inside the fruit and often remain in it at harvest.[1]

Western raspberry fruitworm adult, a small yellowish-brown beetle, on a flower
Western raspberry fruitworm adult, a small yellowish-brown beetle, on a flower. (c) giantcicada, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Adults are small, yellowish-brown beetles 4 to 5 mm long.[1]
  • Larvae are 8 mm long, white with brown areas on the back of each segment.[1]
  • Adults eat between the veins of unfolding leaves, leaving characteristic slits.[1]

Where it lives

The PNW Insect Management Handbook covers it on raspberries and blackberries in the Pacific Northwest.[1]

US map: public records from 29 states since 1990 (GBIF).

Biology and life cycle

Adults overwinter in the soil and emerge in late April or May to feed and lay eggs on flower buds or stems.[1]

Larvae work to the center of the fruit and feed for 30 days or more, then drop to pupate in the top 3 inches of soil; there's one generation a year.[1]

Damage and signs

  • Spring feeding on fruit buds can be serious, and injured blossoms often become distorted berries.[1]
  • Larvae feed on the fruit's core and often remain in harvested berries as contaminants.[1]

Health risk

It feeds on plants; the PNW Insect Management Handbook mentions no risk to people.[1]

Control

Prevention

Adults are hard to see, but careful checks of new leaves and young blossoms in spring, with a hand lens, will find them.[1]

Pesticides

The handbook lists no products for home-garden use.[1]

Common questions

What are the little worms in my raspberries?
They may be western raspberry fruitworm larvae, which feed inside the fruit.[1]
What makes slits between the veins of new raspberry leaves?
Adult raspberry beetles eat the tissue between the veins, leaving characteristic slits.[1]

Sources

  1. Pacific Northwest Pest Management Handbooks (OSU, WSU, University of Idaho), “Blackberry and Raspberry: Raspberry beetle (aka western raspberry fruitworm) (Insect Management Handbook).” pnwhandbooks.org/insect/small-fruit/blackberry-raspberry/blackberry-raspberry-raspberry-beetle-aka-western-raspberry-fruitworm (accessed 2026-10-06)
  2. iNaturalist, “Byturus unicolor taxon page (order and family).” www.inaturalist.org/taxa/215612 (accessed 2026-10-06)

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