Cyphocleonus achates
- Common Name: Knapweed root weevil
- Insect: Beetle (Coleoptera: Curculionidae)
- Generations Per Year: One
- Overwintering Stage: Larvae (in the root)
BIOLOGY: C. achates adults emerge from June to September. They are large (14-15mm long) and live for 2-3 weeks. Females lay one egg at a time in the root crown just below the soil. A female will mate and lay eggs over 100 times. Larvae undergo 4 instars. The fourth instar overwinters and pupates in June.
DESTRUCTIVE STAGE: Larvae (root feeding and root galling)
IMPACT TO HOST: First and second instar larvae reduce root mass. Third and fourth instar larvae form swelling and galls in roots. C. achates can kill knapweed plants in a single year, but populations are often not dense enough to reduce entire stands of knapweed. C. achates will be most effective when released with other knapweed biological control agents.
REDISTRIBUTION: Adults can be collected by picking them directly off of plants in the middle of the day in July. A release is typically 50-75 C. achates.
