Notes on the biology of Larinus minutus Gyllenhal (Col., Curculionidae), an agent for biological control of diffuse and spotted knapweeds

The weevil, Larinus minutus oviposits in open flowers of diffuse and spotte d knapweed [Centaurea diffusa and C. maculosa (Asteraceae)] and the larvae feed on developing achenes. The species is univoltine and overwinters as an adult in soft soil or among debris near the host plant. Overwintered adult s appear on plants by mid-May. Oviposition begins at the end of June and th e new generation starts to emerge by the end of July. Up to 130 eggs per fe male were laid in C. diffusa flowers in cages. One larva destroys 100% of t he seeds in an infested seedhead. During the warm hours of the day lover 30 degrees C) the adults hide under flowers or other parts of the plants and remain inactive.