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

Abstract

The weevil, Larinus minutus oviposits in open flowers of diffuse and spotted 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 adults appear on plants by mid-May. Oviposition begins at the end of June and the new generation starts to emerge by the end of July. Up to 130 eggs per female were laid in C. diffusa flowers in cages. One larva destroys 100% of the seeds in an infested seedhead. During the warm hours of the day (over 30°C) the adults hide under flowers or other parts of the plants and remain inactive.

Increased seed consumption by biological control weevil tempers positive CO2 effect on invasive plant (Centaurea diffusa) fitness

“…As such, there has been much research regarding C. diffusa control (reviewed by Muller-Scharer and Schroeder, 1993;Sheley et al, 1998). L. minutus is one of several biological control agents for C. diffusa (Muller-Scharer and Schroeder, 1993;Lang et al, 2000), and is also used for spotted knapweed (C. stoebe) control (Kashefi and Sobhian, 1998;Lang et al, 2000;Bourchier and Crowe, 2011). These weevils have been used in the United States since the early 1990s (Muller-Scharer and Schroeder, 1993;Sheley et al, 1998;Seastedt et al, 2003Seastedt et al, , 2007.…”

“…Adult L. minutus overwinter in leaf litter or soil near C. diffusa and emerge by early May (Kashefi and Sobhian, 1998), prior to C. diffusa flowering in July (Sheley et al, 1998). Stem and leaf material are consumed until flowers have developed, at which point flowers are consumed by females for ovary development (Kashefi and Sobhian, 1998). Faster-developing plants are often preferred by L. minutus (Seastedt et al, 2003;Lejuene et al, 2005;Bourchier and Crowe, 2011), presumably because adults emerge before flowering and later depend on flowers for food and oviposition.…”

“…These weevils have been used in the United States since the early 1990s (Muller-Scharer and Schroeder, 1993;Sheley et al, 1998;Seastedt et al, 2003Seastedt et al, , 2007. Adult L. minutus overwinter in leaf litter or soil near C. diffusa and emerge by early May (Kashefi and Sobhian, 1998), prior to C. diffusa flowering in July (Sheley et al, 1998). Stem and leaf material are consumed until flowers have developed, at which point flowers are consumed by females for ovary development (Kashefi and Sobhian, 1998).…”

“…Adult feeding can damage bolting C. diffusa stems (Seastedt et al, 2003) and even reduce seed production in some instances (Stephens and Myers, 2013). However, larvae develop inside the flower/seed head of C. diffusa and typically consume or damage 100% of the developing seeds (Kashefi and Sobhian, 1998), often having a larger effect than adults on plant control.…”

Rate of dispersal of spotted knapweed biocontrol beetles (Larinus spp. Curculionidae) in Wisconsin

“…The biology, host specificity, and potential impact of L. minutus were described by Groppe et al (1990), Jordan (1995), and Kashefi and Sobhian (1998), and L. obtusus biology was described by Groppe (1992). Evidence suggests that these two species may actually be variants of a single species, making it extremely difficult to distinguish between adults of L. obtusus and L. minutus when they coexist in the field (Story and Coombs, 2004).…”