Europe
Musk thistle (Carduus nutans), plumeless thistle (Carduus acanthoides), Italian thistle (Carduus pycnocephalus), slenderflower thistle (Carduus tenuiflorus), and bull thistle (Cirsium vulgare)
Eggs are opaque, white, and small. Larvae are white with dark brown head capsules and can be up to 3 mm long. Adults are small (approximately 4 mm long), round, and brown with white mottling. They have obvious spines on their thorax and long snouts.
Overwintering adults emerge in spring and feed on rosettes of host plants. Eggs are deposited on leaf undersides, along the midrib and primary veins of young plants. Hatching larvae move down and feed on tissue at the root-stem junction, developing through three instars. Pupation occurs in the soil in early summer. Adults emerge over the summer but are inactive until fall when they feed superficially on host plant foliage. Adults overwinter in plant litter, emerging again in spring and often living until the next generation of adults begin to emerge. There is only one generation per year.
This weevil has been observed feeding on Cirsium thistle species native to North America. Consequently, interstate transport is not permitted in the USA, and some states have prohibited its redistribution within their borders. Where this biocontrol agent is approved for redistribution, it is imperative to refrain from making releases at sites where known related or susceptible native species co-occur.
Adult feeding on foliage in spring is superficial and has minimal impacts. Larval mining of the root crown can kill developing stems. Though secondary stems often develop later, flowering is delayed and seed production may be reduced.
Randall, C.B., J.E., Andreas, J. Milan, and K. Gladem. 2024. Introduced Thistle Biocontrol Agents: History and Ecology in North America. In: R.L. Winston, Ed. Biological Control of Weeds in North America. North American Invasive Species Management Association, Milwaukee, WI. NAISMA-BCW-2024-8-INTRODUCED THISTLES-A. https://bugwoodcloud.org/resource/files/29169.pdf