Nodding thistle receptacle weevil
.jpg)
Adult nodding receptacle weevils.
Source: Jenny Dymock Biocontrol agent:
Nodding thistle receptacle weevil
Scientific name:
Rhinocyllus conicus
Target weed:
Nodding thistle
Carduus nutans
What do nodding thistle receptacle weevils look like?
The adults are about 6 mm long and are dark brown with lighter speckles. They have the long snout (rostrum) characteristic of weevils.
How would I find them?
The weevils prefer nodding thistles but will also attack:
- plumeless thistle (Carduus acanthoides)
- winged thistle (Carduus tenuiflorus)
- slender-winged thistle (Carduus pynocephalus)
- Californian (Cirsium arvense)
- Scotch thistle (Cirsium vulgare)
What about their life cycles?
Adult females lay eggs on the underside of green flower buds in spring. The eggs are spherical, about 1.5 mm long and covered in a protective capsule of brown insect ‘poop’ known as frass. The larvae are white, legless grubs and burrow through the flower buds into the receptacle and feed during late spring and summer.
They pupate within hard black cells inside the flower heads. From December to April dried seedheads feel hard and lumpy when squeezed between thumb and forefinger and can be easily broken open to reveal a blackened centre. New adults that emerge in early summer may produce another generation but most do not begin to lay eggs again until the following spring.
Where are they established?
They are currently found on the Pouto Peninsula at Campbell Rd, Tangiaue Dargaville/Kaihu and Babylon Rd.
When and how can they be harvested for redistribution?
The adults are found sitting on thistle rosettes in September and October. They can be collected and moved to new sites.