Head-clipping Weevil – Haplorhynchites aeneus
Family Curculionidae – Weevils
Live adult weevils photographed in the wild at DuPage County, Illinois. Size: 10mm
Commonly known as the sunflower head-clipping weevil, this pest clips flower heads from other plants as well.
Insects in the subfamily Rhynchitinae are commonly known as tooth-nosed snout weevils. Adult weevils girdle flower peduncles and leaf petioles, leaving partially severed flowers or leaves hanging on the plant. It is thought only the female weevils engage in girdling, but both genders then congregate inside the now-upside down, partially opened flowers, to feed on pollen, mate, and lay eggs.
Here’s a close up of that plant-shredding proboscis with the rotary-saw teeth. It’s a nasty-looking little bugger.
Weevils expend a lot of time and energy in this clipping behavior. It may function to reduce the suitability of the plant for other flower-feeding insects that otherwise would compete with the weevil and its larvae for resources.
Clipped flower heads
Stem-girdling by weevils has clipped all the flowers off these cup plants at Blackwell Forest Preserve in Warrenville, Illinois. The eggs hatch only after the flower heads drop to the ground, where the larvae feed on the decomposing plant tissue before overwintering in the soil. Pupation and adult emergence occurs the following summer, timed to correspond to the sunflower’s entering its flowering, reproductive phase[1]. I have seen vast swaths of plants thus affected, and not only sunflowers.
Native plants have a hard enough time thriving in suburbia without these noxious little pests. Although, you have to hand it to them – they figured out a way to make ideal nurseries for their babies. That’s how de weevil do.
Adult Female Head-clipping Weevil, Haplorhynchites aeneus
References
- J.P. Michaud, Kansas State University Entomology, Sunflower Head clipping Weevil
- Bruce Marlin, Bugguide.net, ‘Head-Clipping Weevil‘
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