Head-clipping Weevil Haplorhynchites aeneus
Family Curculionidae - Weevils
Live adult weevils photographed in the wild at DuPage County, Illinois. Size: 10mm   Beetles Index
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Adult Female Head-clipping Weevil, Haplorhynchites aeneus
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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.

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.

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.

Head-clipping Weevil
Weevil at stem girdle

Clipped flower Heads
Weevil Damage: Clipped flower Heads


The teeth at the tip of the snout are visible above. The weevil is sitting atop a clipped sunflower head.

References
  1. J.P. Michaud, Kansas State University Entomology, Sunflower Head clipping Weevil
  2. Bruce Marlin, Bugguide.net, 'Head-Clipping Weevil'
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Order Coleoptera: Beetles are the dominant form of life on earth: one of every five living species is a beetle. Coleoptera is the largest order in the animal kingdom, containing a third of all insect species. There are about 400,000 known species worldwide, ~30,000 of which live in North America.  Beetles live in nearly every habitat, and for every kind of food, there's probably a beetle species that eats it.
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