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Canada thistle bud weevil,
Larinus planus (Fabricius) Photo: Bruce Marlin
Photo: David Cappaert, Michigan State University, Bugwood.org
There are over 35,000 species of weevil, with
more than 2,500 species in the United States and Canada alone. All
are strictly herbivorous. Weevil is the common name for
beetles
of the snout beetle family Curculionidae. They are usually small,
hard-bodied insects. The mouthparts of snout beetles are modified
into down-curved snouts, or beaks, adapted for boring into plants;
the jaws are at the end of the snout. The bent antennae usually
project from the middle of the snout. In the case of the acorn
weevils, the snout can actually be longer than the body.
The Cryptorhynchinae weevil pictured here was photographed on
prickly pear cactus at San Antonio, Texas.
Polydrusus weevils are undergoing a population explosion in the
spring and early summer of 2005, near Chicago IL USA. The acorn
weevil, Curculio, is one of the weevils infesting hardwood nuts.
It was found in the large grove of butternut, shagbark hickories and
oaks at the original site of the
Native American burial mounds at
Winfield, IL USA. |
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Acorn Weevil, Curculio sp. Acorn weevils have snouts with small, saw-like teeth at the very end.
There are two types, or genera: the long-snouted acorn weevils (genus
Curculio) and the short-snouted ones (genus Conotrachelus). The
longsnouted acorn weevil's snout may be equal to or greater than the
length of its body. These specimens are, of course, the long-snouted
variety.
Adults of both genera feed on acorns, but only the long
snouted weevils can drill into the shells to feed and lay eggs inside
the nutmeat. The tip of the snouth is actually a miniature saw, and
the weevil places the tip against the shell, circling endlessly
around the pivot point until the shell is pierced. Females place
eggs inside the nut using a long ovipositorthat descends from the
abdomen.
Grub-like acorn weevil larvae hatch from eggs a few days
after they are laid. There may be one to several acorn weevil larvae in
each acorn. Larvae typically go through five growth stages, or instars.
Each instar ends with the molt or shedding of the old skin, providing
the larva with more room to grow. After a few weeks, larvae chew their
way out of the acorn, burrow into the soil to pupate, and eventually
emerge as adults the next year. Short-snouted larvae usually exit from a
single hole that already exists in the acorn, but long-snouted larvae
may chew their own exit hole through the acorn shell. Like larvae of the
short-snouted acorn weevil, acorn moth larvae can feed only on damaged
or sprouting acorns. The grayish female acorn moths lay eggs in damaged
acorns, sometimes in the emergence holes of acorn weevil larvae. It's
easy to distinguish the acorn moth larva, a caterpillar, from acorn
weevil larvae. The acorn moth larva has three pairs of legs near the
head and is generally longer than the legless, fat larvae of acorn
weevils. Larvae of the acorn moth feed on acorns and probably on the
fungi that often grow in damaged acorns. They usually pupate inside the
acorns. 
Boll Weevil, Anthonomus grandis grandis The
Boll Weevil, Anthonomus grandis grandis, is a major pest of cotton
that feeds on fruiting forms, leaf petioles, and terminal growth.
They start on the terminals and leaf petioles, and then lay eggs in
the cotton squares and later in the bolls. The larva within the
squares and bolls stop the squares' growth and the bolls don't open
properly or get boll rot.
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