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Description
Billbugs are gray, brown, or nearly black snout beetles (Fig.
1). The adults of the many species range from 1/5 to 3/4 inch
long. Billbugs play possum when disturbed but are rarely seen,
because they hide in the soil during the day and are active
only at night. The eggs, which they lay in plant stems, are
white to gray and kidney-shaped. The adults frequently gouge
out holes in unfolded leaves in which to lay their eggs, and
these spots appear as a transverse row of punctures in the
expanded leaves. The larvae, off-white, legless, brown to
yellow headed, humpbacked grubs, feed in the center of the
lower section of plant stems or in the roots. They pupate
either in the stems or in the soil among the roots.
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Figure 1. Billbug life cycle
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Life
Cycle
Billbugs overwinter as adults in soil, coarse grass, or litter about
the fields, becoming active when corn begins to come up. Although
winged, billbugs seldom fly, but crawl over the ground in search
of food. They will often migrate one-fourth mile or more. In addition
to corn, billbugs attack nearly all cultivated and wild grasses,
small grains, rushes, and cattails.
The
adults feed at the base of the stalk, often below the ground level.
They move from plant to plant at night, but stay hidden in the soil
during the day, presumably to avoid the effects of the sun. Egg-laying
starts about 10 days after the adults first feed. The females lay
eggs in a hole they gouge in the stem with their mouthparts. It
is not uncommon for a single female to deposit 200 eggs or more.
The eggs hatch in 4 to 15 days. The small grubs feed and develop
for several weeks in the center of the stalks, either below or just
above the ground. Later, they descend to the soil and feed in or
around the roots. Pupation occurs in the stems, roots, or soil.
The adults, which transform in the fall, may remain in the pupal
case or move out and feed before entering hibernation. The life
cycle requires several months for completion, and there is only
one generation each year.
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on image for larger version
Figure 2. Billbug damage ("Deadheart") |
Damage
The larvae, or grubs, cause serious injury by feeding inside
the stems and roots of small grains and cultivated grasses.
This feeding causes the heads to bleach and the straws to fall
or lodge. If several larvae feed within a stalk of corn, the
chances that it will produce an ear are slight. The plants are
usually stunted and easily recognized. |
Scouting
Procedures
Examine 20 plants in each of 5 locations and add the number
of plants damaged to determine percent injury. Look carefully
around the base of these plants and in the soil and debris to
determine if adult billbugs are still present. A plant population
count may also be helpful. |
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on image for larger version
Figure 3. Adult Billbug on Corn
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Figure 4. Billbug damage ("Suckering")
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Threshold
Guide
None established. Rescue treatments maybe warranted when the
damage is widespread and the billbugs can be found. Treatments
are not effective against grubs because they are internal feeders. |
Authors:
Susan T. Ratcliffe (sratclif@uiuc.edu)
Michael E. Gray (m-gray4@uiuc.edu)
Kevin L. Steffey (ksteffey@uiuc.edu)
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