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House and Garden Series
F@stSheet
Ent-1038
The foreign grain beetle, Ahasverus advena (shown above),
and several other minute insects including psocids
and other fungus-feeding beetles, feed primarily on mildews
and fungal spores. This insect, and other similar species
listed below, sometimes become abundant indoors, especially
in new homes. New homes often contain fungal growths on
newly installed lumber or sheetrock that has absorbed water
and produced mildew. These fungi provide a ready food
supply for several insects, resulting in temporary infestations.
In older homes, foreign grain beetles are sometimes pests in
bathrooms or other areas where high humidity permits growth
and development of both the insects and their food.
IDENTIFICATION Adult
foreign grain beetles are minute (2-3 mm-long) with a flattened
body and a squarish shield covering the thorax (pronotum). The
pronotum is slightly wider than long when viewed from above.
Color is reddish brown. The wing covers (elytra) are covered
with rows of punctures and very fine hairs. Antennae are long,
slightly less than half the body length, with a three-segmented
club. The front corners of the pronotum project forward at a
45 degree angle. Other household insects of similar appearance,
and with similar feeding habits, include the Lathridiidae beetles:
the square necked grain beetle, Cathartus quadricollis, whose
pronotum is longer than wide; the rusty and flat grain beetles,
Cryptolestes spp. (with elongated antennae and lateral
raised lines on each side of pronotum, parallel to margin);
and the minute
brown scavenger beetles,which have a pronotum that
is often hairy and distinctly narrower than elytra and three-segmented
tarsi. In addition there are the silken fungus beetles (family
Cryptophagidae) with a pronotum lacking prominent front corner
angles and with punctures on the elytra not in rows. The
merchant and sawtoothed
grain beetles, Oryzaephilus spp., are more
commonly found as pests of stored products, but can be distinguished
by having 6 prominent tooth-like projections on either side
of pronotum.Psocids, also known as booklice, may also be common
indoors. They can be identified by their small size (1 to 2
mm), pale coloration, and a superficial resemblance (under high
magnification) to termites. The common name booklouse comes
from the fact that booklice are relatively easy to see on the
pages of books, where they may feed on mildews growing on the
paper.
BIOLOGY Mildew feeders, like the foreign
grain beetle, can become abundant in moist situations, especially
where molds are present. Eggs are laid singly, or in clusters
of 2-3, and hatch within 4-5 days. Females lay 1-4 eggs per
day over a 20-30 day oviposition period. Life cycle from egg
to adult requires an average of 22 days at 27EC
and 75% RH. Larvae require high humidities. Survival from larva
to adult drops from 95% at 66-92% RH to zero survival at 66%
RH in rolled oats. Both adults and larvae are capable of surviving
on pure cultures of various molds. Foreign grain beetles are
relatively long-lived, with mated males and females having average
lifespans of 159 and 208 days, respectively.Psocids require
high humidity for survival and reproduction. Optimal conditions
are 75% to 95% relative humidity and temperatures of 75 to 82
degrees Farenheit. The average lifespan for one common species
is about 25 days. Each female lays 50 to 60 eggs, and booklice
are capable of rapid reproduction given good conditions.
CONTROL The best control
for mildew-feeding insects is good sanitation, moisture reduction,
and increased ventilation. Pesticides generally provide
little control. However, wall voids infested with foreign
grain beetle may be treated with appropriately labelled insecticides
such as aerosol-formulated pyrethrins or insecticidal dusts.
Infestations may be expected to persist until moisture levels
are reduced to the point that molds or mildews cannot grow.
In new homes with central air conditioning or heating,
several weeks of drying out may be required before the infestation
runs its course. There is no evidence that infestations
will persist once moisture levels have dropped. Control
of psocids can usually be obtained by reducing the relative
humidity of the infested areas to less than 58%.
FOR MORE INFORMATION
For more information about stored product pests that may be
confused with foreign grain beetle, request Extension publication
L-2046, Pantry Pests. These publications, and help with
additional questions about other pest problems, can be obtained
by contacting your local county Extension office.
Author:
Michael Merchant, Ph.D., Urban Entomologist, Texas Cooperative
Extension
Publication information:
This publication is part of the House & Landscape Pest
Series produced by the Department of Entomology, Texas A&M
University, College Station, TX 77843-2475. The most recent
update can be found at:
http://citybugs.tamu.edu/FastSheets/Ent-1038.html
. Series Editor: M. Merchant. For more
information about arthropods, check out the Texas A&M
Entomology Website at http://insects.tamu.edu
Last Revised: 5-21-2007
The information given herein is for educational purposes
only. Reference to commercial products or trade names is made
with the understanding that no discrimination is intended
and no endorsement by the Texas AgriLife Extension Service is
implied. Additional, or updated copies of this fact sheet
may be obtained by contacting the author(s) at the Texas Agricultural
Extension Svc., 17360 Coit Road, Dallas, Texas 75252-6599.
Extension programs serve people of all ages regardless of
socioeconomic level, race, color, sex, religion, disability
or national origin. The Texas A&M University System, U.S.
Department of Agriculture, and the County Commissioners Courts
of Texas Cooperating.
All content and images Copyright © 2000, Texas
Texas AgriLife Extension, unless otherwise noted. All rights
reserved.
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