The merchant grain beetle is very similar to the sawtoothed
grain beetle in appearance, life cycle, and habits. For years
they were considered 1 species until breeding experiments
showed they were 2 different species. This pest is worldwide
in distribution and can tolerate the cooler climates.
Adults about 1/8" (3 mm) long, with flattened body. Color
dark brown. With 6 sawlike teeth on each side of prothorax.
Length of temple (region directly behind eyes) less than half
the vertical diameter of eye. With well-developed wings, and
known to fly.
larva yellowish white. Less than 1/8" (3 mm) long. Elongate,
without urogornphi (paired processes projecting from last
abdominal segment), relatively smooth. Antennae 3-segmented
with 2nd segment longest and 3rd very small. The sawtoothed,
foreign, and squarenecked grain beetles share this same description.
(1) Sawtoothed grain beetle (Oryzaephilus surinamensis) with
length of temple (region directly behind eye) greater than
half the vertical diameter of eye. (2) Other small dark flat
beetles lack 6 sawlike teeth on each side of thorax.
The female lays 22-190 white, shiny eggs either singly or
in small clusters in crevices in food material over several
months. The eggs hatch in a few days. The larvae usually molt
3 times and usually construct a pupal cell or cocoon from
food particles held together with sticky oral secretions.
The life cycle (egg to egg) typically requires 30-40 days
but may require over a year. The optimal developmental conditions
are about 86-95 degrees F (30-35 degrees C) and 70+% relative
humidity. There may be as many as 6-7 generations per year
but the number is very dependent on the temperature. Adults
usually live several months.
The merchant grain beetle cannot attack sound kernels. Its
flat body form permits access through very small cracks and
into imperfectly sealed packages.
can fly and they are attracted to light.
is not commonly found in grains, but appears to prefer oilseed
products, including nuts and cereal products. It most commonly
attacks cereals including rolled oats, rice flour, cake mixes,
macaroni, and cookies. It has also been found infesting nuts,
coconut, and candy bars made with peanuts and puffed rice.
Follow the standard control procedures for stored product