Merchant Grain Beetle
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COMMON NAME: |
Merchant grain beetle |
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SCIENTIFIC NAME: |
Oryzaephilus mercator (Fauvel) |
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CLASS/ORDER/FAMILY: |
Insecta/Coleoptera/Cucujidae |
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METAMORPHOSIS: |
Complete |
INTRODUCTION. The merchant grain beetle is very
similar to the saw-toothed 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.
RECOGNITION. Adults about 1/8"
(3 mm) long, with flattened body. Color dark brown.
With 6 saw like 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.
Mature 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 saw-toothed, foreign, and square necked grain beetles share this same
description.
SIMILAR GROUPS. (1) Saw-toothed 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 saw like teeth on each side of thorax.
BIOLOGY. 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.
HABITS. The merchant grain beetle cannot
attack sound kernels. Its flat body form permits access through very small
cracks and into imperfectly sealed packages.
Adults can fly and they are
attracted to light.
It 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.
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