Common Name: Merchant Grain Beetle
Scientific Name: Oryzaephilus mercator (Fauvel)
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. 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 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. 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.
Follow the standard control procedures for stored product pests.