Merchant Grain Beetle

Scientific Name: Oryzaephilus mercator
Oryzaephilus mercator, the merchant grain beetle, is a major pest of oil seeds, such as groundnut, melon, palm kernels and sunflower seeds. The merchant grain beetle can also feed on and subsequently damage dried fruit and processed cereals.

The merchant grain beetle is widely distributed throughout the globe but is most commonly found in tropical regions and other warmer climates. This species does not survive well in cooler temperatures. The merchant grain beetle prefers to feed on the damaged grain of seeds high in oil however, it is capable of damaging intact grains.

The adult Merchant Grain Beetles are a red-brown color, around 2.5 mm in length, and live an average of 6-10 months. They develop wings in adulthood and can take flight which enables them to infest facilities which were not previously infested. Mature females can produce between 43 and 285 eggs every 28-42 days.

The eggs are microscopic, white and elongated. It takes around 35 days in optimum conditions for the life cycle of the egg to reach completion and enter larval stage. Once developed, larvae are free living within the food commodity. The larvae of the merchant grain beetle progress through 3 instars over 2 weeks before pupation.

The larvae of Oryzaephilus mercator are creamy white in colour with a brown head and 3 pairs of legs. Pupae are red-brown in colour. Pupal development lasts for approximately 1-3 weeks whilst pupation takes place in fragile cocoons formed from the surrounding food material.

Larval feeding by the merchant grain beetle can result in a reduced dry weight and quality of stored oil seeds and nuts, subsequently resulting in financial losses. Oryzaephilus mercator larva feed by burrowing into grain kernels.
During feeding and maturation, the water content within the environment sustaining the merchant grain beetle pests begins to grow in humidity. The humid environment can encourage fungal growth on the remaining food products, further damaging the stock.
Other contaminations caused by these insects include the larval moults and frass (insect waste) which have been shed during growth and possible dead adult insects.

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