29 Aug 2016

Oryzaephilus Mercator, Merchant Grain Beetle

Oryzaephilus mercator, the merchant grain beetle, is a major pest of oilseeds, 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.


Oryzaephilus mercator, 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.

Adult Oryzaephilus mercator beetles are a red-brown colour, around 2.5 mm in length, and live an average of 6-10 months. Oryzaephilus mercator 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 O. mercator 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.

Russell IPM have developed a complete monitoring system, Xlure MST for Oryzaephilus mercator, the merchant grain beetle trapping and monitoring. This trap can be used to demonstrate the presence of the pest or assess the severity of an infestation of Oryzaephilus mercator before it becomes serious. It can also be used to monitor the effectiveness of any control measure being used to treat an infestation of the merchant grain beetle.

Recent Literature

Park, S. I. et al., (2016) Species Identification of Food Contaminating Beetles by Recognizing Patterns in Microscopic Images of Elytra Fragments. PLoS ONE 11(6): e0157940.

A crucial step of food contamination inspection is identifying the species of beetle fragments found in the sample, since the presence of some storage beetles is a good indicator of insanitation or potential food safety hazards. The current practice, visual examination by human analysts, is time consuming and requires several years of experience. Here we developed a species identification algorithm which utilizes images of microscopic elytra fragments. The elytra, or hardened forewings, occupy a large portion of the body, and contain distinctive patterns. In addition, elytra fragments are more commonly recovered from processed food products than other body parts due to their hardness. With leave-one-out cross validation, we achieved overall accuracy of 80% through the proposed global and local features, which indicates that our proposed features could differentiate these species. Through examining the overall and per species accuracies, we further demonstrated that the local features are better suited than the global features for species identification. Future work will include robust testing with more beetle species and algorithm refinement for a higher accuracy.

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Waongo, A. et al., (2015) Diversity and community structure of insect pests developing in stored sorghum in the Northern-Sudan ecological zone of Burkina Faso. Journal of Stored Products Research, Volume 63.

Stored insect pests often create major problems for farmers worldwide. Comprehensive data of insect pests of stored sorghum in Burkina Faso are scarce. Understanding the population structure of insect fauna infesting stored sorghum is important for development of management strategy. Sorghum panicles were collected from January to September 2011 in farmers’ granaries in the Northern-Sudanian ecological zone of Burkina Faso to determine the diversity of insect pests and their importance in post-harvest losses. A total of 14 species of insect pests were recorded, including twelve coleopteran and two lepidopteran species. Species diversity peaked between May and September. The highest insect diversity was recorded in sorghum stored in straw granaries and on red coloured grains when compared with that of sorghum stored in mud granaries and on white coloured grains. Rhyzopertha dominica (Fabricius) appears to be the primary insect pest followed by secondary pests including Oryzaephilus mercator (Fauvel), Cryptolestes ferrugineus (Stephens) and Sitophilus zeamais (Motschulsky). The distribution pattern of the pests in granaries corresponds to the Mandelbrot model in which colonization of species in an environment depends on the physical conditions of that environment and on the species currently present, which suggest a progressive colonization occurs in waves with stocks of grain.

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