The Siamese grain beetle is a worldwide food-infesting species that is commonly found in a wide variety of foods including legumes (beans), rice and rice products, cereals, coffee beans, cotton seeds, nutmeg, cassava roots, sweet potatoes and dried fruits. It is not as commonly encountered as similar appearing beetles, such as the sawtoothed grain beetle, and it is primarily a tropical species. Only damaged rice is subject to attack as sound rice kernels are resistant to larval efforts at feeding.
The female beetle lays her eggs in crevices in fan-shaped clusters of 11 to 14 eggs. Eggs hatch only within a temperature range of 150 to 370C. The larval stage undergoes four molts into the food source in which to pupate. The entire life cycle can be completed in as little as 50 days but usually takes longer.
Inspection for the Siamese grain beetle should be directed at storage bins and bags where rice, beans, seeds and similar materials may be stored. Examine grain for the presence of adult beetles and use a screen, if available, to filter the adults and larvae out of the grain to determine their presence.
Inspect the outside of bags stored on pallets and look in between the flaps for adult beetles hiding there. Lift or move bags to look for beetles within the pallet. If numerous beetles are found outside bags of grain, a grain probe can be used to remove grain from the bags for inspection. Bags may also be opened, with permission from the customer, to check the extent of the infestation.
These beetles most often will be found infesting larger quantities of corn stored in bins, silos, grain elevators and in bags in warehouses. If smaller packages or quantities of infested grain are involved, the grain can be discarded and the cracks in the area where the infested grain was stored treated with a residual insecticides. Small packages of grain can also be frozen for 6 days at –180C to kill all life stages.