Because mealworms are entirely external feeders upon grains, they are not serious pests. Screening and fanning will easily remove them from grain shipments. However, the well-grown larva can do serious injury to whole grains under certain conditions, such as when grain is held for long periods without being moved. The majority of the damage is largely limited to contamination of the products by the worms and their waste products. Proper bin sanitation before introduction of new grain minimizes the need for pesticides.
Good sanitation involves the removal of old grain and dust in and around the grain bin.
This includes removal of old grain from corners, floors, and walls and grain that may have spilled on the exterior of the bin. Any grain remaining when a bin is emptied can harbor insect infestations which will move into the new grain. After the bin is cleaned, and all needed repairs have been made, the floor and wall surfaces both inside and outside the bin should be treated. Take special care to treat all cracks, crevices, and areas around doorways and other places where insects can hide or enter. Spray the bins about four to six weeks prior to storing grain, if the grain is to be stored for more than six months.