Steven Richardson and Qian "Karen" Sun
Primary pests of stored product attack undamaged, whole grains. The larvae feed and develop inside the grain and chew their way out. Some of the primary pests include the Angoumois grain moth, rice weevil, and lesser grain borer. In contrast, secondary pests feed externally, and attack broken, damaged grain and powdered products. They may infest stored food following the primary pests.
Angoumois grain moth (Sitotroga cerealella)
Description: The Angoumois grain moths are light brown or tan with a few black scales on their wings. Total length is 8.5 mm long and their wings fold over their abdomen like the Indian meal moth. The end of their wings is fringed. Larvae are white in color with a light brown head capsule and burgundy mouthparts. Adults can fly but only larvae feed.
Host: Their larvae feed on whole grains but prefer damp grains which is typically caused by water damage or moisture problems. They are also generalists and will feed on a verity of moisture damaged stored grain products like corn, rice, seeds, and oats. However, unlike larvae of the Indian meal moth, larvae of the angoumois grain moth can burrow into whole grain making them a primary pest.
Life cycle: Adults have been recorded depositing up to 283 eggs on the surface of food and it could take about 6 days for larvae to hatch. Larvae can complete their larval and pupal stage inside their food source in around 30 days. The adults mate shortly after emergence and are short lived at about 10 days. Their total life cycle is roughly 5 weeks. Developmental time is temperature and humidity dependent.
Rice weevil (Sitophilus oryzae)
Description: The rice weevil is roughly 4 mm long, dark brown in color, and has a long protruding face with mouthparts at the end. It has two light brown markings on each forewing. Forewings do not fully cover the abdomen. The adults of the species can fly.
Host: The rice weevil prefers to deposit eggs in seeds from whole grains like wheat, rice, and maize, but the larvae and adults of the species will eat most any organic stored plant product.
Life cycle: Adults can live for up to two years. Females, when mated, can lay up to 6 eggs a day and over 300 in their lifetime. Eggs are deposited in a seed or food item by females after they chew through tough seed cases with their mandibles that are also capable of chewing though packaging and cardboard. Females seal their eggs inside seeds with bodily secretions. Once larvae emerge, they can take almost 2 months to become pupae. Larvae will spend the entirety of their larval and pupal stage in the seed. The pupal stage only takes up to 4 days to eclose as an adult.The adult chews a round exit hole, then emerges from the seed and continues feeding. Developmental time is temperature and relative humidity dependent.
Lesser grain borer (Rhyzopertha dominica)
Description: The adults about 3 mm long, dark reddish brown in color, with distinctly shaped 3-segmented club on each antenna. Larvae are white and C-shaped. Adults can fly.
Host: The lesser grain borers feed on a great variety of grains, include wheat, barley, rice, seeds, and dried fruit. These insects can be found infesting cereals, flour, beans, macaroni and herbs.Spices are not suitable for larval development. Infested grain has a slightly sweet, pungent odor.
Life cycle: The life cycle from egg to adult is approximately one month in warm conditions. Females can lay up to 300 to 500 eggs in her life time. The development of larvae is more rapid on whole grain than on food products made from the same grain. The lessor grain borers can tolerate dry grains with only 8-9% moisture content. Developmental time is temperature and humidity dependent.
Akter, T., Jahan, M., Bhuiyan, M. (2013). Biology of the Angoumois grain moth, Sitotroga Cerealella (Oliver) on stored rice grain in laboratory condition. Journal of the Asiatic Society of Bangladesh, Science. 39 (1): 61-67.
Federal Grain Inspection Service, United States Department of Agriculture. (2015). Stored Grain Insect Reference
Simmons, P., Ellington, G. W. (1924). Biology of the Angoumois grain moth-progress report. Journal of Economic Entomology. 17: 41-45.
Steven Richardson is a graduate student, and Qian “Karen” Sun is an assistant professor in the Department of Entomology.
Adult Angoumois grain moth. Photo by Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
Adult, pupa and larva of Angoumois grain moth. Photo by Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
Adult rice weevil. Photo by Gary Alpert, Harvard University, Bugwood.org
Adult rice weevil on grain. Photo by Joseph Berger, Bugwood.org
Adult lesser grain borer. Photo by Gary Alpert, Harvard University, Bugwood.org
Lesser grain borer and infestation. Photo by Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org