Weevils & Beetles
The pests of stored products are so numerous that it is impossible to discuss all of them. The aim of this is to discuss only the major insect pests found in mills, warehouses, processing plants, homes, and retail stores.
The stored product insects of concern to the professional exist under very specific conditions. They are usually found living in products such as dried fruits, spices, flour, bran, peas, dried vegetables, dried flowers, grain, milled cereal products, dog food, nuts, candy, macaroni and spaghetti, cheese, and other similar items.
Stored product pests contaminate – and thus eliminate for human consumption – far more food than they eat. They are most important as pests of stored grain, damaging about 10% of the world’s grain production. Stored product pests are also important in the household and retail stores as “pantry pests” that find their way into packaged cereals, spices, and other foodstuffs.
Many stored product insects feed generally on all types of dried vegetables and animal matter, while others have more definite food preferences. Certain stored product pests originate in crops still growing in the field, while others infest food products during processing and storage. Stored product pests may fly into buildings from the outside, come from secluded areas indoors, or migrate into uninfested items from infested sources, such as food refuse that collects in cracks and crevices. They can also be carried into a building on material other than food products, such as furniture, rugs, and bedding, as well as in or on almost any product of plant or animal origin. For example, some home decorations use dried flowers or grain, which can become infested by stored product pests.
Most pests of stored products are of tropical or subtropical origin. As a result, they live and reproduce best under warm conditions. With only a few exceptions, they cannot live for long at low temperatures, and they usually do not hibernate. Almost all of them are adapted to living on foods with a very low moisture content, although mites and psocids are exceptions, and require a comparatively high moisture content. Very few stored product pests can live and breed at temperatures above 95°F, and most do not lay eggs at temperatures below about 60°F. Certain insects and mites, however, can breed at temperatures of 40°F to 50°F if moisture conditions are suitable; spider beetles, which may be serious pests in the northern parts of the United States, are quite active at these temperatures.
In mills and warehouses, it is essential to inspect regularly for the presence of stored product pests. The first consideration in the prevention of infestation is to have all grain, cereal dust, and other debris in which insects can breed removed (i.e., proper sanitation), as well as pointing out to the owners of the premises that finished products kept too long in storage can be a prime source of infestation to the entire area. Infested goods should be removed from the premises as soon as possible to prevent spread of the infestation to uninfested merchandise.
Insects of stored products can be separated into four groups according to their feeding habits.
· Internal feeders – these insect larvae feed entirely within the kernels of whole grain and palletized product and thus may remain undetected until adults emerge from the kernels. Examples: rice weevil, granary weevil, lesser grain borer, and Angoumois grain moth.
· External feeders – these insects feed on the outside of the grain. They may also chew through the outer seed coat and devour the inside. These are known as external feeders. Examples: Indianmeal moth, drugstore beetle, flat grain beetle, cadelle, khapra beetle, and cigarette (or tobacco) beetle.
· Scavengers – Scavengers feed on grain only after the seed coat has been broken, either mechanically or by some other insect. Examples: confused flour beetle, red flour beetle, Mediterranean flour moth, and sawtoothed grain beetle.
· Secondary pests – Secondary pests feed only on materials that are deteriorating, damp, and have some mold growth present. Some of them feed on mold rather than the food product. Examples: yellow mealworm, foreign grain beetle, some grain mites, and psocids.
Occasional exceptions to these feeding habits may be found; however, as a general rule, each of these insects will feed as indicated.
