Most insects commonly collected in stored grain in Illinois are beetles that range in size from 1?16 inch to more than 1?2 inch long. Adults of most species are red–brown to black, and their fore wings are hardened to form a “shell” over the body.
Larvae of common species are cylindrical and cream colored; some bear fine hairs. Species frequently collected in Illinois grain bins include the sawtoothed grain beetle, flat grain beetle, rusty grain beetle, foreign grain beetle, hairy fungus beetle, larger black flour beetle, red flour beetle, and confused flour beetle.
Like the weevils, beetles that feed and develop outside grain kernels may inhabit any portion of a grain mass. They feed on bits and fragments of several different grains; their buildup usually results from an abundance of broken kernels (fine material) or fungal growth on moist grain.
Their dependence on fines or fungal growth accounts for the description of these insects as secondary pests, “bran bugs,” or “fungus feeders.”
Surface-Feeding Caterpillars:
Most caterpillars that feed in stored grain inhabit primarily the outer portions of the grain mass (usually the grain surface, but also the bottom of the mass just above perforated drying floors or aeration ducts).
These caterpillars are cream colored and about 1?2 inch long when mature. They produce fine, silken webbing as they move about near the grain surface. Mature larvae pupate within a silky cocoon. Adult moths fly and mate in the bin headspace, where they may be seen resting on the bin walls and roof.
The Indianmeal moth is the most common surface feeding caterpillar in stored grain in Illinois. The larvae may web over the grain surface completely, thus preventing proper aeration or fumigation.
The adult Indianmeal moth has a wingspan of about 3?4 inch; the outer half of each front wing is red–brown or copper colored. Malathion resistance is common in Illinois populations of Indianmeal moth. Other surface-feeding caterpillars include the Angoumois grain moth (which feeds within kernels), the Mediterranean flour moth, and the meal moth.
Other Stored-Grain Insects:
Other pests that sometimes infest stored grains include psocids (booklice) and grain mites. These soft bodied pests feed on fungi. An abundance of psocids or grain mites often indicates a more important problem of mold-related deterioration of the grain.
Not all insects in grain are pests. Parasitic wasps, larvae of a predaceous fly species, and predaceous Hemipterans (true bugs) attack certain grain pests. In addition, many field insects, such as European corn borers and sap beetles, are transported inadvertently to grain bins, where they cause no damage.
Preventing Insect Infestations:
Sources of Infestations
Most infestations of stored-grain insects originate from immigration of the insects into the bin from outside. All species of stored-grain insects have numerous food sources on which they survive when stored products are not available.
However, large amounts of stored grain are attractive to these pests, and they invade the bins through any available opening.
Other common sources of stored-grain insects are old grain, grain spills, feeds, seed, and grain debris. Insects often move to new grain from carryover grain, from grain not cleaned from “empty” bins, from feed- supply buildings, and from grain debris beneath perforated bin floors.
Some stored-grain insects infest maturing grain in the field. Although some field infestations probably occur in Illinois, the extent of field originated storage problems is minor.
Sanitation:
To minimize the movement of insects from old grain and grain debris to new grain, thorough cleanup is necessary. At least 2 weeks before storing new grain, clean all grain and grain debris from within and around grain bins. Be thorough; sweep or vacuum bin floors and remove and feed or destroy any grain and grain debris in combines, wagons, and augers.
If grain debris is not removed from the combine, collect and feed or destroy the first few bushels of grain that pass through the combine.
Bin Sprays:
Insects may remain in certain bin locations even after a thorough cleanup. Hard-to-clean sites that harbour insect pests include cracks and crevices in bin walls and the plenum beneath nonremovable perforated floors.
Consequently, application of a residual insecticide should help eliminate lingering infestations of stored-grain insects. Residual sprays also create a barrier for insects that may migrate into a storage area from outside. Applying an insecticide or a fumigant in an empty bin can supplement (but not replace) physical cleanup efforts.
Apply an insecticide to the floor and up to 15 feet up the walls of all bins that will be used to store grain for more than a few weeks during warm weather. Also spray the outside of the bin from the base to a height of 3 feet and treat the ground and vegetation in a 3-foot border around the bin. The best time to apply a residual spray is 2 to 3 weeks before new grain will be stored in the bin. Use one of the following products:
- 8 milliliters of Tempo 2E (cyfluthrin) per 1,000 square feet in sufficient water to cover the area being treated but not to allow dripping or runoff to occur (see product label). Do not apply directly to grain.
- 1.8 fluid ounces of Storcide II (a combination of the active ingredients chlorpyrifos-methyl and deltamethrin) per gallon of water. Apply 1 gallon of spray mixture per 1,000 square feet of bin wall or floor surface. Do not apply Storcide II to bins that will be used to store corn or soybean.
- diatomaceous earth (see product label for application rate of the formulation to be used).
Unless labels specify otherwise, spray bin surfaces to the point of runoff and be sure to treat all cracks and crevices and areas around doors thoroughly. Note and follow all label directions for application methods, protective equipment, and reentry.
Filling the Bin:
Effective insect management in stored grain requires good storage practices. Use a grain cleaner to minimize the amount of fine material that is binned with the grain. Many species of stored-grain insects cannot survive in the absence of broken kernels and grain debris.
Use of a grain spreader evenly distributes remaining fine material and helps to level the grain surface. After the bin is full, if fine material is concentrated in a central core beneath the auger spout, removing one or a few loads from the bin will extract this core of fines.
Periodic removal of the center core during the binfilling process is even more effective for extracting fines. Do not add new grain on top of old because insects will move from the infested grain to the new grain. Do not overfill bins; the leveled grain surface should be at least a few inches below the lip of the bin.
Leveling the grain surface is important for uniform airflow and for effective application of insecticide or fumigant. Store only dry grain. Maintaining moisture levels that prevent the growth of storage fungi is sufficient where fallharvested grain is to be stored only through the winter.
Wheat that will be stored 1 month or longer during warm summer weather should be dried to 12 to 13 percent moisture; corn should be dried to 14 to 15 percent moisture. Aerate to cool stored grain as soon as possible.
Temperatures below 50°F prevent insect feeding and reproduction. Cooling grain to just above freezing kills some stages of many grain insects. Cooling grain to 10° to 15°F will kill nearly 100 percent of common stored-grain pests. Aeration also results in uniform temperatures that prevent moisture migration problems within a bin.
Most grain-storage references recommend aerating to maintain grain temperatures within 15°F of average outdoor temperatures, however, it is unnecessary to aerate to rewarm grain above 50°F.
Authors:
Rick Weinzierl : Department of Crop Sciences
Russell Higgins : Matteson Extension Center
