A complex of weevils, the rice (Sitophilus oryza), granary (Sitophilus granarius), and maize (Sitophilus zeamais) weevils, are among the most destructive pests of grains, seeds, and grain products stored in elevators and bins. They probably are not native to North America, but entered in seeds carried by settlers through ports. These weevils are pests of grain throughout the world.
The rice weevil is a small snout beetle which varies in size, but it averages about three thirty-seconds inch in length. It varies from a dull red-brown to black, and is usually marked on the back with four light red to yellow spots. The rice weevil has fully developed wings beneath its wing covers and can fly readily. The thorax is densely pitted with somewhat irregularly shaped punctures, except for a smooth narrow strip extending down the middle of the back. The larval stage of this insect is a soft, white, legless, fleshy grub which feeds on the interior of the grain kernel. When mature, the grub changes to a naked white pupa and later emerges as an adult beetle.
The maize weevil is a small snout beetle which varies in size, averaging about three thirty-seconds inch in length. It varies from dull red-brown to nearly black and is usually marked on the back with four light reddish or yellowish spots. The maize weevil has fully developed wings beneath its wing covers and can fly readily. The thorax is densely pitted with somewhat irregularly shaped punctures, except for a smooth narrow strip extending down the middle of the dorsal (top) side. An egg hatches in a few days into a soft, white, legless, fleshly grub which feeds on the interior of the grain kernel. The grub changes to a naked white pupa and later emerges as an adult beetle. The rate of development is slightly slower for the maize weevil than for the rice weevil. A minimum of thirty days is required for passing through the egg, larval and pupal stages.
The adult granary weevil is a somewhat cylindrical beetle about two-tenths of an inch (two to three mm) long. The head is prolonged with a distinct snout extending downward from the head for a distance of about one-fourth the length of the body. The weevil is polished red brown to black with ridged wing-covers and a well-marked thorax with oval pits. Unlike the rice and maize weevils, the granery weevil cannot fly. The egg hatches in a few days into a soft, white, legless, fleshy grub which feeds on the interior of the grain kernel. The grub changes to a naked white pupa and later emerges as an adult beetle.
Adult rice weevils live for four to five months and each female lays 300 to 400 eggs during this period. The female uses her strong mandibles to chew a hole in the grain kernel where she deposits a single egg and seals the hole with a gelatinous fluid. During hot weather, the development period for egg to adult may be as few as twenty-six days. This period is greatly prolonged during cool or cold weather. Rice weevils are capable of flight, and infestations may develop in the field prior to harvest.
Maize weevils, for a long time were referred to as a larger strain or race of the rice weevil, but are now recognized as a distinct species. The maize weevil is slightly larger, up to one-eighth inch (four mm) long, and darker than the rice weevil; the degree of variation within each species makes them difficult to tell apart. The thorax of the maize weevil is densely and uniformly pitted with round punctures. An egg hatches in a few days into a soft, white, legless, fleshy grub which feeds on the interior of the grain kernel. After the larval stages are completed the grub changes to a white pupa and later emerges as an adult beetle.
Adult granary weevil live an average of about seven to eight weeks. Each female lays 50 to 200 white eggs during this period. The female uses her strong mandibles to chew a small hole in the grain kernel, where she deposits a single egg in the hole and seals it with a gelatinous fluid. In warm weather, the granary weevil can develop from egg to adult in about five weeks. Cold weather prolongs development. The granary weevil cannot fly and so is most likely to be found where grain is stored, and moves with infested grain.
These weevils are very destructive grain pests. Of the three, the rice weevil is probably the most insidious, owing largely to the ability of flight. All three weevils develop as larvae within the grain kernels. They frequently cause almost complete destruction of grain in elevators or bins, where conditions are favorable and the grain is undisturbed for some length of time. Infested grain will usually be found heating at the surface, and it may be damp, sometimes to such an extent that sprouting occurs. Wheat, corn, macaroni, oats, barley, sorghum, Kaffir seed, and buckwheat are just some of the grains and products on which these weevils feed.
Prevention is the best strategy to avoid insect problems in stored grains. 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 could hide or enter. Spray the bins about four to six weeks prior to storing grain.
Before grain is placed in a bin, it should be screened to eliminate fine materials and broken kernels. Grain placed in a clean bin should be checked at two week intervals during warm months and at one month intervals during cooler months for the presence of hotspots, moldy areas, and live insects. If any of these conditions exist, the grain should be aerated to lower the moisture level and temperature.
Grain that is to be stored for longer than six months may need a protective application of an approved insecticide. Treatments can be applied as the grain is loaded into the bin through the use of a metering device calibrated to apply the proper amounts. After the grain is binned and leveled, a surface dressing can be applied to prevent insects from entering the grain on the surface. If infestation occurs in spite of these precautions, fumigation of the grain will be necessary. Because of the high toxicity of registered fumigants and technical knowledge needed for their proper use, a qualified pesticide applicator should be contacted to perform the fumigation.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Freezing will kill any weevils that are hitchhiking in commercial packaging. You can even store some of these products permanently in the freezer if you have the room. Grain products that are merely refrigerated will be less susceptible, though not immune, from weevil problems.How do you control granary weevils? ›
The best method of controlling Granary Weevils if you have an infestation in your pantry is tossing out all your stored dried food products, doing a detailed cleanup, and vacuuming, then applying Novacide Aerosol to kill adult Rice Weevils and halt the development of eggs and larvae.How do you get rid of weevils naturally? ›
Cloves and bay leaves act as natural repellents to weevils. Place a few bay leaves in your dried food containers to ward off these pests, and position several cloves of garlic around your pantry and kitchen to deter these bugs from making a home in your pantry. White vinegar is also known to kill pesky pantry weevils.How do you control stored grain pests? ›
These include sanitation, monitoring, controlling temperature, carbon dioxide fumigation, and diatomaceous earth, and biological control. Integrating these preventive and intervention methods can contribute to reducing insect problems in organic stored grains.What damage do weevils cause? ›
Bean weevils do not pose threats to human or animal health as they do not bite or sting, but do cause extensive damage to live bean plants and dry stored beans, resulting in expensive losses in crops and food supplies.Do weevils go away on their own? ›
Weevils inside homes
When weevils are found indoors, physically remove them with a vacuum or broom and dust pan. Pesticides are not effective or necessary. These weevils are harmless and temporary and will go away on their own.
Wipe the shelves with hot soapy water or a disinfecting spray then wipe again with white vinegar, which is known to kill weevils. Clean any unaffected items such as cans or containers before returning them to the pantry.How long can a weevil live? ›
On average, adult weevils have a lifespan of two to three months, during which they mate and lay eggs multiple times. There are also a few species of weevils that are parthenogenetic, which means they can produce eggs without mating.How long does it take to get rid of weevils? ›
Put salvageable foodstuffs in the freezer for 4 to 7 days, which should kill any weevil larvae that might be hiding in the product. Items you don't think will withstand freezing—dried herbs, for instance, that may lose their zing—can go in a sealed bag or container and be stored elsewhere.How do you get rid of weevils without chemicals? ›
You can either use cleaning essential oils such as eucalyptus oil, tea-tree oil or vinegar to wipe down the shelves.
Due to past insect problems, we're diligent about storing all foods in glass jars or plastic zip-top bags. Unfortunately, grain weevils (Sitophilus granarius, also called granary weevils or wheat weevils) can chew through paper and plastic packaging.What dont weevils like? ›
A great way to naturally repel weevils is to place cloves and bay leaves in your cupboards to help ward them off. As well as this, you could also try positioning several cloves of garlic around your pantry or kitchen to keep them at bay.What is the most effective way of controlling weevils in stored grains? ›
The primary and most effective means of controlling weevils in your stored grain is to take preventative steps. To help prevent weevil infestations, clean and treat all empty bins thoroughly, including walls, floors, cracks and crevices, prior to loading in grains.What do you spray grain bins with? ›
A residual bin spray, such as Malathion, Tempo or Storcide II, should be applied to all interior bin surface areas two to three weeks before new grain is placed in the bin. The treatment will kill insects emerging from their hiding places (cracks, crevices, under floors and in aeration systems).What kills corn weevils? ›
Freeze the corn for 4 days, which will kill any weevil eggs in the corn.What are weevils attracted to? ›
Weevils are a type of beetle that are primarily attracted to wheat and stored grains. In homes, they can infest pantries and make their way into dry food products. In the wild, they are particularly damaging to crops.