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Grain Beetles Facts
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Common Stored Product Insect Species
Stored product insects (SPI) not only damage foodstuff and raw materials but can also contaminate finished products, hence making them unfit for use. Understanding the appearance, habits and life cycles of SPIs can help to identify the most effective SPI control for your property.
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Lesser Grain Borer
(Rhyzopertha dominica)
Appearance
- Adult is 2–3 mm in length.
- Ranges from red-brown to black-brown in colour.
Lifecycle
- Female produces 200–500 eggs.
- At ideal temperature of 34°C and 70% Relative Humidity (RH), pupation takes up to 3 days.
- At ideal temperature (34°C and 70% RH), life cycle last around 3—4 weeks.
Habits
- Eggs are laid in crevices or on the rough surfaces of a seed.
- Larva will bore inside the grain to continue growing.
- Larva develops faster on whole grain compared to flour.
- Adult mate as soon as they emerge.
- Commonly found in warehouse and store.
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Drugstore Beetle/Biscuit Beetle
(Stegobium paniceum)
Appearance
- Adult is 2–3.5 mm in length.
- Light brown in colour and oval in shape.
- Antennas end with 3–segmented club.
Lifecycle
- Female produces 20–100 eggs.
- Eggs take around 60–210 days to develop into adults, with 1–4 generations per year depending on the temperature.
- Adult lives for about 13–65 days
Habits
- Adults are active fliers, especially during afternoon to evening time.
- Commonly found infesting processed goods such as chocolate, confectionery and biscuits. Also often found on dried food product such as dried herbs and spices.
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Cigarette Beetle
(Lasioderma serricorne)
Appearance
- Adult is 2–3 mm in length.
- Light brown to reddish brown in colour.
- Antennas are about half of its body length and are shaped serrated (saw-like).
Lifecycle
- Female produces up to 30–42 eggs.
- Eggs take 30–90 days to develop, with 3–6 overlapping generations per year.
- Adult lives 23–28 days.
Habits
- Larva produces a cell of food fragments and waste materials to pupate.
- Adults are active fliers, especially during afternoon to evening time.
- Adult do not feed while the larva is the one doing the damage.
- Feeds off tobacco, dry stored food products, spices, seeds, grains and dried plant material.
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Flat Grain Beetle
(Cryptolestes Pusillus)
Appearance
- Adult is 1.5 – 2.5 mm in length.
- Red-brown in colour with flat body.
Lifecycle
- Female produces up to 200 eggs.
- In ideal temperature conditions, the life cycle is about 23 days.
Habits
- Adults walk with a characteristic swaying movement.
- Adults are winged but rarely fly.
- Feeds on cereals, dates, dried fruits and other materials.
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Saw Toothed Grain Beetle
(Oryzaephilus surinamensis)
Appearance
- Adult is about 2.5–3 mm in length.
- 6 sawlike teeth on each side of prothorax
Life Cycle
- Female produces 45–285 eggs.
- Life cycle takes about 30–50 days.
Feeding Habits
- Larvae feed within mass produce.
- Adults are winged but do not fly.
- Often wander from food into cracks, crevices and roof spaces to hide.
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Khapra Beetle
(Trogoderma granarium)
Appearance
- Adult is 2 – 3 mm in length.
- Dark brown in colour with light brown pattern on wing covers.
- Oval in shape.
Lifecycle
- Female can lay up to 35 eggs.
- It takes about a month to complete life cycle.
Habits
- Larvae make the most damage on stored products by shedding cast skin and feeding on materials.
- It can survive up to 9 months without food.
- Commonly found infesting grains, cereals and pulses.
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Copra Beetle/Red Legged Ham Beetle
(Necrobia rufipes)
Appearance
- Adult is around 3.5–7 mm in length.
- Shiny green to bluish green in colour with red legs.
Lifecycle
- Female lays up to 30 eggs per day in cracks or crevices of cured fish.
- Adult lives up to 14 months.
Habits
- Commonly feeds on dried copra and other insects that are attracted to mouldy food.
- Infest areas such as palm kernels, oilseeds, spices, dried fish and other meat products.
- Adults are slow fliers and will bite human when disturbed.
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Grain Weevil
(Sitophilus granarius)
Appearance
- Adult is 3–4.8 mm in length.
- Reddish brown to black in colour.
Lifecycle
- Female lays eggs in grain kernel cavity.
- At ideal temperature conditions (30°C), it takes 30 days to complete life cycle.
Habits
- Newly emerged adult leaves large ragged holes.
- Feeds on grains and hard cereal products such as macaroni and spaghetti.
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Rice Weevil
(Sitophilus oryzae)
Appearance
- Adult is 2.5–3.5 mm in length.
- Brown to black in colour with reddish spots on the back of the abdomen.
- Has a long slender snout.
Lifecycle
- Female lays 300–400 eggs.
- It takes as short as 32 days to complete life cycle.
- Adult lives up to 3–6 months.
Habits
- Female drills a tiny hole in the grain kernel to lay egg in the cavity.
- Grows, feeds and pupates within a grain kernel.
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Confused Flour Beetle / Rust Red Flour Beetle
(Tribolium Confusum)/ (Tribolium Castaneum)
The confused flour beetle was named because of the confusion over its identity. It is a very common commercial and pantry pest.
Appearance
- The confused flour beetle is 3-4 mm in length, the larvae are about 6 mm long.
- The adult is red-brown in color and the larvae are a light honey colour and about.
- It resembles the rust-red flour beetle, except for the antennae which is four segmented and gradually thickens towards the tip - another slight difference is in the shape of the thorax.
- The sides of the rust-red flour beetle are curved, whereas the thorax of the confused flour beetle is straighter. It has well developed wings but seldom flies.
Lifecycle
- Female lays between 400 - 500 eggs, with peak oviposition occurring during the first week.
- Adults may live longer than 3 years, and females may lay eggs for more than a year.
- Eggs are deposited directly in flour, other food material, or attached to the surface of the container. They are white or colorless and covered by a sticky material to which flour can adhere.
- Eggs hatch in 3 - 5 days at 32 - 35°C. Larvae burrow into kernels of grain but may leave their burrows in search of a more favorable food.
Habits
- Feeds off grain, flour, and other cereal products, beans, cacao, cottonseed, shelled nuts, dried fruit, dried vegetables, drugs, spices, chocolate, dried milk and animal hides.
- They cannot feed on whole grain, but can feed on broken kernels that are usually present.
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Booklice
(Psocoptera)
Appearance
- Adult — Size varies according to species. 1/16" - 1/8" long. Pale yellow–brown to dark brown in colour.
- Nymphs — very small, often appear transparent. No larval stages.
Lifecycle
- Liposcelis bostrychophila — prefers high temperatures 25–30°C.
- Lepinotus patruelis — will breed at 5–15°C.
Habits
- Liposcelis bostrychophila — Common in homes.
- Lepinotus patruelis — Common in factories and on pallets.
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Yellow Mealworm Beetle
(Tenebrio molitor)
Appearance
- Approximately 20mm long, yellow mealworm beetles are shiny, dark-brown or black.
- Larvae are a honey-yellow color with hard, highly polished worm-like body.
Lifecycle
- Highly resistant to cold temperatures, females lay about 275 – 600 white, bean-shaped eggs singly or in clusters during spring, which hatch into larvae in 4 – 14 days.
- The pupal stage lasts 7 – 24 days – first white, turning yellow (not enclosed in a cocoon) and finally emerging as adults with a lifespan of 2 – 3 months.
Habits
- Adult yellow mealworm beetles are attracted to night-lights, and the strong fliers are commonly found in dark areas.