Stored food pests
are a large group of insects which are economically important and are
responsible for millions of dollars’ worth material loss every year in stored
foods and other products. There are many species of stored food pests found at
storages, warehouses or food pantries and most of these pests are introduced
into our homes in infested food. Most of the stored food pests can reproduce
quickly and have several to many generations in a year depending on the
environmental conditions whereas many species are active year-round under
suitable conditions. Stored foods are commonly infested include flour, cereals,
cracked grains, baking mixes and processed foods, crackers, macaroni, cured
meats, powdered milk, dried fruits, nuts, popcorn and spices.
Insects that feed
on these products may also infest other grain-based items such as pet foods,
birdseed and ornamental corn. Dried flower arrangements may also be attacked.
Several stages (egg, larva, pupa and adult) of these insects may be present at
the same time in infested products. Because warehouses, no frozen storages,
barns, cereal storages and houses are usually kept warm, these insects may
continually reproduce and many stored product infestations can be found nearly
any time of the year. The many different kinds of insects that infest stored
dried foods are often beetles, weevils and moths, but there are other insects
of different types such as mites, borers, etc. These pests contaminate more food
than they eat, and most people find the contaminated products unfit for
consumption. Thus, let’s look at some of the major beetles since the group is
very large with various different beetles which are infesting different types
of stored food items.
Khapra Beetle – Trogodermagranarium
The Khapra Beetle is
considered to be the world's most destructive pest of stored grain and grain
products. If left uncontrolled, this beetle can cover the surface of stored
grain making it appear alive with crawling larvae. The male is about 2 mm in
length and the female is slightly larger (up to 3 mm) and it is a dark-brown
beetle with yellow-brown to red-brown markings on the wing covers. Their body
is covered with fine hairs which may trap dust, giving them a dirty appearance.
The insect is considered as a dirty feeder since it breaks or powders more
grain than it consumes while contaminating the grain with larval skins and
setae which have been known to cause gastrointestinal irritation. Khapra larvae
feed on rice, peanuts, dried animal skins, as well as its preferred natural
foods such as wheat and malted barley.
The adults are
short-lived insects who complete their adult life in one to two weeks, where
mating occurs almost immediately after adult emergence, with oviposition for
one to six days following. The female lays up to 125 eggs loosely in the
infested material. Eggs hatch in five to seven days and the larvae are yellow
to golden brown which is grown up to 5 mm, while they are covered by thick,
red-brown hairs with two tufts at the end of the abdomen. The larvae undergo 4
- 7 molts, resulting in the shedding of numerous cast skins. In ideal
conditions the life cycle can be completed in as few as 30 days.
Lesser Grain Beetle – Rhyzoperthadominica
The adult beetle is
2.5 to 3 mm in length and black-brown in colour, where their body has a slender
cylindrical form and the head is hidden under the round neck-shield. The beetle
lives and feeds in warehouses and stores, and it is primarily a pest in stored
wheat and corn, but it can infest tobacco, nuts, beans, bird seed, biscuits,
cassava, cocoa beans, dried fruit, peanuts, spices, rodenticide baits, and
dried meat and fish.
Adult females lay
eggs singly or in groups of up to 30, whereas eggs are laid on the outside of
the grain and a female can lay from 300 - 500 eggs. The larvae are whitish with
a yellow head and pupation takes place inside the hollow shell of the seed or
in the "flour" that accumulates with infested grain. In hot summer
conditions it may take as few as 30 days, but the average is about 58 days.
Merchant Grain Beetle – Oryzaephilusmercator
The Merchant Grain
Beetle is a store pest species found feeding in nuts, seeds, biscuits, dried
fruit, grain and various other food products, where it can chew through sealed
packaging such as cardboard boxes, plastic bags and foil wrappings. They also
found in pantries or in food processing areas or warehouses. The adult beetle
is approximately 2.5mm to 3mm in length and dark brown in colour with a
slender, flattened body, which can fly (although it rarely does).
The females lays
about 300 eggs in her lifetime, which are dropped loosely among grain kernels
or tucked into a crevice in a kernel. The tiny eggs are slender and white, and
hatch in three to five days when environmental conditions are optimal. Thus,
larvae emerge and crawl freely about the grain to feed on broken kernels and
larger larvae may tunnel into kernels to feed. The development from egg to
adult requires about three to four weeks.
Rust-red Flour Beetle – Triboliumcasteneum
Rust-red flour
beetle is a very common commercial stored products pest infesting a variety of
grain and food materials. They have been reported in grain, flour, and other
cereal products, beans, cacao, cottonseed, shelled nuts, dried fruit, dried
vegetables, drugs, spices, chocolate, dried milk and animal hides. However,
they can’t feed on whole grain, but can feed on broken kernels that are usually
present and in general, fungi may play a significant role in the nutrition of
rust-red flour beetles. When agitated or crowded, they may secrete chemicals
called quinones, which can cause the infested feed to turn pink and have a
pungent odor.
The adult is about
3.0 to 4.5mm in length and it is red-brown in color. The antenna of the
rust-red flour beetle is distinctly club-like, with a three segmented club and
it has grooved wing covers, which has well developed wings and has been
observed to fly. The female lays approximately 400 - 500 eggs, with peak
oviposition occurring during the first week, which are deposited directly in
flour, other food material, or attached to the surface of the container. Eggs
are white or colorless and covered by a sticky material to which flour can
adhere. Which hatch in 3 - 5 days at 32 - 35°C. The larvae burrow into kernels
of grain but may leave their burrows in search of a more favorable food and
they are fairly active but generally hide within the food, away from light. The
larvae are a light honey color and about 6 mm long with a head and a
distinctive forked process at the tip of the abdomen are slightly darkened.
Development time from egg to adult varies with conditions, however as an
average, it takes about 26 days at 32 - 35°C and >70% relative humidity
(R/H). The adults may live longer than 3 years, and females may lay eggs for
more than a year.
Saw Toothed Grain Beetle – Oryzaephilussurinamensis
The saw-toothed
grain beetle is one of the most common insects in stored grain and cereal
products which is a common pest not only in grain bins, but also, mills,
processing plants, warehouses, and kitchens. It feeds on broken kernels and
grain residues and beetles can chew through sealed packaging such as cardboard
boxes, plastic bags and foil wrappings. The larvae develop in flour, cereal
products, and many other dried foods, including grains, cereals, bread, pasta
products, dried meat, dried fruit and nuts, sugar, chocolate, candy, tobacco
products and drugs.
The insect is
approximately 3 mm in length and brown in colour with a flattened body and
wings are present and developed, but they cannot fly. The female lays eggs
singly or in small batches in the food product which lays about 200 eggs in her
lifetime. Eggs hatch after about 8 days and the mature larva is yellowish white.
The life cycle takes about 35 days and the larvae feed in the top few
centimeters of the food stuff and adults usually live around 6 to 10 months.
Warehouse Beetle – Trogodermavariabile
May be found in
many organic materials such as seeds, grains, most types of packaged foods,
snail baits, dog biscuits, stock feeds, old rodent baits, grain remnants in
sacks, bee and wasp nests, rodent carcasses, dead insects, animal droppings
etc. The hairs dropped by larvae may cause human problems such as asthma, skin
problems or gastric disorders.
Adult insect is
about 1.5 to 4.0mm in length and oval in shape with mostly dark brown in
colour, with mottled lighter brown markings. The larva is up to 10mm long, and
pale cream with indistinct dark brown markings and it has 3 pairs of legs and
is very bristly. Lifecycle usually lasts between 1.5 to 6 months depending on
environmental conditions.
Drug Store Beetle/
Biscuit Beetle – Stegobiumpaniceum
The drugstore
beetle (also known as the Biscuit Beetle) gained its name because initially it
was frequently found feeding on drugs in pharmacies many years ago whereas now
they are customarily found infesting all types of dry stored food products,
spices, seeds, grains and dried plant material as well as packaging materials
such as paper and cardboard. Nonetheless, they are also known to be feeding on
leather, wool, hair and books. Adult will often fly and it is 1.5 - 3mm in
length and red-brown, oval beetles with humped thorax and entire body covers
with fine hairs while elytra (wing cases) have ridges with indentations.
The adult beetles
live from 2 to 4 weeks and during this time the females may deposit between
20-100 eggs. The larvae are small and white approximately 0.5 mm long. The
larval period usually ranges from four to five months, but under favorable
conditions whereas the development from egg to adult may occur in 6 to 8 weeks.
Once the larvae are fully grown, pupation occurs and they remain in this
resting stage for 12 to 18 days. Larvae is active in early stages of
development which can bore into hard substances.
Broadhorned Flour Beetle – Gnatoceruscornutus
The adult is
approximately around 3.5 – 4.5mm in length, male broadhorned beetles have two
enlarged mandibles on the head, giving the appearance of horns and thus their
name. Females are very similar in appearance to the confused flour beetle.
Feeds on flour, dough, semolina etc. and it requires temperature around 15 -
32°C, for growth, where broadhorned flour beetles cannot complete their life
cycle below 10°C. Moth eggs and larvae may supplement the broadhorned flour
beetle diet.
Cigarette Beetle – Lasiodermaserricorne
The Cigarette
beetle is a very common commercial pest and it is about 2-4mm in length, which
is whitish in color, with a head dark brown to tan, and are densely haired. The
beetle is closely resembles the drugstore beetle which has the head bent down
nearly at right angles to the body giving it a humped back appearance when
viewed from the side. The Cigarette Beetle feeds off tobacco, dry stored food
products, spices, seeds, grains and dried plant material, which also been
reported in rice, dried potatoes, paprika, raisins, grain-based mouse bait and
dried straw flowers. Adult beetles often wander away from infested materials
and may be found throughout the area.
The adult beetles
live from 2 to 4 weeks and during this time the females may deposit between
10-100 eggs, which are laid loosely on the infested material. The larval period
usually ranges from four to five months, but under very favorable conditions
the development from egg to adult may occur within 6 to 8 weeks. The larvae are
about 4 mm long and somewhat bent. When the larvae are fully grown, pupation
occurs and itremains in this resting stage for 12 to 18 days.
Confused Flour Beetle – Triboliumconfusum
The confused flour
beetle was named because of the confusion over its identity. It is a very
common commercial and pantry pest. The adult is about 3-4 mm in length, which
is reddish brown in color and 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, which has well developed wings but seldom flies. Insect
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.
Adults may live
longer than 3 years, and females may lay eggs for more than a year which
amounts to 400 - 500 eggs, with peak ovi-position occurring during the first
week. 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 and larvae is light honey coloured and about 6 mm
long.
Copra Beetle/Red Legged Ham Beetle – Necrobiarufipes
The adults is 4.5 mm
in length and upper surfaces of the body are a shiny metallic bluish-green with
underside of the abdomen is dark blue. Their legs are bright reddish-brown or
orange while antennae are reddish–brown with a dark brown or black club at the
tip. The adults can fly and therefore easily disperse to new sources of food
and are also cannibalistic, preying on their own eggs and pupae. They are
destructive in both the larval and adult stages, although the larval stage is
the most destructive. Females lay up to 30 eggs per day in cracks or crevices
of cured fish, where eggs take between four and six days to hatch. The
larvae will grow for 30 to 140 days, become less active and look for a dark
place to pupate and the pupal stage varies between 6 and 21 days. An adult
will mate soon after emerging from its pupal stage and can live for up to 14
months
Australian Spider Beetle – Ptinustectus
Australian spider
beetles are covered in brown and golden hairs, which has a spider-life
appearance and adults grow up to an approximate 2.4 – 4mm in length, while it
live for up to 3 – 4 months at 20 - 25°C. Larvae are often found feeding on
miscellaneous debris, which possesses the ability to bore into various inedible
materials prior to pupation. It is active in dark, damp places, which is often
associated with bird nests.
Flat Grain Beetle – Cryptolestesferrugineus
Adult about 3mm in
length and have a flattened body with very long antennae. Light red to dark
reddish brown, which prefers warm damp conditions and life cycle lasts around
69–103 days at 21°C, 26 days at 38°C. Adults having wings but rarely fly and
they feeds on cereals, dates, dried fruits and other commodities. Larva is
yellowish–white in colour and 0.5mm long growing to 4mm when mature.
Rove Beetle – Paederusriparius
Adult beetle is
about 8 to 9.5mm in length and body colour is an alternating black and red,
which are common in decaying fruit or seaweed, compost with large numbers of
flying larvae. The larvae and adults are general predators of small insects and
other arthropods, including pests of crops, which are most common in spring and
early summer. Female lay eggs singly on moist substances and typically develop
in 3–19 days and the larvae pass through two stages before reaching
adulthood.
Yellow Mealworm Beetle – Tenebriomolitor
Cold weather insect
and they are highly resistant to cold temperatures, which is an important
post–harvest pest and occurs spread all over the world. Adult beetles are
attracted to night-lights, are strong fliers, and are found in dark places,
which is 19mm in length and are shiny, dark–brown or black.
Each female lays
about 275–600 eggs singly or in clusters during the spring, which are white,
bean-shaped and about 0.75mm long and hatch into larvae in 4 to 14
days. The larvae are honey–yellow in colour and they have a smooth, highly
polished, shiny, elongate, hard, worm-like body, which can grow up to 30mm
long. The pupal stage lasts 7 to 24 days during the spring, which are first
white in colour, turning yellow, and are not enclosed in a cocoon. Adults
emerge in the spring or early summer, living for two to three months.
Dermestes Beetle – Dermesteslardarius
Adult – 6 - 9.5mm
in length. And coloured in black with a whitish band across the fore–part of
the elytra with a life span of 2–3 months at 18–25°C while feeding on various
dried foods and animal products including cheese, leather or any dry matter.
Their larvae are comet shape which can quickly move and are brown in colour and
hairy which migrate to pupate in solid material.
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