STORAGE INSECT PESTS
IMPORTANCE
Insect pests have the ability to infest dried fermented cocoa beans and other stored commodities. The
attack usually starts in the holding warehouse and can continue to escalate during transport to the final
destination if conditions are right for the insects to multiply. Losses can be significant as the actions of
the various pests can cause loss of weight, contamination by insect faeces and introduction of fungus
contamination. All or any of these infestations can result in low prices or complete rejection by the
buyers.
These insect pests are common in tropical and subtropical regions. Some such as the flour beetle are
also found in warm temperate regions.
Four of the most common are:
 Cocoa moth
 Flour beetle
 Rice moth
 Tobacco beetle
DESCRIPTION
Cocoa moth
(Cadra cautella, formerly Ephestia cautella)
Flour beetle or red flour beetle
(Tribolium castaneum)
Up to 300 slightly sticky eggs are laid by the
female in the first 3-4 days after mating but few, if
any, in the remaining 4 or 5 days of life. At 30°C
the eggs hatch in approximately 3 days. There
are normally five larval instars and under good
conditions (32.5°C and 70% RH) the larvae
stages are completed in about 22 days. In heavy
infestations the mature larvae leave the
commodity in search of pupation sites, such as
the walls of the store or the spaces between
bags. Before pupation, the larva produces a
cocoon; this is both thinner and looser than that of
the rice moth. The pupal stage is completed in
about 7 days. Under good conditions,
development from egg to adult takes 29-31 days.
The limiting levels of moisture at 30°C are 20 and
90% RH and development is only possible within
a range of 15 to 36°C.
Females lay up to 450 eggs in stored commodities.
The incubation period of the eggs is between 5 and
12 days. All insect stages infest the stored
commodity. The larvae are fully grown in 27-29
days and are 6mm long. Pupation occurs in stored
commodity and the pupa does not produce a
cocoon. Adults emerge from the pupa in 3-7 days.
Adult emergence from the cocoon usually occurs
during the late afternoon. Flight activity and egglaying show a major peak at around dusk and a
minor peak just before dawn.
The developmental period from the egg to the adult
stage is about 20 days under optimum conditions of
35°C and 70% RH, but may be as long as 141 days
at 25°C and 70% RH.
There may be between four and seven generations
in 1 year, depending on weather conditions, and
one generation may take 1-4.5 months. The adults
may live for as long as 18 months, depending on
weather conditions.
Adults fly in large numbers in the late afternoon and
are active from October to May. Beetles fly in the
field between 16.00 and 19.00 h on relatively calm
days, and at temperatures above 26°C.
Migrating adults represent a serious potential for reinfestation of stored grain.
Rice moth (Corcyra cephalonica)
Tobacco beetle (Lasioderma serricorne)
Sexual activity usually begins shortly after adult
emergence; females apparently mate only once
during a 1- or 2-day period after emergence and if
no mating occurs in this period the females are
then not inclined to mate.
Each female lays up to 110 eggs loosely on the
commodity. On hatching, the larvae often eat their
eggshells. At first the larvae are quite active and will
move around on, or bore into, the commodity,
feeding as they go. They will move much more
deeply into a loosely packed commodity than into
one that is tightly packed. There are 4-6 larval
instars. As the larvae grow they become less active
and finally they make a pupal cell out of fragments
of food and waste materials. The pupal stage lasts
for about 9 days at 32-35°C.
There is a pre-egg laying period of about 2 days.
Egg-laying mainly occurs during the night; the
eggs are rather sticky and are usually deposited
on the food or among sack fibres. The greatest
number is laid on the second and third days after
emergence, although egg-laying may continue
throughout life. At 30-32.5°C, eggs take about 4
days to hatch. They are adversely affected by
very low humidity and few eggs hatch below 20%
RH.
Optimum conditions for larval development are
30-32.5°C and 70% RH, at which the period from
egg hatch to adult emergence is only 26-27 days.
There is considerable variation in the number of
larval instars; however, it would appear that
males generally have seven and females have
eight.
The last-instar larvae pupate on store structures,
on or between bags, or within the food. The
adults emerge through the front end of the
cocoon, where there is a line of weakness. The
sex ratio is believed to be 1:1. The adult moth is
nocturnal and is most active at nightfall. Its flight
is rather slow and clumsy; flight is not powerful
but can be sustained. The moths rest away from
draughty places, on shaded store structures or
surfaces of bag stacks; they are thus most
commonly found in dark, sheltered corners of a
store.
The rice moth can tolerate conditions of less than
20% RH on sorghum and millet. This can give the
insect an advantage in dry conditions.
The generation time varies between 25 and 120
days depending on temperature, humidity and food.
Development can take place between 20 and
37.5°C, and at humidities down to 25% RH.
The adults live for 2-6 weeks and do not feed. The
adult is an active flier, especially in the late
afternoon and evening.
The tobacco beetle does not tolerate cold and
adults are killed by exposure to temperatures of
4°C for 6 days and few eggs survive for 5 days at 05°C
MANAGEMENT
Sanitation and hygiene
Cleanliness in the storage warehouse is one of the most important weapons in the war against storage
pests. After the commodity has been shipped the store walls and floor must be swept clean of all rubbish
and spilt commodity. Household bleach can be used to wash the walls and floors, bleach is a strong
chemical, and protective clothing and gloves must be worn when using it.
Old sacks must be discarded in a refuse tip away from the store or burnt. If in a good condition and can
be reused, then the sacks must be thoroughly washed in detergent and dried in strong sunlight.
Cracks in the floor and walls of the store must be filled so that adult insects do not have anywhere to hide.
Wooden pallets that are used to keep the storage sacks off the floor must be scrubbed clean and laid out
in strong sunlight to dry.
Pheromone traps
Commercial traps are available and are very useful for monitoring during storage. These give an early
indication if insects have started to infest the store. Traps should be used in conjunction with regular
inspection of the store.
Chemical fumigation
This is very, very expensive and can only be undertaken by a licensed operator / company. Methyl
bromide at one time was the chemical of choice but its use is now only permitted under very limited
circumstances internationally. Other chemical fumigants such as phosphine and sulphuryl fluoride can be
used in large commercial stores however strict international limits are placed on residues of these
chemicals in commodities.
LOSSES
Losses in store can be considerable. The commodity can be rendered totally unsaleable because of
damage by insect feeding and contamination by insect faeces.
Moulds (fungi) grow over the surfaces and into the commodity causing rotting and introduce mycotoxins.
Mycotoxins are poisons produce by the mould and can cause illness or death in people or animals that
eat the contaminated commodity.
PREFFERED SCIENTIFIC NAME
Taxonomic position
Cadra cautella Walker
(formerly Ephestia cautella Walker)
Cocoa moth
Tribolium castaneum Herbst
Flour or red flour beetle
Corcyra cephalonica Stainton
Rice moth
Lasioderma serricorne Fabricius
Tobacco beetle, cigarette beetle
Domain: Eukaryota
Kingdom: Metazoa
Phylum: Arthropoda
Subphylum: Uniramia
Class: Insecta
Order: Lepidoptera
Family: Pyralidae
Domain: Eukaryota
Kingdom: Metazoa
Phylum: Arthropoda
Subphylum: Uniramia
Class: Insecta
Order: Coleoptera
Family: Tenebrionidae
Domain: Eukaryota
Kingdom: Metazoa
Phylum: Arthropoda
Subphylum: Uniramia
Class: Insecta
Order: Lepidoptera
Family: Pyralidae
Domain: Eukaryota
Kingdom: Metazoa
Phylum: Arthropoda
Subphylum: Uniramia
Class: Insecta
Order: Coleoptera
Family: Anobiidae