|Pests; Insecticides; Vegetable Oils; Biopesticides
|Cereals and pulses have great biological and nutritional value in
human diet. Generally it is agreed that grains stores better and more
cheaply than other major food. The losses during post-harvest handling,
processing, storage and distributions systems vary between 20-60% [1-4]. Everywhere in the world stored products are attacked by a number
of storage enemies. Three major groups of storage enemies are: fungi,
insects and rodents. These organisms can damage a considerable part
of the stored product. Insects, rodents and microorganisms not only
consume and/ or spoil the edible and inedible parts of the stored grain
but also lead to post-harvest deterioration causing economic losses due
to obvious decay and adverse changes in the odor, taste, appearance
and nutritive value [5-7]. In addition, the arthropods transfer bacteria
and pathogenic 2 fungi that stick to their bodies or disseminate them
via faeces [8,9]. If these losses are minimized, the shortage of foods
can probably be reduced. In this context, the improvement of grain
storage conditions / systems is the first step in this direction. Hence an
integrated approach is required for the control of pests and is essential for
maintaining the quality of grains during storage as well as in production
. In many cases small improvements in storage methods may lead to
much better protection of stored product and thus to less loss. A good
storage building is one thing, good safety measures another. According
to De Groot  however, good storage practices combined with good
hygiene, adequate drying and all other safety measures will not always
be effective in preventing storage losses. Storage pests may still manage
to reach the product and leave a trail of devastation. If this occurs
we will have to take other measures to protect our storage product.
Although controlling physical, chemical and mechanical factors to a
large extent can check the degree of deterioration, spoilage of grains,
maximum efforts are required to control the spoilage factors of grains,
such as insects and mites, rodents, birds and micro flora. The major
insect pests are given in Table 1. There are many ways of protecting local
storage products. Time-honored methods such as the use of natural
materials like plants, minerals, and oil are still very effective. Due to
the introduction of chemicals, many traditional storage treatments
are often forgotten. These chemicals are classified as Insecticides and
Roenticides. Some important insectides and rodenticide are as follows:
|4. Chlorpyrifos methyl
|(i) Acute Poisons
|1. Arsenious oxide
|2. Zinc phosphide
|3. Sodium monofluoroacetate
|4. Antu (α-Naphthyl Thiourea)
|(ii) Chronic Poisons
|Insecticides Used For Controlling Storage Pests
|As mentioned before, many insecticides are available but only few
can be used for protection of stored cereals and pulses. Insecticides
which are commonly used discussed further. While describing toxicity,
it is mentioned whether the insecticide is toxic for human beings and
warm blooded animals or not. Always make sure that the container has
a label with instructions for application before purchasing it. Be aware
that pesticides can have different trade names. The active ingredients,
which are being discussed further, should always be mentioned on the
|Malathion may be mixed with grain as a dust or sprayed on walls
or floors. As a dust it is one of the insecticides most widely used to
protect stored cereals and pulses. The product to be dusted must be
well dried; otherwise malathion breaks down very rapidly. Malathion
is not suitable for disinfecting storage structures because it is unstable
on concrete surfaces or whitewashed walls. There should be a gap of a
period of 12-13 weeks between the malathion treatment on grains and
their consumption. In that period malathion breaks down completely
without leaving harmful residues. Some disadvantages of malathion are:
|1. Malathion is not very effective against the lesser grain borer
|2. Some insects like red flour beetle (T. castaneum) (Herbst), strains
of sawtoothed grain beetle (Oryzaephilus surinamensis L.) and
mosquitoes have already developed resistance against malathion
[11,12]. This means that the insecticide is no longer killing
|3. Malathion has a nasty smell.
|4. Malathion is only slightly effective against caterpillars (tent
caterpillars), moths (bud moths, codling moths, pine shoot
moth) and mites.
|Pirimiphos-methyl has a low toxicity for humans and warmblooded
animals. Pirimiphos-methyl is sold with various trade names
viz. Actellic, Actellifog Silosan, Blex. It remains stable, even on relatively
wet grain. It is persistent for several months, which reduce the risk
of re-infestation by a second generation insects or new ones from
outside. Pirimiphos-methyl is active against beetles, moths and mites.
It performs well against species resistant to malathion. Pirimiphosmethyl
is available in different formulations: dusts, wettable powders,
emulsion concentrates and aerosols.
|Bromophos has a relative low toxicity (similar to malathion) for
human beings and their domestic animals. The most common trade
names of bromophos are: Bromofos, Brofene, Brophene, CELA-1942,
ENT-27162, Nexion, Omexan. It is more persistent than malathion on
concrete surfaces and therefore it can be used for disinfection of storage
buildings. It is also more persistent on warm moist grain. Residues of
Bromophos are easily destroyed by heating (cooking or baking) the
cereals in food preparation. A disadvantage is that Bromophos acts
slowly: the adult insect may lay its eggs before it is killed. Bromophos is
available as a dust, (to mix with the stored product), or as an emulsion
concentrate (to treat stacks of bags or walls and floors).
|Chlorpyrifos methyl has a relatively low toxicity for human beings
and domestic animals. The common names are: Brodan, Detmol UA,
Dowco 179, Dursban, Empire, Eradex, Lorsban, Paqeant, Piridane,
Scout, and Stipend. It is effective against a wide range of storage pests
except against lesser grain borer. Mixing Chlorpyrifos methyl with
Bioresmethrin could make a very effective mixture against many
species viz. Sitophilus oryzae (L.), Rhyzopertha dominica (F.) Tribolium castaneum (Herbst), and Oryzaephilus surinamensis (L.) .
|Fenitrothion is very effective against a wide range of insect pests, although it is not fully effective against the lesser grain borer which
mainly attack wheat, corn, rice and millet. Both the larvae and adults
of lesser grain borer are primary pests. They bore irregularly shaped
holes into whole, undamaged kernels and the larvae, immature stages,
may develop inside the grain. Larval and adult feeding in and on grain
kernels may leave only dust and thin brown shells. Fenitrothion can
be used to disinfect storage structures or to protect stored produce.
It is more persistent than Malathion. Mixing Bioresmethrin with
Fenitrothion could make a very effective mixture against many species.
Fenitrothion is far more toxic for human beings and domestic animals
than the insecticides described above. But because it hardly penetrates
into the grains, most of the residues are removed while dehusking. It is
available as dust, emulsion concentrate and wettable powder.
|Similar to Fenitrothion, Methacrifos is far more toxic for vertebrates
than the other insecticides described previously. Methacrifos is useful
in cases where insects are resistant to malathion (maize weevils, rice
weevils, grain weevils and the flour beetles). A special characteristic
of Methacrifos is that it penetrates into the grains, thus killing larvae
inside the kernels. Methacrifos works very well at lower temperatures.
It is available as emulsion concentrate and a 2% dust.
|Bioresmethrin, the synonymous d-trans-resmethrin, is a synthetic
pyrethroid and it has a very low toxicity for humans and animals. It acts
mainly as a contact insecticide but inhalation and ingestion are also
lethal for insects. Bioresmethrin deteriorates rapidly when exposed to
light. Bioresmethrin is effective against the lesser grain borer, so it is
especially useful in situations where the lesser grain borer has developed
resistance against insecticides such as Malathion, Pirimiphosmethyl,
Fenitrothion and Chlorpyrifos-methyl. In these cases Bioresmethrin
can be mixed with these other insecticides to improve efficiency of the
|Deltamethrin, like Bioresmethrin, is a synthetic pyrethroid, and
has a very low toxicity for vertebrates. However, the formulation
of Deltamethrin in vegetable oil has dangerously high toxicity.
Deltamethrin is stable on grain for a long time, but because it does not
penetrate the grains, it is removed by dehusking. Deltamethrin is very
effective against the lesser grain borer which is not very susceptible to
Malathion, Pirimiphos-methyl, Fenitrothion and Chlorpyrifos-methyl.
It also is very effective against the grain weevil (Sitophillus granarius).
|Permethrin also is a synthetic pyrethroid. It has a very low toxicity
to human beings and animals (except for fishes). When dissolved in
oil its toxicity is much higher however. Permethrin is effective against
a large range of insects and especially against the lesser grain borer.
It has little effect against flour beetles though. It is very persistent
on grain and not very sensitive to moisture. Because Permethrin is
effective against the lesser grain borer, it is often mixed with Malathion,
Pirimiphos-methyl, Fenitrothion and Chlorpyrifos-methyl, in cases
where the lesser grain borer has developed resistance. The efficiency
of Permethrin (and other synthetic pyrethroids) is improved by adding
Piperonyl -butoxide. Permethrin is especially important also for the
control of the larger grain borer (Prostephanus truncates), these two
grain borers are of the same family, which is very sensitive to synthetic pyrethroids. Permethrin is available as dust (0.5 %). For the protection
against the larger Grain Borer it seems more effective to store and treat
shelled maize instead of maize (Zea mays) on the cob.
|Pyrethrum show low toxicity to human beings and the domestic
animals. It exerts rapid effect on a various insects, but sometimes after
treatment insects can recover. To overcome this problem, Pyrethrum is
often mixed with some other insecticides, especially Piperonyl-butoxide.
The mixture also is cheaper because a lower doses of Pyrethrum can be
used (Pyrethrum is expensive). Pyrethrum is available as oil solutions
and solution concentrates. Wettable powders and dusts have a short
|Methoprene is effective against a wide range of storage pests. It has
a very low toxicity against human beings and warm-blooded animals.
It is effective against the lesser grain borer, but the Grain weevils, Rice
weevils and Maize weevils are less sensitive to Methoprene. Methoprene
does not directly kill the insects, but it inhibits the reproduction. In this
way it prevents development of large populations of insects.
|Carbaryl is not effective against storage pests in general, but
it is effective against the lesser grain borer as such. It is used in
combination with Malathion, Pirimiphos-methyl, Fenitrothion and
Chlorpyrifosmethyl, in cases where the lesser grain borer has developed
resistance. Carbaryl should only be used in combination with these
insecticides. Care should be taken because Carbaryl is quite toxic.
|Dichlorvos is geneally available under various trade names viz.
DDVP, Dedevap, Nuvan and Vapona. Dichlorvos is highly toxic to
human beings and warm-blooded animals. It vaporizes rapidly and
the vapor is very effective against insects. However Dichlorvos is
not suitable to use as a fumigant, because the vapour is too volatile.
Dichlorvos is therefore mainly used to treat the free space in a store or
to disinfect infested grain when brought into the store. Because of the
high toxicity of Dichlorvos, it is not recommended to use.
|Lindane is highly toxic to humans and animals due to its persistency.
Residues build up in the food chain and have been traced in milk and
meat. As such a there is a danger of chronic poisoning that occurs with
long term use. Though lindane is still available, we recommend not
|DDT has no direct toxic effect on human beings or animals, but
even small quantities of DDT accumulate in the body. Over a longer
period of time the accumulated DDT has proven to be toxic to man
and animals. Residues have been found in mother milk. Therefore we
should never let DDT come into contact with food products or animal
feed. Neither should it be used for treating the external surfaces of bags
containing food products, nor for treatment of the insides of containers
for food products or animal feed or in any situation.
|Rodenticides Used for Control of Rats and Mice
|Rodenticides are poisons that kill rodents. Because these poisons
are meant to kill warm-blooded animals, they are very poisonous to human beings, their children, their domestic animals and to wild
animals. Because the rodenticides are used close to the stored product
there is a good chance that the produce gets contaminated with the
poison. Rodents can poison the food by walking over the poison and
after that spreading it over the food. Therefore we strongly advise
not to use rodenticides. If there is no other way, use them sparingly
and carefully. Another disadvantage of rodenticides is that they cost
money and they are not always in stock. Rodenticides should be used
only when other means have failed and then only by someone who is
familiar with their use and their dangers. Instructions for use should be
included with the container. Use of poison, without proper directions,
should be avoided.
|Types of rodenticides
|The rodenticides that are available will vary from area to area. They
are sold under different trade names. Basically there are two kinds of
poison used for killing rodents: acute poisons and chronic poisons.
|Acute poisons: This is a group of poisons that cause a quick death if
eaten by the rodents in small quantities. These are single dose poisons.
Rodents need to eat only a mouthful of poison to die within half an
hour. However acute poisons are extremely poisonous to man and
domestic animals. A practical problem is the bait-shyness induced by
this type of poison. If the rat finds the taste of the poison suspicious,
he will stop eating it and not swallow enough poison to die. The rat
will recover and for a long time he will refrain from eating this type of
bait or anything that tastes alike. Rodents also learn very quickly; as
soon as a member of the species is found dead from poison the others
will avoid the poison. Acute poisons are extremely dangerous to man
and domestic animals. They must be handled by an experienced person,
who is aware of the precautions to be taken to avoid accidents. Normally
they must be used outside, never in stores containing foodstuffs. The
most common acute poisons are:
|1. Arsenious oxide: Approximately 40 milligrams are needed to kill
a 200 grams brown rat (Rattus norvegicus).
|2. Zinc phosphide: Used in baits to which fats are added to increase
its effect. Less than 10 milligrams is needed to kill a 200 grams
|3. Sodium monofluoroacetate: It is 20 times more toxic than Zinc
|4. α-Naphthyl Thiourea (Antu): Should only be used against the
|Chronic poisons: The chronic poisons or slow poisons are used in
lower dosages than the acute poisons. They are added to a food for the
rat or mice to eat (bait). They must be eaten for a number of days before
death occurs. These poisons cause rodents to bleed inside their bodies.
The bleeding occurs from old wounds and thin tissues inside the body,
and it will not stop. The chronic poisons have no taste and no smell.
The rodents do not know they are being poisoned. This is an advantage
because they continue to eat the poisoned food. A disadvantage may be
that it requires a lot of poison, a lot of bait and a long time to use chronic
poisons well. Another disadvantage is the price. Chronic poisons are
more expensive than acute poisons. On the other hand they are less
dangerous to man (although still highly toxic) and more effective
against rats. The most common chronic poisons used are:
|1. Coumafen (or Warfarin): This was for a long time the most
popular anti-coagulant. Chlorophacinone is now preferred.
|2. Chlorophacinone: Acts in smaller doses than the other slowacting
|3. Bromadiolone: Useful against species that are resistant to
coumafen and chlorophacinone.
|4. Difenacoum: Effective against rats that are resistant to coumafen.
|5. Diphacinone: A bait which is already mixed with a certain
|Chronic poisons are also extremely dangerous to man and domestic
animals. Because the chronic poisons have to be available for the
rodents for a longer period, the danger that children, cats or dog eat
them is much bigger.
|Oil as an Optional Grain Protectant
|The growing awareness of environmental issues as well as health
hazards from synthetic pesticides and associated problems of pests’
resistance to most of the insecticides, modern concept of insect growth
is developed thereby in term controlling their population. Natural
chemicals are environmentally safer than classical insecticides. For
this reason various researchers and users are trying to use organic
pesticides/ biopesticides for this grain storage purpose. During recent
years considerable attention has been paid to: exploitation of plant
materials in protection of food commodities from insect infestations.
Extracts of some plant species viz. Lantana camara , Illicium verum
, Tithonia diversifolia  have been reported to possess strong
insecticidal activity against different storage insects. Plant derived
products namely, azadirachtin from neem (Azadirachta indica),
pyrethrin from pyrethrum (Chrysanthemum cinerariaefolium), carvone
from caraway (Carum carvi) and allyl isothiocynate from mustard
(Brassica nigra) and horseradish(Armoracia Rusticana) oil have
received global attention due to their pesticidal properties and potential
to protect several food commodities [17-20]. Essential oils produced
by different plant genera have been reported to be biologically active
and are endowed with insecticidal, antimicrobial and bio regulatory
properties [19,21-23]. The volatility and biodegradability of flavour
compounds of angiosperms will be advantageous if they are developed
as pesticide insecticide . There may be least a chance of residual
toxicity by treatment of food commodities with volatile substances of
|Numerous vegetable oils can be used as a protective additive. An
advantage is that they are easy to apply. The oils of peanuts (Arachis hypogea), coconuts (Cocos nucifera), safflower (arthamus tinctorius),
mustard, castor beans (Ricinus communis), cotton seeds (Gossypium spp), soybeans (Glycine max.), neem, cucurbits (Cucumis sativus) and
maize (Zea mays) etc. have been used successfully. Not all types of
oil will be effective. For example sunflower seed oil is not effective in
all cases. Use only small amounts of oil (for instance: 2-4 ml per kg
threshed beans) and mix the oil and the product thoroughly. This is
best done in a big pot or something similar, and portion by portion.
After treatment the product can be stored in sacks. Oil can be used
preventively as well as curatively.
|The mechanism by which oil protects the seeds is not completely
clear, but it appears that vegetable oils effect egg laying as well as
embryo and larvae development on the surface of the seed. Vegetable
oils cause the eggs and larvae to die before they can bore into the seed. If
the larvae do manage to penetrate into the seed, because it has not been
sufficiently coated with oil, then the treatment produces no further
effect and the larvae will develop normally. In some cases female insects
are able to lay eggs, but the hatching of the larvae is prevented by the oil.
|Oil may also kill the insect eggs. When the egg is already present
at the surface of the seed or inside the seed, the oil coating prevents
gaseous exchanges. So the larvae inside the egg or the kernel will die
due to lack of oxygen. Some oils such as those derived from neem,
karanja (Pongamia glabra), undi (Calophyllum inophyllum) and kusum
(Schleichera triguga) also have an insecticidal effect, and a small amount
may kill about 90 % of the Cowpea weevil (Callosobruchus maculatus).
The protective effect may last for upto 3 months. These oils are not
harmful to human beings. Oil can be an effective protection or cure
against insect damage. It is important to mix the oil very carefully with
the grain or beans. If a small piece of the kernel is not coated by the oil,
the adult insect can lay its eggs and larvae may enter the kernel.
|Protection of legume-pulses by using vegetable oils
|Legume and pulses are the excellent source of protein, rich in
important vitamins and minerals. Hence make the diet balanced and
nutritive. Bruchid/ pulse beetle (Callosobruchus spp.) spoil the stored
legume to such an extent that a huge portion of total production is gone
|Many researchers have tried to protect legumes from pulse beetle.
Edible oils show a very good effect against insect-pest infestation.
Khalequzzaman et al  used seven vegetable oils viz., sunflower
(Heliunthus annus, L.), mustard, groundnut (Arachis hypogaea, L.),
sesame (Sesamum indicum L.), soybean, olive (Olea europea) and oil
palm (Elaeis guineensis), each were applied at the rates of 5, 7.5, and 10
ml/kg of grain (0.5, 0.75 and 1% v/w concentrations) as grain protectants
of pigeonpea (Cajanus cajan) against the pulse beetles (Callosobruchus chinensis L.). Effects on progeny emergence, loss in grain weight,
and germination up to 66 days after treatment were measured. Adult
emergence was completely prevented and the minimum grain loss was
achieved by groundnut oil at 1% up to 66 days after treatment. Since
treatments with groundnut and palm oils at 5 ml/kg showed high
acceptability by consumers, it can be recommended for C. chinensis
control in stored pigeonpea for approximately two months. Bhatnagar
et al.  also studied the efficacy of vegetable oils against pulse beetle
Callosobruchus maculatus in cowpea. These workers used groundnut,
sesame, soybean, coconut, mustard and neem oil @ 10 ml/ kg grain
and reported that neem oil is the most effective against the pulse beetle
followed by coconut, soybean and mustard oil. Singh et al.  used
soybean oil as seed protectant against the infestation on pigeonpea
and studied the effectiveness of soybean oil as seed protectant against
Callosobruchus chinensis Linn. These workers have reported that
refined and crude oil, each @ 0.5 ml/100 gm grains, caused 100% adult
mortality within one day of their release. In the case of other doses
(0.25 and 0.10 ml), only 40-65% mortality was obtained. They have
further reported that grain treated with refined and crude oil, each
@ 0.5 ml/100gm grain were free from insect damage and without any
apparent loss in the grain weight and seed germination.
|Sandbox seed (Hura crepitans L.) oil was used to observe the
insecticidal activity of oil on oviposition, adult emergence, mortality
of immature stages and reproductive competitiveness of the cowpea
seed beetle, Callosobruchus maculatus . Results obtained show that
sandbox oil significantly reduced oviposition and adult emergence in
both choice and no-choice experiments. Oviposition was reduced by
more than 50 % in the lowest oil treatment (i. e., 0.1 % v/w) while adult
emergence was totally inhibited at all the oil concentrations except at
0.1 % oil v/w. Sandbox seed oil evoked 100 % ovicidal activity at all
the treatment levels while 100 % larvicidal effect was obtained at 0.2 ml, 0.3 ml and 0.4 ml oil per 20 g of cowpea seeds and 100 larvae.
Reproductive competitiveness of the oil-treated bruchids reduced with
increase in the concentration of the sandbox oil applied. The frequency
of the copulation position gained by the males within 30 min reduced
from an average of 14.25 times in untreated males to zero at 1.5 % and
2 % oil treatment levels. Similarly, an average mating frequency of 10.50
times was obtained in the untreated females compared with an average
of nil at 1.5 % and 2 % sandbox seed oil concentrations. Sandbox seed
oil effectively suppressed infestation and population build up by pulse
beetles. Cashew nut oil (CNO), Coconut oil (CONO), Udara nut oil
(UDNO), and Neem leaf oil in controlling stored black beans weevil
(Callosobruchus chinensis) was investigated . The results showed
that the number of eggs and exit holes of C. chinensis were not significant
at 5 % probability level before treatment with the extracts. Then after
two months in storage the black beans were treated with the extracts
and there was significant reduction of rate of oviposition and number
of exit holes. The plots treated with coconut oil extract proved more
effective than other oils Cucurbits (Bitter gourd, small bitter gourd,
Ridge gourd and Bottle gourd) seed oils are also effective against the
pulse beetle (Callosobruchus chinensis). Mishra et al.  used solvent
extracted vegetable oils of these seeds as grain protectant against pulse
beetle. All the vegetable seed oils were found effective and prevented
weight loss at the oil application rate of 6-8 ml/ kg of legume- pulse
grain after 60 days storage under laboratory conditions. The milling
yield and degree of dehusking is improved after oil application. The
small bitter gourd seed oil @ 6-8 ml/kg of grain resulted in the improved
apparent degree of dehusking from 40% to 72.59%, 59.88% to 92.44%,
63.39% to 87.50% and 57.0% to 79.43% for pigeonpea, chickpea (Cicer
arietinum), urdbean (Vigna mungo) and mungbean (Vigna radiata),
respectively. Cucurbits have bitter chemicals called cucurbiacins: that
are the tetracyclic triterpenes having extensive oxidation capacity.
They occur in nature, free as glycosides or in complicated forms of
taxomonic significance. Some kind of co-evolutionary relationship
between cucurbitacae and beetles has been envisaged through the
secondary plant substances such as oxygenated tetracyclic triterpenes
. The toxicity of three concentrations (5%, 10% and 20% w/v) and
spraying schedules (2, 4 and 6 weekly applications) of an extract from
West African black pepper (Piper guineense) for managing two major
post-flowering pests: Maruca pod borers (MPBs) and pod sucking bugs
(PSBs) of cowpea (Vigna unguiculata) was investigated . The higher
concentrations (10% and 20% w/v) and more frequent applications
(4 and 6/week) significantly reduced the numbers of the two insect
pests compared to the untreated control. Pod damage was significantly
reduced and grain yields consequently increased in treated plots
compared with the untreated control.
|The repellent effects of ten oils, Domba (Calophyllum inophyllum
L), Batu (Solanam indicum L), leaf oil and bark oil of Cinnamon
(Cinnamomum verum Presl.), Mustard oil (Brassica juncea Cross.),
Neem oil, Mee oil (Maduka longifolia Koenig.), Castor oil (Ricinus communis L.), Cit-ronella oil (Cymbopogon nardus L.) and Sesame oil
(Sesamum indicum L.) were tested for pulse beetle (Callosobruchus maculatus L.) in the laboratory conditions . Data were recorded on
distribution, ovi-position and adult emergence. Ventilated containers
each with five pairs of newly emerged adults with 20 green gram
seeds were exposed to different oil vapours at the rate of 200μml.
Each container was fixed to a device that provided a tunnel for pulse
beetle to escape from or enter into any container. Cit-ronella oil,
neem oil, cinnamon leaf oil and cinnamon bark oil vapours resulted
in significantly lowest number of pulse beetles after infestation and
their oviposition and adult emergence indicating the highest repellent action and toxic effects. Mustard oil, domba oil, mee oil, castor oil and
batu oil show indications of higher repellent effect 4DAT (Days after
treatment) on the distribution of the C. maculatus. Mustard oil and
Domba oil showed a lower rate oviposition than that of Mee oil, Castor
oil and Batu oil. All the treatments except Sesame oil had significantly
reduced adult emergence at 18DAT (Days after treatment). Sesame oil
showed positive effect on distribution, oviposition and adult emergence
and no repellent activity against the pulse beetle. Essential oil from the
leaves of Bael (Aegle marmelos Correa) was also found effective against
Callosobruchus chinensis (L.) (Bruchidae) in stored gram . Stored
gram (Cicer arietinum) was fumigated with the essential oil at 500 μg/
mL (ppm). The essential oil at different doses significantly reduced
oviposition and adult emergence of C. chinensis in treated cowpea
seeds. The oil protected stored gram from C. chinensis. Limonene (88
%) was found to be the major component in the oil through GC-MS
(Gas Chromatography-mass spectometry) analysis.
|Traditional Indian tree Neem oil as also a good insect-pest
protectant. The toxicity of Neem oil against the pulse beetle
Callosobruchus chinensis Linn. was studied in different pulse grains
and persistant toxicity of neem oil was reported to be highest in the
green peas followed by cowpea and lowest in the bengalgram . He
reported that 100% mortality was observed by neem oil up to 14 days
of treatment in green gram and cowpea. Das  has reported cent
percent mortality within 4 days of released of pulse beetle in chickpea
treated with 1% neem oil. Neem seed oil 1% w/w and soft stone 0.5, 1.0
% w/w and neem seed kernel powder 4% w/w have been reported as
grain protectant of pigeon pea against the pulse beetle Callosobruchus chinensis Linn . They also reported that neem seed kernel powder
and neem seed oil protected the grains for a period of 8 months.
Bajpai and Sehgal  have studied the field efficacy of neem, karanj
and tobacco formulations (2.0% neem oil, 2.0% Karanj oil, 40% w/v
Nicotine Sulphate) against Helicoverpa armigera on chickpea and
reported that the treatment of chickpea with neem, karanj and tobacco
formulation significantly reduced the pod damage and increase the
grain yield over control. Spices are also effective in protecting the
legume- pulses according to . They evaluated the effectiveness
to control the bruchid, Callosobruchus maculatus in cowpea by the
synthetic insecticide Actellic dust, and by the natural protectants ash,
coconut oil, powdered cloves and black pepper. The data collected
included the number of damaged and undamaged seeds, weight
of damaged and undamaged seeds and the number of live and dead
bruchids. Seeds treated with Actellic dust and black pepper powder had
significantly low percentages of damaged seeds. Black pepper powder
and coconut oil showed good potential in protecting cowpea against
bruchid damage. Microbes (fungi and bacteria) can also be used along
with the bioinsecticides for the better results of protection . They
used fungi Beauveria bassiana, Metarhizum anisopliae, Verticillium
lecanii and Bacillus thuringiensis. Cumulative mortality of B. rufimanus
beetles increased gradually by increasing the period of exposure to foam
treated with the different tested oils. In field, B.bassiana, M. anisopliae,
mustard and nigella oils treatments gave the highest protection to broad
bean (Vicia faba) against B. rufimanus infestation. In the duration of 60
days the infestation percentages did not exceed, 13%, 15 %, 20% and
20%, respectively. The highest percent of seed damages was recorded in
the untreated plots. After 5 months, B.bassiana, M.anissoplia, mustard
and nigella treatments had a significantly lower percent of grain damage
and lower seed weight loss (10%, 15%, 17% and 22%), respectively.
|Protection of cereal grains by using vegetable oils
|To protect cereal grains from infestation, different aforesaid chemicals are being used and the residues of these chemicals may cause
harm to humans. So it is necessary to look for a safer way of protecting
the grains. Use of Vegetable oil for grain protection is one of the
options. Many researchers have worked in this direction. Tembo and
Murfitt  used vegetable oils (groundnut, rape seed and sunflower)
at 10 ml/kg and tested alone and in combination with pirimiphosmethyl
at, or of the recommended dosage against Sitophilus granarius
(L.) in wheat grain (Triticum aestivum). All bioassays were conducted
at 20 and 30°C. All treatments caused significant mortality compared
to controls (untreated grain). Treatments with vegetable oils combined
with pirimiphos-methyl at half the recommended dose were as effective
as pirimiphos-methyl at the recommended dose for achieving complete
control. The same treatments remained effective after 90 days of
storage. The vegetable oils alone achieved considerable mortality (60–
80%) within 14 days and there was little difference between the three
oils in their effect. Pirimiphos-methyl activity was dose dependent.
When applied alone, the vegetable oils and pirimiphos-methyl at
reduced rates were less effective than combined treatments. The toxicity
and persistence of treatments did not vary significantly between
20 and 30°C. Viability and water absorption were reduced by the oil
treatments, but particle size distribution after milling was unaffected.
Treatment of grain with pesticide/vegetable oil mixtures could have
important practical implications for parts of the world where pesticides
are expensive or in short supply. Chander et al.  have worked
on storage of milled rice and reported that the milled rice is prone
to various insects and pests which cause extensive qualitative and
quantitative deterioration. Due to indiscriminative use of insecticides,
there has been an increase in the harmful residues causing general
health hazards. These workers have suggested the use of indigenous
plant materials as an alternative to chemical controls. These researchers
have assessed the effect of different plant materials in the form of grits
and powder mixed with milled rice (0.5% conc) and turmeric+ mustard
oil (2.5 gm/kg) on the multiplication of the insects. They have reported
that as the storage period increases the count of insects decrease with
respect to the control. They have further reported that even grits were as
effective as powder in suppressing the populations build up of insects.
|The insecticidal action of five locally available plants namely:
Azadirachta indica (Neem), Cymbopogon citratus (Lemon Grass),
Lantana camara (Lantana), Ocimum basilicum (Basil) and Tagetes
erecta (African marigold) against maize weevil, Sitophilus zeamais
Motsch was investigated by Parugrug and Roxas . Results revealed
that all test materials exhibited repellency action against maize weevil.
Within 96 hours of exposure powdered leaves of neem and lantana were
noted to be highly repellant while powdered leaves of lemon grass, basil
and African marigold were observed to be moderately repellant against
maize weevil. Corn grains treated with powdered leaves of lemon grass
and basil exhibited a low mortality of 5.3% and 0.6%, respectively, at
24 DAII(days after insect introduction). Other test plants revealed
zero adult mortality. None among the test plants manifested antiovipositional
and growth inhibitory action against maize weevil. All
examined corn grains except for carbaryl - treated corn grains showed
larval tunnel. The total development period of the maize weevils
emerged from both treated and untreated corn grains was the same (39
days) and 100% insect survival was noted. The adult body weight was
comparable among treatments. Efficacy of Neem oil as grain protectant
against Sitophilus oryzae and Tribolium castaneum was also supported
by the investigation carried out by Kumar et al.  and Ahmed et al.
|Essential oils of plants are also useful in protecting the grains. It is
clear from the studies of Rupp et al.  He used the extracts of Piper nigrum and the essential oils of Ocimum basilicum and Eucalyptus
globules in the stored corn grain protection against S. zeamais, through
the determination of mortality effect on exposed individuals to treated
grains. To study the poisonous effect of the extracts on adults of S. zeamais, 6 concentrations (50; 25; 12.5; 6.25; 3.125 and 1.5625 %) of
each extract were tested, in 40 g of corn containing 20 adults of S. zeamais of 0-72 h of age. The experiments consisted of 4 repetitions for
each treatment. The same conditions were repeated for the experiments
with essential oils of O. basilicum and E. globulus, where each portion
received oil 0.1 mL in 40 g of corn. The evaluations were made to the
1, 3, 5, 7, 10, 15, 20 and 30 days after the treatments of the grains. The
insects died were counted in each experiment, being discarded after each
evaluation. Significant differences were not observed in the mortality of
S. zeamais in the different concentrations of P. nigrum in relation to
the control, indicating the use of insufficient dosages to promote the
wanted poisonous effect. As for the essential oils, E. globulus stood out
promoting adults’ mortality, however at low levels of efficiency. The
need of new tests of the tested treatments seeking to obtain significant
control of the populations of insects in products stored with the use of
derived natural products of plants is essential. One more essential oil
from leaves of Aegle marmelos was tested for the protection purpose
of wheat from Rhyzopertha dominica (F.) (Bostrychidae), Sitophilus oryzae (L.) (Curculionidae) and Tribolium castaneum (Tenebrionidae)
. The findings emphasize the efficacy of A. marmelos oil as fumigant
against insect infestations of stored grains and strengthen the possibility
of using it as an alternative to synthetic chemicals for preserving
stored grains. Various edible vegetable oil are good grain protectants.
Dey and Sarup  studied the feasibility of protecting maize variety
with vegetable oils to save the losses in the storage due to Sitophillus
oryzae Linn. These workers have reported that out of mustard, soybean,
coconut, groundnut, cottonseed, sesame and castor oils, coconut
and soybean oils at 3.3 ml/kg grain were found to be highly effective
in protecting the grains of various maize varieties. Obeng-Ofori and
Reichmuth  also used plant oils (coconut, sunflower, sesame and
mustard) at 10 and 5 ml/kg alone and in combination with 1,8 cineole,
eugenol or camphor at 0.5, 1.0 and 5.0 ml or mg/kg against Sitophilus granarius (L.), S. zeamais (Mots.), Tribolium castaneum (Herbst) and
Prostephanus truncatus (Horn) in wheat and maize-treated grains
stored for 3 h or 10, 30, 60 and 90 days. All treatments with either plant
oils alone or in combination with each chemical caused significant
mortality compared with untreated grain. Plant oils when used alone
were less effective against the beetles than oils combined with either
1,8 cineole, eugenol or camphor. Mortality significantly decreased with
the time after application except in treatments combining plant oils
and chemicals, which achieved complete control of all beetles exposed
after 90 days storage following application. Treatments with plant oils
and each chemical either alone or in combination inhibited progeny
production by S. granarius, S. zeamais and P. truncatus, irrespective of
dosage used or of storage interval following application.
|Plant oils (cottonseed, soybean, corn, groundnut and palm) at
different dosages were evaluated by Obeng-Ofori  for their ability
to suppress the populations of Cryptolestes pusillus and Rhyzopertha dominica in maize and sorghum. Exposure of adults of both beetle
species to grains treated with 10 ml/kg of the different oils induced
100% mortality within 24 h. A dose of 5 ml/kg of each oil significantly
decreased the progeny produced by R. dominica. Complete protection
was achieved on grains treated with 10 ml/kg. These oils also repelled
the adults of both species. Percentage weight loss caused by R. dominica
in grains treated with 5 ml/kg and 10 ml/kg levels were significantly
lower than in untreated grains. Oil treatment did not affect the germination and water absorption by maize and sorghum grains
compared with untreated grains. The potential use of plant oils in the
management of insect pests in traditional grain storage is discussed.
Root extracts of Decalepis hamiltonii were tested for insecticidal activity
against the stored products pests, Rhyzopertha domonica, Sitophilus oryzae, Stigobium pancieum, Tribolium castaneum and Callosobruchus chinensis . Methanolic extract showed LC 50 value of 0.14 mg/cm2
for all the test species in a filter paper residual bioassay. The extract was
effective as a grain protectant for wheat and green gram. The extract
did not affect the germination of the treated grains. Castor, corn and
karanj oils were found toxic against Sitophilus oryzae and Rhyzopertha dominica in stored maize. Karanj oil was most effective against S. oryzae
with the lowest LD50 and LD95 of 0.0433 and 0.0674μl/cm2, respectively
followed by corn (0.0494 & 0.0978) and castor oil (0.4037 & 0.9080)
by Michaelraj and Sharma . The same trend was also observed
with R. dominica but slightly higher values of LD50 and LD95 than S. oryzae except castor. R. dominica was more susceptible to castor oil in
comparison to S. oryzae. Grain treatment produced more than 90%
mortality of adults of S. oryzae with all the oils at 2.5 ml/kg of grains in
both the exposure periods (10 & 20 days) with the maximum of 100% in
karanj oil followed by castor and corn oils. Karanj oil was significantly
superior over other oils having less number of progeny productions
of Sitophilus oryzae and Rhyzopertha dominica and % damage. In case
of R. dominica, maximum mortality of 66,6% was recorded in karanj
oil at 2.5 ml/kg with the exposure time of 20 days, S. oryzae was more
susceptible to the vegetable oils than R. dominica. Although increased
time of exposure of insects to the oils gave higher mortality, it also gave
more time to the insects, which were alive, to oviposit and feed. So
there was corresponding increase in progeny production and damage.
Oils from neem, yellow oleander (Thevetia peruviana) seeds, and
cotton (Gossypium hirsutum L.) seeds and stabilized natural pyrethrum
(Chrysanthemum cinerariaefolium) blends against adult maize weevils
(Sitophilus zeamais) were investigated . The results indicated that
the natural pyrethrum extract blended with cottonseed oil was the
most potent against maize weevils. Components of Citrus oil, alone or
in combination, show the fumigant insecticidal action and citrus peel
oil can be used as antimicrobial agent, and as an insecticide. Various
medicinal plant powders, ash of plant origin and sorbic acid were found
helpful in reducing the kernel infestation by .
|Limitations for the Use of Oils
|There are also some limitations to the use of oil: Oil can have
an adverse effect on the germination power of the oil treated seeds.
Therefore it is recommended that seed which is intended for sowing
should not be treated with oil. Oils can also be harmful to human beings
[54,55]. Cereals that are intended for food should only be treated with
vegetable oils. Locally made oil may go rancid which will then make the
product taste unpleasant.
|From the above discussion it is clear that the uses of chemicals as
grain protectants serve our goal but also harm the human beings as
the residues of these chemicals are left even after proper control and
washing. These chemical also harm the environment. Therefore, for
safety and to protect the grains from infestation, we have to look for
some eco-friendly materials. Vegetable oils (edible or inedible) are
one of the options. Vegetable oils can be used for the protection of
our valuable grains from insect infestation along with various other
plant materials such as leaves, dust, powder etc without causing an
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