Control Strategies of Stored Product Pests
Shadia E. Abd El-Aziz
The objective of this study was to review the published research works on control strategies of stored product pests. Also, to shed light on alternative environmentally friendly methods to protect stored products from pests attack for healthy food safe. The most promising technique that has been developed and continues to be refined, is monitoring populations with insect pheromones and/or food attractants for detecting stored-product insects. Visual and secondary olfactory cues may be necessary for increased the catch of insects in traps. Near Infrared Spectroscopy was used for the classification of insect species, detection of internal insect pests of wheat (infested or uninfested wheat kernels) and distinguishing between unparasitized weevil larvae in wheat and those parasitized by wasps. It may be possible to use electronic nose systems to try and distinguish between grain colonized by mycotoxigenic and non-mycotoxigenic species and this area needs further investigation. The main advantage of using inert dusts is that they are non-toxic to humans and animals. Inert dusts in stored grain can provide continuous protection from insect infestations and do not affect the baking quality of wheat. Ozone is safe to the environment when used for fumigation. Active research is going on to exploit ozone as a potential quarantine treatment for controlling stored-product pests. Natural compounds from plant sources may have the advantage over conventional fumigants in terms of low mammalian toxicity (not true in all cases), rapid degradation and local availability. Compounds of plant origin can be used only for small-scale applications or for space treatments. Validation studies will be necessary to fully determine the potential for biological controls as replacements for insecticidal protectants, Good hygiene in the grain store or storage depot is important in maintaining grain and seed quality. Computer-based decision support systems that use biological and environmental data to predict population trends and evaluate the need for insecticidal inputs have been developed for stored-product storage systems in several countries. As more of these expert systems are developed management decisions may shift to computer-based pest management.
February 16, 2010; Accepted: April 17, 2010;
Published: July 22, 2010
For thousands of years, insects have been a problem associated with storing
surplus dried food, with evidence from archaeological deposits (Buckland,
1981) and written records (Levinson and Levinson, 1994)
of the storage and infestation of cereals stretching back to 3000 BC. There
is a need to protect stored food from attack by insects because they can destroy
large quantities, particularly during long-term storage (Pimentel,
1991). Allergic reactions to stored food arthropods, including Sitophilus
granarius (L.), have been reported (Van Lynden-van Nes
et al., 1996) and they can cause taint and contamination of grain
with their excreta, cast skins and dead bodies (Scott, 1991).
In developed countries even the mere presence of a few insects in a bulk, at
densities of considerably less than one insect per kg grain, can cause a serious
loss in its market value. In some developed countries grain can be downgraded
or rejected completely if even a single live insect is found (Pinniger
et al., 1984).
In the UK the Food Safety Act (Anonymous, 1990) was amended
recently; now all stores containing grain which might be destined for human
consumption are treated as food premises and subject to inspection to ensure
that food is not contaminated.
Early attempts to control stored grain pests relied on methods such as mixing
dry soil and wood ash with the grain causing lethal dehydration of insects and
the fumigant action of certain plant materials (Levinson
and Levinson, 1989). In one form or another, the use of admixture and fumigation
for the control of storage pests has continued to the present day. However,
as our knowledge of the side effects of modern day, broad-spectrum pesticides
and fumigants has increased, scientists have begun to explore new approaches
to pest control. Concerns over pesticide operator safety and residues in our
food and the environmental have led to a review of all organophosphorus pesticides
by the Pesticide Safety Directorate in the UK; current advice is for farmers
to avoid their use altogether unless there is no alternative (Rooker,
1999). Also, in Egypt, Ministry of Agriculture passed legislation to reduce
agricultural pesticide usage by at least 50% by the year 2000.
The control of pests in commodity storage (farm and commercial) and food plants (food manufacturing processing and warehousing) requires a high degree of professionalism combined with experience and knowledge.
Pest control strategies must utilize combinations of techniques that are effective, economical and emphasize prevention of food product contamination. These strategies must be directed at immediate pest problems; at preventing future infestation problems; and must respond to routine daily needs, yet be flexible to meet emergency pest control situations. Stored-product pest control strategies tend to emphasize the non-chemical aspects of pest control with the judicious use of pesticides.
Unsatisfactory control of pests results in contaminated products that can cause health, financial, legal and aesthetic problems. Financial losses can result from (1) presence of live or dead insects in products and containers; (2) presence of odors, webbing and frass in products and containers; (3) loss in faith in the company by the consumer because of these conditions and (4) direct loss in weight resulting from insect feeding.
Control of stored-product pests is necessary to prevent contamination/adulteration of human foods. Persons involved in commodity/food storage, handling and/or processing have the responsibility to prevent food adulteration. Failure to do so can result in human illness and/or death, the violation of laws, loss of good will and resulting loss of revenue.
INVERTEBRATE STORED PRODUCT PESTS
A variety of pests may be found in stored commodities and food processing facilities, depending upon geographic location, physical nature of the facility and the type of food being processed.
Insects: (Beetles, weevils and borers): Stored grain of almost any kind is subject to attack by insects. Pests which attack whole grain usually develop and feed inside the kernels of grain. These pests are not usually capable of existence outside the grain kernel as immature insects. Examples of whole grain pests are the rice weevil, the granary weevil, the lesser grain borer and the angoumois grain moth.
Other insects which attack grain are usually unable to penetrate whole grain. These insect pests however, can attack grain after it has been either mechanically broken or attacked by whole grain insects. Examples of these secondary pests are the confused and red flour beetles, Indian mealmoth, Mediterranean flour moth and the sawtoothed grain beetle (Table 1, Fig. 1).
Grain mite (Acarus siro L.): Mites will attack not only grain but cheese, flour, pet food, oilseeds, medicinal herbs, hay, deep litter or poultry houses, abandoned beehives and just about any food used by man.
Control: During heavy infestations cast skins and dead bodies accumulate
into fluffy masses that can be blown around. It is a common inhabitant of house
dust and is strongly allergenic. Vacuuming is required if areas are heavily
infested. These signs indicated that storage conditions are too damp. Infested
materials in homes should be discarded and the infested areas thoroughly cleaned.
||Principal stored grain insects, (For safe and effective use
of insecticides, always identify the problem correctly)
|| List of stored grain insects and some biological aspects
In commercial facilities infestations must be fumigated to gain control over
these pests. Heavy infestations have a characteristic sweet or minty odor which
usually necessitates the food be destroyed (Mason, 2004).
MONITORING FOR STORED-PRODUCT INSECTS
Stored-product insects cause significant losses of stored grains, processed foods, fibers and animal products. In general, losses can be minimized when infestations are quickly identified and appropriate control measures implemented.
Monitoring methods: Current monitoring methods for insect infestation vary and depend on the type of insect, commodity and/or storage. They include:
Bulk commodity storage:
||Observation of the commodity surface and over space for insects
and/or evidence of their presence, i.e., webbing, cast skins, dust, odor,
||Examination of commodity samples obtained by various means, i.e., probe
sampling, turning of the commodity, etc.
||Probe (pitfall) traps inserted into the surface of grain masses and left
for varying lengths of time have proven useful as a means of early detection
of live, free-living insects
||Temperature monitoring in grain masses may detect localized increased
in temperature which can indicate the presence of an insect infestation
Pheromone/food attractant monitoring: Numerous methods for detecting
stored-product insects have been developed or are being investigated. The most
promising technique that has been developed and continues to be refined, is
monitoring populations with insect pheromones and/or food attractants.
The incorporation of monitoring methods into existing stored-product pest management
programs can lead to earlier detection of low level infestations and pinpointing
location of infestations. Monitoring information can be used to justify reduction
in pesticide use or the need for intensified surveillance and pest management
procedures. Monitoring results also can serve as an indicator of how well Integrated
Pest Management (IPM) program components are functioning (Campbell
et al., 2002).
|| Status of pheromones for stored-product insects
|A: Aggregation pheromone; F: Food attractant; S: Sex pheromone.
1Same lure for all apecies, separate lure for candra under development.
2May be effective for up to 40 weeks based on USDA studies. 3Trogoderma
traps utilizing food attractants will catch larve of both attagenus and
anthrenus. Commercial sex lures have been marketed (1992) for carpet beetles,
their effectiveness is not known. 4Aggregation pheromone under
development. 5Food lure results have been erratic. Glue boards
currently are almost as effective and more economical. Used with permission:
Stored-product pest monitoring methods. Technical information memorandum
No. 27 armed forces pest management board, June 1992
Pheromone lures have been developed for several stored-product insects (Table
2). Lures developed for species with short-lived adults have proven more
effective. The lure for the lesser grain borer (Rhyzopertha dominica) also
has produced good results. Food attractant lures for stored-product insects
(predominantly an oil lure consisting of oat oil, wheat germ oil extracts and
mineral oil, wheat germ oil extracts and mineral oil) are used for species having
long-lived adults and some larvae. These lures may be used with or without pheromones.
In general, food attractant lures have a smaller effective range than pheromone
lures. They can be used to enhance the effectiveness of pheromone traps for
flour beetles (Tribolium) and to attract Trogoderma, Attagenus
and Anthrenus larvae (Burkholder and Ma, 1985).
Inefficient trap design. Even when a highly attractive semiochemical is used
to draw insects close to the trap, catch may still be low if the trap design
fails to encourage the insects to enter the trap. Visual and secondary olfactory
cues may be necessary; for example, adding vertical stripes to the outside of
funnel traps increased the catch of Ephestia cautella (Walker), by 20
and 45% in moving and still air, respectively, compared with traps without stripes
(Quartey and Coaker, 1992).
Regular checks reduce moisture risk in stored grain: To maintain grain quality, growers are urged to regularly sample the surface of grain bulks to check for insects, rising moisture levels and possible mould damage. The two main causes of moisture damage on the surface of grain bulks are condensation in the headspace (inside the roof of metal storage bins) and moisture migration within the grain bulk.
White painted bins: Heat-reflective white-painted bins reduce heating by sunlight and enhance passive cooling.
The temperature difference at the edges of a grain bulk near the walls and upper surface can be up to 5°C lower in painted bins.
Insulating the outer layers of grain from radiant heating improves the efficiency of aeration-cooling.
Reducing the fluctuations in grain temperature at the edges of a grain bulk between day and night also reduces the effect of night top silo cooling which causes condensation of water from air and wetting of the grain peak.
New method for detection of parasitized stored products with near-infrared
spectroscopy: Near-Infrared Spectroscopy (NIRS) has been used in a variety
of agricultural and food technology applications (Panford,
1987). Recent applications include the classification of insect species,
detection of internal insect pests of wheat (infested or uninfested wheat kernels)
(Dowell et al., 1998) and distinguishing between
unparasitized weevil larvae in wheat and those parasitized by wasps (Burks
et al., 2000). In this technique, the amount of light absorbed by
materials is influenced by the number of molecules of specific constituents.
Thus, quantitative information indicating the amount of chemical components
such as water, oil, starch, sugar, or protein in agricultural products is measurable
with NIRS (Murray and Williams, 1987). Fundamental absorptions
usually occur in the mid-IR region (2500-15,000 nm), but 1st, 2nd and 3rd absorption
overtones occur in the NIR region (700-2500 n). Advantages of measuring absorption
in the NIR instead of mid-IR include lower sensor costs and less sample preparation.
Electronic nose technology for early detection of grain spoilage: Combine
harvesting of both temperate and tropical cereals are most efficient when the
ripened grain is slightly moist. Subsequent drying to safe moisture contents
(e.g., for wheat this is 14% = 0.70 water activity) is essential to prevent
initiation of fungal activity which can result in heating of the stored grain
and ultimately end in spontaneous heating and complete loss of the grain. The
activity of spoilage fungi can also result in the production of mycotoxins by
certain genera, which prevents such moulded grain from being used for either
animal or human consumption. Thus it is very important to detect fungal deterioration
in stored cereal grains at an early stage. This would facilitate and improve
existing management of grain stores. It would also allow remedial measures to
be more effectively implemented, allowing significant losses and grain downgrading
to be avoided. Mycotoxins are fungal secondary metabolites that have been associated
with severe toxic effects to vertebrates produced by many important phytopathogenic
and food spoilage fungi including Aspergillus, Penicillium, Fusarium
and Alternaria species. The contamination of foods and animal feeds with
mycotoxins is a worldwide problem (Kabak et al.,
2006). A wide variety of volatiles are produced by fungi, either in vitro
or when growing on agricultural grain substrates. Potential exists for distinguishing
between species of fungi based on characteristic volatile patterns, which may
be important when key spoilage fungi may be responsible for the production of
harmful mycotoxins. It may be possible to use electronic nose systems to try
and distinguish between grain colonised by mycotoxigenic and non-mycotoxigenic
species and this area needs further investigation.
There is significant interest in methods for the early detection of quality
changes in cereal grains. The development of electronic nose technology in recent
years has stimulated interest in the use of characteristic volatiles and odours
as a rapid, early indication of deterioration in grain quality (Magan
and Evans, 2000).
Electronic nose technology coupled with neural network systems are developing very rapidly, both in terms of sensor development, sensitivity and data processing. This would suggest that in the very near future potential exists for the development of on-line systems through which the quality of stored grain could be monitored remotely as required and enable more efficient and effective long term management of grain storages to be carried out.
Physical control: Insects in stored grain can be controlled by manipulating the physical environment or applying physical treatments to the grain and insects. The variables defining the physical environment that are usually controlled are: temperature, relative humidity or grain moisture content and relative composition of atmospheric gases in the intergranular air. Physical treatments include mechanical impact, physical removal, physical barriers to prevent the entrance of insects, abrasive and inert dusts, ionizing irradiation, light and sound.
Inert dusts: Inert dusts are chemically unreactive dusts that have insecticidal
capability, killing by physical rather than chemical means. Insects coated in
these dusts dehydrate and die. Because the effect is through desiccation, the
effectiveness of inert dusts decreases as relative humidity increases. There
is renewed interest in technology associated with use of inert dusts in grain
storages and a number of reviews have been written (Ebeling,
1971; Banks and Fields, 1995; Golob,
1997; Subramanyam and Hagstrum, 2000; Mahdi
and Khalequzzaman, 2006). Inert dusts have been used for centuries by aboriginal
people in North America and Africa to control insects in their stored grain.
There are five types of inert dusts (Fields and Muir, 1996):
||Sands and other soil components are traditional insecticides
used by aboriginal peoples as a protective layer on top of stored seed (Golob
and Webley, 1980)
||Diatomaceous earth (DE) the fossilized remains of diatoms that are microscopic,
unicellular, aquatic plants that have a fine shell made of opaline silica
(SiO2 + n H2O). (DE) has extremely low toxicity to
mammals (e.g., where DE toxicity for rat LD50 oral >5000 mg
kg-1) (Subramanyam and Hagstrum, 1995)
and (Anonymous, 1991a) are generally regarded as safe
by the USA Environmental Protection Agency. Abd-El-Aziz
and Sherief (2010) made chemical modification to the natural Diatomaceous
Earth (DE) by different mono-, di-, tri-valent metal hydroxides (MOH, M
= Na, Ca, Al) to increase its efficiency. The most effective DE modification
was Ca.DE, which has insecticidal, repellent and ovicidal effects against
Callosobruchus maculatus and can be used effectively in stored grain
integrated pest management program
||Silica aerogel, which is produced by drying an aqueous solution of sodium
silicate, is a light powder that is not hygroscopic (Quarles,
||Non-silica dusts, such as rock phosphate, have been used in Egypt (Fam
et al., 1974) and lime (calcium oxide) provides some control
(Golob and Webley, 1980)
||Particle films (Kaolin and bentonite clays). The kaolinite-based particle
films may also have potential for use as a dry dust material in stored-product
environments, especially in specialty organic markets that prohibit the
use of diatomaceous earth. Several studies were conducted to evaluate the
potential of kaolinite-based particle films to control Tribolium castaneum
(Herbst), the red flour beetle and Tribolium confusum (du Val)
and the confused flour beetle. These two beetle species are major pests
inside milling and processing facilities, food warehouses and food plants.
The particle film M-96-018 was effective against both the Triblium species
and appears to have a potential for use in management programs to control
beetles within storage facilities (Arthur and Puterka,
The main advantage of using inert dusts is that they are non-toxic to humans
and animals. Diatomaceous earths are registered as a food additive in the USA.
Inert dusts in stored grain can provide continuous protection from insect infestations
and do not affect the baking quality of wheat.
Inert dusts kill insects by causing moisture to move out of the insects body. The dust either scratches through (diatomaceous earths) or absorbs (silica aerogel) the insects waxy coating that normally prevents excessive loss of moisture to the dry grain and intergranular air. The dust, because its mode of action is to dehydrate the insect, decreases in effectiveness as moisture content of the grain increases.
The main problem with inert dusts is that they decrease the bulk density of the treated grain. Because bulk density is presently a major factor in determining grain grades the dust can cause a decrease in the monetary value of the grain even though there have been no changes in its nutritional or functional value. The dust causes an increase in friction between the grain kernels so that the grain does not flow as readily as untreated grain. The angle of repose of the grain is increased and the rate of flow in down-spouts and along hopper-bottom floors will be reduced. The use of inert dust results in dusty conditions during application and grain handling. The dust may cause more wear on equipment.
Ionizing irradiation: Two types of ionizing irradiation have been used
to control insects in grain. Gamma radiation can be produced by a radioactive
isotope such as cobalt-60. Beta radiation, which is a beam of electrons, can
be generated electrically. Irradiation with an electron beam is usually safer
and easier to work with because it can be turned on and off while an isotope
is always radiating and humans must be shielded from it (Fields
and Muir, 1996). Ionizing radiation damages organisms by causing the production
of ions or free radicals-charged molecules that are highly reactive. Besides
ionization, chemical bonds can also be broken. To cause immediate death to stored
product insects may require higher doses. Sterilization of many species of insects
can be accomplished at lower doses. Rusty grain beetles are sterilized at only
0.6 kGy but sawtoothed grain beetles and red flour beetles require a 2.0 kGy
dose (Banks and Fields, 1995). The grain mite however,
requires a much higher dose of 4.5 KGy. Sterilized insects will do little harm
to the grain but the grain will continue to appear to be infested and a grain
buyer cannot be certain that the insects are sterilized. Following irradiation
with gamma rays at 0.5 kGy complete insect mortality occurs in 14 days for rusty
grain beetles, 28 days for red flour beetles, 70 days for sawtoothed grain beetles
and 200 days for grain mites. Synergistic interaction indicates that microwaves
radiation can be used with cold storage for management of Oryzaephilus surinamensis.
This treatment could provide an effective and friendly environmental treatment
technique in IPM program (Valizadegan et al., 2009).
The advantages of irradiation with beta rays are:
||A system can be set up to have a high throughput as the grain
enters or leaves an establishment
||The system can be readily automated
||If proper safety controls are built into the system equipment operators
are not exposed to any danger
||All life stages of insects are affected by the radiation
||No harmful chemical residues are left in the grain
||Nutritional values are unaffected at low doses
||Grain temperature is increased les than 0.1°C
The disadvantages of irradiation include the following:
||Adult insects continue to live for sometime
||There is no residual protection from reinfestation from external sources
||The seed is killed by the irradiation required to control insects
||Beta rays (electron beams) penetrate a layer of grain only about one kernel
thick, 0.6 cm, while gamma rays penetrate 30 cm (Zakladnoi
et al., 1982). The grain handling system must be designed to
provide the required thin layer
||The system has a high capital cost; therefore, to be economic it must
have a high throughput for several years
Light and sound: Light may be of some use in luring flying insects into
traps (Banks and Fields, 1995). A 5-min exposure to 1
MHz sound at 14.5 W cm-2 killed all stages of S. granarius at
26°C in wheat but commercial application is unexpected (Banks
and Fields, 1995).
Control of insects with low temperatures: The optimal temperature
for stored product insects is between 25-33°C (Table 3).
Low temperatures reduce insect development and thus lengthen the time before populations increase to a point where they cause significant damage (Table 4).
Mites in damp grain can continue developing down to 2°C. Although no development
occurs at these temperatures, insects and mites remain alive for long periods
and will cause damage if the grain temperature rises. Burrell
(1967) reported that cooling prevented further development of the heavy
infestation but since the insects were not killed, this method of control should
be used as a preventative rather than a cure.
|| Effect of low temperature on developmental stages of various
|*Adapted from: Richard T. Cotton. Pests of stored grain and
Insects exposed to cool temperatures (20-10°C) become acclimatized and
their cold-hardiness can increase by 2 to 10 times. Under normal storage conditions
insects in stored grain are acclimatized as a grain bulk slowly cools by conduction
and free convection to its periphery.
Lowering the temperature of commodities to prevent spoilage is an ancient technique.
Part of the success of the underground storages used in ancient Egypt compared
with above ground stores was due to cooler temperatures of the underground stores
(Banks and Fields, 1995). The effectiveness of aeration
can be increased in tropical climates or in the summer in temperate climates
by cooling the air with refrigeration units. Low temperatures reduce the rates
of development, feeding, fecundity and survival (Logstaff
and Evans, 1983). Temperatures between 13 and 25°C will slow development.
This lengthens the time before populations increase to point where, they cause
significant damage. S.granarius is the only major stored-product insect
that can develop below 20°C and down to 13°C in optimum moisture content
grain (Banks and Fields, 1995). Mites in damp grain only
stop developing at 2°C. Although no development occurs at these temperatures,
insects and mites remain alive for long periods and will cause damage if the
temperature of the commodity rises.
Burks et al. (1999) demonstrated that low temperatures
prevents emergence of unparsitized larvae of the rice weevil Sitophilus oryzae
(L.) while not affecting emergence of parasitoid Anisopteromalus. calandrae.
High temperature disinfestation: Possible methods of heating grain;
hot-air convection, infrared and microwave radiation all appear to require similar
grain temperatures to achieve the same lethal effect. Most heated-air grain-driers
cannot heat the grain uniformly and efficiently to the desired temperature.
Fluidized beds, spouted beds, pneumatic conveyors, a counter-flow heat exchanger
(Lapp et al., 1986), high frequency waves (Nelson
and Kantack, 1966), microwaves (Locatelli and Traversa,
1989) infrared waves and solar radiation (Kitch et
al., 1992) have been used to satisfactorily disinfest seeds. Maximum
kernel temperatures and kernel residence times must be carefully controlled
to obtain disinfestations without thermal damage to the kernels (Evans
et al., 1983). Most of the energy cost of the process is in heating
the grain, evaporating moisture concurrently, plus the unused heat in the exhaust
air. Dielectric heating (but not microwave heating) may heat insect tissue more
rapidly than grain, thus reducing energy costs of heat disinfestations.
Grain temperatures of 60 to 65°C for a few seconds or minutes are necessary
to kill all stored grain insects. The same minimum temperature is required to
kill the insects whichever method is used to heat the grain. Such temperatures
can damage the baking quality of wheat, the malting quality of barley and the
germination of most seeds (Evans, 1987). Thus the temperature
of the grain must be carefully measured and controlled.
Selection of the method to heat the grain will depend on capital costs and energy efficiencies of the various heating systems and the relative costs of various energy sources. The same minimum temperature must be attained to kill the insects when using any of the available methods of heating the grain. The simplest and least costly method is probably heating the grain with hot air in a grain drier or fluidized bed.
Grain can be heated by passing a thin layer of grain under an infrared or microwave radiation source. Separate equipment to cool the grain must also be included in a radiant heating system. Because radiation is produced with electricity, the energy cost of radiant heating is usually higher than using fossil fuels to heat air and grain even though the heated air system is less energy efficient.
Fluidized bed heating is the only method of high temperature disinfestation
developed to the stage of a full-scale prototype for treating more than 100
t h-1 of grain. Others have been successfully demonstrated at laboratory
or pilot plant stages of development (e.g., Sutherland et
Systems, such as fluidized beds, have the advantage that they can easily be adapted for cooling the treated grain after exposure. Such cooling is necessary as grain held for more than brief periods at temperatures that are rapidly insecticidal (>60°C) loses important qualities (e.g., germination, baking quality). Approaches using radiative heating will require grain cooling after treatment, adding to the cost and complexity of the system.
A technique known as. bake-out., where structures are heated to around 50°C
for about one day may hold potential as a structural treatment in grain storage
sheds. Dryacide can assist bake-out effectiveness when applied to hard-to-heat
surfaces such as external walls and cavities (Neeson and
Ozonation: Ozone (O3) is an allotrope of oxygen, which can
be generated by UV-light and electrical discharges in air (corona-discharge).
Ozone generation by electrical discharge is most common and has several advantages,
including greater sustainability of the unit, higher ozone production and higher
cost affectivity. Ozone has a half-life of 20-50 min, rapidly decomposing to
diatomic oxygen, a natural component in the atmosphere. Ozone has a half-life
of 20-50 min, rapidly decomposing to diatomic oxygen, a natural component in
the atmosphere. Because ozone can be easily generated at the treatment site
using only electricity and air, it offers several safety advantages over conventional
post-harvest pesticides. First, there are no stores of toxic chemicals, chemical
mixing hazards, or disposal of left over insecticides or containers (Law
and Kiss, 1991). Second, with a short half-life, it reverts back to naturally
occurring oxygen leaving no residue on the product or to dispose of. Third,
if needed it would be possible to neutralize ozone through techniques such as
thermal activated charcoal, as well as catalytic and chemical abatement (Law
and Kiss, 1991).
Ozone, a known sterilant, can be used as an insect control agent in food commodities
at levels less than 45 ppm. Ozone is readily generated from atmospheric oxygen
and is safe to the environment when used for fumigation. However it is highly
unstable and breaks down to molecular oxygen quickly. A major disadvantage with
ozone is its corrosive property towards most of the metals (Mason
et al., 1998). Mendez et al. (2002)
showed that treatment of grains with 50 ppm ozone for 30 d had no detrimental
effect on popping volume of popcorn, fatty acid and amino acid composition of
corn and milling characteristics of corn. These data indicate that if repeated
ozone treatments are needed, such treatment should not decrease the quality
of grain for end-users. These results suggest that ozonation is a potential
alternative to conventional pest control treatments.
Active research is going on to exploit ozone as a potential quarantine treatment
for controlling stored-product pests (Hollingsworth and
Fumigation: Vijayanna (2006) mentioned that Fumigation
is a method of pest control that completely fills an area with gaseous pesticides
to suffocate or poison the pests within. It is utilized for control of pests
in buildings, soil, seed and grain produce. It is also used during processing
of goods to be imported or exported in order to prevent transfer of exotic organisms.
Fumigants are chemical compounds in gaseous form that enter the body of insect
through the spiracles spread all over via trachea and tracheoles.
Fumigation plays a major role in insect pest elimination in stored products.
Currently, phosphine (from metal phosphide preparations, cylinderized formulations
and on-site generators) and methyl bromide (available in cylinders and metal
cans) are the two common fumigants used for stored-product protection world
over (Rajendran and Sriranjini, 2008). Insect resistance
to phosphine is a global issue now and control failures have been reported in
field situations in some countries (Taylor, 1989; Collins
et al., 2002). Methyl bromide, a broad-spectrum fumigant, has been
declared an ozone-depleting substance and therefore, is being phased out completely.
In view of the problems with the current fumigants, there is a global interest
in alternative strategies including development of chemical substitutes, exploitation
of controlled atmospheres and integration of physical methods (MBTOC,
2002). Recently, the use of sulphuryl fluoride, a structural fumigant for
termite and woodborer control, has been expanded to food commodities and food
handling establishments (e.g., flourmills) in the USA, Canada and Europe (Prabhakaran,
2006). New fumigants such as carbonyl sulphide and ethane dinitrile and
the old fumigant ethyl formate (alone and in mixture with CO2) (Damcevski
et al., 2003) have also been investigated as alternatives for food
and non-food commodities.
Semiochemicals for stored product control: Semiocemicals could be used
to control insect pests by behavioural manipulation. Furthermore, interest has
been shown in plant products, i.e., essential oils and their components, for
fumigant action since it is believed that natural compounds from plant sources
may have the advantage over conventional fumigants in terms of low mammalian
toxicity (not true in all cases), rapid degradation and local availability (Rajendran
and Sriranjini, 2008). Many reviews of the literature have identified many
plant genera containing species producing chemicals with potential as repellents
or antifeedants for the control of insects including stored grain pests (Prakash
and Rao, 1997; Abd-El-Aziz and Ismail, 2000; Abd-El-Aziz,
2001; Dimetry et al., 2002; Sabbour,
2003; Sabbour and Abd El-Aziz, 2007; Haghtalab
et al., 2009; Mondal and Khalequzzaman, 2010).
Compounds derived from plants continue to be assessed for their potential to
control storage pests (Allotey and Azalekor, 2000).
By choosing those plant species that are natives or naturalized introductions
to a particular region, their exploitation as insect control agents should not
pose any of the ethical or quinones problems associated with non-indigenous
plants. These would appear to be a good starting point from which to choose
a repellent, for example to use in a protective band around grain bulks or as
a flushing agent to disinfest store structures. Also, chemicals such as quinines
produced by some storage beetles themselves could be assessed for their potential
as practical control agents. Ideally any repellent used in these ways should
avoid direct contact with the grain unless it can be shown there is no associated
health risk or possibility of tainting. In general it is likely that larger
quantities of repellents than attractants would be required for practical pest
control, so the use of repellents may prove to be more expensive and hold a
greater risk of contaminating the grain. On the other hand, production of repellents
derived from plants may be easier and less expensive than the synthesis of some
more complex attractive semiochemicals.
Evidently, compounds of plant origin can be used only for small-scale applications or for space treatments. They require some carrier gases (e.g., CO2) for even distribution and penetration into the commodities or they can act as adjuvants for conventional fumigants.
The effect of repellents on penetration into packaging by stored-product
insects: Although, finished products can be shipped from production facilities
uninfested, stored-product insects can enter packaged goods during transportation,
storage in the warehouse, or in retail stores. Ultimately, the consumer of the
products holds the manufacturer responsible for any insect infestation, even
if the cause of the problem is poor storage by a third party. The packaging
of products is the last line of defense for processors against insect infestation
of their finished products. There are two types of insects that attack packaged
products: penetrators, which are insects that can bore holes through packaging
materials and invaders, which are insects that enter packages through existing
holes, such as folds and seams and air vents (Highland, 1991;
Newton, 1988). Sitophilus spp., Rhyzopertha
dominica (F.), Plodia interpunctella (Hübner), lasioderma
serricorne (F.),and Stegobium paniceum (L.) are some of the stored-product
insects that are capable of penetrating food packaging. However, Tribolium
spp., Cryptolestes ferrugineus (Stephens),and Oryzaephilus sp.
cannot penetrate intact packages and must enter through existing holes in the
packae (Highland, 1991).
In addition to improving the packaging materials and design, insect repellents
are used to present insects from entering packages by modifying the behavior
of insects (Highland, 1991; Mullen
and Mowery, 2000). Pyrethrins synergized with piperonyl butoxide were approved
for use as a treatment for insect-resistant packaging on the outer layer of
packages or with adhesive in the USA (Highland, 1991).
The repellency of pyrethrins was the primary mode of action against insect penetration
and invasion (Laudani and Davis, 1955). Methyl salicylate,
an insect repellent, has been registered to be used in food packaging to control
stored-product insects in the USA (Radwan and Allin, 1997).
DEET, neem and protein-enriched pea flour are repellent to many stored-product
insects when tested by exposure on filter paper or in preference chambers (Fields
et al., 2001).
The number of S. oryzae, T. castaneum, C. ferrugineus and O.surinamensis
entering pierced paper envelopes that contained wheat and were treated with
DEET was reduced by 99, 86, 97 and 91%, respectively. Neem was less effective
than DEET in reducing penetration and invasion of insects. Protein-enriched
pea flour did not prevent insects entering pierced envelopes (Hou
et al., 2004). Sabbour and Abd El-Aziz (2007)
screened the most suitable packaging materials (muslin, paper (multi-wall paper
(3 layers)), cheesecloth, wax paper, gunny bags and polypropylene) for prevention
of broad bean beetles infestation. Gunny sacks followed by paper bags (multi-wall
paper (3 layers) provided more protection against C. maculatus infestation
than the other tested packing materials.
Microbial control: Synthetic chemical insecticides provide many benefits to food production and human health, but they also pose some hazards. In many instances, alternative methods of insect management offer adequate levels of pest control and pose fewer hazards. One such alternative is the use of microbial insecticides that contain microorganisms or their by-products. Microbial insecticides are especially valuable because their toxicity to non-target animals and human is extremely low. Compared to other commonly used insecticides, they are safe for both the pesticide user and consumers of treated crops.
In general, Bt is very safe to use. The EPA has found no hazards to human health associated with the use of Bt. It has no known carcinogenic or mutagenic properties at field application rates or in laboratory studies. There are no known poisonings or chronic exposure problems. However, in concentrated form, it may cause sensitization in hypersensitive individuals following long inhalation exposure or accidental injection.
Currently, many entomopathogens are used for the control of invertebrate pests
in glasshouses, row crops, orchards, ornamentals, stored products and forestry
(Lacey et al., 2001; Khashaveh
et al., 2008; Mahdneshin et al., 2009).
The effect of two microbial entomopathogens (Bacillus thuringiensis and
Beauveria bassiana and three botanical extracts were studied on three
stored product insects, Plodia interpunctella, Ephestia cautella and
Ephestia kuehniella. Botanical extracts tested when combined with B.
thuringiensis caused a significant enhancement to the pathogens and increased
the mortality in almost all cases (Sabbour, 2003).
Buda and Peciulyte (2008) tested the effect of four
fungi species (Beauveria bassiana, Lecanicillium (Verticillium)
lecanii, Metarhizum anisopliae var. anisopliae and Paecilomyces
farinosus) isolates on adults of Indian meal moth, Plodia interpunctella
and one species tested on mature larvae of the pest. All the fungal isolates
tested were pathogenic, however, with a different effectiveness. During the
first three day period after spraying, the highest mortality (35-40% versus
control) was caused by P. farinosus and M. anisopliae var anisopliae
and there was no significant difference in the survival as compared to control
when B. bassiana and L. (Verticillium) lecanii were
Sabbour and Abd-El-Aziz (2010) mentioned that the persistent
effect of formulated mustard oil with either P. fumosoroseus or Nomuraea
rileyi fungi on foam covering gunny bags displayed several different modes
of action, by reducing oviposition and adult emergence (F1) of Bruchidius
incarnatus. The oviposition was completely inhibited when stored broad bean
seeds were treated with mustard oil + P. fumosoroseus during 20, 40 and
60 days of storage. Application of mustard oil combined with P. fumosoroseus
on foam covering gunny bags provided promising oviposition deterrency, toxicity
and suppressing B. incarnates infestation, persistence and protecting
broad bean seeds from beetles infestation for 120 days during storage.
Heat, desiccation (drying out), or exposure to ultraviolet radiation reduces the effectiveness or several types of microbial insecticides. Consequently, proper timing and application procedures are especially important for some products. Special formulation and storage procedures are necessary for some microbial pesticides.
Biological control of stored product pests: Biological control is an
over-looked component of integrated pest management of stored product pest (Flinn
et al., 1998). Many species of insect natural enemies occurs in stored
product ecosystem (Brower et al., 1996) and these
species represent potential biological control agents for the desired pests.
The anthocorid bug, Xylocoris flavipes (Reuter) is a cosmopolitan predator
of different prey (pests) of stored commodities namely Tribolium castaneum,
T. confusum, Crytolestes pusillus, Rhizopertha dominica and
Trogoderma granarium (Ahmed et al., 1991;
Rahman et al., 2009).
Important natural enemies include parasitoid wasps in the families Braconidae, Ichneumonidae, pteromalidae and Bethylidae and predatory pirate bugs. A collection of other Predators can be found in some situations and these include assassin bugs, hister beetles, pseudoscorpions and predatory mites.
Research during the 1970s and 1980s demonstrated the efficacy of
parasitoids and predators in controlling storage pests. Releases of the warehouse
pirate bug, Xylocoris flavipes, resulted in a 79-100% suppression of
moth populations in small storages of peanuts, up to 99% reduction of sawtoothed
grain beetle populations in 35-quart lots of corn and a 90-98% suppression of
red flour beetles in a simulated peanut warehouse. Rice weevils in wheat spillage
in small rooms were suppressed 96% by the parasitic wasp Anisopteromalus
calandrae. When the egg parasitoid Trichogramma pretiosum and the
larval parasitoid Bracon hebetor were released together in simulated
peanut warehouses, they suppressed Indianmeal moth populations by 84% and almond
moth (Cadra cautella) populations by 98%, B. hebetor alone supressed
almond moth populations by 97.3%. Several other studies have yielded similar
results that suggest these natural enemies should provide effective biological
control of storage pests. However, these experiments were conducted under laboratory
conditions in which the commodities, storage containers or structures and numbers
of pest insects were under strict control. Biological controls did not prevent
economic damage, partly due to the migration of pest species into the experimental
bins. Recently the predatory beetle Teretriosoma nigrescens (Lewis) has
been introduced into west Africa to control Prostephanus truncatus (Horn),
with moderate success (Markham et al., 1994).
Validation studies will be necessary to fully determine the potential for biological
controls as replacements for insecticidal protectants and currently such data
are lacking for most grain storage system throughout the world.
The negative effects of agricultural pesticides on natural control agents is
often cited to support the development of alternatives to chemical controls.
The impact of pesticides on natural enemies and the resulting outbreaks of secondary
arthropod pests have been documented in many field agricultural systems (Croft,
Biological controls are not normally considered to be compatible with protestants.
However, there is potential to select for insecticide resistance in certain
parasitic and predatory species (Baker, 1995; Baker
and Arbogast, 1995). Integrating the use of predatory/parasitic mites and
insecticides for stored-grain pest management requires knowledge of the impact
of the insecticides on the natural enemies or, in other words, their selectivity
to natural enemies (Baker and Arbogast, 1995; Goncalves
et al., 2002). Goncalves et al. (2004)
mentioned that the effect of insecticides on the mite species Acarophenax
lacunatus (Cross and Krantz), an egg parasite of the stored grain pest Rhyzopertha
dominica (Fabr.). Deltamethrin was less selective in favor of the mite species.
Nonetheless the parasitic mite was able to parasitize eggs of R. dominica
on wheat treated with all the insecticides evaluated.
There is great potential for using biological control to control pests in stored products. Research is continuing to determine the proper prescriptions for use of natural enemies in stored grain. Behavioral, ecological and physiological data are being collected that will facilitate effective deployment of parasitoids and predators. Storage situations other than grain bins, such as feed mills, food warehouses and food factories may be targeted areas for biological control in the future. As part of an IMP system for stored product management, biological control should help reduce the use of pesticides on food and provide for high quality food products.
Insect growth regulators: Insect Growth Regulators (IGRs) are chemicals
which mimic hormones that control molting in insects and thereby disrupt development.
Oberlander et al. (1997) reviewed many studies
involving IGRs and stored product-insects. Most of the published research involved
exposure of eggs, 1st instars, or adults on treated grain, in diet or in glass
vials, with subsequent measurements of progeny production. Morphological effects
and reduced fecundity in adults have been reported from some of these studies
with stored-product insects (El- Sayed, 1988).
Many stored-product insects occur not only in raw grains, but also in mills,
processing plants, food warehouses and other indoor areas and there is comparatively
little research with IGRs that is applicable to insect control programs in those
areas. In a recent test late-instar larvae of Tribolium castaneum (Herbst),
the red flour beetle and Triboltium confusum (du Val) were directly exposed
on concrete treated with hydroprene (Arthur, 2001).
Larvae often failed to molt to the pupal stage and adults that did emerge were
usually morphologically deformed and quickly died. In addition, T. castaneum
appeared to be more morphologically deformed and quickly died. In addition,
I. castaneum appeared to be more susceptible to hydroprene than T.
Currently there is renewed interest in developing reduced-risk low toxicity
chemicals, including new formulations of IGRs, to replace older conventional
products used in many agricultural systems, including post-harvest protection
in areas where food is stored. Expanded use of these IGRs could also be facilitated
by identifying physical and biological factors that can compromise efficacy
when IGRs are used as a surface treatment. The new hydroprene formulation were
equivalent to the registered product Gentrol. Tribolium confusion was
less susceptible than T. castareum and residual control of T.confusum,
lasted 6-12 weeks (Arthur and Hoeremann, 2004).
IGRs have been developed commercially and are being use to control insect pests in agriculture, forestry, public health and stored products. IGRs affect the biology of treated insects, for example, both embryonic and post-embryonic development, reproduction, behaviour and mortality. Abnormal morphogenesis is the observed effect of IGR action on the insects. Many of them are more potent than current insecticides, even against the eggs.
Compared with the conventional insecticides, IGRs do not exhibit quick knock-down
in insects or cause mortality, but the long-term exposure to these compounds
largely stops the population growth, as a result of the effects mentioned in
both the parents and progeny (Mondal and Parween, 2000).
Hygiene: Well managed aeration and effective hygiene can overcome 85% of storage pest problems facing grain growers.
By following a few relatively simple strategies, growers can ensure their on-farm
storage systems maintain grain quality for future sales. Once a grain store
has been emptied and physically cleaned, it is normal to reduce the residual
insect populations by use of structural treatments. Until recently, the only
chemicals registered for such usage were azamethiphos or a mixture of fenitrothion
and carbaryl. Another type of treatment has been developed that leaves no synthetic
chemical residues that could contaminate food. The treatment involved spraying
a slurry of Dryacide®, a diatomaceous earth coated with silica
aerogels, on to the structure. This technique has undergone extensive trails
in the field and has been shown to give at least 12 months protection (Anonymous,1991b).
There is an obvious need to assess the efficacy of hygiene procedures and structural
treatments prior to in-loading of grain. Since, inspection and sampling procedures
are labour-intensive, food-baited traps, developed elsewhere (De
Coursey, 1931; Pinniger et al., 1984), have
been used recently in Australia with considerable success and have demonstrated
the long-term benefits of using Dryacide® to suppress residual
populations in empty storage structures (Wright, 1990).
Good hygiene in the grain store or storage depot is important in maintaining
grain and seed quality. Guidelines for hygiene in the grain store include:
||Keep storage areas clean. This means sweeping the floor, removing
cobwebs and dust and collecting and removing any grain spills
||Clean storage rooms after they are emptied and this may include spraying
walls, crevices and wooden pallets with an insecticide before using them
||Placing rat-traps and barriers in drying and storage areas. Cats deter
and help control rats and mice
||Inspect storage room regularly to keep it vermin proof
||Inspect the stored seeds once a week for signs of insect infestation.
When necessary and only under the direction of a trained pest control technician,
the storage room or the seed stock may be sealed with tarpaulin and treated
Building maintenance is an important aspect of hygiene and exclusion in a feed
mill or grain storage facility. Where possible, seal unloading auger, openings
and pipes. Holes should be covered with a screen of fine mesh and any leaky
roofs, seals, joints and holes promptly repaired.
Development and marketing of expert systems: Good control strategies
are based on reliable methods for estimating insect population level to determine
if control measures are warranted. Probe traps and pitfall traps are more efficient
than trier samples for detecting insects in stored grain (White
et al., 1991). Computer-based decision support systems that use biological
and environmental data to predict population trends and evaluate the need for
insecticidal inputs have been developed for stored-product storage systems in
several countries (Jones et al., 1993; Longstaff,
1994). In certain situations protectants may be eliminated and insect control
may be achieved through temperature manipulation or supplemental fumigation
should infestations occur during storage. As more of these expert systems are
developed management decisions may shift to computer-based pest management.
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