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Use of Diatomaceous Earth for the Management of Stored Product Pests

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Abstract

Diatomaceous earth (DE) is almost pure amorphous silicon dioxide, made up of fossilised diatoms; it acts as an insecticide by absorption of epicuticular lipids and fatty acids, leading to desiccation in arthropods. Numerous DE formulations have been attempted for the management of stored-product pests with good results. DE is persistent in its action, poses few or no pest resistance problems, and it leaves no residue. The efficacy of DE is affected by factors such as its provenance, temperature, humidity and characteristics of target pests and substrate. Application of DE at currently recommended doses causes changes in bulk density of the grain; however, the use of enhanced DE formulations provides control at much lower doses. Therefore, new formulations of DEs usually include other low toxicity insecticides.
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Use of diatomaceous earth for the management of
stored-product pests
Mohd Abas Shaha & Akhtar Ali Khana
a Division of Entomology, Sher-e-Kashmir University of Agricultural Sciences and
Technology of Kashmir, Shalimar, Srinagar, India-190 025
Published online: 27 May 2014.
To cite this article: Mohd Abas Shah & Akhtar Ali Khan (2014) Use of diatomaceous earth for the management of stored-
product pests, International Journal of Pest Management, 60:2, 100-113, DOI: 10.1080/09670874.2014.918674
To link to this article: http://dx.doi.org/10.1080/09670874.2014.918674
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Use of diatomaceous earth for the management of stored-product pests
Mohd Abas Shah*and Akhtar Ali Khan
Division of Entomology, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir,
Shalimar, Srinagar, India-190 025
(Received 6 January 2014; final version received 27 March 2014)
Diatomaceous earth (DE) is almost pure amorphous silicon dioxide, made up of fossilised diatoms; it acts as an insecticide
by absorption of epicuticular lipids and fatty acids, leading to desiccation in arthropods. Numerous DE formulations have
been attempted for the management of stored-product pests with good results. DE is persistent in its action, poses few or
no pest resistance problems, and it leaves no residue. The efficacy of DE is affected by factors such as: its provenance,
temperature, humidity and characteristics of target pests and substrate. Application of DE at currently recommended doses
causes changes in bulk density of the grain; however, the use of enhanced DE formulations provides control at much lower
doses. Therefore, new formulations of DEs usually include other low toxicity insecticides.
Keywords: diatoms; enhanced diatomaceous earth; epicuticular lipids; grain bulk density; resistance; storage losses;
stored-product pests
1. Introduction
Diatomaceous earth (DE) is an inert dust derived from
amorphous sediment and comprised of the fossilised carapa-
ces of unicellular algae. It is a light material with low den-
sity and its colour ranges from white to dark grey. It
consists of approximately 8093% silicon dioxide, the
remaining content comprising clay minerals, organic matter,
quartz, calcium and magnesium carbonate (Korunic 1998;
Stathers et al. 2004). DE insecticides are perceived as a
sound option for pest control in grain storage (Quarles
1992). They are both abrasive and slightly absorptive, and
the dust particles adhere to the insect’s cuticle and in doing
so remove the lipid monolayer, causing the insect to desic-
cate (Korunic 1998; Subramanyam and Roesli 2000).
About 1030% of grains produced worldwide are lost
every year due to stored-grain pests (Singh et al. 2009).
Residual insecticides are the most commonly used protec-
tants in stored grain against stored-product pests. These
insecticides are applied directly to the product and provide
protection against stored-grain pests as long as the insecti-
cidal effect persists (Arthur 1996). However, the use of
these protectants poses several drawbacks, as they are
generally toxic to mammals and leave residues in the
product; furthermore, many insect species are resistant to
some residual protectants (Arthur 1996). These limitations
have led researchers to evaluate the potential use of alter-
native control methods, such as botanicals, insect growth
regulators, biological control, microbial control, and inert
dusts. One of the most promising alternatives to contact
insecticides is the application of diatomaceous earths
(DEs). These dusts are applied directly to the grain, with-
out specialized equipment, using much the same technol-
ogy as that employed for residual insecticides. DEs have
some incontestable advantages over residual protectants,
given that they are non-toxic to mammals, can be easily
removed from the product during processing, are very
effective for a wide range of species, and given that only a
physical method is involved, it has been postulated that
physiological resistance is unlikely to occur (Golob 1997;
Korunic 1998; Subramanyam and Roesli 2000). However,
recent studies indicate that resistance to DE can evolve
under certain circumstances (Vayias et al. 2008). Several
DE formulations are commercially available (Subrama-
nyam and Roesli 2000), and many studies document that
they are very effective against a wide range of stored-
product insect species. However, the main drawback in
the use of DEs is that they need to be applied at high-dose
rates, which affect the physical properties, chiefly bulk
density, of the stored grains (Athanassiou and Korunic
2007). This issue is being addressed by the combined use
of DEs with other low-risk control methods known as
enhanced DEs (EDEs), as proposed by Arthur (2003),
with promising results in most cases. Here, we provide a
brief overview of the nature and mode of action of DEs
followed by a summary of recent attempts at evaluating
the efficacy of DEs against stored-grain pests. The factors
affecting efficiency of DEs have been dealt with in detail
followed by an account on effects of DEs on grain quality.
Finally, the possibility of using EDEs for the management
of stored-product pests has been discussed.
2. Nature of diatomaceous earth
Diatomaceous earth (DE) is almost pure amorphous sili-
con dioxide, made up of fossilised diatoms. Diatoms are
unicellular algae and probably the most widespread group
*Corresponding author. Email: khubaib20@gmail.com
Ó2014 Taylor & Francis
International Journal of Pest Management, 2014
Vol. 60, No. 2, 100113, http://dx.doi.org/10.1080/09670874.2014.918674
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of plants on the earth. There are more than 25,000 species
of diatoms with no two having the same morphology
(Round et al. 1992). They are abundant in all aquatic eco-
systems, but also occur in terrestrial environments. About
20 to 80 million years ago, mostly in the Eocene and Mio-
cene epochs, different species of diatoms extracted silicon
from water, producing a hydrated amorphous silica skele-
ton. When the diatoms died the tiny shells sunk, and over
the years these shells formed thick layers. Eventually
these deposits were fossilised and compressed into a soft,
chalky rock that is now called diatomaceous earth. A
well-documented fossil record of diatoms extends back to
the mid-Cretaceous period, but the vast majority of depos-
its are from Eocene/Miocene times. Deposits range in
thickness from a few centimetres to several hundred
metres. The deposit may be finely laminated or massive
(Karunic 1998). DE is used extensively and is prepared
for commercial use by quarrying, drying and milling
(Quarles and Winn 1996).
As mined, DE contains 50% or more moisture. Of the
solids, 8694% is silica, the remainder being chiefly alu-
mina and alkalies from clay. The only change to DE dur-
ing processing is the reduction in the moisture content and
mean aggregate particle size. Moisture is reduced to
26% and milling reduces particle size to between 0.5
and 100 mm with the majority between 10 mm and
50 mm. The result of this process is a fine, talc-like pow-
der or dust considered to be non-toxic to mammals
(Quarles 1992). DE is extremely stable and does not pro-
duces toxic chemical residues or react with other substan-
ces in the environment. According to the Environmental
Protection Agency (EPA) in the United States, natural DE
is described as amorphous silicon dioxide which is classi-
fied as Generally Recognized as Safe (GRAS) as a food
additive (Anon. 1991). The US Food and Drug Adminis-
tration has exempted DE from requirements of fixed resi-
due levels when added to stored grain (Anon. 1961).
Different types of DE are commonly used for the purifica-
tion of water, the clarification of liquors and juices, filtra-
tion of commercial fluids, and the separation of various
oils and chemicals. Other uses include fillers in paints,
paper and rubber. Because DE can absorb two to three
times its own weight in liquids, yet remain free flowing, it
is also employed as a pesticide carrier, and for the safe
storage and transportation of hazardous liquids. DE and
diatomite are also used in numerous commercial products
such as detergents, deodorisers, cosmetic powders, in fil-
tration systems for swimming pools, as a mild abrasive, a
drilling-mud additive, anti-caking agent and animal feed
additives (Snetsinger 1988). Estimated world production
of diatomite in 2011 was 2.1 million metric tons (Mt).
World reserves are thought to be almost 1 billion metric
tons of which about 250 metric tons (25% of the whole) is
in the United States (Crangle 2012). The United States is
the leading producer of diatomite, accounting for 39% of
total world production, followed by China with 21%, Den-
mark with 11%, and Japan with 5%. Diatomite used for
filtration represents 61% of consumption, followed by its
use as a cement additive (13%), as an absorbent (12%),
and as a filler (12%). Other diatomite applications, includ-
ing abrasives, insecticides, insulation, and soil condi-
tioner, accounted for the remainder. Major diatomite
products were sold as various grades of calcined powders
(Crangle 2012).
3. Mode of action and use against stored-grain pests
DE is probably the most efficacious natural dust used as
an insecticide. The dust particles are trapped by the bodies
of the insects as they walk over it. The dust is most effec-
tive against insects with setaceous and rough surfaces.
The mode of action of DE is generally accepted to be a
desiccating effect on the insects (Ebeling 1971; Mewis
and Reichmuth 1998). This indicates that toxicity primar-
ily depends on its physical properties and not on its chem-
ical composition (Subramanyam and Roesli 2000).
Different insecticidal mechanisms have been proposed,
including abrasion of the cuticle (Fields 1998), absorption
of cuticular waxes from the epicuticle surface (Ebeling
1971; Mewis and Ulrichs 1999; Prasantha 2003), damage
to the digestive tract (Smith 1969), blockage of the spi-
racles and tracheae (Webb 1945), and surface enlargement
combined with dehydration (Zacher and Kunike 1931).
Recent research work has concluded that effective absorp-
tion of epicuticular lipids and fatty acids is the primary
mode of action of DE, leading to desiccation in arthropods
(Fields 1998; Mewis and Ulrichs 1999; Prasantha 2003).
The other mode of action of DE is repellence caused by
the physical presence of the dust (White et al. 1966).
“Bathing in sand” is a well known occurrence exhib-
ited by birds and poultry protecting themselves against
mites and other parasites. Four thousand years ago, obser-
vations of such natural phenomena probably led the Chi-
nese to use DE (diatomite) to control pests (Allen 1972).
In 1880 in the United States, it was noticed that road dust
killed caterpillars of the cotton moth (Stelle 1880). Until
the 1950s, clay dusts, sand or silica gels were used more
extensively in practice and in research than was DE. In
the early 1950s, DE was used to fight fruit moths, cucum-
ber beetles, Mexican bean beetle larvae, stored-products
pests and cockroaches (Bartlett 1951). Generally, the
dusts are insect repellents. The repellency depends on the
dosage applied. Increased dosage increases insect repel-
lency, and the negative influence of the dust on parasites
and predators (Flanders 1941; Bartlett 1951).
The use of DE for structural treatment in stored product
facilities was studied by Wright (1990), Desmarchelier
et al. (1993), McLaughlin (1994), Bridgeman (1994), and
Korunic and Fields (1995). Research has also been done
on the effect of DE on numerous other insects such as ants,
bedbugs, textile pests, various caterpillars in agriculture,
crickets, termites, earwigs, June beetles, potato beetles,
silverfish, fleas, as well as on poultry mites, ticks, centi-
pedes, pillbugs, snails, etc. (Wilbur et al. 1971;DeCrosta
1979; Snetsinger 1982,1988; Korunic 2013). Although
different and often completely opposing results were
obtained, there is a general conclusion that can be drawn
about the sensitivity of stored-product insects to DE.
International Journal of Pest Management 101
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The most extensive research with DE has been under-
taken in the field of the protection of stored agricultural
products. Published results of studies with DE also imply
that there is little degradation or loss in efficacy of DE
with time (Arthur 2002), a very desirable quality for an
ideal grain protectant. The effect of DE on various stored-
product insects has been studied by numerous researchers.
Earlier work has been reviewed by Korunic (1998), recent
publications on relative efficacy of DEs against stored-
product pests are summarised in Table 1.
4. Factors affecting efficacy of diatomaceous earths
The insecticidal activity of DEs is affected by many fac-
tors such as source of DE, insect species, grain moisture
content, temperature, method of application, growth stage
of the pest species, and nature of the stored product.
Therefore, it is imperative to ascertain the effect of pre-
vailing conditions for effective use of DEs.
4.1. Relative humidity
The effect of the relative humidity (RH) on DE efficacy
has been reported by several researchers and the results
are consistent for all stored-product insect species tested
so far (Vayias and Athanassiou 2004). It is generally
accepted that, at high RH or moisture content values, des-
iccation through the abrading action of the DE particles
on the cuticle is reduced, because insects may moderate
their water loss (Subramanyam and Roesli 2000; Fields
and Korunic 2000; Mewis and Ulrichs 2001; Athanassiou
et al. 2011). Furthermore, DE particles absorb moisture
from the air, a fact which, when high RH values prevail,
causes an additional reduction in DE efficacy (Subrama-
nyam and Roesli 2000; Arthur 2001; Stathers et al. 2004).
Arthur (2002) reported that on wheat treated with DE, sur-
vival of Sitophilus oryzae increased with increasing RH,
and this effect was evident both in the initial survival of S.
oryzae and the number of F1 adults. According to Vayias
and Athanassiou (2004), a 10% increase in RH (from 55%
to 65%) is sufficient for a considerable reduction in DE
efficacy.
4.2. Temperature
Contradictory results have been reports regarding the
effect of temperature on the insecticidal efficacy of DE.
While using the DE formulation “Dryacide”, Aldryhim
(1990) noted that Tribolium confusum adults were more
susceptible at 20C than 30C. In addition, Fields and
Korunic (2000), using several DE formulations, reported
similar results for adults of the red flour beetle Tribolium
castaneum. On the other hand, Arthur (2000a), when
using the commercial formulation of DE “Protect-It”,
stated that the efficacy of DE against T.confusum and T.
castaneum adults increases progressively with increase of
Table 1. Recent
publications on the use of diatomaceous earth against stored-product pests.
Pest species References
Sitophilus oryzae (L.) Fields and Korunic 2000; Arthur 2002; Athanassiou et al. 2003; Athanassiou et al. 2005;
Athanassiou et al. 2007; Saez and Mora 2007; Athanassiou et al. 2008; Kljajic et al. 2010;
Rojht et al. 2010; Athanassiou et al. 2011; Sadeghi et al. 2012; Stadler et al. 2012
Tribolium confusum du Val Vayias and Athanassiou 2004; Athanassiou et al. 2005; Athanassiou et al. 2007; Mewis and
Ulrichs 2001; Athanassiou et al. 2011; Ziaee and Moharramipour 2012; Arthur and
Fontenot, 2013
Rhyzopertha dominica (F.) Fields and Korunic 2000; Athanassiou and Kavallieratos 2005; Athanassiou et al. 2007;
Vardeman et al. 2007a,2007b; Saez and Mora 2007; Kljajic et al. 2010; Athanassiou et al.
2011; Beris et al. 2011; Sadeghi et al. 2012; Stadler et al. 2012; Arthur and Fontenot, 2013
Tribolium castaneum (Herbst) Fields and Korunic 2000; Collins and Cook 2006a,2006b; Arnaud et al. 2005; Kljajic et al.
2010; Arthur and Fontenot, 2013; Kabir 2013
Sitophilus granarius (L.) Collins and Cook 2006a; Mewis and Ulrichs 2001; Saez and Mora 2007
Oryzaephilus surinamensis (L.) Fields and Korunic 2000; Collins and Cook 2006a; Sadeghi et al. 2012; Arthur and Fontenot,
2013
Ephestia kuehniella Zeller Collins and Cook 2006a,2006b
Plodia interpunctella (Hubner) Mewis and Ulrichs 2001
Blattella germanica (L.) Faulde et al. 2006
Acarus siro (L.) Collins and Cook 2006a
Lepidoglyphus destructor (Schrank) Collins and Cook 2006a,2006b
Tenebrio molitor L. Mewis and Ulrichs 2001
Callosobruchus chinensis L. Matti and Awaknavar 2009
Callosobruchus maculatus (F.) Prasantha 2003; Sadeghi et al. 2012
Cryptolestes ferrugineus (Stephens) Fields and Korunic 2000; Saez and Mora 2007; Sadeghi et al. 2012
Lasioderma serricorne (F.) Sadeghi et al. 2012
Sitophilus zeamais Motsch Demissie et al. 2008; Sousa et al. 2013
Acanthoscelides obtectus (Say) Prasantha 2003; Bohinc et al. 2013
From 2000 onwards.
102 M.A. Shah and A.A. Khan
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temperature. Athanassiou et al. (2004), when using
“SilicoSec” at temperatures between 22C and 32C,
found that mortality of T.confusum adults was increased
as temperature increased from 22Cto32
C. However, in
that study the mortality was reduced at 32C, but this
reduction was evident only at short exposure intervals
(<48 h), while at longer exposures (>7 d), mortality at
32C was significantly increased in comparison with that
at 30C. In that study, the T. confusum adults used were of
mixed and not of standardized age, and this may partially
explain the different levels of mortality at 32C. Gener-
ally, for most of the stored-product beetle species tested
so far, such as Cryptolestes ferrugineus,Sitophilus oryzae,
Sitophilus granarius,Rhyzopertha dominica,Tribolium
confusum and Oryzaephilus surinamensis, there is a posi-
tive correlation between temperature and mortality
(Aldryhim 1990,1993; Fields and Korunic 2000; Subra-
manyam and Roesli 2000; Arthur 2001; Athanassiou et al.
2004; Athanassiou et al. 2011). As such, Sousa et al.
(2013) have suggested that the combination of lower
doses with high temperatures and longer periods of expo-
sure can effectively control insect pests of stored products,
particularly in tropics.
Increased temperature would increase insect move-
ment, causing increased contact with the DE and greater
cuticular damage (Fields and Karunic 2000). Higher tem-
peratures and increased movement would also increase
water loss via the spiracles due to increased respiration.
Losses via the spiracles are estimated to be three times
greater than losses of water through the cuticle for a desert
tenebrionid (Zachariassen 1991). Also, the rate of cuticu-
lar transpiration rises only slightly with temperature until
the transition temperature, which for most insects is above
30C (Wigglesworth 1972). However, increased tempera-
ture would also increase feeding and therefore moisture
replacement through the food and production of metabolic
water. The synthesis of cuticular waxes may be faster at
higher temperatures because of temperature effects on the
biochemical pathways. However, there may be other over-
riding factors such as hormones. Unlike the synthetic
insecticides, DE is inert and does not degrade in a temper-
ature-dependent fashion. Within a grain bulk, the RH will
change slightly with temperature. For stored wheat there
is about a 3% reduction in RH for each 10C increase in
temperature (Pixton and Warburton 1971). However,
these changes would be too small to be responsible for the
observed effects.
4.3. Type of product
The efficacy of DE is determined by the type of storage
product the dust is applied to. Athanassiou et al. (2003),
using “SilicoSec” in doseresponse tests against S. oryzae
adults in peeled rice, paddy rice, barley and maize, found
that mortality notably varied in different types of grain.
Survival of T. confusum adults and larvae was higher in
treated flour than in treated hard and soft wheat (Vayias
and Athanassiou 2004). Athanassiou et al. (2008) carried
out bioassays to assess whether the commodity from
which adults of the rice weevil Sitophilus oryzae had
emerged influenced the insecticidal efficacy of three DE
formulations. The S. oryzae populations tested were
reared on wheat, barley or maize. Barley-reared S. oryzae
were the most tolerant to all formulations and treated
commodities, whereas maize-reared beetles were the most
susceptible ones. DE effectiveness was always lower in
maize than in wheat or barley, irrespective of the com-
modity from which the populations were obtained. Thus,
the grain type, not only as the DE-treated substrate but
also as a rearing medium, affects the DE efficacy. Earlier,
Mewis and Ulrichs (2001) reported higher mortality when
T. confusum individuals were fed on kernels rather than
on flour. White and Loschiavo (1989) also noted that sur-
vival of T. confusum adults was higher in beetles that
were fed with flour after their exposure to DE. Similarly,
Arthur (2000b) recorded that mixing food with DE
increased adult survival of Tribolium spp. As a secondary
pest, the confused flour beetle cannot easily develop in
undamaged seeds, on the other hand, it can develop with
great ease in flour (Aitken 1975; Rees 1995). Thus, one
possible explanation for the increased survival in flour is
that exposed individuals may restore water due to food
consumption. Also, the presence of flour may help insects
to remove the DE particles from the cuticle. Thus, small
food quantities as a result of defective cleaning in a stor-
age facility may reduce DE efficacy (Arthur 2000b).
McGaughey (1972) reported that the dose rate of DE
required for 100% mortality of S. oryzae on rough rice did
not provide complete suppression on milled and brown
rice. The reduced effectiveness of DE on milled and
brown rice was attributed to the absorption of kernel lipids
by the DE particles. Vayias and Athanassiou (2004)
reported that a complete suppression could not be
obtained on rice treated with 1.5 g of SilicoSec/kg, even
after a 14-d exposure interval.
Apart from absorption, it is known that the physical
and chemical properties of the grain determine the amount
of dust that is retained on kernels. In general, the degree of
DE retention varies with the grain type, the grain class, the
dose rate and the dust used (Korunic and Ormesher 2000).
Hence, apart from the degree of adhesion of dust particles,
the structural and compositional properties of the grain are
also very important, due to their influence on insect sur-
vival, development and progeny production. However,
results from a specific DE formulation may not be appli-
cable to all situations: different DEs may adhere differ-
ently to different grain types or even different classes of a
given grain. High oil or lipid content of maize kernels
may cause an increased oil absorption by DE particles and
thus the DE becomes inactivated (Vayias et al. 2006).
According to Korunic (1997), DE adherence to kernels is
a fundamental issue that affects the insecticidal value of a
given DE. Also, Kavallieratos et al. (2005) reported that
the DE formulations “Insecto” and “SilicoSec” adhered
less to maize than to the other seven grains tested. More-
over, DE efficacy was generally lower on treated wheat
than on barley. This is in accordance with the data pre-
sented by Athanassiou et al. (2005), who found that the
International Journal of Pest Management 103
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efficacy of DEs against S. oryzae, during a residual study,
was reduced on wheat more rapidly than on barley. Simi-
larly, Athanassiou et al. (2003) found that SilicoSec was
more effective against adults of S. oryzae on paddy rice
and barley than on maize.
When Baker (1988) evaluated the developmental rate
of various strains of S. oryzae in several grains, he noticed
that maize was the least suitable diet for this species.
Athanassiou et al. (2008) also noticed that the develop-
ment of this species was delayed in maize. Later, Athanas-
siou et al. (2011) reported that DEs were more effective in
barley or wheat than in maize or rice. It seems that the
high level of DE adherence to barley seeds, as has been
noted by Kavallieratos et al. (2005), produces high mor-
tality levels for S. oryzae although barley is the most suit-
able diet for this species.
From a practical point of view, these findings should
be taken into account by researchers when bioassay
response tests with DEs against stored-product pests are
planned, since the rearing medium may seriously affect
the mortality results. Variation in efficacy was also noted
by Chanbang et al. (2007) for combination treatments of
DE and methoprene against Rhyzopertha dominica on
long-, short-, and medium-grain rough rice. Ziaee et al.
(2007) compared the insecticidal efficacy of five DE for-
mulations, against adult T. castaneum on three oilseeds,
viz. safflower, sunflower and sesame, and reported signifi-
cant differences among the three oilseed types. Even at
the lowest treatment rate, adult mortality was high
(>90%) in safflower for all DE formulations. In contrast,
adult mortality was significantly lower in the case of ses-
ame. The lowest application rate enabled complete sup-
pression in progeny production on treated safflower and
the highest number of progeny was recorded for treated
sunflower seeds.
4.4. Growth stage
Larval instars differ in their susceptibility to DE: young
larvae are significantly more susceptible than older ones
(Vayias and Athanassiou 2004). Adults of the confused
flour beetle are much more tolerant to DE than the larvae
and can survive at application rates and exposure intervals
that are lethal to all larval stages. Vayias and Athanassiou
(2004) reported that 90% of larvae were killed by an
application rate of 1.5 g of SilicoSec/kg after only 48 h of
exposure, while the respective figure for adults was only
50%. This different reaction of T. confusum larvae and
adults to DE has also been reported by Mewis and Ulrichs
(2001).
Newly emerged beetles are also more susceptible to
SilicoSec than older ones. In fact, 1- and 2-day-old adults
were found to possess different levels of susceptibility to
DE, suggesting that periods of even 1 d are sufficient to
increase beetle survival. Older adults (7 d old) are consid-
erably more tolerant to DE than the newly emerged bee-
tles (Vayias and Athanassiou 2004). De Paula et al.
(2002), when using the DE formulation Insecto, reported
that adult mortality of T. castaneum in DE-treated wheat
varied significantly with adult age. Although the differen-
ces in DE-tolerance among species or among develop-
mental stages of the same species have not been
investigated in detail, the different level of cuticle thick-
ness and the insects’ behaviour may be responsible for
these variations. Hence, one possible explanation is that
adults and larvae, or even younger and older individuals
of the same developmental stage, may have different
thickness of cuticle or even a different composition of epi-
cuticular lipids, as this has been reported for other species
(Armold et al. 1969). In young larvae the cuticle may be
softer than in older larvae, and thus DE may cause more
rapid cuticle damage which may result in more rapid des-
iccation. Also, young larvae are particularly agile, a
behaviour which increases their contact with the dust par-
ticles as compared to older larval stages prior to pupation,
which are less active. Adult sensitivity to DE is also influ-
enced by these factors. Rigaux et al. (2001), comparing
different strains of T. castaneum, recorded increased DE-
tolerance in the less agile strains. Also, Fields and
Korunic (2000) reported noticeable variation among four
stored-product beetle species regarding the amount of DE
particles that were attached to the cuticle at the adult
stage. Thus, age/instar of the target pests has a conse-
quence for DE-based management.
4.5. Source of diatomaceous earth
DEs from different geological sources or even from the
same location have different physical properties (SiO
2
content, tapped density, oil absorbency, particle size and
pH) that are correlated to their insecticidal efficacy against
stored-product insects (Korunic 1997, 1998; Athanassiou
et al. 2011). Also, Korunic (1997) studied DE formula-
tions collected from worldwide geographic locations and
reported large differences in efficacy against insects, in
their physical properties and in their influence on wheat
bulk density when applied at 50 parts per million (ppm).
Comparison among DEs is difficult because there is sig-
nificant variation in insecticidal activity from the same
geographical source, and only small quantities of DE are
used for laboratory testing. Testing a range of concentra-
tions and estimation of the LD
50
or the LD
95
values could
indicate the effect of DE source on efficacy. SiO
2
content
is a critical factor that affects insecticidal activity of DEs;
however, the other substances such as major mineral
oxides, apart from SiO
2
, may also have a bearing on the
efficacy of DEs. Rojht et al. (2010) determined the effect
of geochemical composition of DE on insecticidal activity
of DE against adults of S. oryzae and reported that silica
was the DE ingredient that was significantly correlated
with efficacy in most of the bioassays. A weak positive
correlation was recorded between S. oryzae mortality and
MnO or CaO content. All significant correlations between
mortality and Al
2
O
3
,Fe
2
O
3
,K
2
O, TiO
2
,Cr
2
O
3
,P
2
O
5
, and
MgO content were negative, while correlation between
Na
2
O content and mortality was generally not significant.
Saez and Mora (2007) reported variable initial mortality
rate from two different types of DEs of freshwater and
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marine origin on four species of insects, Cryptolestes fer-
rugineus,Rhyzopertha dominica,Sitophilus oryzae and S.
granarius, applied either by spraying or dusting.
4.6. Species variation
Stored-product insects show a wide range of susceptibility
to DE (Aldryhim 1990,1993). In general, the most sensi-
tive species are in the genus Cryptolestes, while Sitophilus
spp. are less susceptible, followed by Oryzaephilus,Rhy-
zopertha, and Tribolium spp. which appear to be the most
resistant (Korunic and Fields 1995; Fields and Muir
1996). The differences in tolerance among species is con-
siderable. Under certain conditions, and using DE with a
high efficacy against insects to achieve a 100% mortality
of C. ferrugineus, a dosage of 300 ppm (0.3 g kg
1
) for
24 h was required. However, applying the same dosage
under the same conditions to T. castaneum, 100% mortal-
ity of the insects did not occur even after 21 days (Korunic
1994). Fields and Karunic (2000) reported the following
order of tolerance: C. ferrugineus >O. surinamensis ¼S.
oryzae >R. dominica /T. castaneum.
A few studies have addressed why there are different
susceptibilities among species. Nair (1957) working with
magnesite dust and White and Loschiavo (1989) working
with silica aerogel found that susceptible insects had more
dust adhering to the cuticle. Fields and Karunic (2000)
observed that C. ferrugineus, the most susceptible insect,
had more DE attached to its cuticle than T. castaneum, the
least susceptible. General resistance to desiccation
either through better water retention, better water acquisi-
tion, or greater tolerance of dessication could also be
responsible for these differences in susceptibility. How-
ever, Nair (1957) and Le Patourel (1986) stated that dessi-
cation tolerance did not strictly follow resistance to DE,
whereas Carlson and Ball (1962) found a good correla-
tion. Other factors that may account for differences
between the species are size (volume to surface area
ratio), quantitative or qualitative differences in cuticular
lipids, differences in rate of movement through grain,
behavioural reaction to DE, or desiccation.
4.7. Method of application
Spraying has several advantages over dusting in that
workers are exposed to less dust, the formulation is easier
to apply, and it does not affect grain bulk density as much
(Korunic et al. 1998). Sedimentation of the dust can be
overcome by using agitators in the spray tanks, though in
some facilities access to water is limited. As seen in other
studies (Maceljski and Korunic 1972; McLaughlin 1994),
slurry or spray application reduces efficacy. The sug-
gested reason for this drop in activity is that when DE is
applied as a slurry and than dries there is less contact
between it and the insect than when it is applied dry
(Maceljski and Korunic 1972). Another possibility is that
the particles in solution aggregate, reducing activity. Saez
and Mora (2007) reported a slightly increased rate of
achieving mortality of stored-product insects when
exposed to DEs applied by spraying. However, the overall
mortalities achieved at 8 days showed no significant dif-
ferences between application methods. The sum of indi-
vidual weights of insects indicated that dead insects for
each species treated by spraying were slightly heavier
than those treated by dusting. These differences could be
caused by an increased number of dust particles adhering
to the insects’ bodies (Subramanyam and Hagstrum 1995)
or else by a difference in the weight loss due to desicca-
tion. Saez and Mora (2007) concluded that the spraying
method increases adherence of dusts to an insect’s body.
Collins and Cook (2006b) assessed the efficacy of two DE
formulations applied as dry dust and slurry applications to
wooden surfaces against adult S. granarius, and Lepido-
glyphus destructor and against larvae of Ephestia kueh-
niella. Wood was used as the test substrate as it was
considered to present a realistic challenge to efficacy due
to its three-dimensional structure. Of the various treat-
ments, dry dust was the most effective against all the pest
species, producing 8095%, 100% and 93100% mean
mortalities of S. granarius,E. kuehniella and L. destruc-
tor, respectively, over the 12-week experimental period.
The slurry treatments were less effective than the dry
dusts.
In commercial practice, DEs are applied to structures
using the slurry (wet) and dry blown methods. In Aus-
tralia, Dryacides is applied as a dry dust to grain-handling
machinery, ducts and vertical silos, and slurries are
applied to horizontal grain stores (Golob 1997). Slurries
are useful where there is a need for personnel to avoid
exposure to the very dusty atmospheres created by the dry
blown method; however, some dusts tend to have reduced
efficacy when applied as slurries (McLaughlin 1994;
Gowers and Le Patourel 1984). As a result, recommended
rates of Dryacides are 2 g/m
2
when applied as a dry dust
and 6 g/m
2
when applied as a 10% aqueous slurry. It is
therefore important to evaluate both dry dust and slurry
applications. Generally, slurries are less effective than the
dry dusts, forming a smooth uniform coverage over the
surface of the wood allowing the pests to walk on the sur-
face without picking up much of the deposit. Therefore
higher doses and longer exposure times may be required
if using slurries, although they may be useful where there
is a need to avoid the dusty atmospheres created when
using dry dusts (Collins and Cook 2006).
5. Concerns about the use of diatomaceous earths
5.1. Effects on grain quality
Although the first commercial formulations became
widely available in the 1950s (Quarles 1992), there are
problems associated with the use of DE. When DE is
mixed with grain at the currently recommended dosages
of 5003500 ppm, some physical and mechanical proper-
ties of the bulk commodity are adversely affected: flow-
ability and bulk density are reduced, visible residues are
evident on the grains, moisture readings taken when using
a dielectric moisture metre are affected, and an excessive
International Journal of Pest Management 105
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amount of dust is produced during handling (Korunic
1997; Korunic et al. 1998). The addition of DE to grains
creates greater friction between kernels, which affects
their bulk density and flow properties. Bulk density or test
weight is an extensively used grading factor.
Freshwater DE has very little effect on end-use quality
of wheat (Korunic et al. 1996a). Bread-making properties,
flour yield, protein content of wheat, sedimentation, fat
acidity, flour ash, diastatic activity, and physical proper-
ties of the dough were unaffected by freshwater DE treat-
ments (3500 ppm) even after one year of storage (Fifield
1970). Twenty parts per million of “Dryacide” (modified
freshwater DE) in flour had no effect on the production of
carbon dioxide in dough, nor on the volume or texture of
sponge cakes (Desmarchelier and Dines 1987). Sponge
cakes made from flour containing 100 ppm Dryacide had
a coarser texture and had 710% less volume than cakes
made from untreated flour. However, because milling and
cleaning of wheat remove over 98% of DE (Desmarche-
lier and Dines 1987), grain would have to be treated at
5000 ppm, which is well above recommended application
rates, to leave a level of 100 ppm in the processed flour.
The milling industry is also reluctant to accept grain
treated with DE because of its abrasive nature and possi-
ble damage to milling machinery (Subramanyam et al.
1994). Korunic et al. (1996a) examined the effect of
“Protect-It” on quality, and physical and handling charac-
teristics of cereals. In field tests, wheat treated with Pro-
tect-It at 75 ppm and 100 ppm, concentrations that
controlled C. ferrugineus and reduced T. castaneum popu-
lations, did not cause a reduction in grain flow, nor did
this treatment cause an increase in air-borne dust when
grain was moved using a screw auger. Wheat treated with
300 ppm of Protect-It had reduced grain flow and caused
an increase in air-borne dust. In all tests where grain was
treated with Protect-It and processed, there was no effect
on the end-use quality. This is not surprising as DE is
made up mainly of silicon dioxide, which is chemically
inert (Quarles 1992). Also, processing removes much of
the DE, so that only a fraction of the DE applied is carried
over into the finished product (Desmarchelier and Dines
1987). Unlike synthetic insecticides which are fat-soluble
and migrate to inside the grain kernel (Rowlands 1975),
DE stays on the seed coat making it easier to remove dur-
ing milling or processing. Korunic et al. (1996a) also stud-
ied the effect of dockage in combination with DE on bulk
density, and concluded that regardless of the mechanism
of how dockage changes the bulk densities, the actual
impact of dockage on the importance of bulk density in a
field situation will probably be minor. The only significant
adverse effect demonstrated in this study was the reduc-
tion of grain bulk density: although Protect-It used at
75 ppm and 100 ppm does reduce bulk density, it does not
reduce end-use quality. Korunic et al. (1998) studied the
effect of the enhanced diatomaceous earth (EDE) insecti-
cide “Protect-It” at different concentrations on the bulk
density of wheat, corn, barley, rye and oats at different
moisture levels. The greatest changes in bulk density
occurred when the concentration of EDE ranged from
50 to 200 ppm. At concentrations greater than 500 ppm,
bulk density decreased little with increased EDE concen-
trations. The bulk density reductions in all five grains
tested were significantly higher for the grain at a dry basis
moisture content of 15% than at 12%. The dry application
caused a significantly greater reduction in wheat bulk den-
sity than did the wet application.
Moras et al. (2006) assessed the effects of two DE for-
mulations on technological, physical and cooking charac-
teristics of rice and reported that use of DE was efficient
in grain conservation and also showed no effect on tech-
nological quality and rice cooking parameters with respect
to parboiled and conventionally processed rice, even after
12 months of storage. Bodroza-Solarov et al. (2012)
investigated the changes in quality parameters of wheat
(mealy and vitreous) either non-infested or infested with
S. oryzae, caused by treatments with two types of DE, viz.
an enhanced DE and an inert dust. Non-infested, high-vit-
reous wheat treated with EDE showed the highest mois-
ture absorption. The percentage of test weight reduction
was greater in mealy wheat grain than in the high-vitreous
wheat grain. Significant improvement in dough rheology
was observed in the infested soft and hard wheat, particu-
larly through rise of dough energy.
The magnitude of the adverse effects of DE can be
reduced by lowering concentrations of DE. However,
lower concentrations of the current DE formulations can-
not achieve acceptable levels of control of stored-grain
insects. Use of the new enhanced diatomaceous earth for-
mulations (EDEs) is perceived as a viable option (Korunic
et al. 1996a,1996b).
5.2. Health issues
There is no evidence of acute or chronic toxic effects of
natural DE. It has been shown to be non-toxic when con-
sumed by mammals. Rats receiving daily food containing
5% freshwater DE showed no signs of abnormality after
90 days (Bertke 1964). On farms, cattle have sometimes
been given food containing 12% DE to control worms
and other internal parasites (Allen 1972). Owing to its
demonstrable safety and non-toxicity, no permissible resi-
due levels have had to be prescribed for DE mixed with
grain in the United States. Also, the US Environmental
Protection Agency (EPA) allows the use of DE in product
storage and the food processing industry (Anon. 1961,
1981). DE has been registered as a grain protectant in the
United States, Canada, Australia, Japan, Indonesia, Saudi
Arabia and Croatia (Karunic 1998).
The known possible noxious and dangerous effects on
mammalian health can occur when workers are constantly
exposed to DE with prolonged inhalation of suspended
dust (Omura 1981). According to the International
Agency for the Research of Cancer (IARC), amorphous
silica belongs to group 3: it is classified as non-carcino-
genic. There is inadequate evidence for the carcinogenic-
ity of amorphous silica to humans and to experimental
animals (Anon. 1986). However, DE with a higher per-
centage of crystalline silica (e.g. the calcined DE) could
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be very noxious. As with all other dusts, DE can cause
mild irritation of the eyes, lungs and skin. Professional
workers dealing with DE should be protected with ade-
quate equipment, particularly respiratory masks (Miles
1990).
6. Resistance development against diatomaceous
earths
For DEs, only a physical mode of action is involved, and
according to Golob (1997) the development of physiologi-
cal resistance to DEs is unlikely to occur. However, newer
studies indicate that resistance may be developed at least
in the case of some species (Korunic and Ormesher 2000;
Rigaux et al. 2001; Fields 2003). Resistance development
against DE has been evaluated by a few workers; hence
this section is mainly based on the account put forth by
Vayias et al. (2008). Several studies document that T. con-
fusum adults can tolerate DE dose rates which are lethal to
other species (Aldryhim 1990; Arthur 2000a; Vayias and
Athanassiou 2004; Athanassiou et al. 2004,2005). A
study by Athanassiou et al. (2005) using SilicoSec found
that T. confusum adults could survive at dose rates that
caused 100% mortality to S. oryzae adults. Among stored-
grain insect species, T. confusum is considered to be one
of the least susceptible to DEs (Korunic 1998; Arthur
2000a, 2000b; Vayias and Athanassiou 2004). Vayias et.
al. (2008) reported that after successive laboratory selec-
tion, T. confusum adults become more tolerant to Silico-
Sec. Karunic (1998) evaluated the possibility of the
development of DE resistance or tolerance in adults of the
T. castaneum,R. dominica, and C. ferrugineus under the
laboratory conditions. After exposing five generations of
the red flour beetle adults and rusty grain beetle adults and
seven generations of the lesser grain borer adults to DE,
and recording mortality, the ratios of the LD
50
values of
the selected strains to the DE-susceptible laboratory
strains were 1.3, 2.2 and 1.9, respectively.
Due to the limited use of DEs in practice, most stored-
product insect populations have had no previous contact
with DEs, but the development of resistant strains is feasi-
ble. This fact should be taken into account when a DE-
based control strategy is planned, given that continuous
use of DEs in a storage facility may cause this effect.
Resistance is likely to be expressed more quickly when
DEs are used for treating parts of the grain mass since, in
this way, individuals may be exposed occasionally but
may also remove themselves from the treated material.
Several studies suggest that it is preferable to use DEs in
the entire grain mass (Athanassiou et al. 2004,2005;
Vayias and Athanassiou 2004), or to combine DEs with
other substances, such as low doses of other insecticides
(Athanassiou et al. 2004; Vayias et al. 2006), entomopa-
thogenic fungi (Lord 2001; Akbar et al. 2004), or heat
(Dowdy 1999; Dowdy and Fields 2002). Under laboratory
selection of T. castaneum with Protect-It, Korunic and
Ormesher (2000) recorded a 1.3-fold increase in tolerance
after six generations. By using the same DE, Fields
(2003), after 3 years of laboratory selection, obtained a T.
castaneum population with a 2-fold increase in tolerance,
which was a considerably lower rate of increase compared
with S. oryzae,R. dominica and C. ferrugineus. Vayias
et al. (2008) produced a laboratory population of T. confu-
sum in which each generation was usually more tolerant
than the previous one to SilicoSec, especially at the low
dose rates, where adult survival was increased. This
accords with the finding of Fields (2003) that the develop-
ment of resistance is likely after occasional exposure to
DEs. Tolerance was not observed when adults were
exposed to 1500 ppm for either 7 days or 14 days, but it
was observed (1.3-fold decrease in mortality after 10 gen-
erations) with a 48 h exposure interval. Since all DEs are
based on the activity of SiO
2
which means that the
insecticidal effect is similar among DEs the develop-
ment of resistance to one DE may be transferable to other
DEs as well.
However, the use of EDE formulations may provide a
possible solution to these potential problems (Fields
2003). Regarding the mechanism of resistance, DEs act
only in a physical way on the cuticle, so the reported resis-
tance to DEs is not a physiological response. Rigaux et al.
(2001) found that T. castaneum adults that were less agile
were more tolerant to Protect-It. Apparently, decreased
mobility decreases the contact with DE particles, with a
concomitant increase in survival in the DE-treated sub-
strate. Thus, the resistance reported by Vayias et. al.
(2008) and other workers can be considered as a
“behavioural” and not a “physiological” resistance, since
it is primarily based in the avoidance of increased contact
with DE particles.
7. Efficacy of enhanced diatomaceous earths
Several DE formulations are commercially available and
many studies document that they are very effective
against a wide range of stored-product insect species.
However, the main drawback in the use of DEs is that
they need to be applied at high-dose rates, and these affect
the physical properties, chiefly bulk density, of the stored
grains (Korunic et al. 1998). Also, the presence in the
atmosphere of high DE concentrations containing crystal-
line silica may cause respiration problems (silicosis) to
workers after long exposure. Many DE formulations are
only effective at dose rates of 1000 ppm or more (Atha-
nassiou and Korunic 2007), while most traditional grain
protectants should be applied at dose rates that usually do
not exceed 10 ppm. One of the possible solutions to the
problems caused by the use of DEs in high doses is the
combined use of other, reduced-risk methods, such as
extreme temperatures (Dowdy and Fields 2002), entomo-
pathogenic fungi (Lord 2001; Akbar et al. 2004; Micha-
laki et al. 2006) or low doses of insecticides (Vayias and
Stephou 2009). The combined use of DEs with other low-
risk control methods, as proposed by Arthur (2003), could
be a possible solution for the wider use of DEs as grain
protectants. For instance, Athanassiou and Steenberg
(2007) found that the simultaneous use of DEs with the
entomopathogenic fungus Beauveria bassiana (Balsamo)
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Vuillemin (Deuteromycotina: Hyphomycetes) was effec-
tive against adults of the granary weevil, Sitophilus gran-
arius. Similar combinations have also been examined for
other fungus species as well, with varied results (Micha-
laki et al. 2006,2007). Another combination is the addi-
tion of low doses of insecticides, which could reduce the
effective dose rate of DEs. For instance, Athanassiou
(2006) noted that DEs could be combined with low doses
of the pyrethroid betacyfluthrin. Ceruti and Lazzari
(2005) evaluated the efficacy of different dosages of DE
mixed with powder deltamethrin for controlling Sitophilus
zeamais in stored corn. In the treatments mixing DE with
deltamethrin or using deltamethrin alone, the mortality
was registered since the first day. In the treatments using
only DE, the first dead insects were recorded after the
third day, especially at the highest dosages. It was con-
cluded that treatments using DE combined with low dos-
ages of powder deltamethrin represent an efficient control
measure against S. zeamais in stored corn, because insect
mortality is faster than with treatments using DE alone
and residues of active ingredients are much less compared
with using the insecticide at high dosages. Vayias et al.
(2006) attempted the combined use of DE formulations
and one natural pyrethrum formulation against pupae of
the confused flour beetle, T. confusum, and reported
encouraging results.
Some commercially available DE formulations con-
taining low doses of insecticides have been evaluated,
with promising results. Athanassiou et al. (2008) evalu-
ated a mixture of DE with the plant extract bitterbarkomy-
cin (BBM) against adults of R. dominica and the results of
their study were very promising, since the mixture was
very effective at dose rates of less than 150 ppm. Accord-
ing to Wang et al. (1991), BBM has strong antifeedant
and insecticidal properties at doses of 2550 ppm and has
been tested against several crop pests. In another study,
Athanassiou et al. (2009) found that low doses of BBM
(0.03750.0875 ppm) proved very effective against sev-
eral stored-product insect species, namely S. zeamais,T.
castaneum and C. ferrugineus. Vayias and Stephou
(2009) evaluated an enhanced mixture of DE with BBM
against adults of S. oryzae,T. confusum and C. ferrugi-
neus, which are three major stored-product pest species.
This mixture (DEBBM) was applied at three dose levels
(50 ppm, 100 ppm and 150 ppm) and on four grain com-
modities, namely hard wheat, barley, rice, and maize.
DEBBM efficacy was increased with the increase of dose,
exposure and temperature, whereas it was decreased with
the increase of relative humidity. DEBBM was very effec-
tive against C. ferrugineus, as mortality of this species,
which was achieved with 150 ppm, was always >85%. Of
the remaining species, the least susceptible to DEBBM
was T. confusum. Although DEBBM caused significant
mortality to all three species, progeny production was not
totally avoided. However, progeny production was signifi-
cantly reduced in comparison with the untreated commod-
ities. Athanassiou and Korunic (2007) reported that two
natural DE formulations, enhanced with abamectin
(DEA-P/WP) or bitterbarkomycin (DEBBM-P/WP),
resulted in death of all adults of S. oryzae, even at the low-
est dose rate (100 ppm) of DEA-P, while 100% mortality
was noted at doses 125 ppm of DEBBM-P. For the other
species, mortality was 100% on wheat treated with
75 ppm of DEBBM-P, with the exception of T. castaneum
for which all adults were dead at doses 100 ppm. Prog-
eny production was low, and no progeny were produced
in the cases of R. dominica and C. ferrugineus, for both
DEs.
Riasat et al. (2013) evaluated the virulence of Isaria
fumosorosea alone and integrated with an enhanced for-
mulation of DE (DE þbitterbarkomycin, DEBBM)
against R. dominica on stored wheat. The DE alone sup-
pressed the progeny emergence at higher dose rate as
compared I. fumosorosea alone, but their simultaneous
use further reduced the progeny production of R. domin-
ica. The integrated use of both tested biocontrol agents
synergized the effect of each other and caused the highest
mortality at 25C and 56% relative humidity. The results
clearly demonstrated that I. fumosorosea and enhanced
DEBBM can be integrated to be an effective control mea-
sure for R. dominica in stored wheat.
Yang et al. (2010) carried out laboratory bioassays to
determine the efficacy of garlic, Allium sativum L. (Amar-
yllidaceae), essential oil applied alone or with DE against
adults of S. oryzae and T. castaneum. The results showed
that the combination treatment was significantly more
effective than either treatment alone. In addition, the
results also showed that the simultaneous application of
essential oil plus DE significantly reduced the concentra-
tion of essential oil alone that was required for an effec-
tive treatment, and the application rate of DE could be
reduced when combined with essential oil. Moreover, the
activity of the combination treatment lasted longer than
that of essential oil alone and the survival of eggs or lar-
vae to adult stage was significantly inhibited in the com-
bined treatments against both species, compared with the
use of essential oil alone.
Chintzoglou et al. (2008), Vayias et al. (2009) and
Kavallieratos et al. (2010) carried out laboratory tests to
evaluate the efficacy of DE formulations enhanced with
spinosad against various stored-product pests and reported
improved toxicity at lower doses. Kavallieratos et al.
(2010) found that even the lowest dose was highly effec-
tive (>90%) against R. dominica and S. oryzae. In the
case of T. confusum a combination of longer exposures
with higher doses was required for each formulation to be
effective. They also reported improved adherence ratios
for the tested DE and spinosad formulations. Vayias et al.
(2009) reported that it is possible to combine low doses of
DE (<600 ppm) with spinosad (<1 ppm) to control adults
and larvae of T. confusum, especially at temperatures
>25C. Chintzoglou et al. (2008) concluded that the spi-
nosad dust and DE could be used in combination treat-
ments but efficacy varies with the target insect species
and commodity.
Chanbang et al. (2007) evaluated combination treat-
ments of DE “Protect-It” and the insect growth regulator
methoprene against R. dominica on stored rough rice.
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Application rates of DE and methoprene ranged from 0 to
500 ppm and 0 to 1 ppm, respectively. In the absence of
methoprene, mortality of exposed adults increased as the
concentration of DE increased, but even at the highest
rate of 500 ppm, mortality was not high. There was an
unexpected increase in adult mortality with the addition
of methoprene, so that at 1 ppm methoprene and 500 ppm
DE mortalities in long-, medium-, and short-grain rice
were 77.57%, 77.57% and 58.57%, respectively. With the
inclusion of methoprene there were few progeny produced
in any of the treatment combinations, and the overall aver-
age was 0.6 0.3. Thus, inclusion of insect growth regu-
lators with DE formulations seems to be a very promising
option.
Wakil et al. (2012) reported that DE in combination
with Beauveria bassiana or a neonicotinoid insecticide
thiamethoxam may provide safety for an extended period
against R. dominica. They reported that the mortality of
adults of R. dominica decreased over the 9 months of
storage period and the combined application of the test
materials enhanced the mortality rates compared with
alone treatments. The greatest mortality was observed
with the combination of DE and thiamethoxam. Progeny
suppression was decreased with the extended storage
period. However, the maximum rate of mycosis and
sporulation in the cadavers of R. dominica was observed
where B. bassiana was applied alone at the lowest dose
rate. In another study Wakil et al. (2013) evaluated the
effects of combining thiamethoxam at rates of 0.25, 0.5
and 0.75 mg/kg of active ingredient with the DE formu-
lation SilicoSec at the rate of 100 mg/kg against four
Pakistan populations of the lesser grain borer, R. domin-
ica. Mortality increased with increasing application rates
and exposure intervals for each population. Individually,
thiamethoxam alone was more effective at the highest
dose rate than DE alone, but after 14 days of exposure in
most cases, there was greater mortality with DE than
with the lowest dose of thiamethoxam. Populations dif-
fered in susceptibility to treatments and production of
progeny.
Arthur and Fontenot (2013) evaluated the efficacy of
AlpineÒ, a formulation containing dinotefuran and DE as
aerosol spray and a dust with DE at the rate of 5 g/m
2
and
10 g/m
2
against six adult stored product insect species: T.
castaneum,R. dominica,Oryzaephilus surinamensis,T.
confusum,Dermestes maculatus (DeGeer), and Mezium
affine Boieldieu. Mortality of T. castaneum,R. dominica,
and O. surinamensis generally increased with exposure
interval, and was 90% or more after 3 days of exposure at
both dust rates. Mortality of D. maculatus and T. confu-
sum after 3 days ranged between 50% and 70%. Mortality
of all species except M. affine was generally lower when
exposed to the spray rather than the dust. No late-stage
larvae of T. castaneum,T. confusum and O. surinamensis,
exposed to either the spray or the dusts, emerged as adults.
Based on the results obtained, Arthur and Fontenot (2013)
concluded that the enhanced DE formulation could be
incorporated into management plans for control of stored-
product insects.
8. Conclusion
DEs are the most efficient among all inert dusts for the
management of stored-product pests. The major bottle-
neck in their wider adoption is the decrease in grain bulk
density caused by addition of high doses of DE dusts.
However, inclusion of different classes of low toxicity
insecticides with DE formulations enables control at
lower doses, although results vary with target species.
Thus, the best combinations need to be worked out for
each situation and only then will enhanced DE formula-
tions find a place in the market in competition with cur-
rently used synthetic insecticides.
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... Over the years, Diatomaceous earth (DE) (composed of fossils of phytoplankton) (Shah and Khan, 2014) and Spinosad (a metabolite from the actinomycete Saccharopolyspora spinosa) (Thompson et al., 1997) have demonstrated promising insecticidal activity against stored product pests (Nayak et al., 2005;Huang et al., 2007;Khashaveh et al., 2009;Athanassiou et al., 2014;Nwaubani et al., 2014;Otitodun et al., 2015;Korunic et al., 2016). Hence, this present study was conducted to further substantiate their insecticidal activity and it is aimed at evaluating the insecticidal activity of Diatomaceous Earth (Nigeriaderived) and Spinosad® as well as their residual effect against S. zeamais on stored rice. ...
... Likewise, a study by Otitodun et al. (2015) also demonstrated the efficacy of DE (Nigeria-derived) against S. oryzae and R. dominica. The low efficacy of DE in this present study is likely due to the surface area on which the dust covers, the concentration used, the storage period, source of the DE, insect species used, grain type, grain moisture content and temperature and, method of application, as these factors have been reported to greatly influenced the efficacy (Fields and Korunic, 2000;Nwaubani et al., 2014;Shah and Khan, 2014). ...
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... The diatomaceous earth (DE) is one of the products the most studied to control insects in storages. It is considered to be the most effective natural powder with insecticide properties (Shah and Khan, 2014). The open literature referring to the DE based treatments for bean weevil is very rich (Baier and Webster, 1992;Bohinic et al., 2013;de Oliveira et al., 2018;Jumbo et al., 2019;Wille et al., 2019). ...
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... The diatomaceous earth (DE) is one of the products the most studied to control insects in storages. It is considered to be the most effective natural powder with insecticide properties (Shah and Khan, 2014). The open literature referring to the DE based treatments for bean weevil is very rich (Baier and Webster, 1992;Bohinic et al., 2013;de Oliveira et al., 2018;Jumbo et al., 2019;Wille et al., 2019). ...
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Thesis
ABSTRACT Njomza Buxhaku, Arianit A. Reka, Blagoj Pavlovski Faculty of Natural Sciences and Mathematics, State University of Tetovo, str. Illinden n.n., 1200 Tetovo, Republic of Macedonia, Faculty of Technology and Metallurgy, University of St. Cyril and Methodius, 1000 Skopje, Republic of Macedonia The aim of this research was to obtain porous ceramics as a result of the interaction of trepell(diatomaceous earth) with calcium hydroxide. The trepell was used as a raw material from a place called Gneotino, near the city of Manastir. After preparing various mixtures of trepel and calcium hydroxide, the samples were autoclaved at 135 °C for 180 minutes and it was concluded that the product of the hydrothermal reaction is a light material with a bulk density of 0.80 g/cm3, porosity of 54% and compressive strength (under optimal conditions 23% Ca(OH)2) of 11.16 MPa. Mineralogical analysis (XRPD) of the product shows the formation of new phase calcium hydro silicate as a result of which the material has high compressive strength. Microscopic analysis (SEM) confirms the data of mineralogical analysis, here the composition of the product (calcium hydro silicate) is confirmed and the morphological change that the material has undergone is noticed. Based on these results we come to a conclusion that the product obtained under hydrothermal conditions at a temperature of 135 ° C for a period of 180 minutes represents porous ceramic material and as such it can be used as a material for various uses in construction and thermal insulation material. Keywords: trepell, diatomaceous earth, CSH, SEM, XRPD
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Book
I Development in the Egg.- References.- II The Integument.- Properties of the cuticle.- Formation and shedding of the cuticle.- References.- III Growth.- Moulting.- Metamorphosis.- Determination of characters during post-embryonic development.- Regeneration.- Diapause.- References.- IV Muscular System and Locomotion.- Anatomy and histology.- Physiological properties of insect muscles.- Locomotion.- References.- V Nervous and Endocrine Systems.- Nervous system.- Visceral nervous system.- Endocrine system.- References.- VI Sense Organs: Vision.- Compound eye.- Simple eyes.- References.- VII Sense Organs: Mechanical and Chemical Senses.- Mechanical senses.- Hearing.- Chemical senses.- Temperature and humidity.- References.- VIII Behaviour.- Kinesis and related phenomena.- Orientation.- Co-ordinated behaviour.- References.- IX Respiration.- Tracheal system.- Development of the tracheal system.- Transport of oxygen to the tracheal endings.- Elimination of carbon dioxide.- Respiration of aquatic insects.- Respiration of endoparasitic insects.- Respiratory function of the blood.- Regulation of respiratory movements.- References.- X The Circulatory System and Associated Tissues.- Circulatory system.- Haemolymph.- Haemocytes.- Pericardial cells and so-called 'nephrocytes'.- Fat body.- Oenocytes.- Light-producing organs.- References.- XI Digestion and Nutrition.- Fore-gut.- Peritrophic membrane.- Mid-gut.- Hind-gut.- Secretions of the alimentary canal.- Digestion of some skeletal and other substances of plants and animals.- The role of lower organisms in digestion.- Nutrition.- References.- XII Excretion.- Urine.- Intermediary nitrogen metabolism.- Malpighian tubes.- Histophysiology of the Malpighian tubes.- Accessory functions of Malpighian tubes.- Malpighian tubes during moulting and metamorphosis.- Cephalic excretory organs and intestinal excretion.- Storage excretion.- References.- XIII Metabolism.- Chemical transformations.- Some chemical products of insects.- Pigment metabolism.- Respiratory metabolism.- References.- XIV Water and Temperature.- Water relations.- Temperature relations.- References.- XV Reproductive System.- Female reproductive system.- Male reproductive system.- Mating, impregnation and fertilization.- Some factors controlling fertility and fecundity.- Special modes of reproduction.- Sex determination.- Transmission of symbiotic micro-organisms.- References.- Index of Authors.- General Index.
Article
INSECTO is a commercial diatomaceous earth dust registered in the US for grain treatment at 0.5 to 1 g/kg rates. In the laboratory, male and female adults of different specific ages of the red flour beetle. Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae), were exposed for 7 days to hard red winter wheat treated with 0.25 g/kg of INSECTO at 30°C and 65% RH. The mortality of T. castaneum adults was similar between the sexes, but varied with adult age. Adults that are 0.5 and 2.5-days-old, and those that were 64.5-days old, were about 3 to 6 times more susceptible to INSECTO than 4.5 to 32.5-day-old adults. Mortality of 4.5 to 32.5-day-old adults was similar (4.5 to 5.5%) Therefore, when evaluating the efficacy of diatomaceous earth dusts on T. castaneum, unsexed adults between 4.5 and 32.5 days should be used in bioassays to reduce variation in mortality data attributable to adult age.