Modified Atmosphere as an Alternative Measure for Controlling of Sitophilus
oryzae Reared on Different Stored Grains
Muhammad Mohsan1, Zahid Mahmood Sarwar2*, Zafar
Hussain2, Muhammad Shahbaz Asghar2, Muhammad Adnan Badar3
and Muhammad Rafique Khan4
1Department of Entomology, University of Agriculture
Faisalabad, Punjab, Pakistan
2Department of Entomology, FAST Bahauddin Zakariya
University Multan, Pakistan
3Department of Horticulture, Pir Mehr Ali Shah Arid
Agriculture University Rawalpindi, Pakistan
4Department of Zoology, faculty of Basic and Applied
Sciences, University of Poonch
Rawalakot, Azad Jammu & Kashmir, Pakistan
*For
correspondence: zmsarwar@bzu.edu.pk
Received 07 September 2021; Accepted 28 December 2021; Published 30
January 2022
Abstract
Protection of grains and their products from insect
pests remained a big constraint in the way of food security. Current study
evaluated the effective exposure time to kill the Sitophilus oryzae (L.),
reared on two different diets viz.,
wheat and maize under six Carbon dioxide (CO2) concentrations.
Modified atmospheres (MA) contained 25, 30, 35, 40, 45 and 50% CO2
by volume at ambient temperature, respectively. Twenty S. oryzae adults,
along with a 20 g diet, were released in each airtight exposure chamber (150 mL
capacity). A measured quantity of CO2 gas (99.9%) was released in
exposure chamber by the injection syringe from gas cylinder. Mortality data
were recorded after 24, 48, 72, 96 and 120 h. The mortality rates varied
between the insect cultures reared on maize and wheat diets. S. oryzae,
reared on a wheat diet, showed higher mortality after exposure to all CO2
concentrations as compared to the insect culture reared on the maize diet. At
45% CO2concentration, maximum mortality (100%) was observed after
120 h in case of maize reared insects and (100%) after 96 h in case of wheat
reared S. oryzae. The results revealed that Carbon dioxide, as an
eco-friendly approach, may be used as the best alternative method to minimize
the pest infestation in stored products to avoid insecticide resistance
development in stored grain insect pests. The Carbon dioxide is not included in
the category of toxic gases and has no detrimental or residual effect in the
stored grains. © 2022 Friends Science Publishers
Keywords: Carbon dioxide; Modified atmosphere; Sitophilus
oryzae; Mortality response
Introduction
Stored grains
are a very important source of calories and proteins for human throughout the
world but arthropod pests play a negative role by disturbing the supply of
these grains. Insect pests damaged grains have low marketing value because of
less nutritive quality and bad taste (Alonso-Amelot and Avila-Núñez 2011). Insect pests of stored grains damage stored products by
causing 5‒10% losses
globally while 10‒40% losses in
developing countries (Weaver and Petroff 2005),
including Pakistan (Ahmad 1984). Human
survival mainly depends upon the wheat crop because it contributes major part
in the economy of any country (Yu et al.
2017). Maize is also main and
important food of the world (Kennett et al.
2020). In agriculture, grains constitute the major component of food
items. Grains like rice, wheat and maize cover 43% food calories and 87% grain
production, globally. To fulfill the food requirement of 42% population of
the world, we depend upon maize (Khan 2018).
Unfortunately,
these grains are attacked by numerous kinds of insect pests during storage
conditions. Coleopteron and Lepidopteron insect pests are the most significant
insect pests causing huge destruction to grains in the field and storage (Emana and Tsedeke 1999). The coleopteron
insects attacking stored grains during storage are four types’ beetles. Among
these beetles, rice weevil (Sitophilus oryzae L.) is widely distributed
globally. It is very destructive primary pest of stored grain, mostly prefer
soft grain varieties (Pathak and Jha 2003; Padmasri
et al. 2017).
Insect pests
of stored grains and their products have been controlled by the application of
insecticides. Due to repetition of
insecticides application, insect pests have developed insecticide resistance
against these insecticides (Wallbank and
Collins 2003). Besides the development of insecticide resistance in
insects, some of these chemicals are also banned due to hazardous effects on
human health (Isman 2006) and the
environment (Haines 1995). Resistance and
harmfulness issues of synthetic insecticides have brought about the needs of
discovering more viable and healthier alternatives.
It is in high
demand of the food industry to control arthropod pests through different
eco-friendly control methods. These techniques are also promoted by the
government through financial support and legislation because the food market
needs increased demand for organic grains. Therefore, different non-chemical
and eco-friendly methods have been adopted. Among these, the modified
atmosphere (MA) approach is suitable for the control of stored product insect
pests (Adler et al. 2000; Navarro 2006).
To overcome the infestation of stored commodities pests, the modified
atmosphere technique is considered an environmentally safe method. Montreal
protocol, an international agreement, suggested the scientists develop
different alternatives tore place methyl bromide and similar products due to
health and environmental hazards (Fields and
White 2002).
The use of CO2
as an eco-friendly approach is one of the best options to control stored
insect pests, because this approach has no harmful effects on stored food (Husain et al. 2017). This gas adversely
affects the functions of normal body of beetles a including system of hormones,
nervous system, digestive system, and circulatory system (Nicolas and Sillans 1989) because gas
particles enter the insect body and open the spiracles permanently (Jay et al. 1971). Carbon dioxide can
absorb and desorbed in grains without any chemical reaction and pose almost no
effect on grains chemistry (Yamamoto et al.
1980). Management strategies to control all the developmental stages of
pests through a modified atmosphere take several weeks because it depends upon
the gas concentrations (Riudavets et al.
2009).
The 1st objective of the research was to assess
the required exposure time to get 100% mortality by exposing the adult stage of
S. oryzae to CO2 at 27 ± 2°C temperature and 65 ± 5% relative
humidity
(RH). The 2nd objective of this research was to deliberate the
notions and variations of MA, its impact on pests and on the superiority of the
product being treated, the structure where it may be considered for use, and its
compatibility in commercial settings.
Materials and
Methods
Rearing of homogenous insect culture
The
population of S.
oryzae was collected from stored grains of the local grain market of
district Multan. The collected population was reared under optimum laboratory
conditions at 27 ± 2°C and 65% Relative humidity. Insect cultures were reared
separately on two diets i.e., wheat
and maize in sterilized
ventilated plastic jars (1 L). Grains were also sterilized using an incubator
at 50°C for 10 minutes to kill all living entities if present in grains.
Moisture of grain was maintained at optimal conditions (27 ± 2°C and 65%) for
rearing S. oryzae. From both
cultures, hundred adult pairs were released in separate plastic jars with fresh
diets for egg laying to produce a homogeneous F1 generation. After 2–3 days, adults were sieved out and
eggs were allowed behind on the diets for hatching. These larvae were provided
optimum rearing conditions to pupate. Pupae of first day were collected in
separate bottles on regular basis to obtain a homogenized population. Three
days old adults of these homogenized populations were used for the experiment
(Sarwar et al. 2020).
Carbon
dioxide (CO2) source
Carbon
dioxide (CO2) 99.9% gas cylinder was obtained from medical gas
supplier company, Faisalabad Punjab Pakistan.
Gas purity analysis
Biogas
analyzer BIOGAS 5000 manufactured by “Geotech” was used to confirm the purity of CO2 gas.
Gas application
Sterilized
transparent plastic bottles (250 mL) were used as exposure chambers. Each
bottle was filled with 20 g sterilized respective diet to release 20 adult
insects before injecting gas. Bottles were tightly plugged with special rubber
septa. CO2 gas was applied by injection syringe. The injection
syringe was connected to a three ways stopper to control the movement of gas,
one side was connected to a short hose coming from gas cylinder, other was
connected to the needle for injecting gas and third one was used to regulate
the CO2 gas. A measured quantity of gas was injected into the
exposure chamber after evacuating the same volume from exposure chamber through
the injection plunger. Cylinder pressure was controlled by using pressure
regulator gauges. After treatment bottles were kept undisturbed for definite
periods inside the incubator at 27 ± 2°C and 65% R.H. Carbon dioxide modified
atmospheres (MA) were labeled with 25
(T1), 30 (T2), 35 (T3), 40 (T4), 45 (T5) and 50% (T6) CO2 by volume,
respectively (Shekar et al. 2018).
Data collection and analysis
Table 1: Impact of six
different modified atmospheres and diets on percent mortality (%) of S. Oryzae with respect to time (T1: 25% CO2), (T2: 30% CO2), (T3: 35% CO2),
(T4: 40% CO2), (T5: 45% CO2) and (T6: 50% CO2)
Factors |
Mortality (%) |
Modified atmosphere (MA) |
|
T1 |
27.48E |
T2 |
39.22D |
T3 |
49.38C |
T4 |
62.92B |
T5 |
72.73A |
T6 |
75.85 A |
Diet (Di) |
|
Maize |
44.32 B |
Wheat |
64.89 A |
Time (T) |
|
24 |
25.82 E |
48 |
38.79 D |
72 |
55.18 C |
96 |
70.91 B |
120 |
82.32 A |
LSD (P ≤
0.05) |
|
Ma × diet (P
≤ 0.05) |
NS |
Ma × time (P
≤ 0.05) |
* |
Diet × time (P ≤ 0.05) |
NS |
Ma × diet × time (P ≤ 0.05) |
* |
Any two means
within the column followed same letters are not significant at P ≤ 0.05. * = significant, NS = non-significant at P ≤ 0.05
The
experiment was maintained with four replications along with controlling under
complete randomized design (CRD). Adult mortality data were collected at 24 h
intervals up to complete mortality of treated insects. At the end of each
exposure time, the bottles were opened, and insects were sieved out and
transferred into (9 × 2.5 cm) test tubes having fresh diet. Test tubes were
closed with muslin cloth to prevent insect escape and placed in fresh air for
up to 24 h. After 24 h, dead insects were sieved out to calculate percent
mortality in each treatment. If insects moved, they were considered as live (Annis and Morton 1997).
Corrected percent mortality was calculated using Abbot’s
formula (Abbot 1925). Results were subjected to analysis of variance (ANOVA)
using Statistix-8.1 software and LSD test was performed to compare the means at
5% significance level.
Results
Mortality effect of six modified atmospheres (MA)
against S. oryzae adult on two diets
The overall mortality percent (%) of S. oryzae was significantly (P
≤ 0.05) influenced by different concentrations of carbon dioxide modified atmospheres concerning time periods. The maximum
mortality was recorded in T6 (75.85%) followed by T5 (72.79%), T4 (62.92%), T3
(49.38%), T2 (39.22%) and T1 (27.48%), respectively. Diet also impacted the
mortality rate as the maximum mortality% was recorded in insects feeding on wheat (64.89%) while the mortality
in insects feeding on maize was (44.32%) recorded. Maximum mortality was
assessed after 120 h (88.32%) followed by 96 h (70.91%), 72 h (55.18%), 48 h
(38.79%) and 24 h (25.82%) in all treatments. The interactions (Ma × diet)
and (Diet × time) were observed non-significant at P ≤ 0.05. The two factors interaction (Ma ×
time) and three factors interaction (Ma × diet × time) were recorded
significant at P ≤ 0.05(Table 1).
The mortality (%) increased gradually from T1 to T6 and
maximum mortality was observed in T6 from both diets. The mortality% was recorded
high on wheat diet as compared to maize (Fig. 1).
In the same way, the interaction between MA × time also resulted in a
significant increase in mortality (%). In all treatments, the mortality (%)
increased with the passage of time, and maximum mortality was recorded after
120 h (Fig. 2).
Interaction between three factors MA × diet × time positively increased the mortality (%)
among the treated adults of S. oryzae. The mortality (%) was maximum in T6 and decreased
gradually up to T1. In a comparison of diets, maximum mortality was recorded in
the insects feeding on wheat diet in all treatments as compared to the insects
feeding on maize diet (Fig. 3).
Discussion
Stored
products and commodities have been focused to avoid insect pest infestation
throughout the world by adopting chemical free strategies (Phillips and Throne 2010). Farmers depend upon
the contact insecticide to control the harmful insects of stored commodities.
These insecticides are disliked to use due to their hazardous and
non-degradable effects on other organism (Morrison 2018). Fumigation is one of the most
consistently used methods and several food stuffs are protected by using
phosphine and methyl bromide but unluckily some stored product insects have
gotten resistance against these chemicals (Wang et
al. 2000). keeping in mind, the modified atmosphere is one of the
best alternative method under a controlled atmosphere (Navarro 2006). CO2 be the best
alternative replacement for phosphine and methyl bromide under stored
conditions (Emami et al. 2016).
The main benefit of this technique is that there is no harmful effect of the CO2
in the treated products. The level of oxygen can be maintained by vacuum or
with the infusion of CO2 or other gases (Navarro 2006; Conyers and Bell 2007). Temperature significantly
affects the mortality (%) i.e., high
temperature minimizes the exposure time to get 100% mortality while low
temperature enhances the exposure period and also controls the efficacy of CO2
and other fumigants (Riudavets et al.
2009). Utilization of CO2 fumigation to limit the efficiency
of harmful insects are generally productive for stored products (White and Jayas 2003; Pons et al. 2010).
Our results indicated that the mortality% increased with increase in CO2
concentration. The previous studies proved that the mortality increased with
the enhancement of the modified atmosphere having 20, 40, 60 and 80% CO2
concentration at 20°C used against Sitophilus spp. in maize grains and
modified atmosphere comprising 75% CO2 has fruitful results against S.
oryzae in different commodities (Carli et
al. 2010). Insect pests cannot survive in an environment containing
more than 35% CO2 and less than 1% Oxygen level. Our results were in
line with the findings of Carli et al. (2010) which revealed that mortality
rate of exposed insects is enhanced with increased CO2 concentration
on various diets. Annis and Morton (1997) also evaluated
the efficacy of different concentrations viz., 15%
Fig. 1: Impact of interaction between
modified atmosphere (MA) and diet on the percent (%) mortality of S. Oryzae (T1: 25% CO2), (T2:
30% CO2), (T3: 35% CO2), (T4: 40% CO2), (T5:
45% CO2) and (T6: 50% CO2)
Fig. 2: Impact of interaction between modified atmosphere and time on percent
mortality (%) of S. oryzae (T1: 25% CO2), (T2: 30% CO2), (T3: 35% CO2),
(T4: 40% CO2), (T5: 45% CO2) and (T6: 50% CO2)
Fig. 3: Impact of interaction between modified atmosphere and diet with
respect to time on mortality (%) of S. oryzae (T1: 25% CO2), (T2: 30% CO2), (T3: 35% CO2),
(T4: 40% CO2), (T5: 45% CO2) and (T6: 50% CO2)
to 100% CO2 on the developmental stages of S.
oryzae in wheat in which the most tolerant stage was pupae while 100%
mortality was obtained within 30 days in egg after exposure. The current work
is also co-related with the findings of (Annis
and Morton 1997) where death rate at adult stage increased with the
enhancement of CO2 concentration which was followed by death rate at
larval stage. Eggs of Tribolium confusum and Tribolium castaneum are
not hatch able at 25% CO2 atmosphere and high level of nitrogen and
low level of oxygen had no effect on feasibility and incubation time, while the
enhancement of CO2 concentration showed significant impact on the
incubation period and feasibility (Ali and
Lindgren 1970). Our result was also similar with (Ali and Lindgren 1970) finding which revealed
that adult stage was more vulnerable followed by egg, larvae and pupae and in
our result also showed that adult stage was more vulnerable than larvae.
Carbon dioxide
concentrations have significant effect on mortality of S. oryzae.CO2
showed 56% mortality at 25% CO2 concentration after an
exposure period of 120 h reared on maize diet while mortality was 100% at 50%
CO2 concentration under 50% concentration with in the same exposure
time. Similarly, on wheat diet after an exposure period of 120 h, mortality was
58% at 25% CO2 concentration while mortality was 100% at 45% CO2
and 50% CO2 concentrations within the same exposure time. Results
showed that toxicity of different modified atmospheres increased by increasing
CO2 gas concentration within same exposure periods. The similar findings
were presented by Lindgren and Vincent (1970);
Annis and Morton (1997) on two weevil species such as
S. granarius and S. oryzae.
Results
indicated that time and concentration posed significant effect on insect
mortality reared on two different diets. Insect population reared on wheat diet
was more susceptible as compared to maize diet that needs prolonged exposure
time to achieve complete mortality. Similarly, increased concentrations
decreased the exposure period and vice versa to achieve complete mortality. Present results showed that maximum
mortality % was recorded in wheat
as compared to maize but in previous study described that T. castaneum mortality % increased
with the increase of CO2 concentration and maximum mortality
% was recorded in rice (Sarwar et al. 2021).
Conclusion
Our results indicated that maximum mortality of S. oryzae adult reared on wheat diet
required a minimum of four days exposure period at 45% CO2
concentration. Whereas, on maize diet, the exposure period of five days is
required for maximum mortality at 45% CO2 concentration. It is
indicated that maize diet induces vigor in reared insects as compared to wheat
diet and increased the exposure time to achieve mortality of exposed insects.
The outcomes affirmed that the utilization of high CO2 fixation in a
gastight storehouse and airtight fixed huge sacks is a possible choice to control
the event of occurrence during rice storage.
Acknowledgements
Not Applicable
Author Contributions
Zahid Mahmood Sarwar, Planned and supervised the
research; Muhammad Mohsan, Zafar Hussain and Muhammad Shahbaz Asghar, conducted
the research and wrote the manuscript. Adnan Badar proofread
the manuscript and Muhammad Rafique Khan, helped in English editing and final
formatting according to journal style.
Conflicts of Interest
All authors declare that they have no conflict of
interest
Data Availability
Raw data and Materials are available
Ethics Approval
Not Applicable
Funding Source
Not Available of funds
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