Quantitative losses and physical damage caused to wheat kernel (triticum aestivum L.) by khapra beetle infestation

Abstract

Wheat and other cereals sustain huge quantitative and qualitative losses each year all over the world due to the attack of storage pests. The damage caused by Khapra beetle is comparatively greater than other pests because of its ability to increase rapidly even under unfavourable environmental conditions. A study was therefore initiated to probe into quantitative and physical losses of stored wheat caused by Khapra beetle infestation. We observed more than 20 % loss in weight of seeds after a storage period of 6 months under natural conditions, initially infested with only 10 pairs of Khapra beetle larvae. There was found a strong positive relationship among the progeny development and number of damaged grains as well as with weight loss as depicted by values of the correlation coefficient i.e., 0.95 and 0.87, respectively. Moisture contents also exhibited a strong positive correlation with the loss in weight of wheat grains (R=0.83). The beetle larvae also showed varying levels of preference to different wheat varieties. Wafaq-2001 was found to be the most resistant among the commonly grown varieties of Pakistan. It was therefore concluded that the wheat grains of promising varieties stored for edible and seed purposes must be protected from the attack of Khapra beetle infestation to maintain nutrition, viability of wheat grains and indirectly to ensure the food security.

Full text

Pak. J. Bot., 43(1): 659-668, 2011.
QUANTITATIVE LOSSES AND PHYSICAL DAMAGE CAUSED
TO WHEAT KERNEL (TRITICUM AESTIVUM L.)
BY KHAPRA BEETLE INFESTATION
MUHAMMAD SHOAIB AHMEDANI
1
,
M.I.HAQUE
*2
, SYED NADEEM AFZAL
3
,
M. NAEEM
4
, T. HUSSAIN
5
AND S. NAZ
6
1
Deanship of Quality and Development, King Saud University, Saudi Arabia
2
Department of Plant Pathology, PMAS-Arid Agriculture University, Rawalpindi, Pakistan
3,6
Department of Water Management, Ministry of Agriculture,
Government of the Punjab, Lahore, Pakistan
4
Department of Entomology, PMAS-Arid Agriculture University, Rawalpindi, Pakistan
5
Department of FR &W, University of Agriculture, Faisalabad, Pakistan
*
Corresponding author E-mail: irfhaque@gmail.com
Abstract
Wheat and other cereals sustain huge quantitative and qualitative losses each year all over the
world due to the attack of storage pests. The damage caused by Khapra beetle is comparatively
greater than other pests because of its ability to increase rapidly even under unfavourable
environmental conditions. A study was therefore initiated to probe into quantitative and physical
losses of stored wheat caused by Khapra beetle infestation. We observed more than 20 % loss in
weight of seeds after a storage period of 6 months under natural conditions, initially infested with
only 10 pairs of Khapra beetle larvae. There was found a strong positive relationship among the
progeny development and number of damaged grains as well as with weight loss as depicted by
values of the correlation coefficient i.e., 0.95 and 0.87, respectively. Moisture contents also
exhibited a strong positive correlation with the loss in weight of wheat grains (R=0.83). The beetle
larvae also showed varying levels of preference to different wheat varieties. Wafaq-2001 was found
to be the most resistant among the commonly grown varieties of Pakistan. It was therefore
concluded that the wheat grains of promising varieties stored for edible and seed purposes must be
protected from the attack of Khapra beetle infestation to maintain nutrition, viability of wheat
grains and indirectly to ensure the food security.
Introduction
Khapra beetle (Trogoderma granarium Everts) and other beetles of the Dermestidae
family are considered to be the most destructive stored product pests (Burges, 2008;
Mark et al., 2010). The pest has been given status as an A
2 quarantine organism for
EPPO (Anon., 2007). Besides, it is also of quarantine concern for Canadian Public
Procurement Council (CPPC), Comite Regional de Sanidad Vegetal del Cono Sur
(COSAVE), Junta Del Acuerdo De Cartagena (JUNAC), Organismo Internacional
Regional de Sanidad Agropecuaria, National Plant Protection Organizations (NAPPO)
and Organismo Internacional Regional de Sanidad Agropecuaria (OIRSA). The World
Trade Organization (WTO) committee on Sanitary and Phytosanitary (SPS) measures has
prohibited the importation of wheat and similar grains as well as the flours and meals
thereof in order to protect domestic production and to prevent the introduction and spread
of this notorious pest. This restriction is applicable to products transported from various
countries harboring this pest (Anon., 1981). The import restrictions are supported by the
facts that feeding by Khapra beetle larvae reduces the quality, grade and weight of grain.

MUHAMMAD SHOAIB AHMEDANI ET AL.,
660
In India, average damage level ranged from 6-33 percent of grain in a single storage
season, with maximum damage of 73 percent (Rahman et al., 1945). Loss of weight in
wheat ranged from 2.2 to 5.5 percent. Under optimal conditions, 15% infestation level
caused 2.6% loss in weight and 24% in viability of wheat grains in few months of storage
(Prasad et al., 1977). Khan & Kulachi (2002) collected 220 samples of wheat grains from
different locations of D.I. Khan. They recorded average losses to the tune of 3.4 and 6.5%
by count-and-weight (C&W) and Thousand-grain Mass (TGM) methods, respectively
within 5 months` storage. They also observed presence of black pointed, broken/
shriveled and green/immature grains as well as foreign matter, which were counted as
0.6, 3.1, 0.7 and 30.3 percent, respectively. In Pakistan, first schematic survey of losses
was conducted by Chaudhary (1980) who reported an aggregate loss of 15.3% during
various post-harvest operations of wheat in the country. Jilani (1981) observed 10 to 15%
post harvest losses of food grains in Pakistan, which were chiefly caused by the attack of
insect pests. His report was later on supported by findings of Ahmed (1984). In the same
year Ahmad & Afzal (1984) recorded 22.7% post harvest loss of wheat in Pakistan, out
of which 9.5% occurred during storage period and the remaining 13.2% during harvesting
and threshing times. On country wide basis, storage losses of wheat in Pakistan ranged
between 3.5 to 25% (Irshad & Baloch, 1985). Mohammad (1986) reported that losses of
wheat grains stored for 4 months in house type godowns of Pakistan are 2.03, 8.18 and
1.35% determined by Standard Volume Weight (SVW), TGM methods of loss
assessment, respectively. The respective figures for six months wheat storage resulted in
average weight losses of 1.99, 6.33 and 2.01%, respectively, whereas for 7 months
storage period, losses were recorded as 3.02, 9.41 and 2.06%, determined by S.V.W,
T.G.M. and G.M. methods, respectively (Khan, 1986). Baloch (1986) recorded 4 and 7%
annual storage losses at farm level and in the public sector, respectively.
The weight loss of grain and cost of necessary treatment may result in less profit for
the wholesalers. The present investigations were therefore undertaken to estimate
quantitative and physical damages induced in seeds of commonly grown wheat varieties
of Pakistan by the notorious Khapra beetle. The results will enable the scientists to adopt
appropriate control measures leading protection of wheat seeds as well as to ensure food
security by minimizing the storage losses.
Materials and Methods
The present investigations were carried out in Stored Grain Research Laboratory of
Entomology Department of Pir Mehr Ali Shah, Arid Agriculture University Rawalpindi
during 2004-2008. The materials and methods employed in this study are as under:
Collection of wheat seeds: Seeds of 9 wheat varieties commonly grown in Pakistan viz.,
BWP-97, Manthar, Bhakkar-2000, BWP-2000, GA-2002, Inquilab-91, DWR-97, Panjnad
and Wafaq-2001 were collected from the Regional Agricultural Research Institute,
Bahawalpur, Punjab, Pakistan. One kg sample from each variety was taken and
fumigated with Aluminium phosphide tablets to nullify the possibility of previous
infestation if any. The samples were then cleaned by sieving through 3/8, 3/16, 1/8 and
1/12 inch mesh sieves. From this cleaned wheat, working samples weighing 25 grams
from each variety were drawn (Proctor, 1994) and subjected to analyses for determination
of moisture contents, insect damage, broken and healthy grains.

LOSSES CAUSED TO WHEAT BY KHAPRA BEETLE
661
Collection and mass rearing of insects: Mixed age cultures of T. granarium were
collected from farm houses as well as wheat stores of the Punjab Food Department
located at various places in Rawalpindi district. The cultures were reared on healthy
wheat grains apparently free from insect infestation. To further ensure exclusion of any
undetected population of insects, the wheat samples were subjected to phosphine
fumigation before using the grains as rearing medium (Jood & Kapoor, 1992). The
fumigated grains were put in three glass jars (15 cm × 15 cm × 25 cm), each containing
one kg wheat. The jars were covered with muslin cloth with the help of rubber band and
placed in the laboratory at 30±2°C and 65±5% relative humidity for conditioning. The
grains were used as rearing medium when their moisture contents had reached 10-12%
after fortnight. (Pingale & Girish, 1967). From the mixed age cultures collected from
various destinations, Khapra beetle pupae were separated and kept in an incubator at
32±2°C and 65±5% R.H for adult emergence, which were used for mass rearing after 24-
48h. Ten pairs (10 males + 10 females) of adults were introduced in the jars containing
clean, healthy and fumigated wheat grains with 10-12% moisture contents. The cultures
were maintained in the incubator at 32±2 °C and 65±5% R.H. for a period of three
months for mass rearing. Later on, uniform size larvae of khapra were used in the
experiment.
Exposing wheat seeds to Khapra beetle infestation: Wheat grains weighing 200 grams
from each variety were put in 250 ml glass jars and 20 uniform size larvae of about 1-2
weeks old were taken from the culture and introduced in each jar as triplicates. All the
jars were then covered with muslin cloth with the help of rubber bands. The jars were
later placed in an incubator under semi-warehouse conditions at 25±2°C, 55±5% R.H.
and 12:12 h continuous light: dark conditions for a period of six months. Doors of the
incubator were opened for a period of 30 minutes on alternate days to ensure proper
aeration and to avoid accumulation of Carbon dioxide produced as a result of biotic
respiration. After a period of 6 months, the jars were taken out and further analyses were
made for progeny development as well as physical and biochemical changes induced by
the insect infestation.
Determination of moisture contents: Moisture of the grain was determined to
investigate its correlation with the levels of T. granarium infestation, progeny
development, weight loss, weight of frass, insect’s damaged, broken and healthy grains.
For this purpose, a U.S. made grain moisture tester (Farmex-MT3) was used.
Progeny development: After weighing, the entire grain samples from each variety were
sieved through 1/8, 1/12, 3/16 and 3/8 inches mesh sieves. Live as well as dead larvae,
pupae and adults were counted from each replication of the respective wheat variety by
laboratory magnifying glass ×10³.
Weight loss: The infested grains in each jar were subjected to sieving to separate grain
dust, exuviae and other excretions added due to Khapra beetle infestation. A sample
weighing 25 gram was drawn from the cleaned wheat for assessment of percent weight
loss. For this purpose number and weight of damaged and undamaged grains were
recorded and put in the following equation for determination of weight loss (Gwinner et
al., 1996).

MUHAMMAD SHOAIB AHMEDANI ET AL.,
662
(Wµ × Nd) – (Wd × Nµ)
Percent weight loss =
Wµ × (Nd + Nµ)
× 100
Wµ = weight of undamaged grains
Nµ = number of undamaged grains
W
d
= weight of damaged grains
N
d
= number of damaged grains
Weight of Frass: While determination of weight loss, the weight of exuviae, flour dust,
dead as well as alive adult and immature stages of Khapra beetle and those of other
excretions produced during infestation were measured and collectedly termed as weight
of Frass of the respective sample of each variety.
Comparative resistance of wheat varieties: The rate of progeny development indicated
by the number of larvae produced in each sample, percentage of infested grains and
weight loss were considered as an expression of comparative resistance of each variety to
the Khapra beetle infestation.
Insect damaged, broken and healthy grain count: After removing the frass, sample of
cleaned grain weighing 25 gram was drawn from each replication of the respective wheat
variety. The grains were classified and counted for percent insect damaged, broken and
healthy one by using the following equations.
No. of insect damaged grains
Percent Insect damaged grains =
Total number of grains in the sample
× 100
No. of broken grains
Percent Broken grains =
Total number of grains in the sample
× 100
No. of healthy grains
Percent healthy grains =
Total number of grains in the sample
× 100
Statistical procedures: Data so calculated was subjected to statistical analysis using
multi-factorial completely randomized designs (CRD) in Minitab and MSTATC
packages (Anon., 1990) and the means were compared by Duncan’s Multiple Range tests
at 99 % level of confidence (Gomez & Gomez, 1984).
Results and Discussion
Moisture contents: Jood et al., (1996) observed that 75% infestation level of T.
granarium and R. dominica caused a significant (p<0.05) increase in moisture contents of
the infested grains as in the present investigations Analyses of variance of the data in
Table 1 has depicted significant differences between moisture content of grain before and
after infestation. The moisture percentage values recorded before infestation revealed
non-significant differences in DWR-97, Panjnad and Wafaq-2001, with moisture content
of 8.44, 8.34 and 8.08%, respectively. Similarly non-significant differences were
recorded for percent moisture content values of BWP-97 and Manthar (10.47 and

LOSSES CAUSED TO WHEAT BY KHAPRA BEETLE
663
10.41%, respectively). Moisture content in case of Inquilab-91, GA-2002 was though
statistically similar with each other as well as with BWP-2000, but was found higher than
those of DWR-97, Panjnad and Wafaq-2001. Wheat variety Bhakkar-2000 exhibited a
distinct moisture content of 9.87 %, lower than BWP-97 and Manthar. There was found a
significant increase in moisture content of all the wheat varieties after subjecting them to
artificial infestation with T. granarium larvae for a period of 6 months i.e. between
March-August. The Table 1 also reflects that Wafaq-2001 showed minimum increase in
moisture content from 8.08 to 8.41% after infestation. The other varieties Inquilab-91,
DWR-97 and Panjnad statistically proved similar with each other in respect of increase in
moisture content but ranked lower than those of BWP-97, Manthar, Bhakkar-2000 and
BWP-2000. Maximum increase in the moisture content was recorded in Bhakkar-2000
with 2.09% increase after infestation. The results are also in line with the findings of
Ravan et al., (1987), Jood & Kapoor (1993) and Jood et al., (1993). The increase in
moisture contents over time may be due to the absorbance of atmospheric moisture by the
grain, biotic respiration as well insect excretion.
Progeny development, weight loss and weight of frass: It is evident from Table 2
that maximum progeny development was observed in wheat variety BWP-97 showing
792.7 larvae per 200 gram wheat. Progeny development in case of Manthar-2000 was
although statistically similar to that recorded in BWP-97 but was numerically lower
having 752 larvae per 200 gram wheat. The varieties Bhakkar-2000 and BWP-2000
were also statistically similar in respect of progeny development with 668.7 and 624
larvae, respectively. Minimum progeny development of 189.7 was recorded in case of
Wafaq-2001.
Weight loss caused after 6 months of artificial infestation by Khapra larvae revealed
BWP-97 as one of the most susceptible wheat varieties with 20.25% loss followed by
Manthar, Bhakkar-2000, BWP-2000, GA-2000, Inquilab-91, DWR-97, Panjnad and
Wafaq-2001 with weight loss of 19.53, 18.27, 16.24, 15.47, 15.37, 14.1, 13.81 and 6.2%,
respectively. Data pertaining to the weight of frass also depicted approximately similar
ranking except weight of frass recorded in case of DWR-97 was higher as compared to
that recorded in case of Inquilab-91. There was found a positive correlation between
progeny development, infestation percentage, weight loss and weight of frass. The results
are in conformity with the previous findings made by Ahmad et al., (1986) and Navarro
et al., (1978) who observed a high degree of positive correlation between the progeny
development and the infestation level, grain damage and weight loss of the infested
grains. Bhardwaj et al., (1977) observed 2.5 % weight loss against 5.1 % infestation.
Khattak et al., (2000) while working on the effect of T. granarium infestation on twelve
rainfed wheat lines also found that correlation between progeny development, damage
and weight loss was positive and highly significant (p<0.01). This is because grain is a
living entity, which is affected by biotic and a biotic factors resulting in qualitative and
quantitative loss (Ahmad, 1995; Singh
et al., (1997). Khan & Kulachi (2002) also
reported a positive correlation between the progeny development T. granarium, T.
castaneum and R. dominica and the losses caused by them to weight of grains. Their
results were reconfirmed during an experiment conducted to evaluate losses caused by T.
granarium and R. dominica to different wheat varieties (Syed et al., 2006).

MUHAMMAD SHOAIB AHMEDANI ET AL.,
664
Table 1. Moisture content of wheat varieties before and after exposing to
infestation of Khapra beetle larvae at 25±2°C, 55±5% R.H. and 12:12h
continuous light : dark conditions for a storage period of 6 months.
Moisture content (%)
Wheat varieties
Before infestation After infestation*
BWP-97 10.47a 11.79 a
MANTHAR 10.41a 11.32 ab
BHAKKAR-2000 9.87 b 11.96 a
BWP-2000 9.00 c 10.37 cd
GA-2002 8.59 cd 10.67 bc
INQUILAB-91 8.55 cd 9.69 de
DWR-97 8.44 d 9.63 e
PANJNAD 8.34 d 9.48 e
WAFAQ-2001 8.08 d 8.41 f
Means followed by the same letter in each column are not significantly different by Duncan's
multiple range test (p=0.01)
Table 2. Progeny development, weight loss and weight of frass in wheat varieties
exposed to artificial infestation for at 25±2°C, 55±5 % R.H. and 12:12h
continuous light: dark conditions for a storage period of 6 months.
Wheat varieties
Progeny
development (No.)
Weight loss
(%)
Weight of frass
(gm)
BWP-97 792.70 a 20.25 a 24.47 a
MANTHAR 752.00 a 19.53 a 23.21 a
BHAKKAR-2000 668.70 b 18.27 ab 20.64 b
BWP-2000 624.00 b 16.24 bc 19.25 b
GA-2002 551.70 c 15.47 bc 17.03 c
INQUILAB-91 440.00 d 15.37 bc 13.58 d
DWR-97 472.00 d 14.10 c 14.57 d
PANJNAD 280.70 e 13.81 c 8.663 e
WAFAQ-2001 189.70 f 6.223 d 5.857 f
Means followed by the same letter in each column are not significantly different by Duncan's
Multiple Range Test (p=0.01)
Insect damaged, broken and healthy grains recorded after infestation: The results
pertaining to percent damage to wheat grains caused by T. granarium larvae in different
wheat varieties under natural storage conditions are presented in Table 3. Mean values
did not reveal statistically significant differences among various varieties of wheat in
respect of broken and healthy grains before infestation. Significant differences were,
however, found among the wheat varieties in respect of insect damaged grains before
subjecting them to artificial infestation. Before infestation maximum number of damaged
grains were recorded in variety BWP-97 (2%) followed by Inquilab-91, DWR-97, GA-
2002 and Manthar with 1.66, 1.66, 1.33 and 0.66% infestation, respectively. The
remaining four varieties did not show any sign of grain damage caused due to insect
infestation. Comparison of mean values after infestation showed highly significant
variations among different wheat varieties in respect of insect damaged, broken and
healthy grains. As is evident from Table 3, maximum insect damaged grains (43.37%)
were found in BWP-97 which statistically resembled to Manthar with 42.87% damage.

LOSSES CAUSED TO WHEAT BY KHAPRA BEETLE
665
Table 3. Insect damaged, broken and healthy grains observed in wheat varieties exposed to Khapra
larvae at 25±2°C, 55±5 % R.H. and 12:12h continuous light: dark conditions for a period of 6 months.
Insect damaged grains
%
Broken grains
(%)
Healthy grains
(%)
Wheat varieties
Before
infestation
After
infestation*
Before
infestation
After
infestation*
Before
infestation*
After
infestation*
BWP-97 2.00 a 43.37 a 2.66 b 16.72 a 95.34 b 39.91 f
MANTHAR 0.66 bc 42.87 a 2.00 bc 15.02 ab 97.33 a 42.10 f
BHAKKAR-2000 0.00 c 38.44 b 4.00 a 13.65 b 96.00 b 47.91 e
BWP-2000 0.00 c 34.21 c 1.66 c 11.27 c 98.34 a 54.52 d
GA-2002 1.33 ab 34.45 c 1.66 c 11.17 c 97.00 a 54.38 d
INQUILAB-91 1.66 a 30.27 d 2.66 b 10.43 c 95.68 bc 59.30 c
DWR-97 1.66 a 35.94 bc 3.33 a 6.913 d 95.00 c 57.15 cd
PANJNAD 0.00 c 24.67 e 2.00 bc 5.237 d 98.00 a 70.10 b
WAFAQ-2001 0.00 c 19.97 f 3.33 a 4.973 d 96.67 b 75.06 a
Mean 0.81 33.79 2.59 10.60 96.59 55.60
Means followed by the same letter in each column are not significantly different by Duncan's Multiple Range
Test (p=0.01)
Table 4. Correlation matrix showing relationship of different physical and biochemical changes of
wheat grains induced by larval infestation of Khapra beetle (T. granarium) larvae at 25±2 °C,
55±5 % R.H. and 12:12h continuous light: dark conditions for a period of 6 months.
Parameters
Progeny
Development
Progeny
development
1.000 Moisture
content
Moisture content 0.900 1.000 Weight
of frass
Weight of frass 1.000 0.900 1.000 Weight
loss
Weight loss 0.920 0.835 0.920 1.000 Weevilled
grains
Weeviled grains 0.968 0.864 0.968 0.911 1.000 Damaged/
Broken
Damaged/broken
grains
0.954 0.920 0.954 0.876 0.888 1.000 Healthy
grains
Healthy grains -0.989 -0.907 -0.989 -0.923 -0.986 -0.952 1.000
Whereas minimum percentage of insect damaged grains was found in Wafaq-2001 with
19.97 %. A similar trend was observed in case of broken grains and vice versa with the
healthy grains. These findings are in consistent with those of Badawy & Hassan (1965),
Shah (1969), Azeem et al., (1976), Hameed et al., (1984), Irshad and Baluch (1985),
Ahmad et al., (1986), Irshad et al., (1988), and Khattak et al., (2000) who observed a
positive correlation between infestation caused by T. granarium and damage to wheat
grains. Later on, Syed et al., (2006) carried out investigation to evaluate the comparative
resistance of wheat varieties against infestation of T. granarium and R. dominica
infestation. Their results revealed that grain damage and weight loss percentage was
mainly dependent upon the progeny development which was also dependent on the
varietal preference of the pests used in the investigation.
Results of the present investigations revealed significant increase in progeny
development, weight loss, weight of frass, the number of broken and insect damaged grains
with the increase in infestation level. The Khapra larvae fed on both germ as well as
endosperm of the grain. In most of the cases, entire grain was consumed and partially eaten

MUHAMMAD SHOAIB AHMEDANI ET AL.,
666
husk was the only remain of the grain. In some grains larvae were found camouflaging
themselves inside the shell. A huge quantity of exuviae, flour dust, live and dead larvae and
adults was an indication of the infestation severity and level of susceptibility or resistance in
different varieties tested during the present investigation. Color change as well as foul
odour was also observed in severely infested samples. Correlation matrix (Table 4) better
reflects relationship between different variables investigated in the present investigations.
Wheat variety BWP-97 proved to be the most susceptible and Wafaq-2001 behaved as the
most resistant wheat varieties with minimum weight loss, weight of frass and number of
damaged grains. Literature has revealed that the insect resistance mechanisms of cereal
grains are complex and depend on physico-chemical and bio-chemical properties of the
grain and on the subsequent bio-chemical and physical adaptation of post-harvest insects to
these properties (Warchalewski
et al., 1989; Dobie, 1991; Warchalewski & Nawrot, 1993;
Warchalewski
et al., 1993). Stored grains may have high resistance to insect pests because
of the lack of vital nutrients or the presence of compounds that adversely affect insect
development (Taylor & Medici, 1966; Medici & Taylor, 1966; Yetter et al., 1979; Nawrot
et al., 1985; Gatehouse et al., 1986; Dobie, 1991; Baker et al., 1991; Huesing et al., 1991;
Warchalewski & Nawrot, 1993; Pueyo
et al., 1995; Zhang et al., 1997; Piasecka-
Kwiatkowska, 1999; Piasecka-
Kwiatkowska & Warchalewski, 2000a, b). In general, insects
tend to develop more slowly on resistant grain varieties. Various studies of wheat grain
resistance have been made, but there have been few attempts to determine the particular
factors that govern resistance (Dobie, 1991). The present studies have revealed Wafaq-2001
as the most resistant variety against T. granarium. The results are in conformity with those
of Ahmedani et al., (2009) who observed minimum impact of khapra beetle infestation on
the grains of this variety.
Acknowledgements
The authors are grateful to the Higher Education Commission of Pakistan for
providing adequate funding to carry out this research work.
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(Received for publication 15 April 2009)