Biology of Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on stored maize grains
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Current Biotica 8(1):76-81, 2014 ISSN 0973-4031
Biology of Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on stored maize grains
K. C. Narayana Swamy1, G. P. Mutthuraju1*, E. Jagadeesh2 and G. T. Thirumalaraju1
1
Department of Agril. Entomology, 2Department of Plant Pathology,
University of Agricultural Sciences, GKVK, Bangalore - 560 065 Karnataka, India
*E-mail: mutthuwithu@yahoo.co.in
grains due to insect infestation was up to
Maize (Zea mays L.) is one of the 5.90 million tons.
most important cereal crops in terms of total
production in the world. United States of Among the several insects attacking
America ranks first in area, production and maize grains during storage, Sitophilus spp.;
productivity. The world average yield is lesser grain borer, R. dominica Fabricius;
43.10 quintals per hectare, whereas United red flour beetle, Tribolium castaneum
State of America is topping with 84.62 Herbest; rice moth, Corcyra cephalonica
quintals per hectare followed by China Stainton and angumois grain moth, Sitotroga
(48.80 q/ha). The lowest productivity is in cerealella Olivier are of economic
Nigeria (13.65 q/ha). India stands fifth place importance.
in area and third place in its production and
yield compared to other cereals. During Weevils from the genus Sitophilus
2011-2012, India registered a production of are major pests of stored maize all over the
12.00 million tons with an average world (Grenier et al., 1994). Sitophilus
productivity of 17.60 quintals per hectare oryzae (Linn.) is the most destructive insect
from total cultivated area of 6.50 million pest of the stored raw cereal grains in the
hectares (Anon., 2012). world (Champ and Dyte, 1976). Between the
two species of Sitophilus viz., S. zeamais
After the harvest, grains are (Motsch.) and S. oryzae (Linn.), the former
necessarily to be stored for consumption. causes substantial losses to stored corn
Farmers retain about 70 per cent of their amounting to 18.30 per cent (Adams, 1976).
agricultural produce for seed purpose, While a high damage of 92.40 to 98.30 per
consumption and for sale (Reddy and cent was reported by Bitran et al. (1978) in
Pushpamma, 1980). Most of the farmers are different parts of the world except India. On
small and medium farmers who have no the other hand, S. oryzae causes enormous
proper facilities for drying and storage. losses up to 100 per cent in stored maize in
Consequently, many times grains are India and other countries (Irabagon, 1959,
subjected to attack by insects, rodents and Singh et al., 1974). This evidently indicates
mites resulting in both quantitative and the importance of S. oryzae in storage of
qualitative loss. Estimates of post-harvest maize. Keeping the above facts in view,
losses of cereal grains ranged between 5 to investigations were carried out with the
35 per cent in the world. Government of study of the life history, habits and habitats
India expert committee on food losses which are necessary to have thorough
estimated 9.30 per cent grain losses of which understanding of the situation favorable to
3.50 per cent loss was due to insects alone. the pest and to know the weak links in its
A survey conducted by Mookherjee et al. life history which should be taken advantage
(1968) revealed that the annual loss of for the effective management of the pest.
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Biology of S. oryzae on stored maize determined by subtracting incubation and
grains having 12.50 per cent moisture larval period. Ten pairs of adults were
content under laboratory condition (at released individually in plastic container (10
temperatures 15 to 34°C and relative cm diameter) to observe pre-mating and
humidity 58 to 89%) was carried at National mating period.
Seed Project (NSP), University of
Agricultural Sciences, GKVK, Bangalore The mated females were taken and
during 2012-13. kept in a plastic container (10 cm diameter)
along with the maize seeds to know the pre-
Culture of the rice weevil was oviposition and oviposition periods. The life
initiated by collecting the adult weevils from span of rice weevil adults both in presence and
the infested maize seeds from the university absence of food was observed by enclosing male
farm house. The culture was further and female adults in a glass vials. Ten such vials
maintained in glass jar of 2 kg capacity were maintained for each male and female with
containing the maize seeds. Mouth of the and without food.
container was closed with muslin cloth and
fastened with rubber band. Fresh grains Egg: Eggs were laid singly inside the cavity
were introduced periodically for proper on the grains. The eggs were oval in shape
development of weevils. Thirty rice weevils with one end pointed and other end rounded.
were enclosed with maize seeds in each Freshly laid eggs were translucent and white
glass bottle and these bottles were kept in in colour and became opaque before
ambient conditions. Seeds were replaced hatching. The incubation period ranged from
every morning with uninfested ones. Seeds 4 to 6 days with a mean of 5.10 days at the
containing eggs were separated out by ambient temperature of 15 to 34 Ԩ and 58 to
examining under microscope and were used 89 per cent relative humidity (Table 1). The
for further study. present finding is in agreement with that of
Bhuiyah et al. (1990) who reported 5 to 6
Maize seeds with rice weevil eggs so days of incubation period on maize seeds at
obtained were maintained in a glass vials for 23 to 35Ԩ and 79 to 87 % RH. Sharifi and
incubation. Daily 20 grains, from the day of Mills (1971a) observed 7 days of incubation
oviposition to egg hatching were observed to period on wheat seeds at 27Ԩ temperature
determine the incubation period. On and 70 per cent relative humidity. However,
hatching the larvae of rice weevil were the present findings do not agree with Khan
allowed to feed individually inside the seed. (1948) who found 12 days of incubation
20 grains per day were dissected to observe period at 15Ԩ temperature and 50 per cent
the different stage of larvae. Larval instars relative humidity. Nakakita and Ikenaga
were determined by the presence of moulted (1977) reported that hatching was
skin and range of head capsule width as completely affected at 10Ԩ temperature.
described by (Sharifi and Mills, 1971b). Therefore the observed variation in
Head capsule width was measured by using incubation period may be attributed to the
stage and ocular micrometer. Dissection of different levels of temperature and relative
the maize seed was continued till the humidity under which experiment were
appearance of pupal stage. Twenty seeds carried out.
with eggs of rice weevil obtained in afore
said manner were dissected out daily till the Larva: Under laboratory conditions, there
emergence of adults. Pupal period was were three moults and four instars. Larval
development took place inside the grain.
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Grub is apodous, short, stout, yellowish 9 to 11 days with an average of 10 days
white in colour with brown coloured head. (Table 1). Head capsule width of this instar
There are 13 segments with nine pairs of was 0.55 mm to 0.65 mm with an average
spiracles one pair in thoracic region and the 0.60 mm (Table 2) and body length ranged
rest on abdominal segments. Body is from 1.90 mm to 2.30 mm with an average
covered with small setae. Larval period of 2.10 mm.
ranged from 22 to 34 days with a mean of
27.60 days (Table 1). Larval period varied with
temperature and relative humidity. During
First instar : On hatching, grub entered into the present investigation there were three
the grain directly by feeding on starchy moults with four instars, each stage
material. Duration of first instar ranged from occupying 4.80, 7.10, 9.07 and 10 days,
4 to 6 days (Table 1) with an average of 4.80 respectively and the total larval period
days. Head capsule width of first instar grub occupied 22 to 34 days with an average of
ranged from 0.28 to 0.33 mm with a mean 27.60 days. These results are in closer
0.31 mm (Table 2) and body length agreement with Bheemanna (1986) who
measured from 0.57 to 0.62 mm with a mean reported, 25 to 34 days of larval period on
of 0.59 mm. CSH-5 sorghum genotype with four larval
instars. The present findings are in contrary
Second instar : There was slight increase in with the findings of Bhuiyah et al. (1990)
size with head retracted. The larva looked who reported that larval period ranged from
more plumpy and it resembled first instar. 16 to 20 days in maize seeds. The possible
The duration of second instar occupied 6 to reason for variation may be attributed to
8 days with a mean of 7.10 days (Table 1). temperature and relative humidity regimes
Head capsule width of second instar grub during the investigations.
measured 0.32 to 0.40 mm (Table 2) with an
average of 0.36 mm and the body length was Pupation took place inside the grains.
0.87 to 0.92 mm with an average of 0.89 Pupal period varied from 8 to 11 days with
mm. an average of 9.50 days (Table 1) at 15 to 34
Ԩ temperature and 58 to 89 percent relative
Third instar : Larva increased markedly in humidity. The findings of Bhuiyah et al.
size as compared to first and second instar (1990) lend support to the present results as
with well retracted head. The larvae they also reported 8 to 9 days of pupal
remained inside the grain in curved position. period at 23 to 30 Ԩ temperature 78 to 87
The third instar occupied 8 to 10 days with per cent relative humidity. In contrast to
an average of 9.07 days (Table 1). Head present findings Sharifi and Mills (1971 b)
capsule width of this instar ranged from 0.42 reported 6.3 days of pupal period on wheat
to 0.52 mm (Table 2) with an average 0.48 grains by radiographic method Lopez-
mm and body length ranged from 1.15 mm Cristobal (1953) reported 6 to 16 days of
to 1.25 mm with an average of 1.20 mm. pupal period. The variation in pupal period
may be attributed to varying temperature
Fourth instar : Fourth instar larvae was and relative humidity and change in the host
more or less similar to the third instar larva as well.
except for the size. The grub at this stage
was quite inactive and remained in curved After emergence adults remained
position. Duration of this instar ranged from inside the grains for 1 to 2 days. Newly
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emerged adults were reddish brown in egg scooped on the grain and turned back to
colour, which gradually turned to black in deposit the egg and scooped portion was
due course of time. Adult were elongate, covered with gelatinous material. Similar
sub-cylindrical and having four orange kind of observations were made by
coloured patches on elytra. Externally both Bheemanna (1986) and Sattigi et al., (1987).
male and female looked alike but on closer
observation, the rostrum of the male was Fecundity and Adult longevity : Normally,
comparatively thick, closely punctured females deposited single egg on each grain,
rough and less curved, while in female it however, two eggs on a grain were also
was elongate, slender smooth, shining, found occasionally. The fecundity ranged
slightly curved and sparsely punctured. from 12 to 84 with an average of 56.50.
Head is prolonged into snout and at the tip Most of the eggs were laid during first week
mouthparts are situated. Antennae were of oviposition period (Table 1).
short and geniculate type. The adults were
similar to the description made by Khan Without food adult females survived
(1948) and Halstead (1963). only for 8 to 16 days with an average of
10.50 days, while, males survived for 6 to
Total life cycle : Total life cycle from egg to 11 days with an average of 8.44 days. With
adult took 34 to 49 days with an average of food, adult females survived for 86 to 122
42 days at 15 to 34Ԩ temperature and 58 to days with an average of 116.33 days but
89 per cent relative humidity (Table 1). males survived for 72 to 117 days with an
These findings are in agreement with Howe average· of 97.86 days (Table 1). These
(1952) and Bheemanna (1986) who made observations are in agreement with Bhuiyah
similar observations. et al., (1990) who reported that longevity of
adult males and females with food was 114
Pre-mating, Mating, Pre-oviposition and to 115 and 119 to 120 days, respectively.
Oviposition period : The pre-mating period
observed during present study ranged from 5 CONCLUSION
to 8 days with an average 6.50 days. The
mating of the weevil was observed during On stored maize grains, Sitophilus
day time from 9.00 am to 6.00 pm. Hot sun oryzae has taken an incubation period of
shine seem to favour mating. The mating 5.10 days, larval and pupal period of 27.60
period ranged from 35 to 70 minutes with an days and 9.50 days, respectively. The
average of 56 minutes (Table 1). fecundity was 56.50 eggs per female and the
total life cycle was 42 days from egg to
The pre-oviposition period ranged adult.
from 8 to 11 days with an average of 8.65
days on maize grains. The oviposition ACKNOWLEDGEMENT: The authors
period ranged from 9 to 29 days with an are thankful to National Seed Project, UAS,
average of 25 days on maize grains (Table GKVK, Bangalore for providing research
1). The female adult before depositing the and lab facilities during the study period.
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Table 1: Biology of rice weevil, S. oryzae on stored maize grains
Parameters Duration
Incubation period (days) 5.10±0.95
First instar (days) 4.80±0.92
Second instar (days) 7.10±0.88
Third instar (days) 9.07±0.90
Fourth instar (days) 10.00±0.99
Total larval period (days) 27.60±5.23
Pupal period (days) 9.50±1.47
Total life cycle (days) 42.00±7.44
Pre-mating period (days) 6.50±1.54
Mating period (minutes) 56.00±18.55
Pre-oviposition period (days) 8.65±1.33
Oviposition period (days) 25.00±6.45
Adult longevity of female with food (days) 116.33±15.35
Adult longevity of male with food (days) 97.86±18.75
Adult longevity of female without food (days) 10.50±3.65
Adult longevity of male without food (days) 8.44±2.15
Fecundity (number) 56.50±25.66
n=25
Table 2: Morphometric parameters of different larval instars of S. oryzae
Larval stages Head capsule width (mm) Body length (mm)
First instar 0.31±0.02 0.59±0.03
Second instar 0.36±0.04 0.89±0.02
Third instar 0.48±0.04 1.20±0.05
Fourth instar 0.60±0.01 2.10±0.02
n = 10 of each instar
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