STUDIES ON BIOLOGY AND MORPHOMETRICS OF IMPORTANT SPODOPTERA SPECIES
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Date
2018
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PROFESSOR JAYASHANKAR TELANGANA STATE AGRICULTURAL UNIVERSITY
Abstract
The present study entitled “Studies on biology and morphometrics of important Spodoptera
species”was carried out at Department of Entomology, College of Agriculture, PJTSAU, Rajendranagar, Hyderabad
during 2017 - 2018.
During the period of study, biology and morphometrics of important Spodoptera
species viz., S. litura, S. mauritia and S. exigua on respective host (S. litura on castor, S.
mauritia on rice and S. exigua on chickpea) were documented under laboratory conditions.
With regard to S.litura the total life period lasted for 32.13±5.48 days with a fecundity of
890.50±16.26. S.mauritia took 38.37±4.62 days with a fecundity of 1013.10±21.92 eggs and
S.exigua 32.38±5.13 days with a fecundity of 308±25.46 eggs indicating the total development
period for Spodoptera spp in general ranging from 26.65 to 42. 99 days.
Observations on morphological variations in different stages of three species of
Spodoptera revealed a clear difference where eggs of S.litura were spherical in shape, yellowish
creamy in color covered with yellowish brown hairs, S. mauritia has spherical shaped eggs that
were green in color covered with greyish hairs and S.exigua had typically white colored eggs
covered with white scales giving a fuzzy or cottony appearance.
In the case of active feeding larval instar i.e., 3
rd and 4th instars which cause much crop
damage in the field, variation in the morphology was observed as, body color being dark green
dosally with large black spot on 1st and 8th abdominal segments and pale greenish yellow
ventrally in S.litura. The third instar larva has three yellowish bands which were not clear but
later in the fourth instar these bands became distinct with a central band being bright orange and
the lateral ones yellow in colour. In the case of S.mauritia, the third instar was pale green in
color with lateral reddish lines and fourth instar had three dull white longitudinal lines with black
intermittent dots on each segment arranged dorsally along the length of the body where as fifth
instar larvae became greenish black with prominent black triangular markings. In the case of
S.exigua, third and fourth instars were pale green in color with stripes on dorsal and lateral
surface of the body. Fifth instar larvae of S.exigua typically showed colour polymorphism
recording about 34 morphs ranging in colors from green, black, pink to yellow in combination.
Being different from S.litura and S.exigua, S.mauritia had sixth instar which was grayish black
in color having prominent wide and dark triangular markings dorso laterally
With regard to larval behavior while rearing in the laboratory during the period of study,
cannibalism was observed in S.exigua where the fifth instar larvae were observed feeding on
both the larvae and pupae of their own species.
In the present study, the arrangement of crochets on the planta of prolegs of three species
of Spodoptera was found to be uniordinal homoideous mesoseries. However, their arrangement
in a single row differed by being half circular with a deep curve in the inner line crochet
arrangement in S.litura, complete half circle in S.mauritia and half circle with slight deepness in
the lower line of crochets in S.exigua
Reddish brown to dark brown pupae were observed commonly both in S.litura and
S.maurita though the pupae were light brown in colour in S.exigua.
Adult female of S. litura was brown with crisscross cream colored streaks and male had
white prominent band on forewings. Where as in S. maurita, female had grayish brown
forewings with dark spot in the middle and male has bright grayish forewings. Typically male of
S.mauritia showed tuft of hairs on forelegs differing from S.litura and S.exigua. In the case of
S.exigua, forewings were mottled gray and brown in color with an irregular banding pattern and
light colored bean-shaped spot where females were brightly colored than males.
The morphometrics data showed that among the three species of Spodoptera, diameter of
the egg ranged from 0.41 to 0.56 mm being bigger in S.exigua as 0.56 and smaller in S.litura as
0.41 where as S. mauritia have 0.43. The body length and width from first instar to fifth instar
was 1.49 ± 0.09 mm and 0.23 ± 0.03 mm, 4.44±0.82 mm and 0.51±0.07 mm, 11.92±1.48 mm
and 1.49±0.06 mm, 23.15±0.55 mm and 3.44±0.87 mm and 37.72±0.45 mm and 5.94±1.47 mm,
respectively in S.litura. In the case of S.mauritia, first to sixth instar, body length and width was
1.30 ± 0.14 mm and 0.38 ± 0.07 mm, 2.64±0.28 mm and 0.51±0.02 mm, 5.56±0.22 mm and
1.23±0.16 mm, 16.50±0.23 mm and 2.30±0.12 mm, 27.00±0.10 mm and 3.49±0.28 mm and
36.50±0.08 mm and 5.60±0.45mm, respectively. In the case of S.exigua, body length and width
from first to fifth instar was 1.23 ± 0.16 mm and 0.27 ± 0.03 mm, 4.51±0.25 mm and 0.84±0.05
mm, 9.13±0.68 mm and 1.55±0.15 mm, 13.63±0.76 mm and 2.25±0.20 mm and 22.00±1.47 mm
and 3.37±0.41 mm, respectively.
Pupae were small being 12.00 mm in S.exigua and big in S.mauritia being 16.40 mm in
size where S.litura had medium size of 14.05 mm. Adults of S exigua was having less body
length and wing span ranging from 11.00 to 13.00mm and 25.00 to 26.00mm respectively.
However, S.mauritia was mediam in size having a body length of 16.00 to 18.00 mm and wing
span ranging from 30.00 to 34.00 mm. S.litura has a body length ranging from 15.50 to 17.50
mm and wing span of 37.00 mm.
With regard to growth ratio of Spodoptera species, S.litura has the growth ratio between
1
st and 2nd instar as 1.44, 2nd and 3rd as 1.38, 3rd and 4th as 1.40, 4th and 5th as 1.59. The average
ratio of increase in head capsule width in each instar was calculated as 1.45. Revealing
consecutive larval instars followed a more or less regular geometrical progression of 1.45. In the
case of S.mauritia, growth ratio between 1st and 2nd instar was 1.68, 2nd and 3rd was 1.52, 3rd and
4
th was 1.46, 4th and 5th was 1.98, 5th and 6th was 1.45 showing an average ratio of 1.62 for all the
consecutive larval instars. In case of S.exigua, growth ratio between 1st and 2nd instar was 1.41,
2
nd and 3rd was 2.61, 3rd and 4th was 1.05, 4th and 5th was 1.64 with an average of 1.68 which was
observed as slightly deviating from dyar’s law. In specific, it was 2.61 between 2nd and 3rd instar
deviating from the geometrical linear growth.
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D10,284