Intl. J. of Molecular Zoology, 2013, Vol.3, No.4, 14
-
16
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15
Table 1 Effect of pesticides on metamorphosis of silkworm
bombyx mori
(
Percentage (%) change over control given in parenthesis)
Pesticide
Concentration
Surviving larvae
(
at 5
th
day)
Normal pupae
Larval Pupal
intermediates
No. of emerged
moths
Deformed
moth
Control
-
99
98
0
96
0
Dichlorovos
0.0001
n = 100
95
( 4.04)
94
( 4.25)
1
92
( 4.34)
2
0.0002
n = 100
90
(6.06)
83
(15.30)
2
84
(12.5)
3
0.0003
n = 100
81
(18.18)
79
(19.38)
1
73
(23.95)
5
0.0004
n = 100
78
(21.2)
73
(25.51)
4
67
(30.21)
6
0.0005
n = 100
75
(24.24)
70
(28.57)
5
61
(36.46)
8
Vijay neem
0.0010
n = 100
90
(9.09)
87
(11.22)
1
85
(11.45)
2
0.0020
n = 100
86
(13.13)
83
(15.30)
2
75
(19.79)
6
0.0030
n = 100
77
(22.22)
73
(25.51)
4
65
(32.29)
8
0.004
n = 100
70
(29.29)
61
(37.75)
8
48
(50.00)
13
0.0050
n = 100
64
(35.35)
56
(42.85)
8
41
(57.29)
15
Dose dependent inhibition of larval growth and
morphogenesis in silkworm
Bombyx mori
could be
accounted due to reduced physiological change
brought about by reduced food intake and weight
gains as reported in
Heliothis virescens
(
Barnby and
Klocke, 1989, Joseph, 2000). The present study
revealed that 4.04% of larval mortality was due to
0.0001%
concentration of Dichlorovos. In the neem
pesticide sprayed leaves fed larvae the mortality rate
was 9.09% for a concentration of 0.001% and 35.35%
for a concentration of 0.005. Similarly a dose dependent
reduction was noticed in the moth emergence. Moth’s
emergence rate was reduced to 11.45% for a
concentration of 0.001% and a reduction of 57.29%
was noticed for a concentration of 0.005%. From the
present study it was found out that among the two
pesticides, neem pesticide has a more lethal effect
than Dichlorovos (Table 1). The two pesticides had an
impact on the development of normal pupae also. The
reduction in the development was found to be dose
dependent. The development rate was reduced to
4.25%
for a concentration of 0.0001% Dichlorovos
and 28.57% for a concentration of 0.0005% Dichlorovos.
The development of normal pupae was more affected
in the case of larvae fed with neem sprayed leaves. A
maximum of 42.85% reduction in the development
rate was noticed for a concentration of 0.005 neem
pesticide (Table 1).
In the present study, pesticides caused a lower
percentage of pupation and adult emergence in treated
insects in conjunction with increased pupal and adult
abnormalities. This was in acceptance with the
findings of Nagapasupathy et al. (2005) (Schmutterer,
1990;
Tiwari et al., 2006). The silkworm larvae fed
with pesticides treated foliage resulted in persistant
growth inhibition at different levels of metamorphosis
when compared to
Dichlorovos Vijay
neem showed
much morphogenetic inhibition effect.
2
Materials and Methods
Eggs of the silk worm breed LXCSR2 were procured
from Government sericulture grainage at Tenkasi,
Tamilnadu and were raised up to 3
rd
instar in a rearing
house. Controlled temperature (24
℃-
27
℃
)
and humidity
(75%
-
80%)
were maintained and appropriate measures
were taken to prevent parasitization by uzifly. The
silkworms were fed with mulberry leaves and standard
rearing practices were followed (Krishnaswami et al.,
1971).
Two pesticides (
Dichlorovos
,
Vijay
neem) were
used for this experiment. III instars (soon after the
second ecdysis) of uniform size from a pooled batch
were divided into eleven groups of 100 larvae each.