Biology Reference
In-Depth Information
shows that three of four extracts possesses a
lethal effect on the
D. melanogaster
larvae
(Table 15.4). Against
D. melanogaster,
ver-
bascoside, gedunin, the extracts of ethyl
acetate and methanol at 20 mg/ml showed
92.0, 87.1, 67.0 and 65.0% of mortality
effect, respectively, and at concentrations of
50 and 100 mg/ml the percentage of mortal-
ity of the larvae after 72 hours was 100%
for verbascoside, gedunin, ethyl acetate and
methanol extracts.
out that ethyl acetate, possessing an LD
95
of
20.0 mg/ml, was more active as an insecti-
cide than gedunin or any of the three extracts
(Me-Ced, Me-Myrt and Me-Yuc) used as
positive controls.
15.5.6 Insect growth inhibitory
activity for
S. frugiperda
larvae
At intermediate concentrations of extracts
(10.0 to 35.0 mg/ml) specific inhibition of
each larval growth stage, e.g. growth and
weight gained (up to 75% of length), was
observed (Table 15.5). Moreover, ethyl acetate
extract produced the strongest inhibition
(11.5 and 11.1%, at 10.0 and 20.0 mg/ml,
respectively) of growth and weight increase
15.5.5
Insecticidal activity against
larvae of
S. frugiperda
The effects of methanol extracts of
C. talcana
on growth and development of larvae of
first instar of
S. frugiperda
was evaluated
initially at a concentration of 100 mg/ml.
The results for
S. frugiperda
larvae are out-
lined in Table 15.5. Interestingly, at 21 days
the number of larvae and pupae decreased
drastically in all treatments. For example, at
a concentration greater than 35.0 mg/ml for
n
-hexane, 20.0 mg/ml for ethyl acetate and
to concentrations greater than 10.0 mg/ml
for methanol extracts the pupation was very
low (Table 15.5). When pupation did occur
serious abnormalities were observed, and
this phenomenon was observed in similar
form to
D. melanogaster
, ecdysis and sclero-
tization were incomplete. Ultimately, all
pupae under ethyl acetate and methanol
treatments died at concentrations above
35.0 mg/ml (Table 15.5).
In experiments of not-choice carried
out against larvae of first instar of
S. fru-
giperda
and neonate larvae of
D. mela-
nogaster
during the first 6 days, the effects
of the ethyl acetate and methanol extracts
were 100% lethal at concentrations greater
than 35.0 and 20.0 mg/ml, respectively,
whereas verbascoside and gedunin were
100% lethal at concentrations greater than
10.0 and 50.0 mg/ml, respectively. The 95%
lethal doses (LD
95
) of these extracts against
S. frugiperda
are: methanol (20.0 mg/ml),
hexane (95.0 mg/ml) and ethyl acetate (20.0
mg/ml). Thus, methanol, ethyl acetate
extracts and verbascoside all exhibited
100% larval mortality and gave the highest
insecticidal activity. It is important to point
Table 15.4.
Mortality percentage of
D. melanogaster
larvae, after 72 h of the application of the extracts at
different concentrations in larvae's diet.
Concentration
(
m
g/ml)
Extract
Mortality (%)
LC
50
control
0.0
Aqueous
10
0.0
20
0.0
50
0.0
100
0.0
Ethyl acetate
10
13.3 ± 0.6a
17.25
20
67.0 ± 0.6b
50
100 ± 1.0c
100
100 ± 1.0c
Hexane
10
7.0 ± 0.6a
43.2
20
13.3 ± 0.6a
50
63.3 ± 0.6b
100
100 ± 1.0c
Methanol
10
30.0 ± 1.5b
15.5
20
65.0 ± 3.4b
50
100 ± 4.47c
100
100 ± 4.47c
MeOH-Yuc
20
55.5 ± 1.9b
17.04
50
90.5 ± 2.9c
100
100 ± 3.7c
Verbascoside
20
92.0 ± 2.7c
8.08
50
100 ± 1.7c
100
100 ± 1.1c
Gedunin
20
87.1 ± 3.9c
11.93
50
100 ± 2.0c
100
100 ± 1.1c
Each value corresponds to the average of the three
different experiments ± SE. The values followed by the
same letter are not significantly different. The significance
level is
p
<95%. The LC
50
are expressed as
m
g/ml.
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