Biology Reference
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the highest mortality percentage, with 94.5%
at 10 ppm after 72 h. The same extract
showed a mortality of 100% at concentra-
tions above 25 ppm (Table 15.10).
Additionally, the effects of ethyl acetate,
methanol and
n-
hexane extracts on growth
and development of first instar larvae of
S. frugiperda
were evaluated initially at
concentration of 2.0 ppm; the results are
outlined in Table 15.11. Interestingly, meth-
anol and ethyl acetate extracts induced a
significant decrease in larval survival at
7 days. After 21 days the number of larvae
and pupae decreased drastically in all treat-
ments. When pupation did occur, serious
abnormalities were observed, and this phe-
nomenon was observed in similar form to
D. melanogaster
, where ecdysis and sclero-
tization were incomplete.
In not-choice experiments against first
instar larvae of
S. frugiperda
and four instar
larvae of
D. melanogaster
during the first 6 days,
the effects of the ethyl acetate and methanol
extracts were 100% lethal at concentrations
greater than 50 ppm (data not shown). The con-
centrations that show 95% lethal doses (LD
95
)
of these extracts against
S. frugiperda
were:
methanol (31.0 ppm),
n
-hexane (27.0 ppm)
and ethyl acetate (42.0 ppm).
15.5.12
Antifeedant activity against
S. frugiperda
The methanol,
n-
hexane and ethyl ace-
tate extracts of
C. microphylla
showed a
high feeding dissuasive activity against
S. frugiperda
larvae in the election assays
(Table 15.9). The consumption of leaves
treated with these extracts was significantly
lower than in the controls and, in the case of
the
n-
hexane extract, there were high levels
of feeding inhibition, according to Hassanali
and Lwande (1989). With the ethyl acetate
extract, just a significant reduction of
the consumption was observed; therefore,
the effect of this extract, on the larvae can
be considered as moderate. The methanol
extract at 10 ppm showed a reduced to mod-
erate effect (66%) and the most active extract
was always
n
-hexane with 75% showing
high deterrence power.
15.5.13
Insecticidal activity
Not-choice assays showed that three of
four extracts possessed a lethal effect on the
T. molitor, S. frugiperda
and
D. melanogaster
larvae (Table 15.10). Against
S. frugiperda,
the extracts of
n
-hexane, ethyl acetate and
methanol at 10 ppm showed 80, 70 and 70%
of mortality effect, respectively. Against
T. molitor
at 10 ppm only
n-
hexane at 10 ppm
showed a significant effect with a high
percentage of mortality (73.5%). Against
D. melanogaster
the
n-
hexane extract showed
15.5.14 Insect growth inhibitory activity
against
S. frugiperda
larvae
Intermediate concentrations (between 10.0
and 25.0 ppm) of extracts specifically
Table 15.9.
Antifeedant inhibition (AI) obtained from antifeedant election tests, using different
concentrations of extracts of
C. microphylla
on
S. frugiperda
larvae.
Concentration
[ppm]
Ethyl
Acetate
Control
Aqueous
n
-Hexane
MeOH
Me-Ced
Gedunin
1
0
−5
5
5
13
5
21
5
0
−10
20
25
33
25
33
10
0
−15
40
75
66
37
45
25
0
−40
80
80
79
62
51
50
0
−51
85
98
90
89
89
100
0
−79
90
100
100
99
95
Results expressed as AI(%) = Antifeedant inhibition = [(1−T/C) × 100]. Control contains only solvent (Ethanol 15%);
Me-Ced and gedunin were used as positive controls.
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