Biology Reference
In-Depth Information
Table 15.13.
GI and RGI of
S.
frugiperda
as a function of increased concentrations of ethyl acetate,
MeOH and
n
-hexane extracts from
C. microphylla
, Me-Ced and gedunin.
a
Compounds
Concentration (ppm)
GI
b
RGI
c
Control
0.99 ± 0.045
a
Me-Ced
2.0
0.99 ± 0.050b
1.00
10.0
0.84 ± 0.085b
0.85
25.0
0.75 ± 0.031b
0.75
50.0
0.69 ± 0.055b
0.70
Ethyl acetate
2.0
0.75 ± 0.031b
0.75
10.0
0.59 ± 0.040b
0.60
25.0
0.25 ± 0.035c
0.25
50.0
0.00
0.00
MeOH extract
2.0
0.99 ± 0.050b
1.00
10.0
0.69 ± 0.055b
0.70
25.0
0.25 ± 0.040b
0.25
50.0
0.00
0.00
Hexane extract
2.0
0.25 ± 0.015c
0.25
10.0
0.03 ± 0.015c
0.03
25.0
0.00
0.00
50.0
0.00
0.00
Gedunin
10.0
0.77 ± 0.060b
0.77
25.0
0.51 ± 0.040b
0.51
50.0
0.10 ± 0.010c
0.10
a
Mean of three replicates.
b
Means followed by the same letter within a column after ± standard error values are not
significantly different in a Student-Newman-Keuls (SNK) test at
p
<0.05 (treatments are compared by concentration to
control).
c
RGI
treatment
= GI
treated
/ GI
control
.
15.5.17
Insect growth inhibitory activity
against
T. molitor
S. frugiperda
and of 25 days, of
T. molitor
,
was carried out (Table 15.14). At 2.0 ppm of
n
-hexane extract apolysis was promoted to
the fifth instar but moulting was inhibited,
whereas oral injection at 10.0 ppm resulted
only in a delay of the normal moult to the
fifth instar. Increasing the oral dose of
three extracts (
n
-hexane, ethyl acetate and
methanol) to 10, 25 and 50 ppm induced the
appearance of precocious pupal structures in
the larvae (prothetely) (Marks, 1980), in some
cases (>30%) of the treated fourth instar lar-
vae. These larvae moulted directly to pupae.
As mentioned, prothetely can sometimes be
elicited experimentally in larvae by appli-
cation of juvenile hormone or juvenile hor-
mone mimics (Truman and Riddiford, 2002).
Thus,
n
-hexane extract induced prothetely
expressed in precociousness, browning and
death of pupae and in a high adult mortality
(data not shown). Consequently,
n-
hexane
extract exhibited 100% larval mortality and
gave the highest insecticidal activity.
The
n-
hexane extract caused a strong
decrease in the number of larvae of
T. molitor
that reach pupation (45% at 5.0 ppm), and
ethyl acetate extract has this same effect
without significant differences (39% at 2.0
ppm) (Table 15.15). With these extracts, as
well as methanol, the larvae had a briefer
time of pupation and emergence; however,
many of the pupae were not viable and died
(Table 15.15). At higher levels (>10 ppm)
these extracts exhibited potent acute toxicity
on larvae and pupae of
T. molitor
. In addition
to a shorter pupal stage for those pupae that
emerged, many pupae did not emerge. That
effect was observed at 10, 25 and 10 ppm for
n
-hexane,
methanol
and
ethyl
acetate
extracts, respectively (Table 15.15).
These results suggest that compounds
in
n-
hexane and ethyl acetate extracts
from
C. microphylla
have effects on
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