Biology Reference
In-Depth Information
Table 15.12. Insect growth regulatory activity of the ethyl acetate, MeOH and n -hexane extracts from
C. microphylla , Me-Ced and gedunin against S. frugiperda larvae in a not-choice bioassay a .
7 Days
21 Days
Pupation
Treatment
GWI 50 b
GLI 50 c
MC 50 d
EI 50 b
pI 50 e
PI 50 f
n -Hexane
8.6
5.3
3.9
0.55
0.26
3.46
Ethyl acetate
3.1
3.1
9.7
0.77
0.11
2.11
MeOH
4.0
8.4
3.5
3.10
0.49
4.62
Gedunin
2.7
5.9
27.9
0.66
0.18
9.96
Me-Ced
5.5
14.5
7.8
13.4
1.13
12.4
a The parameters in ppm values. b The GWI 50 and EI 50 correspond to the growth inhibition in weight at 7 and 21 days,
respectively, and were calculated as the dose corresponding to midpoint between complete inhibition (100% of control)
and no effect by the computer program ANOVA ( p <0.05) under Microcal Origin 6.1. c GLI 50 corresponds to the growth
inhibition in length at 7 days and was calculated as the dose corresponding to midpoint between complete inhibition
(100% of control) and no effect by the computer program ANOVA ( p <0.05) under Microcal Origin 6.1. d MC 50 is the
concentration producing 50% mortality. e pI 50 corresponds to -log EI 50 . f PI 50 corresponds to concentration producing 50%
of pupation and was calculated as the dose corresponding to midpoint between complete inhibition (100% of control)
and no effect by the computer program ANOVA ( p <0.05) under Microcal Origin 6.1.
the pI 50 values are very low for n- hexane
(0.26) and ethyl acetate (0.11), for instance.
(Halse et al. , 1993; Delgado et al. , 2011).
Because they have activity on morphologi-
cal (moulting) processes, it is possible that
they act in similar manner to structures
such as ecdysteroids but with a new mode
of action. Its action is similar to juvenile
hormone mimics that occur in higher
plants. However, this extract from C. micro-
phylla with similar activity to known juve-
nile hormone mimics does not have exactly
the same chemical structure as phyto-
ecdysteroids. As mentioned, there is an
ample body of literature about biological
activities of phytoecdysteroids (Simon and
Koolman, 1989; Sláma and Lafont, 1995;
Schmelz et al. , 1999; Saez et al. , 2000;
Savchenko, et al. , 2000; Dinan, 2001), but
there are no reports about insecticidal
activity of extracts from C. microphylla
species with this type of activity, and this
is the first report about insecticidal activ-
ity in this species.
15.5.15 Growth inhibition and
relative growth index for S. frugiperda
Larvae reaching the pupal stage in the
groups of lowest concentration either do
not pupate or emerge from pupae with
deformities. Thus, in all treatments the
average time to reach the mean weight of
the adult stage relative to the time needed
for control larvae to reach the adult stage
was significantly delayed. The growth
index (GI or number of surviving larvae/
total larvae used) and relative growth
index (RGI or GI treated /GI control ) (Table
15.13) show that the strongest effects are
between 2.0 and 10.0 ppm by n -hexane
extract (RGI 0.25), and at 25 ppm by
methanol (RGI 0.25). These parameters,
together with the LD 95 (the lethal dose
producing 95% of death) and LD 50 values,
established that the greatest effects were
shown at 25.0 ppm by n- hexane (100%
mortality), and by ethyl acetate and meth-
anol at 35.0 ppm, respectively (100%
mortality).
Interestingly, the phytochemical com-
position of the n- hexane extract of this study
is mainly long-chain n- alkanes (Table 15.8)
15.5.16 Acute toxicity on last-stage
larvae of S. frugiperda and T. molitor
In order to determine a possible correlation
between IGR, acute toxicity and moulting
disruption caused by these extracts, oral
injections of 2, 10, 25 and 50 ppm of all
extract samples into ten larvae of 21 days, of
 
 
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