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both the insecticidal and IGR activity of
C. talcana
extracts.
Preceding experimental observations
suggest that insecticidal and growth inhibi-
tion of our extracts may be due to inhibi-
tion of a proteinase, ETH and other
polyphenol oxidases (PPO) that could bind
to these compounds. These targets have
been demonstrated for other compounds of
natural origin (Kessler and Baldwin, 2002;
Kubo
et al.
, 2003a,b; Céspedes
et al.
, 2005),
together with other examples such as the
insecticidal activity of extracts with similar
content of phenylethanoids from
Stachys
byzantine
(Asnaashari
et al.
, 2010) and the
antioxidant and cholinesterase inhibition
of
Verbascum xanthophoeniceum
(Georgiev
et al.
, 2011) among many other references
of the literature. We are working in the elu-
cidation and a dissection of the activities,
sites and mechanisms of action of these
extracts and compounds from
Calceolaria
species.
In summary, the insecticidal activity
of our extracts from aerial parts from
C. talcana
may be due to a synergistic effect
shown by the ecdysone-like activity of the
extracts in the test system used in this
investigation.
The sites and mode of action of these
extracts continue to be investigated and
probably correspond to a combination of
antifeedant action, which is known at the
molecular level that could have the fol-
lowing targets: midgut phenol oxidase,
proteinase, ETH, tyrosinase or other PPOs
and cuticle synthesis inhibition, as well
as moulting sclerotization toxicity, as has
been found for other natural compounds
(Kubo 1997; Céspedes
et al.
, 2000, 2006;
Kubo
et al.
, 2003a,b; Torres
et al.
, 2003;
Céspedes and Alarcon, 2011) and extracts
(Feng
et al.
, 1995).
15.5.19
Remarks for
C. talcana
These results suggest that the effective-
ness demonstrated by the ethyl acetate
extract could be due to a synergistic effect
of verbascoside in combination with
another anti-insect compound(s) present
in the extract or to the presence of a com-
pound with higher activity than verbas-
coside. Although verbascoside showed
effectiveness, its presence alone does not
fully explain the activity of the extract. In
order to answer this issue, we are cur-
rently conducting a bio-guided fractiona-
tion and the results will be published on
completion.
These plant extracts may be considered
to be efficient IGRs, as well as having simi-
lar activity to phytoecdysteroids, as was
evidenced by their significant inhibition of
moulting processes. They also had potent
insecticidal and growth inhibitory activi-
ties, probably because the absence of polar
compounds in the hexane extract results in
a significant loss of its IGR activity, as was
shown by the total phenolic content of
polar extracts (Table 15.16; Céspedes
et al.
,
2005, 2006, 2009). The most active ethyl
acetate extracts contain verbascoside as the
major compound (a phenylethanoid glyco-
side). Ethyl acetate and methanol extracts
had good potency that was comparable to
gedunin, Me-Yuc, Me-Ced and Me-Myrt
(Céspedes
et al.
, 2000, 2006, 2009; Torres
et al.
, 2003; Céspedes and Alarcon, 2011).
These findings suggest that the ethyl acetate
extract could play an important role in
Table 15.16.
Total phenolic content of
C. talcana
extracts.
Extract
Concentration
n
-Hexane
144.3 ± 12.5a
Ethyl acetate
578.9 ± 19.6b
Methanol/water residue
355.0 ± 15.8c
Verbascoside*
72.3 mg/g extract
15.6
Conclusions
Values are expressed as
m
mol catechin equivalent/g
extract. Values are the mean ± standard error from three
replicates (
n
= 3). Different letters show significant
differences at
p
<0.01, using the Tukey test. *The
concentration of verbascoside corresponds to mg of
compound per g of extract.
The effect of verbascoside, ethyl acetate and
methanol extracts on reducing insect
growth, increasing or shortening develop-
ment time, modifying the apolysis during
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