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14
12
10
8
6
4
2
0
b
b
a
a
n.d.
Control
CH
2
CI
2
(1000)
CH
2
CI
2
(100)
50% EtOH
(1000)
50% EtOH
(100)
Fig. 13.5.
Delays in development. PT
50
(Pupariation time 50%): time necessary for 50% of the individuals
under study to pupariate. a and b, significant differences with respect to control (
p
<0.05). n.d., not determined.
120
c
100
c
c
80
b
b
60
40
20
a
0
Extract or fraction
Fig. 13.6.
Pre-pupariation mortality. a, b and c, significant differences with respect to control (
p
<0.05).
development of the moth
Helicoverpa
punctifera
. These authors did not determine
whether the insecticidal activity was due to
a toxic effect of the cyclotide or to an anti-
alimentary effect leading to death by starva-
tion of the insect. Kalata B1 also presented
haemolytic activity; this effect would
explain the insecticidal activity by damage
to the membranes of the insect's gut. It
should also be borne in mind that insects
have digestive proteases located in the mid-
gut that catalyse the release of peptides and
amino acids from the ingested proteins
(Jongsma and Bolter, 1997). Lepidopterous
and Dipterous insects, such as
C. capitata
,
employ serine proteases to digest proteins.
These insects have a midgut with an opti-
mum pH for this enzymatic activity
(pH 8-11.5). A plant defence mechanism
involves the synthesis of protease inhibi-
tors. These inhibitors are proteins that can
be constitutively found in many plant
organs or can be induced as a response to
the attack by herbivorous organisms, acting
at the intestinal level of the insect to inhibit
the digestion of plant proteins. Although
Kalata B1 and B2 do not have any effect on
trypsin, chymotrypsin or a amylase of
Helicoverpa
, the cyclotides TI-I and TI-II
are the first ones of the trypsin inhibitors
subgroup that have been identified (Hernandez
et al
., 2000) and display homology with a
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