Biology Reference
In-Depth Information
Table 18.6 Comparison of the effectiveness of ALA + Dpy light sprays with dark sprays in T . ni
Experiment
Treatment a
Larval death after 3 days in the greenhouse (%)
DSP b control
A
21
DSP treated
90
change c
DSP
Δ
69
LSP d control
B
25
LSP treated
94
LSP
Δ
change
69
DSP b control
C
14
DSP treated
93
DSP Δ change
79
D
LSP control
5
LSP treated
83
LSP Δ change
78
Adapted from Rebeiz et al. 1988a
a Treatment was either by spraying with 20 mM ALA + 15 mM Dpy (A and B) or by spraying with
40 mM ALA + 30 mM Dpy (C and D) at a pH of 3.5 and a rate of spray equivalent to 40 gal per
acre. First instar larvae were used
b DSP ¼ dark spray
c
Δ change ¼ control - treated
d LSP ¼ light spray
18.3 Use of 1,10-Orthophenanthroline (Oph)
as a Porphyric Insecticide Modulator
During preliminary evaluation of the mode of action of Putative photodynamic
herbicide modulators (Rebeiz et al. 1988b ) it was observed that all modulators
that exhibited significant herbicidal activity fell in two major groups: (a) a group
that enhanced the conversion of ALA to Proto, hence its designation as a “primitive
modulator group”, since Proto is an early precursor of chlorophyll (Chl) in plants, and
(b) a group that enhanced the conversion of ALA to Pchlide, one of the terminal
precursors of Chl, hence its designation as an “advanced modulator group”. Since
insects and plants share the same porphyrin-heme biosynthetic pathway between ALA
and Proto it was conjectured that primitive photodynamic herbicide modulators may
also exhibit significant porphyric insecticidal properties.
It was also observed elsewhere that 1,10-orthophenanthroline (Oph) is an espe-
cially potent primitive photodynamic herbicide modulator, which induced the
formation of massive amounts of Proto and Mg-Proto in a variety of weed species
(Rebeiz et al. 1991 ). It was therefore a good candidate for additional investigation
of its potential porphyric insecticidal properties.
18.3.1 Porphyric Insecticidal Properties
of 1,10-Phenanthroline (Oph)
In initial experiments, third instar T . ni were sprayed with 40 mM ALA with and
without 30 mM Oph. After 17 h of dark-incubation some of the treated larvae were
 
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