Porphyric Insecticides - Chlorophyll Biosynthesis and Technological Applications - page 402

Fig. 18.1 Room temperature emission spectra in hexane-extracted acetone of T . ni larvae treated
with ALA + Dpy or with solvent only (control). Third instar larvae were treated with 40 mM
ALA + 30 mM Dpy, or solvent only and placed in darkness at 28 C for 17 h. Control and
ALA + modulator-treated larvae were homogenized in ammoniacal acetone. Excitation was at
400 nm. The spectra were recorded at emission and excitation slits of 4 nm. ( a ) Hexane-extracted
acetone extract of control larvae; the emission peak at 674 nm is that of pheophorbide a; ( b ) extract
of treated larvae; ( c ) authentic Proto in hexane- extracted acetone (Reproduced from Rebeiz
et al. 1988a )
and significant larval mortality after three photoperiods (Table 18.1 ). A high degree
of correlation was observed between Proto accumulation in darkness and larval
death in the light (Table 18.1 ). A few hours after exposure to light, the larvae
became sluggish and flaccid due to loss of body fluids. Death was accompanied by
extensive desiccation (Fig. 18.2 ).
In follow-up experiments, third instar T . ni were sprayed with ALA + Dpy, and
the treated larvae were placed in darkness overnight to allow for Proto accumula-
tion. While some larvae were exposed to light to trigger photodynamic death, others
were left in darkness for an equal period of time. It was observed that some larval
death occurred during the overnight dark incubation before exposure to light
(Table 18.2 , A2, B2).
At that time the cause of this dark-death phenomenon was not understood. Later
on, a hypothesis was proposed explaining the molecular basis of this dark-death.
The growth of larvae that survived the initial 17-h dark-incubation was not inhibited
by further dark incubation (Table 18.2 , A1, A2 and B1, B2). The bulk of larval
death occurred during illumination of treated larvae (Table 18.2 , A2-A4 and
B2-B4). During illumination the accumulated Proto disappeared probably as a