Porphyric Insecticides - Chlorophyll Biosynthesis and Technological Applications - page 414

Table 18.9 Effect of various concentrations of added FeCl 3 on Proto accumulation and
photodynamic damage in third instar T . ni larvae

Larval death
(%) Treatment Proto content (nmol/100 mg protein)

1 mM ALA 1.1 0.0

1 mM ALA 0.5 mM Oph 46.7 74.0

1 mM ALA + 0.5 mM Oph + 0.5 mM FeCl 3 11.2 14.7

1 mM ALA + 0.5 mM Oph + 1.0 mM FeCl 3 2.1 6.7

1 mM ALA + 0.5 mM Oph + 2.0 mM FeCl 3 0.8 1.3

Adapted from Rebeiz et al. ( 1990a )

All three cations were effective in blocking porphyric insecticidal damage in the
following order Fe +++ Zn ++ (Gut et al. 1993 ). Table 18.9 summarizes the

effects of various concentrations of FeCl 3 on Proto accumulation and photody-
namic damage in third instar T . ni .FeCl 3 strongly inhibited Proto accumulation and
photodynamic damage. The inhibitory action of this metallic cation is further proof
that insecticidal photodynamic damage is a Proto-dependent phenomenon.

Fe ++

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18.4 Tissue Cellular and Subcellular Sites of Tetrapyrrole
Accumulation in Various Insect Tissues

For a more thorough understanding of the mode of action of porphyric insecticides,
the phenomenology of tissue, cellular and subcellular sites of tetrapyrrole accumu-
lation in representative insect species was investigated.

18.4.1 Site of Tetrapyrrole Accumulation
in Sprayed T. ni Larvae

To determine the site of tetrapyrrole accumulation in T . ni larvae sprayed with ALA
(40 mM) + Dpy (30 mM), the integument, hemolymph and gut of sprayed early
fifth instar larvae were separated and analyzed for pigment content. On a unit
protein basis, about 59 % of the accumulated Proto was observed in the hemo-
lymph, 35 % in the gut and 6 % in the integument (Lee and Rebeiz 1995 ).

18.4.2 Tissue and Organ Response to Porphyric
Insecticides in Several Insect Species

Further understanding of the response of insect organs and tissues to porphyric
insecticide treatment was obtained by investigating the response of isolated organs