Porphyric Insecticides - Chlorophyll Biosynthesis and Technological Applications - page 411

Table 18.7 Effect of ingested ALA, Oph AND Dpy on the biosynthesis and accumulation of
Proto and Zn-Proto and on the extent of larval death in T. ni a

Proto content Zn-proto content

Larval death b
(%)

Experiment Treatment (nmol/100 mg protein)

A Control 0.0 0.0 14.5

16 mM ALA 1.5 0.0 5.2

12 mM Oph 88.1 1.3 40.4

16 mM ALA + 12 mM Oph 224.6 1.5 94.4

B Control 0.0 0.0 4.5

16 mM ALA 2.6 0.0 4.7

12 mM Oph 14.3 1.9 51.4

16 mM ALA + 12 mM Oph 160.2 2.0 95.4

C Control 0.4 0.0 18.2

16 mM ALA 3.1 0.0 49.3

12 mM 2,2 0 -Dpy 20.3 8.8 11.4

16 mM ALA + 12 mM 2,2 0 -Dpy

55.2 11.4 100.0

Correlation between pigment content and larval death 0.703 0.721

Level of significance 2.1 % 0.9 %

Adapted from Rebeiz et al. ( 1990a )
a Third instar larvae were placed on control and baited diets and held for 17 h in darkness.
The larvae were then sampled for tetrapyrrole content, and placed in the light for observation of
photodynamic injury
b Refers to larval death at the beginning of the fourth photoperiod, i . e . after 3 days in the growth
chamber

18.3.4 Insecticidal Effectiveness of Ingested ALA

and Oph or Dpy

Since control of insects by ingestion is as viable an option as control by spraying,
and offers certain advantages under household conditions, studies were conducted
to determine whether combinations of ALA and porphyric insecticide modulators
would be effective if ingested with the food. Initially the effect of ALA (16 mM
final concentration) and Oph (12 mM final concentration) were determined by
incorporating them into the diet of T . ni larvae. Upon exposure to light, following
17 h of dark incubation, larvae underwent violent convulsions and vomiting and
died within 20-40 s. Tetrapyrrole analysis of the treated larvae immediately after
dark incubation revealed significant amounts of Proto and Zn-Proto accumulation.
Correlation between tetrapyrrole accumulation and larval death was significant
(Table 18.8 , A). Similar results were obtained when ALA and Dpy were admini-
stered to the larvae with the diet (Table 18.8 , C). The above results indicated that
in addition to contact via spraying, porphyric insecticides had the potential to be
very potent when ingested.