Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Previous studies have shown that phosphine (PH{dollar}\sb3{dollar}) inhibits cytochrome oxidase and that a direct relationship exists between oxygen concentration during fumigation and insect mortality. This study was undertaken to test the hypothesis that mortality is due to cumulative damage of cellular components by free radicals derived from superoxide (O{dollar}\sb2\sp\div){dollar} generated by the inhibited respiratory chain.;Hydrogen peroxide {dollar}\rm(H\sb2O\sb2),{dollar} a product a O{dollar}\sb2\sp\div{dollar} dismutation, was measured spectrophotometrically using yeast cyctochrome c peroxidase as an indicator. The respiratory inhibitors; PH{dollar}\sb3{dollar}, antimycin and myxothiazol stimulated the release of {dollar}\rm H\sb2O\sb2{dollar} from mitochondria isolated from granary weevils (Sitophilus granarius). Peroxide release increased with the addition of {dollar}\alpha{dollar}-glycerophosphate. It was concluded that glycerophosphate dehydrogenase was a source of {dollar}\rm H\sb2O\sb2{dollar}. The concentration of quinone, a major source of {dollar}\rm O\sb2\sp\div{dollar}, was low in granary weevils compared to other species and was unaltered after in vivo PH{dollar}\sb3{dollar}-treatment. Difference spectra, obtained using isolated inhibited mitochondria, provided information about sites of {dollar}\rm O\sb2\sp\div{dollar} generation.;The effect of PH{dollar}\sb3{dollar} on the antioxidant system of PH{dollar}\sb3{dollar}-sensitive (S) and resistant (R) insect was observed. Glutathione was not affected by fumigation (LD{dollar}\sb{lcub}70{rcub}{dollar}). Peroxidase activity, measured using p-phenylenediamine, was the same in S and R insects. After treatment (LD{dollar}\sb{lcub}30{rcub}{dollar}) activity was reduced by 65% in S and 45% in R insects. Catalase activity was significantly higher (62%) in S than R. It was inhibited by 34% in S insects after PH{dollar}\sb3{dollar} treatment (LD{dollar}\sb{lcub}30{rcub}{dollar}) but unaffected in R insects. Superoxide dismutase activity was the same in S and R insects. Two isozymes were present. After fumigation of S insects, activity of the cyanide-sensitive isozyme increased two-fold while the cyanide-insensitive isozyme was not affected. No change was observed in R insects.;Damage to cellular components resulting from attack by oxygen-derived radicals was measured. Polyunsaturated fatty acid content was decreased relative to saturated fatty acid content after S insects were exposed to PH{dollar}\sb3{dollar} in vivo. Sulphydryl group content was also decreased (31%) following fumigation while H+-ATPase activity was increased by 11%. A 30% decrease in ATPase activity was observed after isolated mitochondria were exposed to a free radical-generating system.



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