Nicholas R. Price

Some biochemical aspects of phosphine action and resistance in three species of stored product beetles

The inhibitory effects of phosphine on cytochrome-c oxidase and catalase have been investigated. Cytochrome-c oxidase is inhibited by treatment of insect homogenates in vitro. Catalase is inhibited in susceptible insects poisoned with phosphine in vivo. Resistant insects absorb less phosphine than susceptibles.

Comparison of the oxidant damage induced by phosphine and the uptake and tracheal exchange of 32P-radiolabelled phosphine in the susceptible and resistant strains of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae)

Abstract The activity of antioxidant enzymes and the effects of phosphine on them were compared in a susceptible and two resistant strains of Rhyzopertha dominica (F.). Phosphine treatment lowered the activity of catalase and peroxidase and raised the activity of superoxide dismutase and the content of lipid peroxides in the susceptible insects. The generation of toxic oxyradical species appeared to be taking place in insects as a consequence of the interaction of phosphine with the mitochondrial respiration. Compared to the extent of oxidant damage in the susceptible insects, phosphine treatment caused only minor effects in a laboratory-selected strain while it produced no significant effects in a highly resistant field strain, even when treated at higher doses. The dietary administration of buthionine sulphoximine (BSO) lowered the content of glutathione in the resistant insects but caused no appreciable change in the susceptible strain. There were no appreciable effects on the susceptibility of BSO-treated strains to phosphine or on the uptake of 32P when treated with 32P-radiolabelled phosphine. In a “pulse-chase” style experiment, the resistant insects showed a much lower uptake of 32P and a significantly greater exchange of gaseous [32P]PH3 compared to the susceptible strain. The mechanisms of insect resistance to phosphine are discussed in the light of these results.

Esterase activity in homogenates of three strains of the rust red flour beetle Tribolium castaneum (Herbst)

Abstract 1. Esterase activity was measured in two malathion-resistant and one malathion-susceptible strain of the flour beetle Tribolium castaneum . 2. No A-esterase activity was found in homogenates of any strain. 3. The resistant Kano C strain showed only half of the esterase activity of the other two strains towards α-naphthylacetate, p -nitrophenylacetate and phenylacetate. The significance of this finding in relation to the resistance mechanism of the Kano C strain is discussed. 4. Some properties of the enzymes hydrolysing phenylacetate in insect homogenates and sheep serum are compared.

A comparison of the uptake and metabolism of 32P-radiolabelled phosphine in susceptible and resistant strains of the lesser grain borer (Rhyzopertha Dominica)

Abstract 1. The uptake of radiolabelled phosphine by a resistant strain of Rhyzopertha dominica was much reduced compared to that of the susceptible strain. 2. The production of metabolites was qualitatively the same in both strains though the resistant insects metabolised a higher percentage of the absorbed dose. 3. Implications with respect to resistance mechanisms are discussed.

Insecticide-insensitive acetylcholinesterase from a laboratory selected and a field strain of housefly (Musca domestica) (L.)

1. Acetylcholinesterase from the heads of a strain of houseflies selected for resistance to the carbamate insecticide methomyl, and from a methomyl-resistant field strain was found to be less sensitive to inhibition by methomyl than that from a susceptible strain. 2. The enzyme from resistant insects was also more tolerant to malaoxon, dichlorvos and bomyl but not to azamethiphos. 3. The decrease in sensitivity to inhibition appeared to be due to an increase in affinity for substrate.

Phosphine toxicity and catalase activity in susceptible and resistant strains of the lesser grain borer (Rhyzopertha dominica)

Abstract 1. Phosphine inhibits catalase activity in Rhyzopertha dominica in vivo . 2. Base levels of catalase are higher in a strain of the insect selected for resistance to the gas and in a field strain found to be highly resistant. 3. Uptake of phosphine and inhibition of catalase are lower in resistant strains than in a susceptible strain.

A comparison of some effects of phosphine, hydrogen cyanide and anoxia in the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae)

The effects of phosphine, hydrogen cyanide and anoxia on levels of ATP, pyruvate and lactate in Rhyzopertha dominica are compared. The effect of phosphine on anaerobiosis is not directly comparable either with HCN or anoxia. Reduction of catalase by feeding 3 amino 1,2,4 triazole does not enhance the toxicity of phosphine in treated insects.

Action of a juvenile hormone analogue on the activity of Periplaneta americana corpora allata in vitro and on juvenile hormone III levels in vivo

Abstract The effects of the juvenile hormone (JH) analogue fenoxycarb (ethyl[2-(4-phenoxyphenoxy)-ethyl]carbamate) on the activity of corpora allata (CA) from adult female Periplaneta americana have been investigated. The in vitro biosynthesis of JH III by isolated CA was inhibited by about 85% in the presence of a high concentration (1 × 10−4 M) of fenoxycarb. However, at lower concentrations (1 × 10−6 M and 1 × 10−8 M) no inhibition of JH biosynthesis was apparent. Topical treatment of adult female cockroaches with fenoxycarb (100 μg/insect) did not reduce the subsequent rate of JH III biosynthesis by CA in vitro. By contrast, the same treatment markedly reduced the titre of endogenous JH III in intact cockroaches. These results suggest that CA activity in adult female P. americana may be controlled by negative feedback, and that this system of control is dependent on the maintenance of contact between the CA and nervous or humoral factors in the intact insect. Alternatively, it is possible that treatment with fenoxycarb increases the rate at which endogenous JH is metabolized.

Endogenous Juvenile Hormone III Titres and In Vitro Rates of Hormone Biosynthesis by Corpora Allata During the Reproductive Cycle of Adult Female Periplaneta Americana

The endogenous titres of juvenile hormone III (JH III), and the in vitro rates of juvenile hormone biosynthesis by isolated corpora allata have been measured at intervals during the reproductive cycle of adult female Periplaneta americana. There was a close correlation between the rates of JH III biosynthesis and endogenous hormone titres. Only JH III was detected in whole body extracts, and hormone titres reached a peak (mean approximately 29 ng/g) at about the mid-point of the ootheca production cycle.

The uptake and penetration of pirimiphos-methyl into susceptible and resistant strains of the rust red flour beetle—Tribolium castaneum, herbst (coleoptera: tenebrionidae)

Abstract 1. The uptake and penetration of 14 C-labelled pirimiphos-methyl into two strains of T. castaneum are compared. 2. Less radioactivity penetrated into the internal tissues of the resistant strain compared to the suceptible strain. 3. The differences in uptake could not be accounted for by increased excretion of radiolabel by the resistant strain.