G. C. Rock

Studies on the mechanism of azinphosmethyl resistance in the predaceous mite, Neoseiulus (T.) fallacis (family: Phytoseiidae)

An organophosphorus-resistant strain of the predaceous mite, Neoseiulus (Typhlodromus)fallacis (Garman), degraded more azinphosmethyl than a susceptible strain both in vivo and in vitro. The in vitro degradation of azinphosmethyl required glutathione as a cofactor, and the activity was associated with the soluble fraction of the mite. The major metabolite identified in vivo and in vitro was desmethyl azinphosmethyl. The higher rate of desmethylation of azinphosmethyl by the resistant mite appears to be responsible in part for resistance. No apparent difference in the pI50 was observed between the two strains in vitro, indicating that the mechanism of resistance was not associated with a modified cholinesterase. The resistant strain had a higher nonspecific estersase activity than the susceptible strain and also two extra electrophoretic esterase bands. These extra bands were also found with two other resistant strains.

Observations on the occurrence and feeding habits of Balaustium pulmani (Acari: Erythraeidae) in North Carolina apple orchards

Abstract Balaustium putmani Smiley was collected within and beneath apple tree canopies from late April to late August during 1975–77 in western North Carolina.

Diapause in the phytoseiid mite, Neoseiulus (T.) fallacis☆

Abstract Female Neoseiulus (Typhlodromus) fallacis exhibited an adult reproductive diapause. Induction of diapause was dependent upon both photoperiod and temperature. The critical photoperiod at 15·6°C occurred between 11·75 and 12·0 hr light/day for a strain collected at Brunswick, New Jersey and reared in the laboratory under long light periods for ca. 2 years prior to testing. When the F 1 progeny of a strain collected at Wilkesboro, North Carolina was reared under a 11·75 hr light/day, 15·6°C regime along with the New Brunswick strain the photoperiodic response of the two strains was similar. Further studies with the New Jersey strain showed that the incidence of diapause at a short light period was averted entirely at 26·7°C. Little difference was shown in the developmental rates of mites under a short and long light period. Diapause duration was reduced at 15·6°C by exposure to a long light period. When held constantly at a short light period, an increase in temperature from 21·1 to 26·7°C reduced the duration of diapause. This reduction may reflect an effect of temperature on diapause termination as well as post-diapause development. Although diapause termination was influenced by both photoperiod and temperature, it occurred eventually under all experimental conditions, including those initiating diapause. There was no significant parental effect on the incidence of diapause in F 1 and F 2 progeny of adults reared under either a short or long light period. However, parental preconditioning did alter diapause intensity. When parents and offspring experienced a short light period, the resulting diapause duration was significantly longer than when parents experienced a long light period and the offspring experienced a short light period.

Dietary amino requirements for Heliothis zea determined by dietary deletion and radiometric techniques.

Abstract Feeding tests using a diet containing 18 allo free, l -amino acids as the major source of nitrogen showed that valine, leucine, lysine, arginine, histidine, isoleucine, threonine, tryptophan, phenylalanine, and methionine were indispensable for larval growth. Although larval growth rates, pupal weights, and survival to the pupal and adult stages on the amino acid diet were comparable to those obtained on a casein-wheat germ diet, most adults reared on the amino acid diet showed wing and/or body deformities. To verify further the larval dietary amino acid requirements, amino acid synthesis from glucose-U- 14 C was investigated. Fourth instar larvae were reared on a synthetic diet containing glucose-U- 14 C and the specific activities of the individual amino acids isolated from the whole carcass and from the protein extracted from the carcass were determined. The results of the radiometric study agreed with those obtained from feeding tests in that the radioactive carbon incorporated into the carbon chain of valine, leucine, lysine, arginine, histidine, isoleucine, threonine, and methionine showed sufficiently low 14 C activity that they could be classified as indispensable nutrients. The relatively high labelling in aspartic acid, glutamic acid, glycine, serine, alanine, and cysteine indicated that the insect is capable of synthesizing these amino acids from glucose. Results of the radiometric study were inconclusive regarding the dietary need for phenylalanine, tyrosine, and tryptophan: however, feeding studies showed the phenylalanine and tryptophan were indispensable and tyrosine was dispensable. Proline was shown to be dispensable by the deletion technique, and the relatively low 14 C labelling in proline was accounted for by dilution of the 14 C with unlabelled components of the diet during the indirect synthetic route from glucose to proline rather than by limited synthesis of proline from glucose.

Studies on the mechanisms responsible for variable toxicity of azinphosmethyl to various larval instars of the tufted apple budmoth, Platynota idaeusalis

Abstract The susceptibility of tufted apple budmoth larvae, Platynota idaeusalis , to azinphosmethyl decreases with each successive instar. A comparison between fifth and third instars showed that the fifth instars have a higher level of glutathione S -transferase activity per milligram of protein, a lower content of cytochrome P -450 per milligram of protein, and absorb a lesser percentage of and LD 01 dose than the third instar. Results of metabolism were consistent with these findings. In addition to these factors, the fifth instar larvae may have a threshold mechanism for eliminating penetrated azinphosmethyl from the body, unchanged. This allows the fifth instar larval population to withstand increasingly higher doses of azinphosmethyl without a proportional increase in mortality.

Interaction of larval age and dietary formaldehyde on the susceptibility of tufted apple budmoth (Lepidoptera: Tortricidae)to Bacillus thuringiensis☆

Abstract Laboratory tests of Bacillus thuringiensis var. kurstaki (strain HD-1) against Platynota idaeusalis reared on a semisynthetic diet showed that the LC50 values for neonates and 9-day-old larvae showed no significant difference in susceptibility; however, 14-day-old larvae were significantly more susceptible than neonates or 9-day-old larvae. There was no evidence of any interaction between 14-day-old larvae reared on the semisynthetic diets with and without formaldehyde and B. thuringiensis toxicity at any assessment reading. Likewise the toxicity of B. thuringiensis to 14-day-old larvae reared on apple leaves did not differ from the B. thuringiensis toxicity of 14-day-old larvae reared on semisynthetic diets with and without formaldehyde.

Nutrition and metabolism of sulphur amino acids in Argyrotaenia velutinana larvae.

Abstract Larval growth and survival to the adult stage of Argyrotaenia velutinana reared under axenic conditions and on a chemically defined diet was optimal at 0·1% dietary l -methionine level. Concentrations of 0·8% resulted in amino acid imbalance. About 75 per cent of the optimal dietary methionine requirement could be spared by l -cysteine, indicating the possibility of the conversion of methionine to cysteine via the cystathionine pathway. d -Cysteine was not as effective in sparing methionine as the l -isomer. Nutritional evidence for the presence of the cystathionine pathway was obtained as homocysteine and cystathionine spared about 75 per cent of the optimal dietary level of methionine. Inorganic sulphate did not spare the methionine requirement. Failure of larvae to grow on homocysteine in the absence of methionine suggested that homocysteine is not converted to methionine. Methionine did not spare the dietary choline requirement supporting the generalization that transmethylation reactions involving methionine and choline are impaired or absent in insects.

Metabolism of sulphur amino acids via the cystathionine pathway in Argyrotaenia velutinana larvae

Abstract In a previous study, cysteine and intermediates of the cystathionine pathway (homocysteine and cystathionine) were found to spare approximately 75 per cent of the dietary methionine requirement of Argyrotaenia velutinana larvae indicating a possible conversion of methionine to cysteine in this insect via the cystathionine pathway. To further verify the presence of the cystathionine pathway, studies of methionine and cysteine metabolism were conducted using A. velutinana larvae fed diets containing radioactive ( 35 S) methionine or cysteine. Ion-exchange chromatography of the protein-free amino acid fraction of larvae fed diets containing 35 S-methionine revealed the presence of radioactive methionine, methionine sulphoxide, cystathionine, and taurine. In the protein fraction radioactivity was found in methionine, methionine sulphoxide. and cyst(e)ine. Transfer of the radioactive label from 35 S-methionine to cystathionine and taurine in the protein-free fraction and to cyst(e)ine in the protein fraction confirms the findings of nutritional studies that A. velutinana larvae are capable of converting methionine to cysteine via the cystathionine pathway. The absence of radioactive methionine, methionine sulphoxide, and cystathionine in the protein and protein-free fractions from insects fed 35 S-cysteine showed that the cystathionine pathway from methionine to cysteine is not reversible in this insect. The presence of unknown radioactive peaks in the protein and protein-free fractions from larvae fed either 35 S-methionine or cysteine indicated the possibility of sulphur amino acid metabolism by routes other than the cystathionine pathway.

The essential dietary fatty acid requirement of the tufted apple budmoth, Platynota idaeusalis

Abstract The tufted apple budmoth, Platynota idaeusalis (Walker), was reared non-axenically for two successive generations on a casein-based semisynthetic diet. The qualitative essential fatty acid requirement for growth, development and normal pupal-adult ecdysis was studied using the non-axenic casein-based semisynthetic diets with and without various 99% pure fatty acids. Linoleic or linolenic acids caused accelerated larval development; linoleic, linolenic and arachidonic acids showed similar activity in body weight gain and survival to pupal-adult ecdysis. Linoleic or linolenic acids were active in alleviating wing deformities; arachidonic acid was partially active in alleviating wing deformities at the one dietary concentration evaluated. Activity of arachidonic acid as an essential fatty acid for P. idaeusalis is unique among insects, except for mosquitoes. The essential fatty acid deficiency syndrome of the adult, resulting from the larvae feeding on fat-deficient diets, was greatly reduced when larvae were fed on a diet adequate in essential fatty acid during either their early or late development.

Utilization of d-isomers of the dietary indispensable amino acids by Argyrotaenia velutinana larvae☆

Abstract Studies were made of the ability of larvae of the red-banded leaf roller, Argyrotaenia velutinana , to utilize the d -forms of the indispensable amino acids for growth and survival in lieu of their l -isomers using chemically defined diets and axenic conditions, d -phenylalanine, d -methionine, and d -histidine were the only d -amino acids which were readily utilized. On diets containing the complete amino acid mixture, the d -forms of phenylalanine and methionine were utilized more than 80 per cent as effectively as their l -isomers and d -histidine about 50 per cent. However, if l -tyrosine and l -cystine were omitted from the diets, d -phenylalanine and d -methionine were no more than 20 per cent as effective as their l -isomers at equimolar amounts. The optimal dietary levels of d -phenylalanine ( l -tyrosine omitted), d -methionine ( l -cystine omitted), and d -histidine were estimated from graded concentrations and insects were reared for two successive generations on d -phenylalanine and d -methionine and three successive generations on d -histidine at the optimal levels. If the d -forms of phenylalanine, methionine, and histidine were added to a diet simultaneously survival was poor; however, if any two of the three d -amino acids were added simultaneously the growth and survival response was similar to that obtained when the d -amino acids were added individually. The d -forms of threonine and tryptophan significantly stimulated larval growth when fed with suboptimal quantities of their l -isomers. The d -forms of isoleucine, valine, arginine, lysine, and leucine had no significant effect, either stimulatory or inhibitory, on larval growth.