Inhibition of Telenomus sphingis an egg parasitoid of Manduca spp. by trichome/2-tridecanone-based host plant resistance in tomato

The resistance of accession PI 134417 of the wild tomato Lycopersicon hirsutum f. glabratum C. H. Mull to Manduca sexta (L.) (Lepidoptera: Spingidae) and Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) is conditioned by the high densities of 2-tridecanone-containing, glandular trichomes associated with the foliage. In laboratory experiments, rates of parasitism of M. sexta eggs by Telenomus sphingis (Ashmead) (Hymenoptera: Scelionidae) were lower among eggs on PI 134417 foliage than among eggs on foliage of the cultivated tomato L. esculentum Mill. (cv. Better Boy). The latter is characterized by a significantly lower density of type VI glandular trichomes than PI 134417 and an absence of 2-tridecanone. Parasitism by T. sphingis was also reduced among eggs on foliage of the F₁ hybrid between PI 134417 and L. esculentum. The hybrid foliage lacks 2-tridecanone but has a density of type VI glandular trichomes that is intermediate between those of PI 134417 and L. esculentum, indicating that elevated densities of type VI glandular trichomes adversely affect T. sphingis. This conclusion was further substantiated by the finding that there were no differences among plant lines in the levels of parasitism of M. sexta eggs when the eggs were on foliage that had been divested of glandular trichomes.In bioassays in which T. sphingis adults or immatures in host eggs were exposed to filter paper treated with 2-tridecanone at rates comparable to those associated with PI 134417 foliage, 2-tridecanone was acutely toxic and caused high levels of mortality. In addition, at high concentrations, 2-tridecanone vapors were repellent to T. sphingis adults. However, when exposed to PI 134417 foliage, few T. sphingis adults were killed.Parasitism of M. sexta eggs was unaffected when the eggs were deposited by moths reared as fifth instar larvae on diet containing 2-tridecanone and/or 2-undecanone at levels comparable to those associated with PI 134417 foliage.     

Response of insecticide-resistant and susceptible Colorado potato beetles, Leptinotarsa decemlineata to 2-tridecanone and resistant tomato foliage: the absence of cross resistance

Insecticide-resistant Colorado potato beetles (CPB), Leptinotarsa decemlineata, from Long Island, New York and susceptible beetles from North Carolina were tested for response to 2-tridecanone and foliage of the CPB resistant wild tomato, Lycopersicon hirsutum f. glabratum C. H. Mull, PI 134417. Populations did not differ in their response to 2-tridecanone or PI 134417 foliage. Exposure of beetles to sublethal doses of 2-tridecanone did not increase tolerance of either population to subsequent exposures to 2-tridecanone. It was also found that the New York beetles suffered higher mortality than North Carolina beetles on CPB susceptible L. esculentum foliage and PI 134417 foliage from which the glandular trichomes, which contain 2-tridecanone, were removed. Survival of North Carolina beetles was lower on PI 134417 foliage without trichomes than on L. esculentum foliage.

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Résumé La lutte contre Leptinotarsa decemlineata, sur la tomate et des autres récoltes, compte ordinairement sur les insecticides. Cette confiance a causé plusieurs populations de cette espèce à développer une résistance aux insecticides. Accession PI 134417 de la tomate sauvage, Lycopersicon hirsutum f. glabratum C. H. Mull, est résistant à L. decemlineata, en grande partie à cause de la presence de 2-tridécanone dans les éxtremités des poils glandulaires du feuillage. Notre étude entreprendait à rechercher la possibilité d'une résistance croisée aux insecticides et au 2-tridécanone.Les coléoptères de Long Island, New York, ceux qui sont résistants aux insecticides et ceux susceptibles de North Carolina, éprouvaient pour une réponse au 2-tridécanone et au feuillage résistant.Les deux populations de coléoptères ne diffèrent pas dans sa réponse au 2-tridécanone ou au feuillage résistant. Nous ne trouvons pas d'évidence d'une résistance croisée.Aussi, nous trouvons que les coléoptères de New York ne survivaient pas aussi bien que ceux de North Carolina au feuillage résistant sans les éxtremités des poils glandulaires et au feuillage susceptible. La survivance était plus basse sur le feuillage résistant sans les éxtremités des poils glandulaires que le feuillage susceptible seulement avec les coléoptères de North Carolina.

     

Interaction of fertilizer regime with host-plant resistance in tomato

The effect of fertilizer regime on trichome- and lamellar-based resistance in the wild tomato species, Lycopersicon hirsutum f. glabratum C.H. Mull accession PI 134417, to three insect pests of tomato, the tobacco hornworm, Manduca sexta (L.), the colorado potato beetle, Leptinotarsa decemlineata (Say), and the tomato fruitworm, Heliocoverpa zea (Boddie), was examined. Increasing the rate at which NPK fertilizer was applied, from 1.8 to 19.6 g/plant/week, reduced the trichome-based resistance of PI 134417 to M. sexta and L. decemlineata by lowering both the density of type VI (sensu Luckwill, 1943) glandular trichomes and the amount of 2-tridecanone contained in the tips of these trichomes. 2-Tridecanone is a toxic methyl-ketone responsible for glandular trichome-mediated resistance in PI 134417 to M. sexta and L. decemlineata. A similar increase in the application rate of NPK fertilizer reduced the lamellarbased resistance of PI 134417 to L. decemlineata and H. zea. The meachanisms for this reduction of resistance are unknown, but may be related to improved nutritional quality of hosts at higher fertilizer regimes.     

2-Undecanone, a pupal mortality factor in Heliothis zea: sensitive larval stage and in planta activity in Lycopersicon hirsutum f. glabratum

2-Undecanone, a compound found in the tips of the Type VI glandular trichomes of the wild tomato species Lycopersicon hirsutum f. glabratum C. H. Mull (accession PI 134417), when incorporated in artificial diet, was previously shown to cause pupal deformity and mortality among Heliothis zea (Boddie). In the present study, the developmental stage of H. zea sensitive to the effects of dietary 2-undecanone was determined by rearing larvae through the fourth instar on diet with or without 2-undecanone, then transferring them to new diet either with or without 2-undecanone. Dietary levels of 2-undecanone (0.055% wet wt) were representative of concentrations found in PI 134417 foliage. Ingestion of 2-undecanone during the fifth instar was both necessary and sufficient to cause pupal mortality. Rearing fifth instar H. zea on PI 134417 foliage with glandular trichomes intact (2-undecanone present at 0.084±0.026% wt wt) or with the trichomes, and hence 2-undecanone, removed indicated that these effects occur in planta. Potential implications of these findings for using 2-undecanone-mediated resistance for insect pest management are discussed.

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Résumé Il a été démontré précédemment que l'undécanone-2, présente dans les extrémités des trichomes glandulaires de type VI de la tomate sauvage Lycopersicon hirsutum glabratum C. H. Mull (accession PI 134417), provoque déformations et mortalité chez les chrysalides de Heliothis zea (Boddie) lorsqu'elle est incorporée dans une nourriture artificielle. Dans cette étude, le stade de développement de H. zea sensible aux effets de l'undécanone-2 a été déterminé en élevant les larves jusqu'au 4e stade sur une diète contenant ou non de l'undécanone-2, puis en les transférant sur une nouvelle diète avec ou sans undécanone-2. Les concentrations en undécanone-2 utilisées (0.055% du poids frais) étaient comparables aux concentrations présentes dans les feuilles du PI 134417. L'ingestion de l'undécanone-2 durant le 5e stade s'est avérée nécessaire et suffisante pour provoquer une mortalité au stade chrysalide. L'élevage du 5e stade de H. zea sur des feuilles de PI 134417 dont les trichomes sont intacts (l'undécanone-2 est présente à la concentration de 0.084±0.025% du poids frais) ou sur des feuilles dont les trichomes, et par conséquent l'undécanone-2, ont été éliminés, a démontré que les effets toxiques se produisent in planta.L'undécanone-2 pourrait être un facteur de résistance efficace des tomates, mais probablement uniquement dans les régions où H. zea est polyvoltime sur la tomate et où les premiéres générations se développent sur le feuillage pendant toute la période larvaire avant la maturation des fruits. Normalement, les premiers stades larvaires de H. zea se nourrissent de feuilles et les derniers stades des fruits. Les fruits ne contenant pas d'undécanone-2, les chenilles qui se développeraient sur les plants en fructification pourraient échapper aux effets toxiques.

     

Interaction ofManduca sexta resistance in tomato with insect predators ofHelicoverpa zea

Resistance in accession PI 134417 ofLycopersicon hirsutum f.glabratum toManduca sexta L. results from the presence of the methyl ketones 2-tridecanone and 2-undecanone in the type VI trichome glands on foliage of these plants. Short (24 h) and long term (neonate to adult) laboratory experiments usingM. sexta-resistant and susceptible foliage and methyl ketone treated filter paper disks were conducted to evaluate the direct (plant-mediated), and indirect (prey-mediated) effects of this resistance on two predators ofHelicoverpa zea eggs,Coleomegilla maculata (DeGeer) andGeocoris punctipes (Say). Direct effects of resistance were manifest as reduced egg consumption and increased mortality for both predators. Indirect effects were manifest as reduced egg consumption byG. punctipes, but were not observed forC. maculata. Results of experiments using methyl ketone-treated filter paper disks instead of foliage were similar.     

Accumulation and turnover of 2-tridecanone in Tetranychus urticae and its consequences for resistance of wild and cultivated tomatoes

In this study we assessed the dynamic changes of 2-tridecanone in a herbivorous mite (Tetranychus urticae) on tomato (Lycopersicon esculentum, cv. Moneymaker), a plant with methyl ketones in the tetracellular tips of the glandular trichomes (Type VI). We showed that spider mites accumulate 2-tridecanone when foraging on cultivated tomato. Thus, the rate of mite–trichome contact multiplied by the amount of toxin per trichome tip exceeded the relative rate of toxin turnover multiplied by the amount of toxin per mite. The relative rate of toxin turnover was estimated to be 1.1 per day on cucumber, a plant without this toxin. The amount per trichome tip varied from 0.33 ng for middle-leaf trichomes to 1.26 ng for main-stem trichomes. Hence, to achieve a static level of 2-tridecanone equal to 8–17 ng per mite – representing the level we found in mites on middle leaves – the rate of mite–trichome contact should be 26–57 per day. Because methyl ketone apparently accumulates in the spider mites on tomato, the rate of mite–trichome contact is probably higher than that. We expect the accumulation of ketones to occur especially on the stems of cultivated tomato, since this is the area most densely occupied with glandular hairs and because here the hairs have higher levels of the methyl ketones.Using dose–response relationships assessed earlier (Chatzivasileiadis and Sabelis, 1997, 1998), we estimated that the number of mite–trichome contacts causing 50% mortality per day is equal to 88 on a tomato stem, whereas it equals 70 for another strain of spider mites collected from cucumber. On wild tomato, L. hirsutum f. glabratum (PI 134417), just one to two contacts would suffice to cause 50% mortality per day. We suggest that methyl ketones from glandular hairs on tomato are an important mortality factor for spider mites on wild tomato and probably also on cultivated tomato.     

2-Undecanone, a constituent of the glandular trichomes of Lycopersicon hirsutum f. glabratum: Effects on Heliothis zea and Manduca sexta growth and survival

The effects of 2-undecanone, a compound found in the glandular trichomes of the wild tomato, Lycopersicon hirsutum f. glabratum C. H. Mull, PI 134417, on the larvae of Heliothis zea (Boddie) and Manduca sexta (L.) were studied by rearing the larvae on artificial diets containing this chemical. 2-Undecanone increased larval mortality of H. zea in the first 48 h when combined with 2-tridecanone, but not alone, and caused deformity and mortality of H. zea pupae both alone and in combination with 2-tridecanone. 2-Undecanone had no effect on M. sexta larvae or pupae. Potential implications of these findings for insect pest management are discussed.

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Résumé Le 2-undécanone est une methyle cétone qui se trouve avec le 2-tridécanone dans les extrémités des poils glandulaires des feuilles de la tomate sauvage: Lycopersicon hirsutum f. glabratum C. H. Mull, PI 134417. Notre étude entreprendait à rechercher le rôle du 2-undécanone dans la resistance de cette plante à Heliothis zea et Manduca sexta.Les produits chimiques synthétiques s'étaient incorporés en diète artificièlle sur laquelle les insectes ont élevés. Le 2-undécanone a causé peu de mortalité des larves de H. zea sauf quand il soit combiné avec le 2-tridécanone, dans quel cas on trouve, dans les premiers 48 heures, une augmentation de mortalité, en comparaison au 2-tridécanone seul. Aussi le 2-undécanone a causé les difformités des nymphes de H. zea et la mortalité dans l'étage de nymphe, toutes les deux seul et en combinaison avec le 2-tridécanone. En contrast, le 2-undécanone n'a pas produit un effet sur les larves ou nymphes de M. sexta.L'élevage sélective des lignes de tomates de niveau plus élevé de 2-undécanone pourrait utile pour la lutte contre le H. zea. En combinaison avec des niveaux élevés du 2-tridécanone, c'est possible de reduire les populations nuisibles des larves. Il peut aussi réduire le nombre des lépidoptères adultes produit dans la récolte de tomate. Toutefois, il ne serait pas probablement de valeur dans la lutte contre le M. sexta.

     

On the intracellular localization of the ecdysone 20-monooxygenase in Musca domestica. L

The cytochrome P-450-dependent 20-monooxygenation of ecdysone is catalyzed both by mitochondria and microsomes isolated from Musca domestica (L.) larvae; however, about 50% of the activity is associated with mitochondria, and 37% is associated with microsomes. Pretreatment of larvae with ecdysone results in an increase in Vmax and a decrease in Km values in mitochondria but not in microsomes. Phenobarbital, a known cytochrome P-450 inducer, increases the cytochrome P-450 levels in microsomes without affecting the 20-monooxygenase activity, but both the cytochrome P-450 levels and monooxygenase activity are depressed in mitochondria from phenobarbital-pretreated larvae. The ecdysone 20-monooxygenase activity is equally distributed between mitochondria and microsomes in adult insects. Pretreatment of the insects with ecdysone does not significantly modify the 20-monooxygenase activity of either mitochondrial or microsomal fractions, but the cytochrome P-450 levels are reduced in mitochondria. Phenobarbital also depresses the mitochondrial cytochrome P-450 levels while markedly increasing the microsomal cytochrome P-450 levels. However, no significant changes in ecdysone 20-monooxygenase activity are produced by phenobarbital pretreatment. The effects of ecdysone on adult cytochrome P-450 are mostly evidenced in mitochondria isolated from females, whereas in males the changes are not statistically significant. It is concluded that the mitochondrial ecdysone 20-monooxygenase is under regulatory control by ecdysone in the larval stage, which suggests that only the mitochondrial activity has a physiological role during insect development in M. domestica. In adults, both the mitochondrial and microsomal ecdysone 20-monooxygenase activities are not responsive to ecdysone, which, coupled to their high Km values, indicates that the reaction may not be of physiological importance in adult insects and that the mitochondrial cytochrome P-450 species being depressed by ecdysone in females are possibly not involved in ecdysone metabolism.     

The biochemical genetics of permethrin resistance in the Learn-PyR strain of house fly

Permethrin resistance in the Learn-PyR strain of house fly was examined in four genetically derived substrains, each being homozygous for a different resistant autosome of the Learn-PyR strain. The resistance of these derivative strains was characterized toxicologically and biochemically. The relative levels of resistance to permethrin conferred by each autosome were 5>3>1>2. Three factors were associated with resistance: (1) increased mixed-function oxidase (MFO) activity associated with elevated levels of cytochrome P-450, cytochrome b₅, and NADPH-cytochrome c reductase (P-450 reductase) activity; (2) target-site insensitivity (kdr); and (3) decreased cuticular penetration. Permethrin resistance factors on chromosome 1 consisted of a piperonyl butoxide (PB)-suppressible mechanism correlated with increased levels of cytochromes P-450 and b₅; on chromosome 2, a PB-suppressible mechanism associated with elevated amounts of cytochrome P-450; on chromosome 3, decreased cuticular penetration, kdr, and increased amounts of P-450 reductase activity; and on chromosome 5, a largely PB-suppressible mechanism correlated with elevated levels of cytochrome P-450 and P-450 reductase activity.     

Glandular trichomes of Solanum berthaultii and its hybrids with potato deter oviposition and impair growth of potato tuber moth

Glandular trichomes on foliage of the wild potato species, Solanum berthaultii Hawkes, deter oviposition by the potato tuber moth (PTM), Phthorimaea operculella Zeller and negatively affect other important performance parameters. Oviposition deterring factors are localized in the glandular trichomes of S. berthaultii. When mechanically transferred to foliage of a susceptible potato cultivar, trichome contents reduced egg laying by 97%. Removal of glandular trichomes from S. berthaultii foliage using a combination of chemical and mechanical procedures increased oviposition rates ca. 210-fold. Removal of trichomes also led to increased mobility of larvae on the leaf surface, more leaf feeding, shorter larval development and larger pupae. The resistance conferred by glandular trichomes of S. berthaultii provides an important genetic trait potentially useful for management of PTM.     

Growth, food consumption and mortality of Heliothis zea larvae on foliage of the wild tomato Lycopersicon hirsutum f. glabratum and the cultivated tomato, L. esculentum

Larvae of Heliothis zea (Boddie) were fed foliage of the resistant wild tomato Lycopersicon hirsutum f. glabratum C. H. Mull (PI 134417) and susceptible L. esculentum (cultivar Walter), either with the glandular trichomes removed or with the trichomes intact. Response variables measured included larval mortality, larval weight, consumption rate (CR), and efficiency of conversion of ingested material (ECI). Resistant foliage was found to contain factors in both the trichomes and leaf lamellae which increased larval mortality, reduced larval weight, reduced CR, and, except in second instars, reduced ECI. Susceptible foliage also contained trichome-based factors which increased larval mortality and decreased weight, as well as CR of second instars and ECI of fifth instars. Implications of these findings for breeding resistant tomato cultivars are discussed.

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Résumé La tomate sauvage, Lycopersicon hirsutum f. glabratum C. H. Mull (PI 134417) est fortement résistant à Heliothis zea. Les études préalables ont indiqués que la résistance est associée avec la présence de 2-tridécanone dans les extrémités des poils glandulaires de la tomate sauvage, et que les facteurs dans la lamelle des feuilles sont peut-être impliqués. À déterminer la présence des facteurs lamellaires et à caractériser de plus les facteurs de résistance dans les extrémités des poils glandulaires aussi, nous nourrissions les larves du feuillage résistant de PI 134417 et du feuillage susceptible L. esculentum (lignée Walter) les deux avec les extrémités des poils glandulaires enlèvés ou avec les extrémités des poils glandulaires intacts. Nous mesurions la mortalité des larves, les poids des larves, la taux de consommation relative et l'efficacité de conversion de matière mangé.On se trouvait le feuillage résistant à contenir les facteurs, tous deux dans le feuillage lamellaire et dans les extrémités des poils glandulaires, qui causaient l'augmentation de mortalité, les poids plus basses, la taux de consommation relative plus basse, et, hormis dans le cas des larves en phase deuxième, l'efficacité de conversion réduite. Le feuillage susceptible contenait aussi les facteurs dans les extrémités des poils glandulaires qui augmentaient la mortalité, diminuaient les poids et la taux de consommation relative des larves en phase deuxième, et diminuaient l'efficacité de conversion des larves en phase cinquième. Cettes conclusions indiquent la présence des facteurs de résistance en outre de 2-tridécanone et peuvent fournir les indices à l'identité de ces facteurs.

     

A 2.6 kb intron separates the signal peptide coding sequence of an anther-specific protein from the rest of the gene in sunflower

Summary Metabolism of sulfonylurea herbicides by Streptomyces griseolus ATCC 11796 is carried out via two cytochromes P-450, P-450_SU1 and P-450_SU2. Mutants of S. griseolus, selected by their reduced ability to metabolize a fluorescent sulfonylurea, do not synthesize cytochrome P-450_SU1 when grown in the presence of sulfonylureas. Genetic evidence indicated that this phenotype was the result of a deletion of > 15 kb of DNA, including the structural genes for cytochrome P-450_SU1 and an associated ferredoxin Fd-1 (suaC and suaB, respectively). In the absence of this monooxygenase system, the mutants described here respond to the presence of sulfonylureas or phenobarbital in the growth medium with the expression of only the suhC,B gene products (cytochrome P-450_SU2 and Fd-2), previously observed only as minor components in wild-type cells treated with sulfonylurea. These strains have enabled an analysis of sulfonylurea metabolism mediated by cytochrome P-450_SU2 in the absence of P-450_SU1, yielding an in vivo delineation of the roles of the two different cytochrome P-450 systems in herbicide metabolism by S. griseolus.     

The effect of the cytochrome P-450 system inducers on the development of drosophila melanogaster

D. melanogaster development was markedly retarded and its survival decreased by larvae treatment with compounds being strong inducers of the cytochrome P-450 2B in mammals— phenobarbital (PB^*), perfluorodecaline (PFD), transstilbene oxide (TSO), and triphenyldioxane (TPD). At the same time, the weak inducer hexobarbital or the selective cytochrome P-450 inducer in mice but not in rats 1,4-bis[2-(dichloropyridyl-oxy)]-benzene (DPB) did not affect the larvae development. The cytochrome P-450 1A1 inducers benzo(a)anthracene (BA) and β-naphtoflavone (BNF) were also not effective. The toxicity of phenobarbital was shown to be decreased by the cytochrome P-450 inhibitor piperonyl butoxide by adding 20-hydroxyecdysone or by treatment with aminophylline—the indirect enhancer of ecdysone production in the larval prothoracic gland. The hypothesis of the moulting hormone degradation as the cause of elevated larvae mortality resulting from the induced high mixed function oxidase activity has been discussed.     

Foliar pubescence and resistance to potato moth, Phthorimaea operculella, in Lycopersicon hirsutum

Pubescence characteristics for six accessions of Lycopersicon hirsutum Dunal and five accessions of L. hirsutum f. glabratum CH Mull. were determined and compared with those of an accession of cultivated tomato (L. esculentum Mill.). Removal of trichome exudates from excised leaflets using ethanol solution resulted in a reduced mortality and increased survival of potato moth (Phthorimaea operculella (Zeller)) neonates for the accessions that were most lethal when not treated with ethanol solution. No such treatment effect was evident for L. esculentum or for the L. hirsutum accession with least effect on neonates when its trichomes were intact. In a glasshouse experiment with caged intact plants, mortality of neonate P. operculella placed on the abaxial surface was greater on seven accessions than for L. esculentum.Neonates were less severely affected on the adaxial surface. Eleven days after inoculation, no live larvae were found on LA 1927, PI 127827, PI 134418, and PI 134428, and numbers on other accessions were lower than for L. esculentum. Eventual emergence of adults followed a similar trend. Multiple regression of insect data against pubescence indicated a significant correlation between density of type IV and VI trichomes and neonate mortality, decreased larval development and decreased adult emergence. Non-glandular type V trichomes were positively correlated with high survival of insects to 11 days and to adult. Though factors other than glandular trichomes are likely to be important, increased density of type IV and VI, along with reduced type V, are shown to be important to select in breeding for P. operculella resistance.     

Alkaloid metabolism by cytochrome P-450 enzymes in Drosophila melanogaster

The cytochrome P-450 family of enzymes is the primary means of foreign compound detoxification in virtually all organisms. Cytochrome P-450s have been strongly implicated in the metabolism of cactus alkaloids, and consequently, the observed patterns of host plant utilization by cactophilic species of Drosophila in the Sonoran Desert. The current study looked for evidence of alkaloid-metabolizing P-450 enzymes in a non-cactophilic species, D. melanogaster. The results of in vitro metabolism assays indicate the presence of a phenobarbital-inducible P-450 in adult D. melanogaster which is capable of metabolizing alkaloids. P-450 quantification data suggest that the enhanced level of metabolism is not the result of an overall increase in total P-450 content. Results from larval viability and adult longevity studies indicate that D. melanogaster's in vitro activity does not produce an enhanced in vivo tolerance of alkaloids.     

Potential of adultOrius insidiosus [Hemiptera: Anthocoridae] as a predator of the fall armyworm,Spodoptera frugiperda [Lepidoptera: Noctuidae]

Orius insidiosus (Say) was observed to successfully prey on eggs and earlier instar larvae of the fall armyworm (FAW),Spodoptera frugiperda (J. E. Smith). Significantly more neonates of FAW were killed per 24 h than either 1, 2 or 3 d old larvae. Female and male predators exhibited a typical type-II functional response when preying on varying densities of eggs or neonates of FAW.      

Toxicity of acephate to larvae of gypsy moth as a function of host plant and bioassay method

We examined toxicity of acephate to third-instar gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), under different conditions of administration method, availability of food to larvae during bioassay, host plant, and activity of detoxifying enzymes. Larvae that had been fed field-collected foliage of white alder (Alnus rhombifolia Nutt.) were less susceptible 48 h after treatment with topically applied acephate if they were allowed to continue feeding on foliage during the bioassay period (LD₅₀= 60.6 μg/g larva ) than if they were not (LD₅₀= 13.5 μg/g larva ). All surviving larvae were replaced on their original food plant after the 48-h bioassay; of these, 14.4% of the larvae not fed during treatment died before pupation, compared with 1.3% of the larvae fed alder during treatment. The LD₅₀ obtained for topically treated larvae reared and treated on Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, (51.1 μg/g larva) was comparable to that obtained for larvae fed alder (60.0 μg/g larva) throughout treatment. Larvae treated orally with acephate, however, were slightly more susceptible when reared on Douglas-fir (LC₅₀, 20.3 ppm ) than when reared on alder (LC₅₀, 27.0 ppm ). Post-treatment mortality in orally treated larvae was 10.3% in those fed alder and 9.5% in those fed Douglas-fir. Higher cytochrome P-450 activities in larvae reared on Douglas-fir apparently did not enhance tolerance to acephate. Both sexes of orally treated larvae took significantly longer to pupate than did controls on both foliage types, as did topically treated males fed Douglas-fir. Pupal weight generally was slightly, but not always significantly, higher in treated than untreated larvae under all dietary and treatment regimes.     

Function and regulation of cytochrome P-450 in alkane-assimilating yeast

Transition of n-hexadecane utilizing cultures of Candida maltosa to oxygen-limited growth caused an up to 6-fold increase of the cellular cytochrome P-450 content. Enhanced cytochrome P-450 formation required protein de novo synthesis and was not due to a change of the apo/holo-enzyme ratio as demonstrated by cycloheximide inhibition and immunological quantitation. The effect of low oxygen concentration (pO₂=3–5%) was simulated by selective inhibition of alkane hydroxylation with carbon monoxide (at a pO₂ of 70–75%). Enhanced cytochrome P-450 formation occurred even when a constant growth rate was maintained through utilization of a second non-repressive growth substrate. However, the presence of n-alkanes was an essential precondition. It was concluded, that the cytochrome P-450 formation was mainly regulated by the intracellular inducer concentration which depends on the relative rates of alkane transport into the cell and the actual alkane hydroxylating activity of the enzyme system.Abbreviation cyt cytochrome     

Expression of cytochrome P-450lpr Is developmentally regulated and limited to house fly

Expression of house fly cytochrome P-450_lpr was examined using immunoblotting in male and female adult LPR house flies, mixed sex adult house flies at 12 different ages, larvae, and pupae. P-450_lpr was expressed in both male and female adult house flies. P-450_lpr was clearly present in all adult stages examined, was barely detectable in pupae, and could not be detected in larvae. Thus, cytochrome P-450_lpr is developmentally regulated and present in both sexes of house fly. Expression of cytochrome P-450, immunologically homologous to house fly cytochrome P-450_lpr was examined in other species using immunoblot analysis. Eleven animal species were tested in the orders Diptera, Hymenoptera, Lepidoptera, Orthoptera, Acari, and Rodentia, using microsomes in some species from both induced and noninduced animals or insecticide-resistant and susceptible strains. P-450_lpr appears to be restricted to house flies, as none of these species contained cytochrome P-450 that reacted with antiserum to cytochrome P-450_lpr.