Metabolism of Δ0-, Δ5-, and Δ7-Sterols by Larvae of Heliothis zea

Heliothis zea was reared on artificial diets containing Δ⁵-sterols (cholesterol, campesterol, or sitosterol), Δ⁷-sterols (lathosterol, epifungisterol, or spinasterol), or Δ⁰-sterols (cholestanol, epicoprostanol, campestanol, or sitostanol) in order to determine how different dietary sterols affect the type of sterols present in the tissues of the late-sixth-instar larva. Although all of the dietary sterols (except epicoprostanol) supported the growth of the larvae, not all of the sterols were metabolized to the same end products. In each case, at least 80% of the sterols in the tissues of the larvae retained the same nucleus as that of the dietary sterol, indicating that H. zea carries out very little metabolism of ring B of Δ⁵-, Δ⁷-, and Δ⁰-sterols. The larvae dealkylated the Δ⁵-, Δ⁷-, and Δ⁰-alkylsterols to 24-desalkylsterols, but a greater percentage of the Δ⁵-alkylsterols were metabolized in this manner. The sterols present as free sterols in the larva were also present as esterifed sterols which accounted for 2–4% of the total sterols. Therefore, the sterol composition of the tissues of H. zea can be altered by varying the dietary sterols.     

Binding of insecticides to lipophorin and arylphorin,two hemolymph proteins of Heliothis zea

The binding of different insecticides to hemolymph proteins of the corn earworm, Heliothis zea, was studied by an analytical isoelectric focusing technique. Two proteins capable of binding hydrophobic substrates were discovered and identified as lipophorin and arylphorin. Lipophorin, the major lipoprotein of Heliothis zea, demonstrated rather unspecific binding of xenobiotics of different hydrophobicities. Arylphorin, a putative storage protein, revealed strong affinity for compounds of medium polarity, binding only weakly to insecticides of higher or lower polarity.     

The identification of 24-methylene-24,25-dihydrolanosterol and other possible ergosterol precursors in Phycomyces blakesleeanus and Agaricus campestris

The following sterols have been isolated from the fungi, Phycomyces blakesleeanus and Agaricus campestris: ergosterol, lanosterol, 24-methylene-24,25-dihydrolanosterol and episterol. 4,4-Dimethyl-5α-ergosta-8.24(28)-dien-3β-ol and 4α-methyl-5α-ergosta-8,24(28)-dien-3β-ol have been tentatively identified. Evidence for the incorporation of label from l-methionine-[methyl-¹⁴C] into some of these sterols in P. blakesleeanus has been obtained. The significance of these sterols in ergosterol biosynthesis is discussed.     

Dietary self-selection for vitamins and lipid by larvae of the corn earworm, Heliothis zea

Last instar larvae of the corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), require lipid and certain vitamins in their diet in order to complete larval development. When experimental larvae were offered two nutritionally incomplete diets, each lacking a different one of the requirements, they invariably ate from both diets, self-selecting a mixture that was nutritionally superior to either diet alone.

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Résumé Les chenilles de dernier stade d' H. zea (Boddie) (Lep.:Noctuidae) ont besoin de lipides et de certaines vitamines dans leur régime alimentaire, probablement parce qu'elles n'en contiennent pas assez provenant des stades précédents. Quand deux régimes incomplete ont été fournis aux chenilles (chacun privé différemment de l'un de ces consituants: lipide, chlorure de choline ou un ensemble de vitamines), elles ont consommé systématiquement des deux régimes et autosélectionné un aliment de qualité supèrieure à celle de chaque régime séparément. D'un autre côté, les chenilles témoins à qui on a offert deux régimes identiques et nutritionnellement complets, ont choisi apparemment leur aliment au hasard, et presque la moitié d'entre elles ont consommé exclusivement on presque exclusivement l'un des régimes, tandis que l'autre moitié a choise exclusivement or presque exclusivement l'autre.

     

The role of the frontal ganglion and corpora cardiaca/corpora allata complex in post-feeding weight loss in adult Heliothis zea

Abstract A post-feeding diuretic response has been observed in adult Heliothis zea (Boddie) (Lepidoptera: Noctuidae). 2-day-old starved adults which were allowed to feed to repletion on a 10% (w/v) sucrose solution lost 49.1% (females) and 85.8% (males) of the weight of the ingested meal during the first hour following feeding. Ligation between head and thorax or frontal ganglionectomy, when performed immediately following feeding, each resulted in a significant and permanent reduction in this normal weight-loss. Injection of homogenates of the corpora cardiaca/corpora allata (CC/CA) complex into non-ligated insects immediately after feeding also reduced significantly the post-feeding weight-loss, but this inhibition was transient and disappeared after 1 h. Dissection and weighing of the crop from either ligated, frontal ganglionectomized, or CC/CA-injected insects confirmed the crop as the predominant site of fluid retention in each case. We suggest that a soluble antidiuretic factor from the CC/CA acts in conjunction with the frontal ganglion to control the rate of crop emptying and subsequent diuresis by regulating the volume of ingested fluid that is passed into the haemolymph from the crop/midgut.     

Behavioral changes and growth inhibition in last instar larvae of Heliothis zea induced by oral and topical application of precocene II

In diet choice tests, newly-ecdysed fifth instar Heliothis zea larvae randomly chose diet containing 4 mM precocene II or diet without precocene II but initially preferred to feed on diet without precocene II. After two days, however, they were found more frequently on diet containing precocene II. Nevertheless, larval growth and development were inhibited when forced to eat diet containing precocene II. Removal of the maxillae, the site of the primary gustatory receptors, did not prevent the growth inhibition caused by larval consumption of diet with precocene II. Topical treatments with precocene II also caused larval growth inhibition, and daily treatments were more detrimental to the larvae than a large single dose. Addition of methylenedioxyprecocene (6,7-methylenedioxy-2,2-dimethylchromene) to the diet did not reverse the observed larval growth inhibition and this compound was itself significantly toxic. These results indicate that larval growth and development are disrupted after precocene II ingestion, but not because of preingestive discrimination by olfaction and gustation.     

Self-selection and utilization efficiency of Heliothis zea larvae feeding on seeds and the walls of snap bean pods

First instar Heliothis zea larvae tended to feed on the leaves of snap beans, but later instars preferred to burrow in the pods. Fifth instars offered only leaves grew poorly because they ate them in small quantities, presumably because of deterrency. The utilization efficiency and growth of fifth instars fed pulp was slightly but significantly inferior to that of seed-fed larvae but was greatly superior to that of leaf-fed larvae. Since the dry matter content of pulp is less than one-third that of seeds, larvae allowed to eat only pulp had abnormally large fresh weight intakes and devoted about three times as much time to feeding as did seed-fed larvae. Larvae offered a mix of seeds and pulp ate both and had a total fresh weight food intake somewhat greater than that of seed-fed larvae but much less than that of pulp-fed larvae. Eating both seeds and pulp offers no obvious nutritional advantage but presumably offers a significant ecological advantage. It is argued that the number of foraging trip a larva must make to discover pods is minimized by feeding on a mix, thus reducing exposure to mortality factors such as predation.     

Associations of cholesterol and vitamin D metabolites with the risk for development of high grade colorectal cancer

BackgroundVitamin D deficiency is repeatedly reported in colorectal cancer (CRC). Since cholesterol and vitamin D share common precursor 7-dehydrocholesterol (7-DHC), it would be important to explore the associations of key vitamin D metabolites and serum lipid parameters in patients with high and low grade CRC. The aim of this study was to analyze relationships between serum 25(OH)D3, 24,25(OH)2D3 and 7-DHC levels and serum lipids in patients with CRC, and to evaluate their potential for prediction of risk for development of high grade CRC.MethodsWe recruited 82 patients CRC and 77 controls. 7-DHC, 25(OH)D3 and 24,25(OH)2D3 were quantified by LC-MS/MS methods.Results7-DHC, 25(OH)D3 and vitamin D metabolic ratio (VDMR) were significantly lower in CRC patients than in control group (P<0.001, P<0.010, P<0.050 and P<0.050, respectively). 25(OH)D3 levels were higher in patients with grade I CRC when compared to grade II (P<0.050). All vitamin D metabolites positively correlated with total cholesterol (TC) concentration in CRC patients. 25(OH)D3 was significant predictor of increased CRC risk (P<0.010). After adjustment for TC concentration, 25(OH)D3 lost its predictive abilities. However, 25(OH)D3 remained significant predictor of poorly differentiated type of cancer (P<0.050).ConclusionsWe found significant positive association between vitamin D status and serum total cholesterol. Although low 25(OH)D3 was found to be a significant risk factor for CRC development, the obtained results primarily suggest profound impact of cholesterol level on vitamin D status in CRC. However, our results suggest that low 25(OH)D3 might independently contribute to development of poorly differentiated tumor.     

Oxidation of 7-dehydrocholesterol and desmosterol by human cytochrome P450 46A1

Cytochrome P450 (P450 or CYP) 46A1 is expressed in brain and has been characterized by its ability to oxidize cholesterol to 24S-hydroxycholesterol. In addition, the same enzyme is known to further oxidize 24S-hydroxycholesterol to the 24,25- and 24,27-dihydroxy products, as well as to catalyze side-chain oxidations of 7α-hydroxycholesterol and cholestanol. As precursors in the biosynthesis of cholesterol, 7-dehydrocholesterol has not been found to be a substrate of P450 46A1 and desmosterol has not been previously tested. However, 24-hydroxy-7-dehydrocholesterol was recently identified in brain tissues, which prompted us to reexamine this enzyme and its potential substrates. Here we report that P450 46A1 oxidizes 7-dehydrocholesterol to 24-hydroxy-7-dehydrocholesterol and 25-hydroxy-7-dehydrocholesterol, as confirmed by LC-MS and GC-MS. Overall, the catalytic rates of formation increased in the order of 24-hydroxy-7-dehydrocholesterol < 24-hydroxycholesterol < 25-hydroxy-7-dehydrocholesterol from their respective precursors, with a ratio of 1:2.5:5. In the case of desmosterol, epoxidation to 24S,25-epoxycholesterol and 27-hydroxylation was observed, at roughly equal rates. The formation of these oxysterols in the brain may be of relevance in Smith-Lemli-Opitz syndrome, desmosterolosis, and other relevant diseases, as well as in signal transduction by lipids.     

Uptake of cholesterol and cholestanol by the intestine,hemolymph, and fat body of Heliothis zea

The effect of the concentration and structure of dietary sterol on its uptake and distribution in the intestine, hemolymph and fat body was studied in sixth-instar larvae of Heliothis zea. When cholesterol (cholest-5-en-3β-ol) was inoculated per os into the foregut of larvae, it was rapidly taken up by the intestine. Some of the dietary sterol then passed into the hemolymph, primarily via the midgut, during at least the first 9 h after inoculation, while at least 7% of the dose remained associated with the intestine. The amount of dietary sterol per 0.10 g of hemolymph increased until it reached 3–6% of the dose after 9 h. The amount of sterol per 0.10 g of the fat body increased to as much as 5% of the dose after 10 h. As the concentration of sterol in the dose increased from 0.3 to 15 μg/4 μl, the amount of sterol associated with the intestine, hemolymph, and fat body also increased. When cholesterol was inoculated intrahemocoelically, instead of per os, the amount of sterol in the hemolymph decreased, for at least the first 8 h after inoculation, and may have been absorbed, at least in part, by the intestine. The absence of a double bond in cholestanol (5α-cholestan-3β-ol) had no significant effect, at least 5 h after inoculation, on the uptake and distribution of this sterol in the intestine, hemolymph, and fat body of the larva. The results of this study indicate that although larvae of H. zea fed cholestanol have a slower rate of growth than those fed cholesterol, this may be due to differences in the utilization of the two sterols rather than to differences in their uptake by the tissues.     

Incorporation of methionine-[methyl-2H3] and mevalonic acid-[2-14C,(4R)-4-3H1] into Phycomyces blakesleeanus sterols

Ergosterol, episterol, 4α-methyl-5α-ergosta-8,24(28)-dien-3β-ol and 24-methylene-24,25-dihydrolanosterol, isolated from Phycomyces blakesleeanus grown in the presence of methionine-[methyl-²H₃], each contained two deuterium atoms; lanosterol, however, was unlabelled. The ¹⁴C:³H atomic ratio of the following sterols isolated from P. blakesleeanus grown in the presence of mevalonic acid-[2-¹⁴C,(4R)-4-³H₁], was: ergosterol, 5:3; episterol, 5:4; ergosta-5,7,24(28)-trien-3β-ol, 5:3; 4α-methyl-5α-ergosta-8,24(28)-dien-3β-ol, 5:4; 24-methylene-24,25-dihydrolanosterol, 6:5; lanosterol, 6:5. The significance of these results in terms of ergosterol biosynthesis is discussed.     

The metabolism of ingested and injected [3H]ecdysone by final instar larvae of Heliothis armigera

ABSTRACT. When larvae of Heliothis armigera (Hüber) are fed on a diet containing [³H]ecdysone they produce large quantities of ecdysone 22-palmitate, probably in the gut. The radiolabel is excreted in the faeces chiefly as ecdysone 22-palmitate, but appreciable quantities of unchanged ecdysone are also found together with traces of ecdysone 2-and 3-acetates. No polar metabolites are found with ingested ecdysone, and the ecdysone probably did not penetrate the gut wall, since on injection into the body, ecdysone was appreciably converted into polar metabolites.     

Response of females of the braconid parasitoid Microplitis demolitor to frass of larvae of the Noctoids, Heliothis zea and Trichoplusia ni and to 13-methylhentriacontane

Microplitis demolitor Wilkinson, a solitary larval parasitoid of several species of Noctuidae, has been imported into the United States from Australia. A closely related species, Microplitis croceipes (Cresson), is native to the United States. The host-selection behavior of M. demolitor females is similar to that of M. croceipes in that it is stimulated by kairomones (including 13-methylhentriacontane) in the frass of Heliothis zea (Boddie) larvae, larval diet affects the kairomonal activity of the frass, and exposure to frass prior to release stimulates host-selection behavior. M. demolitor females also respond to frass from Trichoplusia ni (Hübner) larvae that had fed on Pink Eye Purple Hull Cowpea cotyledons.

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Réponse de femelles de Microplitis demolitor sur la nourriture de chenilles de noctuelles et sur 13-methylhentriacontane

Résumé Microplitis demolitor, un parasitoïde solitaire de plusieurs espèces de chenilles de noctuelles, a été introduit d'Australie aux Etats-Unis comme agent potentiel de contrôle biologique. Les fèces des chenilles d'Heliothis zea et Trichoplusia ni élevées sur des cotyledons de pois (Pink Eye Purple Hull Cowpea) stimulent les femelles à sélectionner un hôte, mais les fèces des chenilles des deux espèces élevées sur diète CSM ne possèdent pas cette activité. Un extrait hexanique des fèces des chenilles de H. zea élevées sur cotyledons de pois stimule également ce comportement, de même que le 13-methylhentriacontane, substance présente dans les fèces des chenilles de H. zea (Jones et al., 1971). Les femelles de M. demolitor exposées immédiatement avant leur lâcher en serre aux fèces des chenilles de H. zea, nourries de cotyledons de pois, parasitent un plus fort pourcentage (41.7%) de chenilles de H. zea que cells qui n'ont pas été exposées aux fèces (13.9%).Le comportement de sélection de l'hôte des femelles de M. demolitor est donc semblable à celui des femelles de Microplitis croceipes, un parasitoïde étroitement apparenté indigène des Etats-U-nis. La femelle, par exemple, est stimulée par une kairomone des fèces des larves de H. zea nourries sur des cotyledons de pois (incluant le 13-methyl-hentriacontane), la diète affecte l'activité kairomonale des fèces, et une exposition préalable aux fèces avant le lâcher stimule le comportement de sélection de l'hôte.La stimulation du comportement de sélection de l'hôte, au moment du lâcher peut être utilisée pour améliorer l'efficacité des lâchers des parasitoïdes dans les programmes de contrôle biologique.

     

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.

     

Relationship of Heliothis zea predators, parasitoids and entomopathogens to canopy development in soybean as affected by Heterodera glycines and weeds

The influence of canopy development in soybean on the survival of corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), egg and larval stages and population dynamics of arthropod fauna were evaluated in field trials during 1986–88 in eastern North Carolina. Soybean canopy size decreased as soybean cyst nematode, Heterodera glycines Ichinohe (Nematoda: Heteroderidae), initial population densities increased. Plant species composition of the soybean canopy was affected by weed population densities. Mortality of H. zea larvae due to parasitism and infection with entomopathogens was greater in closed canopy and (or) weedy soybeans than in very open and (or) weed free soybeans. Predation and parasitism of corn earworm eggs were similar across nematode and weed density treatments. Natural enemy populations increased to highest levels during July in closed canopy and (or) weedy soybeans, coinciding with availability of largest prey population reservoirs. A delay in colonization of very open and (or) weed free soybeans by beneficial arthropods until mid to late August allowed greater H. zea larval survival than in closed canopy and (or) weedy soybeans. Arthropod species richness was generally greatest in closed canopy and (or) weedy soybeans during mid to late July, with differences becoming nonsignificant in August and early September. Mean and maximum ambient temperatures were higher and relative humidities lower in open canopy than in closed canopy plots. These conditions were less favorable for development of pathogens and natural enemies.     

Structure and enzymology of Δ-3-ketosteroid isomerase

The three-dimensional structures of Δ⁵-3-ketosteroid isomerases from two different bacterial species have been determined. The structures reveal an unusually apolar active site, in which each of several competitive inhibitors of the enzyme are held by two hydrogen bonds with the general acids Tyr14 and Asp99, and by hydrophobic interactions. The hydrogen bond between the Tyr14 hydroxyl and the C3 oxyanion of a transition-state analog is a low-barrier hydrogen bond, as indicated by a highly deshielded nuclear magnetic resonance. Structural and other biochemical studies have enabled the proposal of a detailed catalytic mechanism for Δ⁵-3-ketosteroid isomerase and provided a major thrust towards understanding the mechanism not only in chemical terms but also in energetics terms.     

The rate of ATP synthesis catalyzed by reconstituted CF0F1-liposomes: Dependence on ΔpH and Δψ

The kinetics of proton-transport coupled ATP synthesis in CF₀F₁ reconstituted into asolectin liposomes was investigated upon energization of the membrane by an artificially generated ΔpH and Δψ. With a rapid mixing system the rate of ATP synthesis was measured at short reaction times (under 200 ms) where all parameters (ΔpH, Δψ, substrate and product concentrations) remain practically constant at their initial values. The rate of ATP synthesis depends, in a sigmoidal way, on ΔpH, the maximal rate being 200 ATP per CF₀F₁ per s. At constant ΔpH, an additional diffusion potential increases the rate until the maximal rate is reached.