Effect of water stress on abundance of twospotted spider mite on soybeans under greenhouse conditions

A rope wick technique was used to establish different levels of water stress in potted, greenhouse-grown soybean, Glycine max (L.) Merrill, plants. Water stress reduced, within a single generation, the overall abundance (number of mites/cm² leaf) of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) and particularly influenced female mites and eggs. Mites were most numerous in the upper strata of soybean plants on youger and possibly more nutritious leaves.

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Influence de l'arrosage sur l'abondance de Tetranychus urticae sur soja, Glycine max en serre

Résumé Un arrosage par capillarité contrôlé a été utilisé pour maintenir différentes teneurs en eau dans des pieds empotés de G. max. Le stress hydrique a réduit, en une génération, la densité de T. urticae (nombre d'acariens/cm² de feuille), et particulièrement celle des femelles et des oeufs. Les acariens étaient plus nombreux sur les feuilles les plus jeunes et peut-être les plus nutritives des strates supérieures des pieds de soja.

     

Electronic effects in the acylation of alpha-chymotrypsin by substituted N-benzoylimidazoles

Rate constants for the acylation of alpha-chymotrypsin by a series of acyl-substituted N-benzoylimidazoles have been determined by proflavin displacement from the active site. The second-order acylation rate constants k2/Km are large [e.g., that for N-(m-nitrobenzoyl)imidazole is 1.7 X 10(4) M-1 s-1 at pH 7.5], even though Km must be quite large (plots of k vs. k/[S]0 have infinite slopes). The values of k2/Km are nearly independent of pH in the range 5.0-9.0 when the substituent group is electron donating. Electron-withdrawing substituents produce an increase in k2/Km with increasing pH until a maximum is reached near pH 7. This is also the case in acylation by the N-[p-(dimethylamino)benzoyl]-N'-methylimidazolium ion (pKapp = 6.5). While the reaction of the N'-methylated derivative is via a positively charged species at all pH values, the unmethylated compounds react through both the neutral species and the conjugate acids, with the observed pH dependence depending on the relative values of the rate constants. The limiting value of k2/Km for the N-[p-(dimethylamino)benzoyl]-N'-methylimidazolium ion is 2.1 times less in D2O than in H2O. Thus, His-57 must be participating in the acylation reaction as a general base. The limiting values of k2/Km for the corresponding N'-methylated and unmethylated derivatives differ by a factor of only 150, which is similar to the difference in the second-order rate constants for nonenzymatic OH- -catalyzed hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)     

A Belonostomus tenuirostris (Actinopterygii: Aspidorhynchidae) from the Late Jurassic of Kelheim (southern Germany) preserved with its last meal

A Belonostomus tenuirostris (Agassiz, 1833) from Late Kimmeridgian (Late Jurassic) of Kelheim (Solnhofen area; Bavaria, southern Germany) that was preserved with three prey fishes in its digestive tract is described. Two of the prey fishes can be assigned to cf. Leptolepides (Orthogonikleithridae), whereas the third possibly represents a juvenile Caturus sp. (Caturidae). This is the first record of a Belonostomus with several prey animals, and the first evidence of a caturid predated by an aspidorhynchid.     

Ploidy levels and DNA synthesis in fat body cells of the adult mosquito,Aedes aegypti: The role of juvenile hormone

Adult females of the mosquito Aedes aegypti showed two cycles of DNA replication in the fat body based on microspectrophotometric measurement of changes in nuclear DNA. The first cycle began after emergence and resulted in 80% of diploid fat body cells becoming tetraploid and 20% becoming octoploid by the end of the third day. The second replication cycle occurred 48–72 h after a blood meal and resulted in an increase in octoploid nuclei to 67% Topical application of juvenile hormone or methoprene to abdomens isolated at emergence stimulated an increase in ploidy levels above that normally seen in situ. Synthesis of DNA, estimated by incorporation of injected [³H]-thymidine, rose after emergence and remained high for 2 days. Synthesis increased again after a blood meal, reached a peak by 6 h, and returned to low levels by 24 h after the meal. The timing of DNA synthesis and a measurable increase in ploidy were temporally separated. The ploidy increase, but not DNA synthesis, was correlated with increases in juvenile hormone levels.     

Amplification of ribosomal genes and formation of extrachromosomal nucleoli in oocytes of starfish Henricia hayashi (Asteroidea: Echinasteridae)

DNA and RNA specific dyes, Ag-NOR staining and in situ hybridization were used for studying the nucleolar apparatus in the growing oocytes of Henricia hayashi (Asteroidea: Echinasteridae). A plasmid containing ribosomal genes of Drosophila melanogaster (Kolchinsky et al., 1980) labelled with 3H by nick-translation served as an rDNA probe. Multiple extrachromosomal nucleoli are formed by the cascade type as a result of growth and subsequent fragmentation of the chromosomal (primary) rDNA body and its derivative extrachromosomal (secondary) rDNA bodies. Ribosomal genes were shown in all nucleolar structures. Argentophilia of the primary and secondary DNA bodies appears to be due to the dense packing of the rDNA-containing material. Ag(+) NORs were detected in the extrachromosomal multiple nucleoli and NOR complexes. Amplification of rDNA is a highly probable conclusion from the existing data.     

Attachment of the potato leafhopper to soybean plant surfaces as affected by morphology of the pretarsus

The pulvilli of the potato leafhopper, Empoasca fabae (Harris), seem to provide a suitable mechanism for the attachment of the insect to smooth leaf surfaces. Based on morphological structure of the pretarsal and direct observations, we propose that primary orientation of the leafhoppers on smooth surfaces is achieved through a series of motions involving mainly the pulvilli. The highly irregular surface produced by the trichomes of pubescent soybean cultivars impedes normal attachment for feeding or oviposition. This impediment explains in part the near immunity of pubescent soybean and the converse susceptibility of glabrous soybean plants to the potato leafhopper.

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Résumé Les pulvilli d'Empoasca fabae paraissent fournir un mécanisme convenable pour la fixation des insectes aux surfaces lisses des feuilles.En nous basant sur la structure morphologique des prétarses et sur des observations directes, nous suggérons que l'orientation primaire sur des surfaces lisses est réalisée à partir de mouvements concernant surtout les pulvilli.La surface des cultivars pubescents de soja, rendue très accidentée par la présence des trichomes, empêche une fixation normale permettant l'alimentation et la ponte.Cet obstacle explique en partie la quasi immunité des sojas pubescents et, à l'inverse, la sensibilité des sojas glabres aux attaques d'E. fabae.