Effect of canopy cover,seeding depth,and soil moisture on emergence of Centaurea maculosa and C. diffusa*

The effects of canopy cover, seeding depth, and soil moisture on emergence of Centaurea maculosa Lam. and C. diffusa Lam. were studied. Canopy cover had no effect on ermergence rate (seedlings/day/100 seeds) of either species. Seeds of both species emerged faster when placed on the soil surface. Emergence rate decreased as seeding depth increased. Both species required more than 55% initial soil moisture to initiate emergence, with 65–70% being optimum. Percentage emergence followed exactly the same trend as emergence rate. C. maculosa had better emergence characteristics over a wider range of conditions than C. diffusa, possibly being some of the reasons for the former having a wider geographical distribution in the United States and Canada.     

Metabolic fate of [14C]endrin in bluegill fish

Bluegill absorbed 85% of 1 ppb of endrin from water within 48 hr under static exposure conditions. The absorbed radiocarbon was eliminated linearly with a half-life of about 4 weeks. Analyses of eliminated radioactivity revealed only conjugated metabolites. 12-anti-Hydroxyendrin and 12-syn-hydroxyendrin were tentatively identified by cochromatography using thin-layer chromatography/autoradiography and gas chromatography. These metabolites were also present as conjugates in the fish organs. Seventy-three percent of the absorbed radioactivity recovered from fish extracts was in the form of unchanged endrin.     

Comparative inhibition of the juvenile hormone esterases from Trichoplusia ni,Tenebrio molitor, and Musca domestica

Twenty-seven compounds were screened as potential inhibitors of juvenile hormone esterases. Of these compounds O-ethyl-S-phenyl phosphoramidothiolate provided the best inhibition for the cabbage looper, Trichoplusia ni (Hubner), and the yellow mealworm, Tenebrio molitor L., while the juvenile hormone esterases of the house fly, Musca domestica L., were best inhibited by a juvenoid carbamate (1-(m-phenoxy-N-ethyl carbamate)-3,7-dimethyl-7-methoxy-2E-octene). The inhibition patterns of T. ni and T. molitor are similar, while those of M. domestica are relatively different. Further studies on the juvenile hormone and α-napthyl acetate esterases of T. ni showed that they could be differentially inhibited. Diisopropyl phosphorofluoridate and an alkyl trifluoromethyl ketone selectively inhibit the hydrolysis of α-naphthyl acetate and juvenile hormone, respectively, while O-ethyl-S-phenyl phosporamidothiolate inhibits both enzymes. The juvenile hormone esterases of T. ni also appear to be unique enzymes that are selective for juvenile-hormone-like molecules. The in vivo inhibition of T. ni juvenile hormone esterases by O-ethyl-S-phenyl phosphoramidothiolate slows the in vivo hydrolysis of juvenile hormone and results in delayed pupation and malformed larvae that resemble larval-pupal intermediates. Thus, the esterases involved in juvenile hormone metabolism appear to be important in juvenile hormone regulation.     

Physiological actions of dinoterb,a phenol derivative: 2. Effects on isolated plant mitochondria and chloroplasts

Dinoterb, a contact herbicide, affects respiration and photosynthesis of mitochondria and chloroplasts. On mitochondria, at low concentrations, it acts as an uncoupler of oxidative phosphorylation; at higher concentrations, it inhibits the electron transport chains, probably before cytochrome c. On chloroplasts, dinoterb has a stimulatory effect on oxygen uptake in the reduced dichlorophenol-indophenol→methyl viologen couple; however, it is also an inhibitor of the Hill reaction and its site of inhibition is located before plastoquinone, near photosystem II.     

Studies on bovine demodecosis in northern Nigeria

Summary The study reported in the present paper discusses the clinical and histological picture of bovine demodecosis and the morphology of Demodex mites as seen in four cows suffering from generalized demodecosis. There were no clinical signs of other skin affections. Changes in both the number and the appearance of visible skin lesions were seen and related to the level of nutrition and the exposure to sunshine of the cattle. Histological sections of some skin nodules showed the presence of mite colonies in the hair follicles. Only adults were seen in the sebaceous glands. Microscopical study of the morphology of the mites revealed the presence of two types of demodicids in the skin lesions and three types from epilated eyelashes. Morphological criteria are presented to aid in identification of species and of life stages.     

Precocene II metabolism: Comparative in vivo studies among several species of insects,and structure elucidation of two major metabolites

Several species of insects, exhibiting varying responsiveness to the juvenile hormone antagonist precocene II (6,7-dimethoxy-2,2-dimethylchromene), were challenged topically with a tritiated preparation of the title compound. Metabolism of [³H]precocene II was subsequently examined by withdrawing hemolymph samples from treated animals at appropriate time intervals and characterizing the extractable radiolabel chromatographically. Quantitative (or qualitative) differences observed between the respective metabolic profiles were found not correlative with specimen sensitivity to precocene. Production of two heretofore unreported metabolites, identified by spectral and chemical means as O-β-glucosides of 6- and 7-monodemethylated precocene II, was demonstrated in both sensitive and insensitive species. No evidence for the presence of a hemolymphborne, biologically effective “activated metabolite” produced in vivo by precocene-susceptible insects could be found. The latter finding may well argue for in situ bioactivation of precocene at the target tissue(s) by these sensitive insects.     

The effect of some Frescon analogs on the aquatic snail,Lymnaea stagnalis: II. Correlation of neurotoxicity to Molluscicidal effectiveness

Although the molluscicide Frescon is a strong neurotoxin to the Lymnaea stagnalis central nervous system in vitro, it is probable that the exposure of the whole animal to this molluscicide fails to result in central nervous system abnormalities: Frescon does not appear to reach the brain in sufficient quantity to disrupt its normal activity. However, only those Frescon analogs found to be neurotoxic were molluscicidal, suggesting some related mode, if not site, of action. Frescon and its analogs may act by affecting excitable tissues other than the nervous system (e.g., the snail musculature) by altering certain functional and/or structural membrane properties.     

Britain's Pest Monitoring Network for Aphids and Moths1

There is a need for continuous monitoring of insect populations to provide, in the short term, early warning of the presence of pests and, in the long term, to record and analyse faunal changes resulting from changes in agricultural practice and urbanisation, and the rate of spread of pests and resistance to pesticides. The Rothamsted Insect Survey examines aerial populations of two major insect groups throughout the year. Two hundred and sixty species of aphids are sampled daily at a height of 12 m by a grid of 21 suction traps. Early warning of the migration of 32 aphid species of economic importance is provided in weekly bulletins issued to farmers and advisers. This aerial sampling is generally cheaper, quicker and provides earlier warning of the presence of aphids than crop sampling. Six hundred species of moths are sampled by 195 light traps and the data are being used to assess the magnitude and reasons for seasonal, annual and long-term changes in the insect fauna, especially of pest species. The information on both insect groups is stored on magnetic tape and computerized maps are produced to illustrate the distribution in time and space of given species and as a research tool in studies on their population dynamics. The prospects and value of extending this system to continental Europe, and the help and expertise that Rothamsted could give in the eventuality, are outlined. Les populations dinsectes doivent dtre soumises à un recensement continu afin dassurer, à court terme, un avertissement précoce de la presence des ravageurs, et, à long terme, la possibilite d'enregistrer et d'analyser les changements qui interviennent dans la faune à la suite de I'evolution des pratiques agricoles et de I'urbanisation, et de déterminer la vitesse de dissémination des ravageurs ainsi que leur résitance aux pesticides. Le «Rothamsted Insect Survey » observe les populations de deux groupes d'insectes durant toute L'année. Deux cents soixante espèces de pucerons sont échantillonnées quotidiennement dans 21 localites differentes à L'aide de pièges à succion disposes a 12 m au-dessus du sol. Les exploitants et les conseillers sont avertis, par des bulletins hebdomadaires, des migrations de 32 espèces de pucerons d'importance économique. L'échantillonnage aérien semble être meilleur marché et plus rapide qu'un échantillonnage réalisé au niveau de la culture;de plus, il assure un avertissement plus précoce. Six cents espèces de lépidoptéres sont recensées au moyen de 195 piéges lumineux dans le dessein danalyser la magnitude et les causes des variations saisonnieres, annuelles, et à long terme surtout en ce qui concerne les ravageurs. Les données ainsi recueillies sont enregistrées sur bandes magnétiques et servent à L'etablissement de cartes à L'aide d'ordinateurs; ces cartes indiquent la distribution temporelle et spatiale de chaque espèce et constituent un élement important dans l'étude de la dynamique des populations. L'extension de ce réseau à L'Europe continentale présente deL'intérêt et la façon dont la Station de Rothamsted peut y apporter son soutien est exposée dans la présente communication.     

An Approach to Forecasting the Incidence of Potato and Cereal Aphids in Scotland1

Many potato and cereal infesting aphids in Scotland are either completely cr partially anholocyclic. This makes forecasting their first appearance and abundance on crops difficult, when compared with holocyclic species such as Aphis fabae Scopoli. This paper describes an analysis of the early movement of nine aphid species, commonly found on potatoes and cereals in Scotland, in relation to winter and early spring climate. Data on their early movement have been extracted from the catches in three of the sjx.12–2.rn suction traps now operating in Scotland in cooperation with the Rothamsted Insect Survey. The particular importance of early spring temperature has been established. The extension of this work to develop a predictive forecast of summer activity of anholocyclic aphid species is discussed. En Ecosse, une forte proportion de pucerons des pommes de terre et des céréales est entièrement ou partiellement anholocyclique. Ceci complique la prévision sur le moment de leur première apparition et sur leur abondance par rapport aux espéces holocycliques telles qu'Aphis, fabae. Cette étude concerne les déplacements précoces de neuf espéces de pucerons retrouveés fréquemment sur les pommes de terre et les céSreales. Les données sur les deplacements ont été obtenues à partir de trois des six piegès à succion de I2,2 m installes en Ecosse en cooperation avec le « Rothamsted Insect Survey », Il est apparu que la température printanière revêt une importance particuliere. Les recherches se poursuivent dam le but d'établir des prévisions sur le développement estival des espèces anholocycliyues de pucerons.     

Insect epoxide hydrolase: Properties of a purified enzyme from the southern armyworm (Spodoptera eridania)

An epoxide hydrolase purified from midgut microsomes of southern armyworm (Spodoptera eridania) larvae exhibited high activity toward monosubstituted epoxides (1,2-epoxyoctane, 1,2-epoxypropane, and styrene oxide) and lower activity toward cis-1,2-disubstituted epoxides (cyclohexene oxide, and the cyclodienes HEOM, HCE, and chlordene epoxide). Trisubstituted epoxides (2-methyl-2,3-epoxyheptane and JH-1) as well as several cyclodiene insecticides (dieldrin, endrin, endo-epoxyaldrin, and anti-heptachlor epoxide) were refractory to enzymatic attack. It is concluded that both lipophilic and steric factors dictate the substrate specificity of the enzyme. With cyclohexene oxide the enzyme yields the 1R, 2R enantiomer of the trans-diol. The purified enzyme is inhibited by several epoxides and mixed-function oxidase inhibitors and the potency of 3,3,3-trichloro-1,2-epoxypropane and sodium picrylsulfonate suggest the importance of electronic factors in the inhibitory mechanism. Studies with specific amino acid modifiers suggest the presence of an essential lysine or histidine residue at the active site and indicate that the enzyme lacks a metal ion requirement and an essential cysteine residue. The purified enzyme has a molecular weight of 46,000 daltons and amino acid analysis and immunochemical studies show it to be very similar to, but not identical with, the epoxide hydrolase from mammalian liver microsomes.