Action of the ecdysteroid agonist tebufenozide in susceptible and artificially selected beet armyworm

Toxicity assays with tebufenozide, the first commercial non-steroidal ecdysteroid agonist, against a laboratory strain of the beet armyworm, Spodoptera exigua (Hübner), demonstrated the promise of this new compound for the control of this important pest. Experiments to select insects artificially from the laboratory strain by continuous exposure of larval instars to corresponding LC₂₅ doses of tebufenozide for over 12 generations (G₀→G₁₂: 14–15 months), revealed no loss in susceptibility to the insecticide for up to five generations. Moreover, retention and fate of ¹⁴C-labelled tebufenozide were investigated using G₆ larvae from the selection experiments and the results compared with those for the susceptible (G₀) larvae. In addition, piperonyl butoxide, an inhibitor of monooxygenases, when ingested by larvae along with tebufenozide, increased the susceptibility of intoxicated larvae to this ecdysteroid agonist, indicating its oxidative metabolism in Spodoptera larvae. © 1998 Society of Chemical Industry.     

The geopolitical economy of Thailand's marine plastic pollution crisis

Currently approximately 9 million tons of plastic enter the world's oceans annually. This is a major transboundary problem on a global scale that threatens marine wildlife, coastal ecologies, human health and livelihoods. Our concern in this paper is with the environmental governance of marine plastic pollution that emanates from Thailand, the sixth biggest contributor globally. By zooming in on land‐based polluters in Thailand, we highlight both the systemic nature of the marine plastic problem and the relative impunity with which drivers of transboundary environmental harm function at all levels of governance. Drawing from 19 interviews conducted with actors from the public, private and non‐profit sectors, we examine three stages of the problem: production, consumption and waste management. We found that three major barriers prevent Thailand's government, private sector and citizens from engaging in the sort collective action needed to reduce marine plastic pollution. They are: (i) insufficient incentives to enact political change; (ii) scalar disconnects in waste management; and (iii) inadequate public and private sector ownership over plastic waste reduction. As the state alone cannot change corporate and consumer behaviour, we argue that multi‐stakeholder efforts across organisational scales of governance and administrative boundaries are needed to address the barriers.     

Effect of a combination of chlorine dioxide and thiophanate-methyl pre-planting seed tuber treatment on the control of black scurf of potatoes

The pre-planting seed tuber treatments of chlorine dioxide (ClO₂), thiophanate-methyl (TPM), and a combination treatment of ClO₂, followed by TPM, were evaluated for control of stem canker and black scurf (Rhizoctonia solani), and storage rots; black scurf, common scab (Streptomyces scabies), dry rot (Fusarium spp.) and silver scurf (Helminthosporium solani) on potato (Solanum tuberosum L.) cv. Kennebec. Field experiments were conducted in two consecutive years, 1999 and 2000, at the Agriculture and Agri-Food Canada Research Farm in Harrington, Prince Edward Island (PEI), Canada. The combination treatment of ClO₂ (200 μg g⁻¹) and TPM (50 g active ingredient100 kg⁻¹ of tubers) significantly (P=0.05) reduced stem canker and black scurf on progeny tubers at harvest and after storage. The low incidence of scab and dry rot in untreated controls hindered the evaluation of the efficacy of the combination treatment and also showed that conditions were not favourable for disease development during this period at Harrington. The combination treatment was not effective on silver scurf in storage. A comparison among control, ClO₂, TPM, and the combination treatment indicates that pre-planting ClO₂ treatment may have killed the majority of the black scurf sclerotia on the tuber surface and that the combination of TPM fungicide treatment following ClO₂ treatment gave protection to progeny tuber by suppressing the growth of the R. solani. A higher marketable yield was observed in the combination treatment as compared with the untreated control. Phytotoxicity was not observed in tubers treated with the combination treatment.     

A manganese(IV)/iron(III) cofactor in Chlamydia trachomatis ribonucleotide reductase

In a conventional class I ribonucleotide reductase (RNR), a diiron(II/II) cofactor in the R2 subunit reacts with oxygen to produce a diiron(III/IV) intermediate, which generates a stable tyrosyl radical (Y*). The Y* reversibly oxidizes a cysteine residue in the R1 subunit to a cysteinyl radical (C*), which abstracts the 3'-hydrogen of the substrate to initiate its reduction. The RNR from Chlamydia trachomatis lacks the Y*, and it had been proposed that the diiron(III/IV) complex in R2 directly generates the C* in R1. By enzyme activity measurements and spectroscopic methods, we show that this RNR actually uses a previously unknown stable manganese(IV)/iron(III) cofactor for radical initiation.     

Comparison of the total phenolic and ascorbic acid content of freeze-dried and air-dried marionberry,strawberry, and corn grown using conventional,organic, and sustainable agricultural practices

Secondary phenolic metabolites play an important role in plant defense mechanisms, and increasing evidence indicates that many are important in human health. To date, few studies have investigated the impact of various agricultural practices on levels of secondary plant metabolites. To address this issue, the total phenolic (TP) content of marionberries, strawberries, and corn grown by sustainable, organic, or conventional cultural practices were measured. Additionally, the effects of three common postharvest processing treatments (freezing, freeze-drying, and air-drying) on the TP content of these agricultural products were also investigated. Statistically higher levels of TPs were consistently found in organically and sustainably grown foods as compared to those produced by conventional agricultural practices. In all samples, freeze-drying preserved higher levels of TPs in comparison with air-drying.     

Colonization and survival capacities underlying the multifaceted life of Rhodococcus sp. PBTS1 and PBTS2

Little is known about the epidemiology of the newly emerged disease on pistachio rootstock designated pistachio bushy top syndrome (PBTS). Here, we analysed the survival and colonization capacities of the two causative agents, Rhodococcus corynebacterioides-like PBTS1 and R. fascians PBTS2, in the different habitats they occupy. Additionally, we examined their chromosomal sequences for genes that would support their ecology and provide experimental evidence for some of their predicted functions. We demonstrate that the soil competence of PBTS2 is better than that of PBTS1 and that both bacteria behave chemotactically, allowing them to translocate from soil to the rhizoplane. Once on the rhizoplane and the phylloplane, the PBTS bacteria form extensive epiphytic biofilms, probably aided by exopolysaccharide production. From these biofilms, the bacteria colonize the plant's interior tissues through the formation of ingression sites, likely created by the localized activity of cell wall-degrading enzymes. The observed systemic spreading of the PBTS strains throughout the plant tissues is probably mediated by surface motility and agrees with the occurrence of symptoms in both the aerial and root parts of the plant host. Based on all available information, we provide a working model on this pathosystem to be used as a conceptual framework for future research.     

Carboxylamidases inSpodoptera exigua: properties and distribution in the larval body

Resistance to many insecticides demonstrated by the beet armyworm,Spodoptera exigua (Hübner), can be caused by the action of carboxylamidases. A colorimetric method, based on the hydrolysis of 4-nitroacetanilide to 4-nitroaniline by carboxylamidases, was used for evaluating biochemical properties of these detoxifying enzymes in beet armyworm. The optimum pH and temperature were 7.5 and 38°C, respectively. K_m (Michaelis constant) and V_max (maximal velocity) at 28°C were 2.3 X 10^-4 M and 2.06 nmol min^-1 mg protein^-1, respectively. The enzyme activity was evaluated in several body parts and located mostly (66.2%) in the midgut. The soluble fraction (supernatant of 105,000g) contained the highest enzyme activity relative to the total (69.3%), and exhibited the highest specific activity. Carboxylamidase activity was totally inhibitedin vitro at a concentration of 10^-6 M methomyl. The analysis of thein vitro inhibition kinetics indicated the ability of methomyl and diflubenzuron to inhibit carboxylamidases noncompetitively. Over 95% inhibitionin vivo was obtained when the larvae were fed with castor bean leaves dipped in 250 mgl ^-1 of methomyl. Thein vivo enzyme activity could be reduced to half with a pretreatment of 15 mgl ^-1 diflubenzuron.     

Albumin and cytochrome P450 binding characteristics of juvenile hormone and its analogs

Binding data were gathered for the cecropia juvenile hormone (methyl(E, E cis)-10,11-epoxy-7-ethyl-3,11-dimethyl-2,6-tridecadienoate) and two of its analogs {isopropyl(2E, 4E)-11-methoxy-3,7,11-trimethyl-2,4-dodecadienoate; (E)-4-[(6,7-epoxy-3,7-dimethyl-2-nonenyl)-oxyl]-1,2-(methylenedioxy)benzene} with bovine serum albumin and rat hepatic microsomal cytochrome P₄₅₀. The proteins were found to bind the juvenile hormone and juvenile hormone analogs with affinity constants ranging from 10⁵ to 10⁶M^?1. Thermodynamic calculations suggest that the binding of all three compounds is electrostatic in nature and that the size of the ether and ester substituents can greatly influence the binding to proteins. The juvenile hormone and its analogs all formed spectrally apparent Type I complexes with oxidized cytochrome P₄₅₀; one of the juvenile hormone analogs formed a spectrally observable product adduct with reduced cytochrome P₄₅₀. The product complex may contribute many of the hormonal effects observed for this compound.