Effects of Single Metals and their Mixtures on Selected Enzymes of Carcinus Maenas

In this work, the acute effects of copper, chromium and mixtures of both metals on females of the marine crab Carcinus maenas were investigated. The parameters indicative of toxicity were mortality and the activity of the enzymes acetylcholinesterase (AChE), lactate dehydrogenase (LDH) and glutathione-S-tranferases (GST). LC50 values determined at 96 hr were 51.8 mg L^-1 for copper, 49.8 mg L^-1 for chromium and 15 mg L^-1 Cu + 43.6 mg L^-1 Cr for the mixture of both metals. Copper, chromium and the mixtures of both metals significantly inhibit haemolymph AChE, ovarian LDH and hepatopancreas GST after an in vivo exposure of 96 hr to concentrations lower than NOEC values for mortality. Furthermore, the mixtures tested showed a more pronounced effect than individual agents.     

Mode of action of the plant-derived silphinenes on insect and mammalian GABAA receptor/chloride channel complex

The silphinenes are tricyclic sesquiterpenes that have antifeedant and toxic effects in insects and structural similarity to the known GABA antagonist, picrotoxinin. In murine synaptoneurosomes, silphinenes block GABA-stimulated influx of ³⁶Cl⁻ with EC₅₀s in the range of 10-30 μM. In insects, silphinenes were tested in neurophysiological recordings of central neurons from third instar Drosophila melanogaster larvae. Silphinenes reversed the blockage of neuronal firing induced by GABA, but had little effect below 100 μM. The structure-activity profile observed in the murine chloride flux assay was also observed in the larval neurophysiological assay, indicating little selectivity for the silphinenes. A reference silphinene was equally active on nerve preparations from the rdl strain of D. melanogaster, which is resistant to channel-blocking antagonists via an altered GABA receptor. This latter finding suggests that silphinenes interact with the insect GABA receptor in a manner somewhat different from PTX, and that rdl resistance in the field may have little effect on silphinene efficacy.     

Antifeedant and sublethal effects of imidacloprid on Asian citrus psyllid,Diaphorina citri

BACKGROUND: Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, transmits the causal bacteria of the devastating citrus disease huanglongbing (HLB). Because of the variation in spatial and temporal uptake and systemic distribution of imidacloprid applied to citrus trees and its degradation over time in citrus trees, ACP adults and nymphs are exposed to concentrations that may not cause immediate mortality but rather sublethal effects. The objective of this laboratory study was to determine the effects of sublethal concentrations of imidacloprid on ACP life stages. RESULTS: Feeding by ACP adults and nymphs on plants treated daily with a sublethal concentration (0.1 µg mL^?1) of imidacloprid significantly decreased adult longevity (8 days), fecundity (33%) and fertility (6%), as well as nymph survival (12%) and developmental rate compared with untreated controls. The magnitude of these negative effects was directly related to exposure duration and concentration. Furthermore, ACP adults that fed on citrus leaves treated systemically with lethal and sublethal concentrations of imidacloprid excreted significantly less honeydew (7–94%) compared with controls in a concentration‐dependent manner suggesting antifeedant activity of imidacloprid. CONCLUSIONS: Sublethal concentrations of imidacloprid negatively affect development, reproduction, survival and longevity of ACP, which likely contributes to population reductions over time. Also, reduced feeding by ACP adults on plants treated with sublethal concentrations of imidacloprid may potentially decrease the capacity of ACP to successfully acquire and transmit the HLB causal pathogen. Copyright © 2009 Society of Chemical Industry     

Effects of pymetrozine, an antifeedant of Hemiptera, on Asian citrus psyllid, Diaphorina citri, feeding behavior, survival and transmission of Candidatus Liberibacter asiaticus

BACKGROUND: Vector‐borne plant disease management can be enhanced by deployment of antifeedants in addition to the use of broad‐spectrum neurotoxic insecticides. The effects of pymetrozine on Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, feeding behaviour, survival and transmission of Candidatus Liberibacter asiaticus (Las), the presumed causal pathogen of huanglongbing, were investigated. RESULTS: Pymetrozine applied at 52 and 104 µg mL^?1 to citrus plants [Swingle citrumelo (X Citroncirus webberi Ingram and Moore)] modified the feeding behavior of ACP and increased the amount of time spent performing non‐penetration behaviors while decreasing the time spent performing ingestion behaviors compared with the controls 1 day after treatment. However, the antifeedant effect of pymetrozine subsided 5 days after application. Pymetrozine reduced the survival of both adults and nymphs on treated plants compared with the control. However, it had a greater impact on survival of nymphs than on survival of adults. Pymetrozine applied at 52 and 104 µg mL^?1 on Las‐infected ‘Valencia’ sweet orange plants [Citrus sinensis L. (Osbeck)] reduced acquisition (12 and 21% respectively) and transmission (11 and 18% respectively) of Las by feeding ACP adults compared with the controls; however, these reductions were not statistically significant. CONCLUSIONS: Pymetrozine exhibited moderate antifeedant effects by modifying the feeding behavior of ACP adults with short residual activity. The impact of pymetrozine on survival of nymphs was greater than on adults at the higher concentrations tested. Pymetrozine also reduced the acquisition and transmission of Las by feeding ACP adults up to 21 and 18%, respectively, compared with untreated controls. Copyright © 2010 Society of Chemical Industry     

An application of digital imagery analysis to understand the effect of N application on light interception,radiation use efficiency,and grain yield of maize under various agro-environments in Northern Mozambique

Light-based analysis is a fundamental approach to quantify the effects of factors determining crop growth in a given environment. The objectives of this study are to confirm the applicability of a digital imagery technique to extract green leaf areas for estimating light interception (LI) of maize canopy and to understand the effect of fertilizer application on the LI and radiation use efficiency (RUE) of maize under various agro-environments in Northern Mozambique. A locally recommended variety, Matuba, was grown in a single season with three different N application rates (0, 30, and 80 kgN ha^?1) at one hot/dry low-elevation site, two hot/humid mid-elevation sites, and one cool/humid high-elevation site. Repeated measurements with quantum sensors revealed that the digital imagery is applicable to estimate the LI of maize except for leaf-senescing period close to maturity. The N application demonstrated profitable yield increases with agronomic nitrogen use efficiencies (kg grain yield per kg N input) of 20.6–35.3 kg kg^?1 except for the low-elevation site with severe drought stress. In the mid-elevation sites, the yield increases were mostly explained by the improvement of RUE while the effect on LI was small because the vegetative growth was naturally vigorous under high temperatures irrespective of N inputs. At the high-elevation site, the N application improved its stagnant initial canopy development and increased both RUE and LI. The simple and inexpensive imagery technique should be useful to identify physiological basis of maize responses to fertilizer application and its interaction with regional environment even under poorly equipped regions in the tropics.     

Effects of dimethoate and beta-naphthoflavone on selected biomarkers of Poecilia reticulata

The main objective of the present study was to investigate if a battery of enzymatic biomarkers was suitable for use as effect criteria in acute toxicity tests with Poecilia reticulata. To attain this objective, the in vivo effects of dimethoate and beta-naphthoflavone on acetylcholinesterase (AChE), cytochrome P4501A-dependent monooxygenase activity of 7-ethoxyresorufin O-deethylase (EROD), glutathione S-transferases (GST), lactate dehydrogenase (LDH) and Na⁺-K⁺-ATPase activities of P. reticulata were studied. After 96 h of exposure to sublethal concentrations (0.063 mg l⁻¹ to 1 mg l⁻¹) of the pesticide, an inhibition of the enzymes AChE and GST, as well as an induction of LDH was observed. The compound beta-naphthoflavone significantly induced both EROD and GST. The remaining enzymes analysed were not significantly altered by the exposure to beta-naphthoflavone (0.82 mg l⁻¹ to 1.7 mg l⁻¹). These results suggest that in vivo toxicity tests based on the biomarkers used in this study are sensitive and present advantages to conventional acute tests based on mortality, since they were able to detect sublethal effects in a short-period of time (96 h) indicating target and/or detoxification mechanisms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Performance of pre-commercial release formulations of spinosad against five stored-product insect species on four stored commodities

Two liquid and one dry pre-commercial release spinosad formulations were evaluated at the labeled rate of 1?ppm against five stored-grain insect species on wheat, short-grain rice, long-grain rice, and maize. Except on maize, efficacy of spinosad was compared with a currently registered grain protectant, chlorpyrifos-methyl (3?ppm) plus deltamethrin (0.5?ppm). The 7- and 14-day mortalities of the lesser grain borer, Rhyzopertha dominica, were 99.0-100.0% on spinosad and chlorpyrifos-methyl plus deltamethrin-treated wheat, short-grain rice, and long-grain rice. Adult progeny of R. dominica after 42?days on these commodities decreased by 99.7-100.0% relative to progeny production on untreated wheat. Mortality and reduction in adult progeny of the rice weevil, Sitophilus oryzae, on the three commodities, and that of the maize weevil, Sitophilus zeamais, on maize and the red flour beetle, Tribolium castaneum, on wheat were 100.0% only with chlorpyrifos-methyl plus deltamethrin. The liquid spinosad formulations were most effective against the Indianmeal moth, Plodia interpunctella, on maize and wheat. Except for R. dominica, the effectiveness of spinosad on the other species varied with the formulation, exposure time, and commodity. Chlorpyrifos-methyl plus deltamethrin was effective against insect species on the commodities tested.     

Can the Activities of Acetylcholinesterase and Glutathione S-Transferases of Crangon crangon (L.) be Used as Biomarkers of Fuel Oil Exposure?

This work aimed to determine the sensitivity of acetylcholinesterase (AChE) and glutathione S-transferases (GST) activities of Crangon crangon (L.) to the water-accommodated fraction (WAF) of the fuel oil spilled by the oil tanker Prestige, in order to assess their usefulness as markers for this kind of pollution. Laboratory exposure of shrimps to WAF of weathered Prestige fuel oil showed no significant interference with AChE activity. Significant induction of GST activity was observed, potentially as a result of high concentrations of polycyclic aromatic hydrocarbons. However, these results were only obtained with the higher WAF concentrations tested. It was concluded that AChE and GST activities of C. crangon were not useful biomarkers for short-term exposure to the WAF of fuel oil spilled by the tanker Prestige and carried to the beaches of Galicia (NW Spain).