Taste sensitivity of detritivorous mosquito larvae to decomposed leaf litter

Dietary leaf litter chemistry is known to play an important ecotoxicological role in the plant–mosquito interaction in subalpine flooded areas surrounded by vegetation because of differential larvicidal effects of insoluble polyphenols formed during the leaf decaying process. This dietary interaction was investigated through comparative evaluation of the role of toxic/nontoxic leaf litter in both larval foraging and feeding behavior, by using different samples of decomposed alder leaf litter and larval Aedes aegypti as experimental references. Track analysis showed significant differences in larval foraging behavior in the absence or presence of leaf litter. Comparative alimentary preference investigations and further track analysis suggested that larvae are unable to detect leaf litter toxicity. These characteristics of the larval behavioral feeding pattern suggested that: (1) decomposed leaf litter may be involved as an important attractive food source in the habitat selection and evolutionary history of culicids, and (2) preingestive behavioral mechanisms appear to be minimally involved in the differential larval dietary adaptation to toxic leaf litter. These results may have interesting consequences for culicid biological control.     

Involvement of Ligninlike Compounds in Toxicity of Dietary Alder Leaf Litter Against Mosquito Larvae

The toxicological characteristics of dietary decomposed alder leaf litter against mosquito larvae were further investigated through enzymatic and chemical purification of a phenoliclike cell-wall fraction isolated from crude litter. The toxicity of the subfractions obtained was controlled by standard bioassays on third instars of Aedes aegypti chosen as a reference target species. Enzymatic hydrolyses of the cell-wall fraction were performed with caylase, pectolyase, esterase, and -glycosidase, in order to release, respectively, cellulose material and phenolic compounds bound to lignins. These treatments did not affect the larvicidal activity and the phenolic activity of the cell-wall fraction. Chemical alkaline and acid hydrolyses were carried out to break ester and glycosidic bonds of the cell-wall fraction. Comparison of HPLC profiles of the hydrolysates from both toxic and nontoxic fractions did not reveal differences between the phenolic acids released. Aluminum chloride, known for its phenolic complexing activity, counteracted the larvicidal activity of the cell-wall fraction. Altogether, these results suggest the involvement of ligninlike compounds in the toxicity of dietary alder leaf litter against larval mosquitoes. The toxicity of this fraction, which was very sensitive to drastic and smooth oxidations, seemed to be associated with a strong oxidative potential. These results are discussed in relation to a possible mode of action of lignins in the plant–mosquito interactions.     

Larvicidal Effect of a Cell-Wall Fraction Isolated from Alder Decaying Leaves

Decaying alder leaves in water from Alpine Aedes breeding sites, particularly their toxicity to larval Culicidae, were investigated and characterized with comparative toxicological and chemical methods. Bioassays that used third-instar Aedes aegypti as a reference species indicated that the larvicidal effect of crude leaf litter varied with decaying age of the litter, while no toxicity was detected from leaching water of the mosquito breeding sites. Ten-month-old leaf litter was the most toxic. Comparison of the different soluble and insoluble fractions obtained after sequential extraction of decomposed litter allowed us to localize the toxicity factor to an insoluble cell-wall fraction. The toxicity seems to be linked to phenolic activity. It is higher than that found for tannic acid solutions used as a reference to mimic the larvicidal effects of the molecules naturally occurring in decaying litter. The pattern of establishing the larvicidal effect of alder leaf litter in water of Alpine Aedes breeding sites is discussed.     

Light-dependent effects of alpha-terthienyl in eggs,larvae, and pupae of mosquitoAedes aegypti

Alpha-terthienyl is toxic toAedes aegypti larvae in the dark, but its activity is much enhanced in the presence of ultraviolet light. The development of first-instar larvae treated with alpha-terthienyl and ultraviolet light was followed until the emergence of adults. The LC₅₀ value for first instars was about 0.002 ppm. Practically all the larvae which survived 24 hr reached adulthood. Fourth-instar larvae were also sensitive to photochemical treatment. When their development into adults was followed, the LC₅₀ value was 0.45 ppm. Contrary to earlier reports, alpha-terthienyl was also phototoxic in pupae, but not when the adults were about to emerge. The LC₅₀ value was ca. 0.06 ppm for pupae which were 1 or 2 days old. This is the first example where the activity of a photoinsecticide has been demonstrated in pupae. Alpha-terthienyl did not affect the hatching of eggs.     

1,8-Cineole (Eucalyptol), a mosquito feeding and ovipositional repellent from volatile oil ofHemizonia fitchii (Asteraceae)

The mosquito feeding and ovipositional repellency of the major monoterpenoid present in the volatile oil ofHemizonia fitchii (Asteraceae), i.e., 1,8-cineole, was investigated. Although 1,8-cineole did not exhibit any significant mosquito larvicidal activity, it was moderately effective as a feeding repellent and highly effective as an ovipositional repellent against adultAedes aegypti (yellow fever mosquito). The ovipositional repellency of 1,8-cineole, coupled with the presence of severalHemizonia chromenes previously shown to possess mosquito larvicidal activity, may therefore account in large part for the observed suppression of local mosquito populations which was associated withH. fitchii plants in northern California.Part III in the series Biologically Active Constituents of North American Plants. For Part II, see Klocke et al., 1986.     

Differential Sensitivity of Mosquito Taxa to Vegetable Tannins

The sensitivity of larval Culicidae to vegetable tannins was investigated in different taxa representative of the fauna from alpine hydrosystems (Aedes rusticus, Culex pipiens) and foreign noxious fauna (Aedes aegypti, A. albopictus). Bioassays reveal that tannic acid at concentrations of 0.1–6 mM is significantly more toxic for C. pipiens than for Aedes taxa, and A. aegypti is more sensitive than A. albopictus and A. rusticus. Comparison of the rank order of sensitivity among taxa with the associated levels of cytochrome P-450, esterase, and glutathione-S-transferase activities suggests that cytochrome P-450 and esterases may be involved in the detoxification of tannins. A possible involvement of these detoxifying enzymes is also revealed in vivo by the synergistic effects of S,S,S-tributyl phosphorotrithioate (esterase inhibitor) and piperonyl butoxide (P-450 inhibitor). The differential sensitivity to tannins among taxa is discussed in terms of ecological implications within mosquito communities from alpine hydrosystems, where the acquisition of tannins–detoxifying enzymatic systems may be considered as a key innovation.     

Delayed phototoxic effects of 8-methoxypsoralen,khellin, and sphondin inAedes aegypti

At concentrations up to 6.7 ppm, 8-methoxypsoralen, sphondin, and khellin are not toxic to first-instar larvae of the mosquitoAedes aegypti. The irradiation of sensitized larvae with long-wavelength ultraviolet light did not always produce any immediate toxicity enhancement, but delayed effects were clearly visible. These were observed over the development of the organisms from first-instar larvae to adults. No adverse effects were noted when larvae were irradiated in the absence of sensitizers, or when they were placed in solutions of sensitizers which had been previously irradiated with the same light sources. 8-Methoxypsoralen was slightly more phototoxic than its isomer sphondin. Khellin, recently reported to undergo photoinduced cyclization with DNA components, showed minimal phototoxicity in the concentration range used.     

Evaluation of organic infusions and synthetic compounds mediating oviposition inAedes albopictus andAedes aegypti (Diptera: Culicidae)

Oviposition responses of gravidAedes albopictus andAe. aegypti were evaluated to natural organic infusions (hay infusion, larval rearing water, and field-collected larval water) as well as compounds isolated from hay infusion (3-methylindole, 4-methylphenol, 4-ethylphenol, indole, and phenol) known to elicit oviposition inCulex mosquitoes. In laboratory bioassays, significant oviposition responses were obtained fromAe. albopictus, but not fromAe. aegypti, to dilutions of hay infusion and field water. Oviposition responses of both species were moderate to the synthetic compounds tested in the laboratory (0.01–100 µg/liter). Only 3-methylindole (0.1 µg/liter) and 4-ethylphenol (1.0 µg/liter) elicited significantly more oviposition byAe. albopictus than did well water. Of the synthetic compounds tested withAe. aegypti, only phenol (1.0 µg/liter) and 4-ethylphenol (0.1 µg/liter) elicited significantly more oviposition than did well water. Significant repellency or oviposition deterrence for both species occurred in response to at least one high concentration of most of the compounds tested. In field cage evaluations, oviposition responses byAe. albopictus were strongest to larval water and field water, moderate to hay infusion and 3-methylindole (100 µg/liter), and low to well water. A mixture of five synthetic compounds mimicking hay infusion was no more effective than 3-methylindole alone. ForAe. aegypti, oviposition responses were greatest to larval water and least to 3-methylindole. In an olfactometer, gravid females of both species oriented more to field water than to well water and onlyAe. albopictus oriented more to larval water or hay infusion than well water. In general, gravidAe. albopictus responded more strongly to oviposition stimuli than didAe. aegypti.     

Modeling and simulation of a sulfolane extraction process

Modeling and simulation for a sulfolane extraction process were performed. The process investigated in the present work consists of two tray columns, one of which is used for extraction and the other one for washing. The modified θ-method was employed for the modeling of the process. The computation of the equilibrium state of a two-phase system is one of the key issues in the modeling and simulation of extraction processes. In the present work the UNIFAC method was used for the computation of related thermodynamic properties and equilibrium states. Results of simulations showed good agreement with actual plant operation data.     

Chemical composition of degrading mangrove leaf litter and changes produced after consumption by mangrove crabNeosarmatium smithi (Crustacea: Decapoda: Sesarmidae)

The leaves of the mangroveCeriops tagal contained 3.2–4.1% (all percentages relate to dry weight) ofd-1-O-methyl-muco-inositol previously unreported in mangroves. They consisted of 37% aqueous acetone-water-soluble material, 18% water-insoluble polysaccharides, and ca. 50% polyphenols, which include soluble and insoluble tannins and lignin. The polysaccharide component sugars were glucose, arabinose, uronic acids, mannose, xylose, galactose, and rhamnose in the proportions 28262210752, respectively. The leaves were pectate rich, and the low level of glucan was presumed to consist mainly of cellulose. After four weeks of biodegradation, ca. 60% of the acetone-water-soluble material was lost from the leaves. Degradation processes greatly altered the polysaccharide components in the leaves. Pectates were rapidly degraded, while other polysaccharides, although reduced proportionately, resisted degradation at about the same level, and all component sugars were found in the 8-week-old leaves. Apparent lignin contents increased from 15 to >30% during biodegradation up to eight weeks. The yields of the major fractions in corresponding fecal material fromNeosarmatium smithi showed a similar trend to the diets. An enrichment of the insoluble residue was noticeable due to the digestion of dialyzable material. The fecal carbohydrate content was greatly reduced (7–11%) and the apparent lignin increased (27–39%) due to its resistance to degradation. All dietary polysaccharide component sugars were found in the fecal residues, including some uronic acids. The leaves also contained a readily water-soluble fraction (15%) which consisted of pectates strongly complexed with proanthocyanidins.     

An evaluation of supercritical fluid extraction as an analytical tool to determine fat in canola,flax, solin,and mustard

Supercritical fluid extraction (SFE) with carbon dioxide was used to extract oil from soft oilseeds (flax, solin, canola, and mustard). Oil content determinations from the SFE method AOCS Am 3–96, with and without ethanol as a modifier, were compared to results obtained with an exhaustive extraction using petroleum ether (FOSFA as in AOCS Am 2–93). Without the modifier, oil recoveries using SFE were 10 to 15% lower than oil contents by the FOSFA method for the flax and canola samples. For mustard, the oil recoveries by SFE were about 20 to 30% lower than oil contents by the FOSFA method. In the presence of the modifier, oil recoveries for flax and canola were about 3% lower than the FOSFA recoveries. Varying the time, temperature, and amount of modifier (ethanol) showed that recoveries increased with time, pressure, temperature, and amount of modifier independently of the oilseeds tested. Kinetics of the SFE extraction showed that the oil recoveries increased with the extraction time and reached a plateau after 60 min. Multiple extractions (2×30 min), however, gave better recoveries than a single extraction for the same amount of time (60 min). The best results were obtained using multiple extractions without modifier or a combination of multiple extractions first without and then with 15% modifier. Under these last two conditions, oil recoveries were close to 100% for flax, solin, and canola, but mustard oil recoveries were still 10% lower than recoveries using the FOSFA method. Mustard samples gave the lowest oil recovery from SFE when compared to FOSFA method recoveries whatever conditions were tested, suggesting a matrix effect on the oil recovery. The acyl lipid content of the various extracts was studied using the sum of all FA expressed as TAG as a measure of acyl lipid extraction. The acyl lipid contents of the extracts were close to 100% when no modifier was used during the SFE. In the presence of modifier, the acyl lipid contents of the extracts were 10 to 15% lower than the results obtained without modifier. The amount of acyl lipid in the extract decreased as the quantity of modifier increased. This suggests that increasing the ethanol modifier increased the amount of polar compounds extracted without significantly increasing the total amount of lipids. The FA profiles were constant throughout the various extraction procedures.     

Attractancy and species specificity of 6-acetoxy-5-hexadecanolide,a mosquito oviposition attractant pheromone

Four stereoisomers of 6-acetoxy-5-hexadecanolide, a mosquito oviposition attractant pheromone, were bioassayed for their activity on mosquitoes. Only (–)-(5R,6S) isomer was active in attractingCulex quinquefasciatus Say females for oviposition at dosages of 0.5 g/100 ml water and above with the floating-cap method. The activity of this isomer increased 50-fold when it was applied directly to the water surface. The other three isomers, (+)-(5S,6R), (+)-(5R,6R), and (–)-(5s, 6s), were not active. The active isomer was ovipositionally attractive not only toC. quinquefasciatus but also toC. tarsalis Coquillett; however, it was 100 times more active in the former than in the latter species.Aedes aegypti (L.) andAnopheles quadrimaculatus Say were not attracted to the pheromone, thus suggesting that the pheromone is genus-specific.     

Allelopathic effects ofPolygonum aviculare L. II. Isolation,characterization, and biological activities of phytotoxins

In earlier work, we found thatPolygonum aviculare had pronounced allelopathic effects against several test species. Four inhibitors were isolated from livingPolygonum plants, three of which were glucosides. Four different inhibitors were isolated fromPolygonum residues and soil underPolygonum stands, and none of these occurred in soil fromCynodon dactylon (L.) Pers. stands. Three of these were glycosides containing both fructose and cellobiose as the sugars. Color reactions of all the inhibitors indicated that they are phenolic in nature. All the inhibitors reduced seed germination and/or seedling growth ofChenopodium album L. Moreover some of them inhibited growth of different strains ofRhizobium andAzotobacter.     

Effects of bilberry (Vaccinium myrtillus L.) litter on seed germination and early seedling growth of four boreal tree species

Laboratory and greenhouse bioassays were used to test for inhibitory effects of senescent and decomposed leaves and aqueous extract from bilberry (Vaccinium myrtillus L.) against seed germination and seedling growth of aspen (Populus tremula L.), birch (Betula pendula Roth.), Scots pine (Pinus sylvestris L.), and Norway spruce [Picea abies (L.) Karst.]. Aqueous extracts from bilberry leaves were inhibitory to aspen seed germination and seedling growth and also induced root damage and growth abnormalities. Addition of activated carbon removed the inhibitory effects of extracts. Senescent leaves reduced pine and spruce seed germination, but rinsing of seeds reversed this inhibition. Senescent leaves were more inhibitory than decomposed leaf litter, suggesting that the inhibitory compounds in bilberry leaves are relatively soluble and released at early stages during decomposition. Spruce was generally less negatively affected by litter and aqueous extracts than the other tested species. This study indicates that chemical effects of bilberry litter have the potential to inhibit tree seedling recruitment, but these effects were not consistently strong. Phytotoxicity is unlikely to be of critical importance in determining success for spruce seedling establishment.     

Synthesis and Larvicidal Activity against Culex pipiens pallens of New Triazole Derivatives of Phrymarolin from Phryma leptostachya L.

Twelve new triazole derivatives of Phrymarolin were prepared from Phrymarolin I and the structures of all the derivatives were fully characterized by ¹H-NMR, ¹³C-NMR and MS spectral data analyses. Larvicidal activities against 4rd instar larvae of Culex pipiens pallens of these Phrymarolin analogues were assayed. Although the triazole derivatives of Phrymarolin showed certain larvicidal activity, they showed lower activity than Phrymarolin I. The typical non-natural groups triazole substituents reduced the larvicidal activity of Phrymarolin derivatives.     

Simultaneous effects of ferulic andp-coumaric acids on cucumber leaf expansion in split-root experiments

Experiments were conducted to determine how plant responses to mixtures of allelochemicals may change as the proportion of roots in contact with allelochemicals is modified. Thirteen-day-old cucumber seedlings were treated with ferulic and/orp-coumaric acid in a split-root nutrient culture system. Leaf areas were determined just prior to treatment and at harvest, 24 hr after treatment. Ferulic acid was more inhibitory to cucumber leaf expansion thanp-coumaric acid. The effects of ferulic andp-coumaric acids on leaf expansion were additive. For individual acids, mixtures of ferulic andp-coumaric acids in the same container and combinations of ferulic andp-coumaric acids in separate containers, the inhibition of leaf expansion was directly related to the product of the concentration of the acid(s) and the proportion of roots treated with the acid(s). Pretreatment with 0.2 or 0.4 mM ferulic acid and subsequent treatment with 0.5 mM ferulic acid failed to show evidence of acclimation by cucumber seedlings.The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of products named, nor criticism of similar ones not mentioned.     

GC/MS characterization of mate tea leaves extracts obtained from high-pressure CO2 extraction

This work presents a study concerning the chemical characteristics and analytical separation process of the essential oil obtained from high-pressure carbon dioxide extraction of Ilex paraguariensis. The experiments were performed in a laboratory-scale unit in the temperature range of 20–40 °C, from 100 to 250 bar. A blend of the I. paraguariensis extracts was percolated through a preparative chromatographic column, containing silica gel, and successively eluted with 150 mL of each of the following solvents: hexane, toluene, dichloromethane, ethyl acetate, acetone and methanol. The raw extract and its fractions were analyzed by gas chromatography coupled to mass spectrometry detection (GC/MS). The fractionation procedure showed to be a good clean up technique due to the isolation of different classes of compounds in each fraction. Chromatographic analyses allowed the identification of caffeine, fatty acids and esters, phytol, squalene, Vitamin E, stigmasterol derivatives and saturated hydrocarbons.     

Water and ethanol as co-solvent in supercritical fluid extraction of proanthocyanidins from grape marc: A comparison and a proposal

Supercritical carbon dioxide (SC-CO₂) extraction of grape marc was studied using water (W) and ethanol (EtOH) as co-solvent at 15% (w/w), 100 and 200 MPa, and 313.15, 323.15 and 333.15 K to analyze their influence upon total phenols of the extracts. The overall extraction curves were determined and suggested 10 MPa and 313.15 K as the best operating conditions for SC-CO₂ + 15%W extraction, and 10 MPa and 333.15 K for SC-CO₂ + 15% EtOH. The phenolic yields obtained were 63.4 g/kg of extract for SC-CO₂ + 15% W and 38.8 g/kg of extract for SC-CO₂ + 15% EtOH. An alternative method combining Sc-CO₂ + 15% W extraction, followed by SC-CO₂ + 15% EtOH was tested. This procedure provided the best results allowing to obtain the highest phenolic yield (68.0 g/kg of extract), phenol content (733.6 mg GAE/100 g DM), proanthocyanidins concentration (572.8 mg catechin/100 g DM) and antioxidant activity (2649.6 mg α-tocopherol/100 g DM). SC-CO₂ methods were compared with methanol extraction.     

Sequential extraction of bioactive compounds from Melia azedarach L. in fixed bed extractor using CO2, ethanol and water

Melia azedarach L. is a plant with wide use in folk medicine since it contains many bioactive compounds of interest. The present study aimed to extract bioactive compounds from M. azedarach fruits by a sequential process in fixed bed using various solvent mixtures. Extractions were performed at 50 °C and 300 bar in four sequential steps using supercritical CO₂ (scCO₂), scCO₂/ethanol, pure ethanol, and ethanol/water mixture as solvents, respectively. The efficacy of the extraction process was evaluated by extraction yield and kinetics, and analysis of extracts by: (1) thin layer chromatography (TLC), (2) phenolics content, (3) reduction of surface tension of water, (4) gas chromatography (GC–MS), (5) electrospray ionization mass spectrometry (ESI–MS) and (6) antiviral activity. The overall extraction yield reached 45% and TLC analysis showed extracts with different composition. extract obtained from CO₂/ethanol mixture (SCEE) exhibited the greatest ability to reduce surface tension of water from 72.4 mN m⁻¹ [1] of pure water to 26.9 mN m⁻¹ of an aqueous solution of 40 g L⁻¹. The highest phenolics contents were observed in both the hydroalcoholic extract and scCO₂/ethanolic extract. Volatile oils were not detected in the supercritical extracts by GC–MS. MS analyses identified the fatty acids: linoleic, palmitic and myristic acid in the supercritical extract (SCE), and the phenolics: caffeic acid and malic acid in the other extracts. In addition, SCE and SCEE extracts showed significant inhibition percentage against Herpes Simplex Virus Type 1. The extraction process proposed in the present study produced extracts with significant potential for application in food and pharmaceutical industries.