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1.
The polyamine analogue, keto-putrescine, was shown to provide substantial control of infections by six economically important plant pathogens, with EC50 values ranging between 57 and 82 mg litre?1. However, keto-putrescine was relatively less effective in vitro against Phytophthora infestans, Pyricularia oryzae and Pyrenophora avenae, with EC50 values ranging from 145 to 340 mg litre?1. In contrast, the polyamine analogue N-acetylputrescine had to effect on in-vitro growth of P. avenae or P. oryzae or infection of barley seedlings with powdery mildew. When P. avenae was grown in the presence of keto-putrescine, there were small, insignificant reductions in ornithine decarboxylase activity, with more substantial, significant reductions in S-adenosylmethionine decarboxylase activity. These changes were accompanied by a 43% reduction in spermidine concentration and increased concentrations of spermine and cadaverine.  相似文献   

2.
Fresh rhizomes of Zingiber officinale (ginger), when subjected to steam distillation, yielded ginger oil in which curcumene was found to be the major constituent. The thermally labile zingiberene‐rich fraction was obtained from its diethyl ether extract. Column chromatography of ginger oleoresin furnished a fraction from which [6]‐gingerol was obtained by preparative TLC. Naturally occurring [6]‐dehydroshogaol was synthesised following condensation of dehydrozingerone with hexanal, whereas zingerone and 3‐hydroxy‐1‐(4‐hydroxy‐3‐methoxyphenyl)butane were obtained by hydrogenation of dehydrozingerone with 10% Pd/C. The structures of the compounds were established by 1H NMR, 13C NMR and mass (EI‐MS and ES‐MS) spectral analysis. The test compounds exhibited moderate insect growth regulatory (IGR) and antifeedant activity against Spilosoma obliqua, and significant antifungal activity against Rhizoctonia solani. Among the various compounds, [6]‐dehydroshogaol exhibited maximum IGR activity (EC50 3.55 mg ml ?1) while dehydrozingerone imparted maximum antifungal activity (EC50 86.49 mg litre?1). © 2001 Society of Chemical Industry  相似文献   

3.
Strains of Pseudocercosporella herpotrichoides collected in France on winter wheat give either fast-growing mycelial colonies with regular margins or slow-growing mycelial colonies with irregular margins. Most of the fastgrowing isolates were sensitive to triadimenol (EC50 below 2mg litre?1), but some of them were resistant to this inhibitor of sterol C-14 demethylation. In contrast, all the slow-growing strains were highly resistant to triadimenol (EC50 greater than 100 mg litre?1). This resistance was also expressed in inhibition of germ-tube elongation. Positive cross-resistance was observed between most of the inhibitors of sterol C-14 demethylation, with the exception of some imidazole derivatives (clotrimazole, prochloraz). All the fast-growing strains were tolerant to fenpropimorph and fenpropidin whereas the slow-growing ones were susceptible; the reverse was true with piperalin and tridemorph. All the field isolates were inhibited to the same extent by the inhibitors of squalene-epoxidase, nafifine and terbinafine. Two types of mutant resistant to triadimenol have been induced under laboratory conditions from sensitive fast-growing strains. The most common mutants were resistant to all the inhibitors of sterol C–14 demethylation and also in some conditions to fenpropimorph, tridemorph and the inhibitors of squalene-epoxidase. The other mutants were characterised by a reduced spectrum of cross-resistance between triadimenol and the other inhibitors of sterol biosynthesis. The field isolates and laboratory mutants resistant to triadimenol and propiconazole were also resistant to each of the four enantiomers of these two fungicides.  相似文献   

4.
The dosages of methyl bromide required to control insect pests can be expressed as concentration, time (Ct) products for concentrations down to a certain minimal level, here defined as the efficacy threshold, below which Habers Ct rule (C×t=k,a constant for mortality) no longer applies. Twelve strains of seven species of stored-product beetle were tested to identify efficacy threshold concentrations at 15°C and 25°C. For each strain the efficacy threshold was higher at 25°C than at 15°C. Different species differed widely in the threshold levels identified. Strains with a higher than usual tolerance to methyl bromide than their standard stock counterparts had slightly higher efficacy thresholds at 25°C but not at 15°C. The order of tolerance of the standard stocks to methyl bromide at 15°C was Tribolium confusum> T. castaneum> Oryzaephilus surinamensis> Rhyzopertha dominica> Sitophilus granarius> S. zeamais> S. oryzae, and at 25°C Tribolium castaneum > T. confusum> R. dominica> O. surinamensis> S. granarius> S. zeamais> S. oryzae. The order of efficacy thresholds largely reflected the order of susceptibility, S. oryzae and S. zeamais having the lowest efficacy thresholds of about 0.6 mg litre?1 at 15°C and 1.3-2.0 mg litre?1 at 25°C, while Tribolium spp. had the highest, 1.3-2.0 mg litre?1 at 15°C and 2.5-4.0 mg litre?1 at 25°C.  相似文献   

5.
Foliar applications of synthetic pyrethroids were made to several crops to determine residue levels at various intervals after application. On onions, residues of cypermethrin, permethrin and fenvalerate were negligible > 0.1 mg kg?1, 7 days after application. On lettuce, residues of fenvalerate and permethrin were 0.8 mg kg?1. On celery, residues of fenvalerate did not decline and ranged from 0.12 to 0.25 mg kg?1 during the 14-day period. On green bush-beans, residues of permethrin and cypermethrin did not decline during the 14-day period and ranged from 0.1 to 0.6 mg kg?1. By day 7, residues of cyfluthrin, cypermethrin, deltamethrin, fenvalerate and permethrin on strawberries were less than the acceptable maximum tolerance of 0.1 mg kg?1 with the exception of cypermethrin, applied at the rate of 0.14 kg a.i. ha?1 which gave a residue of 0.14 mg kg?1.  相似文献   

6.
Ephestia elutella larvae in diapause were exposed at 25°C to methyl bromide at 12 mg litre?1 for 3.5 or 7.5 h and then immediately exposed to a lower concentration. The minimum effective concentration (that at which Haber's rule, concentration × time = k, a constant for mortality, still applied) was about 3 mg litre?1 in tests with no previous exposure toa high concentration, but it was about 2.5 mg litre?1 for individuals surviving a 3.5 h exposure to 12 mg litre?1, and was about 1.6 mg litre?1 for those surviving a 7.5 h exposure to 12 mg litre?1. These exposures to 12 mg litre?1, respectively, killed 2–20% and 50–75% of larvae exposed, and hence the smaller the proportion of survivors of exposure to a high concentration, the lower the minimum effective concentration needed against them. Thus the low concentration persisting at the end of a practical fumigation should contribute significantly to the success of the treatment and be much more effective than any similar low concentration present soon after the introduction of gas.  相似文献   

7.
The toxicity of the naturally derived insecticide spinosad was tested against the gypsy moth, Lymantria dispar. Bioassays using red oak leaf disks, treated with spinosad in a Potter spray tower, yielded an LC50 value of 0.0015 µg AI cm−2 (3‐day exposure; 13‐day evaluation; 2nd instar larvae). Applied to foliage to run‐off in the laboratory (potted red oak seedlings) and the field (4 m‐tall birch trees), spinosad effectively controlled 2nd instar larvae at concentrations ranging from 3 to 50 mg litre−1. Toxicity in the laboratory, and efficacy and persistence in the field, were comparable to those achieved with the insecticide permethrin. Laboratory studies supported field observations that control was achieved in part by knockdown due to paralysis. In addition, laboratory results demonstrated that crawling contact activity may play an important role in field efficacy; 50% of treated larvae were paralyzed 16 h after a 2‐min crawling exposure to glass coated with a 4 mg litre−1 spinosad solution. © 2000 Society of Chemical Industry  相似文献   

8.
The fumigant toxicity of various volatile constituents of essential oils extracted from sixteen Korean spices and medicinal plants towards the rice weevil, Sitophilus oryzae L (Coleoptera: Curculionidae), was determined. The most potent toxicity was found in the essential oil from Mentha arvensis L var piperascens (LC50 = 45.5 µl litre?1 air). GC–MS analysis of essential oil from M arvensis showed it to be rich in menthol (63.2%), menthone (13.1%) and limonene (1.5%), followed in abundance by β‐pinene (0.7%), α‐pinene (0.6%) and linalool (0.2%). Treatment of S oryzae with each of these terpenes showed menthone to be most active (LC50 = 12.7 µl litre?1 air) followed by linalool (LC50 = 39.2 µl litre?1 air) and α‐pinene (LC50 = 54.9 µl litre?1 air). Studies on inhibition of acetylcholinesterase activity of S oryzae showed menthone to have a nine‐fold lower inhibitory effect than menthol, despite menthone being 8.1‐fold more toxic than menthol to the rice weevil. Different modes of toxicity of these monoterpenes towards S oryzae are discussed. © 2001 Society of Chemical Industry  相似文献   

9.
Between 1995 and 1997, 278 grape downy mildew (Plasmopara viticola) populations originating from European vineyards were characterised for their sensitivity to cymoxanil in a leaf-disc assay. The sensitivity profile revealed a wide distribution, with minimum inhibitory concentrations (MIC) ranging from 10 to more than 800 mg litre−1. EC50 values ranged from 1 to more than 800 mg litre−1 with an average of 125 mg litre−1. The sensitivity distribution was stable between 1995 and 1997. Surprisingly, populations from Portugal appeared significantly more sensitive than those from France or Italy, which could not be linked to differential cymoxanil usage in these countries. P viticola populations collected outside Europe and never exposed to cymoxanil appeared significantly more sensitive than exposed European populations, with an average EC50 value of 10 mg litre−1. The level of sensitivity of European P viticola populations was relatively unaffected by the number of cymoxanil applications made during a season or by the number of years of cymoxanil use. No link was found between the level of sensitivity in the leaf-disc assay and the level of performance of the cymoxanil mixtures used in the fields where the populations originated. Specific field trials conducted in Italy and Portugal have shown that the performance of cymoxanil-based mixtures remained good even on populations of the grape downy mildew fungus characterised as less sensitive in the leaf-disc assay. While there are no baseline sensitivity data for pre-commercialisation P viticola populations, the results of our study suggest that a shift in sensitivity (12.5-fold) may have occurred in some areas since introduction of cymoxanil on grapes nearly 20 years ago. Because cymoxanil is never used alone, it is difficult to determine whether or not practical resistance is occurring in European vineyards. © 1999 Society of Chemical Industry  相似文献   

10.
The effect of droplet diameter (36-274 μm) and concentration (10-400 g litre?1) of permethrin on the knockdown and mortality of 2nd-instar Plutella xylostella larvae was investigated. Larvae were placed on brussels sprout leaf discs treated with residual deposits of permethrin applied as ULV or emulsion formulations. The LD50 of permethrin decreased with droplet size at all concentrations tested. This effect could not be accounted for solely by increased drop numbers per unit area of leaf, suggesting that for both formulations transfer of permethrin to larvae is more efficient for deposits composed of small drops. The concentration of permethrin in the ULV formulation could be reduced to approach a minimum quantity of toxicant per unit area to maintain 50 per cent mortality. The approach to the minimum dose varied with drop size and drop number per unit leaf area. The ULV formulation was approximately 2.7 times more effective at killing larvae than the emulsion, presumably as a result of greater availability of toxicant and transfer to larvae.  相似文献   

11.
In order to obtain residue data from the application of the algicide endothal in Italian rice paddy fields, two experiments were carried out using a 50 g kg?1 granular formulation in a small pond and the same granular and two liquid formulations in actual paddy fields of the Italian rice growing area. Endothal decay in the pond water was very rapid, reaching residue levels of 0·01-1·02 mg litre?1 in two days and 0·004-0·01 mg litre?1 at the third day. The muddy soil of the pond was free from measurable endothal residues( <0·02 mg kg?1). In the paddy-field waters, the endothal decay was slower, with an average half-life time of 3·3 days, independently of the type of formulation. The actual residues in water after 6 days ranged from 0·3 to 1·3 mg litre?1 according to the initial amount of product applied, and, consequently, to the initial concentration in water. Rice samples collected at the normal harvest time from the two paddy fields, treated with three different formulations, showed no endothal residue at the minimum detectable level of 0·01 mg kg?1.  相似文献   

12.
Petroleum spray oil (2, 4 and 6% in water) was applied to Valencia orange, Citrus sinensis (L.) Osbeck, for the control of Chinese wax scale, Ceroplastes sinensis del Guercio, using a low-volume ( <2000 litre ha?1)air-blast (LV AB) sprayer, a low- to high-volume (L-HV) (up to 7000 litre ha?1) sprayer with four fan-assisted rotary atomiser (FARA) spray heads mounted on a vertical tower, and a high-volume (>7000 litre ha?1) oscillating boom (HV OB) sprayer. The most effective sprayer was the L-HV FARA sprayer. The most cost-effective treatment was a 20 ml litre?1 (60 litre oil ha?1) spray applied at 3000 litre ha?1 by the L-HV FARA sprayer. It gave mortality equivalent to a standard 20 ml litre?1, 10 700 litre ha?1 spray (214 litre oil ha?1) applied by the HV OB sprayer but with 72% less spray and significantly less oil deposited per cm2 of leaf area. Equivalent or significantly (P = 0·05) higher mortality than that given by the 10 700 litre ha?1 HV OB spray was given by the 40 ml litre?1, 3000 (120 litre oil ha?1) and 60 ml litre?1, 2180 and 3000 litre ha?1 (130·8 and 180 litre oil ha?1) L-HV FARA sprays, but the 60 ml litre?1 sprays deposited more oil per cm2 than the 20 ml litre?1 HV OB spray and were considered to be potentially phytotoxic. The least effective sprayer was the LV AB sprayer, which applied a 60 ml litre?1 spray (57·6 litre oil ha?1) at 960 litre ha?1. Linear relationships were established for Chinese wax scale mortality, transformed using an angular transformation (arcsin proportion), versus log10 spray volume for the 20, 40 and 60 ml litre?1 sprays applied by L-HV FARA at 1260,2180 and 3000 litre ha?1, mortality versus log10 μg oil cm?2 and log10 μg oil versus log10 volume of oil sprayed.  相似文献   

13.
The antifeedant effect of five organotin compounds (fentin acetate, fentin hydroxide, fentin chloride, cyhexatin and fenbutatin oxide) and of three other compounds known to possess antifeeding activity (guazatine triacetate, 4′-chloroacetophenone isobutyrylhydrazone and thiram) was investigated by feeding treated alfalfa to larvae of Boarmia selenaria. The three fentins and cyhexatin were highly active at 0.1 g litre?1, the order of activity at this concentration being fentin chloride > fentin hydroxide > fentin acetate ? cyhexatin, whereas the other compounds were practically inactive at either this or a somewhat higher concentration (0.5 g litre?1). Guazatine triacetate had a concentration-independent antifeedant effect at much higher concentrations (5–20 g litre?1).  相似文献   

14.
Carbohydrate metabolism was studied in the hepatopancreas, mantle, intestine and foot of the snail Lymnaea acuminata, exposed to 40% and 80% of the LC50 dose of phorate (12 and 24 mg litre?1, respectively) for 24 and 48 h. Following treatment with the pesticide, the rate of oxygen consumption and the glycogen contents were reduced, while the levels of lactic acid and reducing sugars were enhanced. Withdrawal of the pesticide for 7 days after exposure of the snails to 12 mg of phorate litre?1 for 48 h did not reverse these changes.  相似文献   

15.
The effects of the fungicides benomyl, thiophanate-methyl and triadimefon on the chrysomelid beetle Gastrophysa polygoni were investigated in the laboratory. Contact with a suspension of benomyl (1.5 g a. i. litre?1 did not affect the hatchability of the eggs. Larvae were reared on shoots of knotgrass (Polygonum aviculare) that had been sprayed with suspensions of benomyl, ranging in concentration from 0.1 to 5.0 g a. i. litre?1. The mortality to the adult stage, of larvae reared on shoots treated with concentrations of benomyl of 0.5 g a. i. litre?1 and above, was significantly higher than that of control larvae. At concentrations of 2.0 g a. i. litre?1 and above, no larvae survived to the adult stage. The LD50 was 0.78 g a. i. benomyl litre?1. The LT50 values at concentrations of 1.0, 2.0 and 5.0 g a. i. benomyl litre?1 were 22.6, 12.6 and 5.3 days, respectively. The mean weights of adults bred from larvae that had been reared on shoots treated with benomyl (0.5 and 1.0 g a. i. litre?1) were significantly less than those of adults bred from control larvae. The mortality of larvae, reared on shoots of P. aviculare treated with triadimefon (0.5 g a. i. litre?1) or thiophanate-methyl (1.0 g a. i. litre?1), was also significantly higher than that of control larvae. Females kept on plants of P. aviculare treated with benomyl (1.5 g a. i. litre?1) laid similar numbers of eggs to those kept on untreated plants, and the hatchability of the eggs was not affected.  相似文献   

16.
Laboratory studies were conducted to determine the effect of the naturally derived compound spinosad on Ceratitis capitata Wied. (Diptera, Tephritidae). The organophosphate fenthion was used as a standard. Direct dose-dependent mortality and reduced fecundity were observed in oral treatment of adults with spinosad. The LC90 values 14 h and seven days after treatment were 19·50 and 0·49 mg litre−1 respectively. Fenthion was less active (the LC50 eight days after treatment was 1·17 mg litre−1) and did not affect the fecundity of the fly. Adults were also very susceptible to spinosad and fenthion via residual contact. For spinosad, 100% mortality was recorded 48 h after treatment for a dose of 10 mg litre−1. Spinosad was more effective than fenthion in suppressing larval development when neonate larvae were reared on treated diet supplemented with a range of concentrations from 0·02 to 0·83 mg kg−1 diet. Last-instar larvae were much less susceptible to spinosad or fenthion when exposed via dipping or when they pupated in treated medium and both products had similar performance. A lack of ovicidal activity was observed in direct egg-treatments with spinosad but significant reductions from 1 mg litre−1 onwards were recorded for fenthion.  相似文献   

17.
Twelve ureas and thioureas with 1,3-diphenyl- and 1-phenyl-3-(2-pyridyl) were tested as potential herbicides in a simple screen against two species of algae Chlorella fusca and Anabaena variabilis. Several were shown to inhibit growth at 100 mg litre?1 but only 1-[2,4-bis(azidosulphonyl)phenyl]-3-(2-pyridyl)urea and 1,3-bis(4-isopropyl- idenehydrazinosulphonylphenyl)thiourea showed any activity at 1 mg litre?1. This compares with the well-established urea herbicide diuron which, in identical tests, gives similar inhibition of growth at concentrations as low as 0.01 mg litre?1.  相似文献   

18.
The performance of low concentrations of methyl bromide against diapausing larvae of Ephestia elutella at 15 and 25°C was assessed in extended exposure periods. At concentrations of 1.9 mg litre?1 and below, test batches required higher concentration-time (ct) products for 100% kill at 25°C than at 15°C. The minimum concentration at which the concentration: time relationship still applied was between 1.3 and 1.9 mg litre?1 at 15°C, whereas at 25°C it was between 2.7 and 4.0 mg litre?1. For many individuals within each population sample, however, lower concentrations at moderate dosage levels remained lethal. At 25°C, a ct product of about 90 mg litre?1 h gave between 53 and 77% kill at 6.1, 4.0, 2.7 and 1.9 mg litre?1. The trends observed suggest that the most tolerant members of the population have an enhanced ability to detoxify methyl bromide at the higher temperature. The implications of the results for the build-up of resistance and for practical control measures are discussed.  相似文献   

19.
The toxicity of cyromazine and a commercial formulation, ‘Vetrazin’®, to Chironomus zealandicus (thummi) Hudson and Deleatidium sp. was investigated. Under acute test conditions, the LC50 values for each species were quite comparable. For C. zealandicus, the value varied according to instar, 100–400 mg litre?1 for second- and third-instar to 1000–10000 mg litre?1 for older fourth-instars. For the one size class of Deleatidium tested (c.10 mm long), the value was 300–400 mg litre?1. High control mortalities of C. zealandicus limit that species' usefulness as an acute bioassay candidate. Under chronic test conditions, cyromazine showed a high toxicity to eggs or early-instar larvae of C. zealandicus. The maximum acceptable toxicant concentration for cyromazine against C. zealandicus was approximately 17.5 μg litre?1. The possibility of water contamination at this level is discussed. Whole-of-life chronic tests with C. zealandicus indicated that the most susceptible stage was in the egg or soon after larval emergence. These results highlight the dangers of using short-term acute toxicity results to formulate environmental exposure limits for modern pesticides that do not have dysfunction of the nervous system as their mode of action.  相似文献   

20.
Non-cyclopropane pyrethroid esters of different substituted 2-phenoxy-3-methylbutanoic acids have been synthesised using the three alcohols—3-phenoxybenzyl alcohol, α-cyano-3-phenoxybenzyl alcohol and 3, 4-methylene-dioxybenzyl alcohol. Among the 35 esters synthesised and tested against Culex quinquefasciatus Say, the Bancroftian filariasis vector, for both larvicidal and adulticidal activities, α-cyano-3-phenoxybenzyl 2-(4-fluorophenoxy)-3-methylbu-tanoate, with an LC50 value of 2.5 × 10?3 mg litre?1 for larvicidal activity, and α-cyano-3-phenoxybenzyl-2-(4-chlorophenoxy)-3-methylbutanoate, with an LD50 value of 30 times; 10?4 ug insect?1 for adulticidal activity, were found to be as effective as fenvalerate, a well-known non-cyclopropane pyrethroid ester. Structure-activity studies showed that the insecticidal activity is dependent on the nature and position of the substituent in the phenyl ring of the acid moiety and also on the type of alcohol moiety.  相似文献   

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