摘要:

AbstractDroplets, falling under gravity through air that is not moving relative to the target, will impact on any object in their path, while charged droplets will be drawn to objects of earth potential along paths normal to the lines of equipotential; thus near the catching surface, they will move directly towards it. If the air is moving relative to the target, it will tend to move the droplets with it. The greater the drag to mass ratio of a droplet, the more rapidly any initial motion it has through the air will cease, and it will move through the air only very slowly under the effects of gravity and any electromagnetic potential. Air flowing past an object is able to change its path rapidly, but droplets moving with the air are less able to do this. Their ability to avoid impact increases with decrease in droplet size and wind speed, and with increase in the size of the catching surface. Thus small smooth stems catch big droplets in a high wind efficiently, but large smooth branches in a light wind will not catch many small droplets. Artificial cylinders and ribbons are poorer at catching droplets than natural surfaces, which are rarely smooth and often hairy. Hairs or spikes on a surface greatly increase the catch efficiency of droplets carried in the wind.A droplet several hundred micrometres in diameter is so dominated by gravity that it will fall in a near vertical path even in a moderate wind, impacting on any horizontal surface that obstructs its path. Its chances of reaching a vertical stem are negligible unless it runs off or splashes from a near horizontal surface. Conversely, a small droplet will be carried almost horizontally in any wind and is most likely to impact on vertical surfaces or flapping leaves. It has a much greater chance of getting inside the canopy without being caught because most leaves are near horizontal, and once there, it must rely on the turbulence induced by the wind for transport and impaction on undersurfaces or hairs. Because turbulence is reduced as the droplet nears the ground, it is very difficult to catch droplets on the lower parts of the crop within the canopy. To bounce, a droplet must have enough surplus kinetic energy to rebound clear of the surface, allowing for the energy losses in deforming the droplet in the bounce process; moreover, the surface must not be significantly wetted by the drop. Thus the droplet must be moderate to large in size, must be moving rapidly relative to the surface, and must have a high surface tension to contain it as a droplet, even at its extreme deformation. Surface condition is of great importance; the presence of hairs and the type of roughness affect the probability of maintaining an air film between the surface and the droplet. In general, droplets below 150 μm diameter are unlikely to bounce, but adding small amounts of surfactant to the droplet formulation can increase this size by several times. Any one plant leaf can vary considerably over its area because of age, abrasion and local surface shape. A film of water on a wet surface ensures an air film is maintained and the droplet will bounce

ISSN:0031-613X    

DOI:10.1002/ps.2780150202

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractToxicity tests reveal that the zebrafish (Brachydanio rerio) is very sensitive to malathion, an organophosphorus insecticide, and 24 to 96‐h LC50values showed a gradual decrease as the exposure time was increased. Zebrafish exposed to long‐term sublethal concentrations failed to spawn and invariably exhibited skeletal deformities. Possible causes of the reduced gonadosomatic index and skeletal deformities are discus

ISSN:0031-613X    

DOI:10.1002/ps.2780150203

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractTwo substrains of Aedes aegypti, already resistant to DDT and pyrethroids, were further selected using either DDT or permethrin by mass exposure of the females only. DDT selection over 14 generations raised the resistance to DDT so far that no accurate LC50values could be determined. Selection with permethrin raised the tolerance to an irregular plateau 7–10 times the original. DDT selection in the adults raised the DDT resistance of the larvae, but this could be partly overcome using a dehydrochlorinase inhibitor. The resistance to pyrethroids was increased but tolerance of dieldrin, malathion and propoxur compounds was little changed. Permethrin selection of the adults raised resistance to pyrethroids more than DDT selection but also increased DDT resistance. Similar patterns were found for the larval insects. A strain from Demerara in Guyana showed both DDT and pyrethroid resistance, including strong resistance to pyrethrins together with dieldrin and propoxur. It was concluded that two major independent resistance mechanisms existed in the selected strains, a dehydrochlorinase affecting DDT alone, and an unknown mechanism, probably nerve insensitivity (kdr) affecting both DDT and pyrethroid

ISSN:0031-613X    

DOI:10.1002/ps.2780150204

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractPenetration, metabolism and excretion of [14C]DDT and [3H]transpermethrin were studied in three strains of Aedes aegypti L. after topical application of 10 nl of a solution of the insecticide in 2‐ethoxyethanol. The standard susceptible strain was compared with a DDT‐selected strain (BKS) and a permethrin‐selected strain (BKPM). No significant penetration resistance was observed in either resistant strain, but both showed high DDT‐dehydrochlorinase activity which contributed to the DDT resistance. A non‐metabolic factor was also involved. Rates of transpermethrin metabolism were very similar in all three strains and substantially higher internal concentrations of transpermethrin were required to produce toxic effects in both BKS and BKPM mosquitoes. By analogy with other insect species, it is concluded that transpermethrin resistance in these strains is of the kdr type, while the DDT resistance is a mixture of kdr and DDT‐dehydr

ISSN:0031-613X    

DOI:10.1002/ps.2780150205

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe present state of knowledge of ergosterol biosynthesis is reviewed briefly in order to provide a contextual framework for the following papers which deal with its inhibition, the compounds that cause this inhibition, and their mode of action. The paper concentrates upon the post‐squalene segment of the process as it occurs in fungi because the commercially important inhibitors of ergosterol biosynthesis are fungicides that block steps within that proces

ISSN:0031-613X    

DOI:10.1002/ps.2780150206

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractDiclobutrazol [(2RS, 3RS)‐1‐(2, 4‐dichlorophenyl)‐4, 4‐dimethyl‐2‐(1,2, 4‐triazol‐1‐yl)pentan‐3‐ol] decreased the rate of growth of Ustilago maydis during the log phase. Marked changes in sterol composition were observed with a decrease in ergosterol and an increase in methyl‐sterols, indicating a block in the removal of the 14‐methyl group. The inhibition was of rapid onset (<4 h). Changes in other lipid constituents were minor and there was no build up of unsaturated fatty acids. The fungicidal activity resides in the (2R, 3R)‐isomer, which is known to be more potent in blocking a yeast 14‐demethylase enzyme than the (2S, 3S)‐isomer. This relationship held in the 4‐chlorophenyl homologues, which as a group were less fungicidal and less potent inhibitors than the 2, 4‐dichlorophenyl compounds. The evidence presented indicates that the primary lesion caused by the fungicide was a build up of membrane sterols containing extra methyl groups; this, in combination with a loss of ergosterol, is believed to prevent proper membrane ordering and thus

ISSN:0031-613X    

DOI:10.1002/ps.2780150207

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe C‐14 demethylation of the sterols, dependent on cytochrome P‐450, and the C‐22(23) desaturation of sterols are reactions in the ergosterol biosynthesis pathway that are regarded as primary target sites in the toxicity of fungicides of the pyrimidin‐5‐ylmethanol type. Currently, there is no evidence for target sites in other pathways of comparable sensitivity, although the failure of added ergosterol to reverse the fungitoxicity suggests the existence of such sites. The mitochondrial respiratory systems in Ustilago maydis and Aspergillus nidulans are insensitive to this type of fungicide and are not regarded as primary targets of fungitoxicity in these organisms. Appreciable evidence indicates that the primary targets in higher plant growth regulation are reactions, dependent on cytochrome P‐450, that assist in the conversion of kaurene to kaurenoic acid in the gibberellin (GA) biosynthesis pathway. Growth retardation by high concentrations of pyrimidin‐5‐ylmethanols, which is not reversable by GA, apparently involves action at sites outside the GA biosynthesis pathway. The data derived from various studies of the mechanisms of fungitoxicity and growth regulation suggest that any undetected primary targets of the pyrimidin‐5‐ylmethanols are likely to be haem enzymes, similar to the cytochrome P‐450 involved in ster

ISSN:0031-613X    

DOI:10.1002/ps.2780150208

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractFenpropimorph was found to be highly active against Penicillium italicum (EC500.01/μg ml−1). Conidia of P. italicum, treated with low concentrations of fenpropimorph, swelled in size and showed distorted germ tubes. During the initial stages of mycelial growth, fenpropimorph had little or no effect on the dry weight increase, which became strongly inhibited within 24 h after addition of the toxicant (0.05, 0.1 and 0.2 μg ml−1). Irregular deposition of β–1,3 and β–1, 4 polysaccharides, probably chitin, was observed after treatment with fenpropimorph or imazalil. Fenpropimorph (0.05 and 0.2 μ ml−1) caused the accumulation of a major demethyl‐sterol that was different from ergosterol. It was identified as ergosta‐8, 14, 24(28)‐trien‐3β‐ol by mass, infrared, ultraviolet and proton nuclear magnetic resonance, spectrometric procedures. At both concentrations, the accumulation was already detected after incubation for 2 h. In contrast, imazalil (0.1 μg ml−1) caused the accumulation of several methyl‐ and dimethyl‐sterols which were tentatively identified as eburicol (24‐methylene‐24, 25‐dihydrolanosterol), 4, 14α‐dimethylergosta‐8, 24(28)‐dien‐3‐one, 14α‐methylergosta‐8, 24(28)‐dien‐3‐one and obtusifoliol (4, 14α‐dimethylergosta‐8, 24(28)‐dien‐3α‐ol). The accumulation of ergosta‐8, 14,24(28)‐trien‐3β‐ol indicates inhibition of the Δ14‐redu

ISSN:0031-613X    

DOI:10.1002/ps.2780150209

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe antimycotic N‐substituted imidazoles and triazoles, such as imazalil, ketoconazole and itraconazole, interfere selectively at low concentrations (≥0.01nm) with the 14α‐demethylase system (which is dependent on cytochrome P‐450) of fungal cells, for example, Candida albicans and Penicillium italicum. This results in a decreased availability of ergosterol and the accumulation of 14α‐methyl‐sterols such as lanosterol. Cholesterol synthesis in a subcellular fraction of rat liver, in intact fibroblasts, and in vivo in rat liver, was much less sensitive, for example, to ketoconazole. The imidazole derivatives imazalil, miconazole, ketoconazole and parconazole, and the triazole derivatives propiconazole, terconazole and itraconazole affect the cytochrome P‐450 species of microsomal fractions from Saccharomyces cerevisiae and rat liver. Cytochrome P‐450 of rat‐liver microsomes was much less sensitive to these azole derivatives, in parallel with the lower sensitivity of cholesterol synthesis. Using unilamellar vesicles composed of phosphatidylcholine, phosphatidyl‐ethanolamine and diphosphatidylcholine, multilamellar vesicles of dipalmitoylphos‐phatidylcholine, and intact S. cerevisiae, it was shown that the substitution of ergosterol by lanosterol leads to functional changes in the membranes. It is speculated that the selective interaction of the azole derivatives with the yeast microsomal cytochrome P‐450 leads to the accumulation of 14a‐methyl‐sterols and results in changes in the permeability of the membranes and leakages. The observed inhibition of growth may have its origin in these changes. Miconazole, ketoconazole and deacylated ketoconazole (R‐39519) also affect the growth of Staphylococcus aureus, miconazole being 12.5 and 14 times, respectively, more active than R‐39519 and ketoconazole. The greater antibacterial activity of miconazole coincides with its greater inhibition of the biosynthesis of C‐55 isoprenoid alcohol and vitamin K. The phosphorylated derivative of C‐55 isoprenoid alcohol has functional importance in the biosynthesis of bacterial cell wall and membrane polymers, and the menaquinone vitamin K plays a role in the electron transport of Gram‐positive bacteria. The reduced synthesis of these vital compounds may contribute to t

ISSN:0031-613X    

DOI:10.1002/ps.2780150210

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractImazalil and fenpropimorph caused morphological changes in sporidia of Ustilago maydis and in germinating conidia of Penicillium italicum, as observed by fluorescence microscopy using an optical brightener. Sporidia of U. maydis appeared swollen, distorted, multicellular and, sometimes, branched; conidia of P. italicum swelled in size, and extension of the germ tubes was strongly inhibited. Mycelium of P. italicum, treated with fenpropimorph, showed much enlarged hyphal diameters and relatively short distances between septa. Imazalil and fenpropimorph also caused an irregular deposition of β–1,3 and β‐1,4 polysaccharides, probably chitin, in U. maydis and P. italicum. The latter phenomenon is discussed in relation to the following observed effects of fungicides that inhibit ergosterol biosynthesis: differences in effect on the morphology of budding and filamentous fungi; preferential inhibition of yeast‐hypha conversion in dimorphic fungi; disorganisation of septum formation in budding fungi; and inhibition of spheroplast formation from buddin

ISSN:0031-613X    

DOI:10.1002/ps.2780150211

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY