摘要:

Two species ofAphelenchoideshave been found in nematode‐diseased strawberries from several places in Britain. They are identified asAphelenchoides fragariae(Rit‐zema‐Bos, 1891) andA. ritzema‐bosi(Schwartz, 1911) and the differences between them are fully discussed.A. olesistus(Ritzema‐Bos, 1893) is considered a synonym ofA. fragariae(Ritzema

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1950.tb00945.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

The minimum times required for killing the chrysanthemum eelworm (Aphelenchoides ritzema‐bosi, Schwartz) in water, over a range of temperatures have been determined and the technique employed is described. A temperature of 115° F. for 5 min. is preferable to the usual standard treatment of 110° F. for 20–30 min. and enables stools to be treated with less retardation of cuttings or death of stools, with a consequent great increase in the number of cuttings obtained. The results are of special value in connexion with varieties susceptible to damage by the hot water trea

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1950.tb00946.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

Petkus winter rye seed was subjected to ultrasonic vibrations of i Mcyc./sec. frequency in order to test the possibility of their having a vernalizing action. Seed which had not been soaked, fully imbibed seed, germinating seed (radicle showing) and seedlings with about 2 mm. long coleoptiles were treated with two intensities of ultrasonics for two periods of exposure.There is a slight favourable effect on germination rate of the unsoaked seed, but injury or death is caused by higher doses applied to the imbibed or germinated seed. Time to flowering was not affected by this treatment and no vernalization resulted.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1950.tb00947.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

A detailed study was made of the histology of apparently healthy clove trees and of trees expected to die from sudden death disease, in an attempt to find either a diagnostic character of the disease or some indication of a possible pathogen.The apparently healthy clove tree differs from a typical dicotyledon in a number of ways. This is especially true of the vascular system where, not only are the bundles bicollateral, but, in the stem, secondary thickening occurs in theinternalphloem, necrosis of the first formed cells keeping pace with the production of new cells. A definite cambium is found only to the exterior of the xylem and this is exceptionally narrow and the cells have very delicate walls. Phloem necrosis may occur in any part of the tree. The development and lignification of the xylem is very uneven, but this seems to bear no relation to the season. Tyloses are formed in the vessels of the root and, to a less extent, in those of the stem. Starch reserves are usually small, but large quantities of tannins, oils and calcium oxalate are secreted in all tissues. The oil may be contained in special schizogenous glands which are abundant in the aerial parts of the tree. Much mechanical tissue, consisting of fibres and stone cells, is formed in the pith and cortex of the stem and in the phloem in all parts of the tree, but lignification of this tissue is very uneven. Occasional dead cells are found in all tissues, even in the primary meristem. In the leaf, the plastids develop very unevenly; this is followed by retarded development of the pigment in some parts, resulting in a flecked appearance. Stomata are exceptionally numerous; in the leaf, they are confined to the lower surface and always communicate with very small cavities. Air spaces in the mesophyll are very small and are almost non‐existent in other tissues. Bodies, morphologically similar to the amorphous intracellular inclusions due to some viruses but differing chemically from them, are abundant in the leaves.Some of these characters are usually associated with a diseased condition, but they occur in both healthy and diseased cloves in the Zanzibar Protectorate. In the sudden death suspect, some may occur earlier or be more accentuated than in the healthy tree. This evidence alone might suggest that sudden death is merely the culmination of a long period of adverse conditions, but other evidence suggests very strongly that the disease is due to a pathogen. Of the groups of organisms which may cause disease, only fungi were found. These occurred in the absorbing roots but are unlikely to be the pathogens causing sudden death, for, until the tree has actually wilted, very few hyphae are present, and no more than are found in healthy trees. Nothing incompatible with the suggestion that sudden death is caused by a virus was foun

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1950.tb00948.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

Fertilizer treatments that greatly influenced the growth of tobacco and potato plants in pots had little effect on the number that became infected with potato virus Y when the plants were colonized by equal numbers of infective aphids, though the number was slightly decreased by nitrogen and increased by phosphorus.The number of local lesions produced on leaves of tobacco andNicotiana glutinosaby tomato aucuba mosaic and tobacco mosaic viruses was increased by additions of both nitrogen and phosphorus, provided that these also increased growth. The predominant effect of both nutrients in increasing susceptibility was indirect by increasing plant size, but over certain critical ranges both elements also increased the numbers of lesions produced per unit leaf area. Conditions of maximum susceptibility approximated closely to those producing optimal growth, and susceptibility, whether measured by lesions per half‐leaf or per unit area, was decreased by a deficiency or excess of either element. Sometimes the addition of nitrogen reduced susceptibility when still increasing plant growt

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1950.tb00949.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

An analysis of the results of experiments in different parts of England and Wales from 1941 to 1947 on the spread of potato leaf roll and rugose mosaic showed that leaf roll spread was correlated with the number of alateMyzus persicae(Sulzer) caught on sticky traps throughout the potato‐growing season; there was some correlation with the maximum count ofM. persicaeper 100 leaves, but this possibly results from the correlation between trapped aphids and the number per 100 leaves. Spread of rugose mosaic (potato virus Y) was correlated to a lesser degree with number ofM, persicae, perhaps because other aphid species are often vectors. With both diseases higher correlations were obtained when the infected plants were dispersed among the healthy crop than when they were placed together in a row. It is concluded that it is possible to predict the average health of potato stocks in the following year from average trap data; further work may enable the health of individual stocks to be predicte

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1950.tb00950.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

Whilst sheep myiasis caused byLucilia sericatais a severe economic problem in Great Britain, it rarely reaches such proportions in countries bordering Western Europe. Possible reasons for this relative absence of myiasis were investigated in Denmark.During the period 19 July‐15 August 1948, trapping studies showed that blowflies normally associated with myiasis in Great Britain, and particularlyL. sericata, occurred fairly abundantly in the Mols area of Jutland.The reactions of DanishL. sericatato attractive materials placed on sheep were similar to those shown by the species under British conditions. The number of egg batches laid on sheep in response to chemical stimuli were fewer than would have been expected in Great Britain.Studies on the fleece microclimate showed that relative humidities of 50 % or more frequently occurred on the skin surface. Humidities 3 cm. above the skin were markedly lower. Except during or immediately after rain, humidities high enough to ensure the hatching of blowfly eggs were never recorded.It is concluded that the absence of myiasis in Denmark and its relatively low incidence in other countries is not due to the existence on the Continent of a strain ofL. sericatadiffering in oviposition habits from the British specie

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1950.tb00951.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

This paper describes the design and operation of a suction trap which takes in air at a constant rate in winds up to 12 m.p.h. The catch is deposited in a collecting tube into which closely fitting disks fall, one every hour, thus segregating the catch into successive hourly samples. The trap is electrically driven; it operates in all weathers and heavy rain does not disorganize the catch.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1950.tb00952.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

The toxicity of a series of organo‐phosphorus compounds to the overwintering eggs ofAphis pomiDeg.,Operophtera brumata(L.) andMetatetranychus ulmi(Koch) was examined by a laboratory technique. The eggs ofM. ulmiwere highly resistant to all the compounds tested, those ofOperophtera brumatawere most susceptibleto P‐nitrophenyl diethyl thionphosphate (E 605) and those ofAphis pomitop‐nitro‐phenyl diethyl phosphate (E 600). With analogues of the last‐mentioned compound there is evidence that their toxicity toA. pomieggs is associated with the presence of electron‐attracting substituents in the benzene nucleus. A number of organo‐phosphorus compounds, including hexaethyl tetraphosphate andp‐nitrophenyl diethyl thionphosphate, were highly toxic under laboratory conditions to the active summer stages ofMetatetranychus ulmi, but the summer eggs of this mite were rather more resistant. Field trials of hexaethyl tetraphosphate andp‐nitrophenyl diethyl thionphosphate for the control of the aphidsBrachycaudus helichrysi(Kalt.),Phorodon hutnuli(Schr.) andAphis pomiDeg. showed these substances to be effective substit

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1950.tb00953.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

A method is described by which non‐volatile contact insecticides may be applied as dusts in a modified Barcroft respirometer with the minimum of disturbance. The technique makes it possible to observe the initial effects of insecticides on insect respiration.This apparatus has been used to study the effects on the respiration of adultTribolium castaneumHbst. of a number of insecticides, including so‐called inert dusts, and other finely divided solids, some of which are used as diluents.At 80% R.H. neither talc, carborundum, Almicide (Al2O3), stockalite, nor decolorizing charcoal caused any appreciable immediate change in the rate of oxygen uptake ofT. castaneum, but after 24 hr. the highly toxic substances, Almicide and charcoal, had caused a marked increase. At 20 % R.H. talc caused an increase in oxygen uptake only after 48 hr., but Almicide was shown to cause an almost immediate slight increase in respiration and a rapid evolution of water vapour. It is suggested that the increase in respiration may result from an increased metabolism to replace water lost through the cuticle.3:5‐Dinitro‐o‐cresol (D.N.C.), p‐nitrophenyl diethyl thionphosphate (E 605), γ‐isomer of benzene hexachloride (γ‐B.H.C), D.D.T., pyrethrins, toxaphene, chlordane, hexaethyl tetraphosphate all caused an increase in oxygen uptake before killingT. castaneumbut lauryl thiocyanate did not. Toxaphene and chlordane required a much longer time to cause an increase in respiration than did any of the other subtances tested.D.N.C. in sublethal concentrations caused an increase in the rate of respiration ofT. castaneum.Concentrations of D.N.C. giving 100% kill caused a rapid increase in oxygen uptake of which the magnitude and duration were independent of concentration.E 605 caused an increase in respiration after a time delay which was dependent upon the concentration used. The magnitude and duration of the increase in the rate of oxygen uptake were not greatly affected by the concentration of E 605.The effects of the concentration of y‐B.H.C. and the pyrethrins are complex and require further study. Both substances can affectT. castaneumwithout affecting respiration. Knock‐down can occur without affecting

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1950.tb00954.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY