摘要:

A description is given of the effect of alternation of temperature on the emergence of larvae from cysts of the potato‐root eelworm. Both potato‐root diffusate and anhydrotetronic acid have been used as hatching stimulants. When the temperature is alternated between 25 and 150C. there is a significant increase in the number of larvae emerging. The effects of using pre‐warmed as opposed to cold diffusate on cysts of different ages and of renewing the difrusate twice a week instead of once a week are also examined. A maximum has been found in the response‐concentration curve when cysts are stimulated by anhydrotetron

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1955.tb02501.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

摘要:

Three physiologic races of loose smut (named Ci, C2 and C3), found in wheat varieties grown at Cambridge, differ from those identified in Holland. The resistance or susceptibility of fifty‐seven wheat varieties to races Ci, C2 and C3 has been determined. Experiments have shown that infection of an ear can take place over a period of several days. There is a close relationship between the percentage of plants attacked and the severity of attack in a single plan

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1955.tb02502.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

摘要:

Forty‐seven isolates representing twenty‐seven species ofChaetomiumwere tested for their ability to control seedling blight of oat seedlings caused byFusariumspp., chieflyF. nivale(Fr.) Ces. In pot tests the majority of the isolates were ineffective, but certain isolates ofChaetomium cochliodesPall, andC. globosumKunze gave a large measure of control and were as effective as an organic mercury seed dressing. Control of disease was also obtained when living material was attached to the surface of oat seed and when infested seed was soaked in cell‐free filtrates from cultures of isolates which reduced diseasein vivo.Substantial control of disease was obtained when infested seed was sown in soil to which cultures of C. cochliodes had been added 10 months previously. This antagonist was able to grow through unsterile soil in the presence of certain added substrates.The results of pot experiments were confirmed in field experiments.Isolates of Chaetomium which controlled disease in pot and field experiments were not strikingly antagonistic to Fusariirm nivale in pure culture on agar

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1955.tb02503.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

摘要:

Fifty‐four aryloxyalkanecarboxylic acids have been examined as systemic fungicides. Of these, four which produced negligible damage in broad‐bean seedlings yet conferred systemic fungicidal protection to broad beans againstBotrytis fabaeand to tomatoes againstAlternaria solanixverestudied in detail. The direct fungicidal activity of twenty compounds was assessed againstB. fabaeandPythium ultimum.No correlation between fungicidal and systemic fungicidal action towardB. fabaewas established. Other possibilities regarding their mode of action as systemic fungicides are discussed. The systemic fungicidal activity of a‐phenoxyziobutyric and 2:4:6‐trichlorophenoxyacetic acids in beans and of the latter compound in tomato plants was found to depend upon seasonal factors, but for 3‐phenoxybutyric and 5‐phenoxycaproic acids such variation was not observed. Results obtained in the bean test by two methods of assessment were found to correlate. The potato petiole test (van Raalte) for assessing systemic fungicidal activity was studied and modified. Evidence was obtained that the results might be unreliable owing to toxic effects produced by the compounds on the petiole tissue. Attempts were made to avoid this complication, but when phytotoxicity was eliminated, little fungicidal activit

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1955.tb02504.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

摘要:

Investigations are described on the general behaviour of diethyl‐5‐(a‐ethylthioethyl) phosphorothiolate (demeton‐S) labelled with32P, after leaf application to beans, apples andColeus; and to the roots of beans growing in soil or sand.Following leaf application, three processes, evaporation, breakdown into toxic non‐volatile compounds, and absorption, occurred concurrently and effectively removed unchanged demeton‐S from the leaf surface within a few hours. The evaporation gave rise to a fumigant action on Aphis fubue. Both demeton‐S and its degradation products were absorbed, the former degrading rapidly within the tissue untreated foliage. In no instance following leaf application could any unchanged demeton‐S be found elsewhere in the plant. Analyses showed a higher proportion of primary toxic degradation products in the treated than in the untreated leaves.Translocation from treated leaves was never sufficient to kill aphids feeding on the Following root application to beans in soil or sand, aphids feeding on the shoot tips were killed after z days; unchanged demeton‐S was translocated following root application.Demeton‐S and its toxic derivatives appeared to move much more freely in xylem than in phloem tissue; movement from xylem to phloem must occur, but subsequent transport within the latter tissue is limited.Autoradiographic evidence confirmed the limited extent of mov

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1955.tb02505.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

摘要:

When large seeds such as broad bean are soaked in certain systemic insecticides, notably demeton, the plants which they produce are toxic to aphids. With small seeds the effect is difficult to detect.Experiments with demeton solutions and broad beans show that equal quantities of water and demeton are absorbed. Beans vary greatly in the rate at which they absorb solution, so, to reduce variations, about 24 hr. soaking is necessary. The insecticidal activity of the plant is directly related to the quantity of solution absorbed by the seed. Larger bean seeds absorb more solution than small beans and the plants are more toxic. After short periods of soaking (4 hr.) there is more insecticide in the seed coat than in the cotyledons, after 24 hr. there is more in the cotyledons. Some of the toxic material in the seed reaches the growing plant via the soil and roots. The material in the cotyledons can pass directly to the growing plant. As some of the material absorbed by the seed passes into the soil, any factors such as an increase in soil volume or heavy watering which tend to dilute the insecticides reduce the quantity of toxic material reaching the plant. The same quantity of demeton is more effective when absorbed by a seed than when watered on to the soil around it. Seeds soaked in insecticide, dried, and stored for one month produced plants toxic to aphids.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1955.tb02506.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

摘要:

Nineteen alkyl iodides have been tested as fumigants against the grain weevil,Calandragranaria, using the technique previously described. Relative toxicities, and also the toxicities of mixtures of selected pairs of iodides, were determined.Secondary and tertiary isomers were in general less toxic than the primary, irrespective of whether the toxicity was measured by molar LD 50' or the corresponding relative saturation (Pt/pB) values. Despite differences in LD 50', isomeric primary iodides often acted at about the samep,/p, value. It is suggested that these observations provide evidence that, although chemical reactivity appears to be the principal factor determining the values of LD so's in the iodide series, such physical factors as phase distribution also play their part, and their effect becomes noticeable for the primary isomers, for which the chemical reactivities may be nearly the same.The deaths of individual grain weevils which had been exposed to iodides were more or less delayed. The change of the kill with time was, under standard conditions, the same when all except methyl and the tertiary iodides were used, which suggests that with these possible exceptions, all the iodides have the same type of chemical action on the organisms. The toxicities of mixtures of selected iodides tended to confirm this, for they varied from about 1.0 to 1.25 times the value predicted from the toxicities of the single iodides using the similar action equation. Despite the apparent similarity in mode of action the LD 50's and pt / p8 values varied widely, as did the ratios of the LD 50's of successive homologues in different isomeric series. This suggests that neither the magnitude of the pt / p8 value, nor the way in which it changes from member to member in a series, gives always a useful indication of the type of action shown by a compound or group of compounds.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1955.tb02507.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

摘要:

The administration of carbon dioxide in sublethal concentrations or for sublethal periods of time gave rise to an increased resistance to its effect in a strain ofDrosophila melanogastersusceptible to the toxic effects of this gas. The effect did not appear to be permanent.The successive administration by spraying of sublethal concentrations of DDT and BHC did not increase the resistance of a strain of D. melunoguster to their effects, either in the insects sprayed or their progeny. Only when the dosages were such as to give a high death‐rate did a significant increase of resistance of the progeny of the treated insects take place; the tendency was if anything to increase susceptibility, although the indications were not in favour of DDT acting as acumulative poison.In a preliminan series of tests the topical application of D D T in sublethal doses to the adult insects resulted in a reduction in the amount or in the rate of egg layin

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1955.tb02508.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

摘要:

Attempts to measure the dispersion, population density and longevity of blowflies are described. The experiments were made at Aber, Caernarvonshire, in 1943 on a narrow strip of coastal farm land (if x f ml.). Two liberations of laboratory‐bredLucilia sericata(Mg.) were made. On the second occasion 286 flies of each sex were marked, and nine males and nineteen females were captured, the last capture occurring 15 days after liberation. The population density of this species was estimated to be approximately seven males and sixteen females per acre for the 840‐acre strip on the day of the second liberation.On 24 days during the period 20 August–20 September 1943, field‐caught L. caesar (L.) females were marked, and trapping both by meat and chemical baits was continued for a further 3 weeks. 3600 females were marked, 847 being recaptured at least once, and sixteen on at least four occasions. In the later part of the blowfly season, a life of 5–6 weeks is apparently not unusual for L. caesar females. The population drawn upon by the traps at the liberation centre fluctuated between 700 and 30,000 during the 4‐week period. This may have represented a very localized concentration equivalent to 6–238 females per acre. Dispersion of marked L. caesar was low. On the assumption of a maximum spread of 5 miles, some 63 % of the marked flies remained within 4 mile of the libe

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1955.tb02509.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

摘要:

The cotton whitefly,Bemisia tabaciGenn., is important in the Sudan first as the vector of leaf‐curl virus, and secondly because it, principally when immature, directly damages plants. It damages both leaf‐curl‐resistant and susceptible varieties, and during recent years the increase in DDT spraying against the cotton jassid has increased the numbers and importance of the cotton whitefly.The macroscopic effects of the nymphs on the leaves include: (I) ‘asal’ (honeydew), often produced in quantities sufficient to cover the leaves and contaminate the lint in open bolls; (2) chlorotic spots caused by the saliva of feeding nymphs removing chlorophyll and starch; (3) development of anthocyanin; (4) leaf shedding and a reduced growth rate.The stylets of nymphs on the lower leaf surface can reach the phloem, except when they follow a convoluted path. The stylets usually penetrate between the epidermal cells. Penetration through the parenchyma is predominantly intercellular, and the objective is the phloem. Stylets terminated in the phloem in 82% of examples examined, with the remainder ending in the parenchyma. Only one case of partial penetration of the xylem occurred. A stylet, or salivary, sheath is rare; it is a delicate structure with an annular construction. Stylet tracks occur rarely and indicate probing in the region of the phloem.Damage to the tissues is limited to slow chloroplast destruction and occasional plasmolysis; the phloem is neither blocked nor obviousl

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1955.tb02510.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY