摘要:

Infection with beet yellows virus depressed the dry‐matter yield of sugar‐beet plants by decreasing both leaf area and net assimilation rate (N.A.R.). It did not reduce the number of leaves.The lower N.A.R. of infected plants may occur because photosynthesis is slowed by chlorosis of the leaves or by changes associated with it. Plants infected at the end of June had 30‐50% of their leaf area yellowed from mid‐August. Later infection caused less yellowing. The yellowing almost sufficed to account for the decrease in N.A.R., if yellowed parts of leaves do not photosynthesize. However, the similar diurnal fluctuations of carbohydrate in the laminae of healthy and infected leaves suggests that photosynthesis may not be much slowed by infection; if so, the decrease in N.A.R. indicates a large increase in respiration rate, especially of the root.The effects of yellows on leaf area and N.A.R. appear to be independent; late‐sown plants suffered a greater reduction of leaf area, but a smaller reduction in N.A.R., than early‐sown plants; similarly treated plants showed the same reduction of leaf area in two successive years, but the decrease in N.A.R. was much greater in the second.Most of the loss of dry matter was in the root; the dry weight of the petiole (including stem tissue) was also decreased but the dry weight of leaf lamina was little affected.Yellows greatly increased the reducing sugars in the leaf lamina, and caused smaller increases in sucrose and starch. These effects appeared when the leaves showed only etch symptoms. The increase in starch was greatest at this time, but the effect on sugar content subsequently increased with the development of yellowing.Yellows reduced the water content, nitrogen content and the arealweight ratio of the leaf lamina. The change in nitrogen content, but not the others, could be accounted for by the rise in carbohydrate.Yellows had no effect on the water content of petiole and root; it increased the nitrogen content of these parts. It reduced the sucrose content of the root, but the loss of sugar yield was mainly attributable to decreased root weight.Infection with beet mosaic virus decreased the dry weight of sugar‐beet plants only when nitrogenous fertilizer was applied. As with yellows infection, the loss of dry matter resulted from reductions in both leaf area and N.A.R. Unlike yellows, mosaic depressed the dry weight of leaf lamina, as well as of petiole and root.Mosaic had no effect on carbohydrate content, water content or arealweight ratio of the leaf lamina, or on water content of petiole and root. It increased the nitrogen content of all parts of plants that received no nitrogenous fertilizer, but not of nitrogen‐treated plants. It slightly increased the sucrose content of the root.Infection with beet mosaic virus at the end of June caused a 20 yo loss of sugar yield from plants that received nitrogenous fertilizer. Yellows infection of similar plants at the same date reduced the sug

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb02364.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

Multiple regression analysis of the data described in a previous paper identified alateMyzus persicaeof the spring and summer migrations as the most important factor affecting spread of beet yellows virus in the sugar‐beet root crop in England.Apterae ofM. persicaespread little virus, and the contribution of alatae and apterae ofAphis fabaewas negligible.A simple mathematical model of the spread of infection was developed. Assuming that the crop is visited byNaphids at a time when the proportion of plants infected isk0, the predicted proportion of infection for a time 3–4 weeks later (k1) isk1=k0+ 100(1‐k0) (1‐e‐N1), whereI=p[(1‐k0)t+k0t‐1]/k0.This formula adequately accounts for the observed spread of infection whenN=1/10 sticky trap count for the 3–4 weeks preceding the time whenk0infection is observed;p= probability of infection by a single aphid =½;t= number of movements per aphid effective for spreading beet yellows virus = 5.The good fit of this formula to the observed data supports the results of the regression analyses in showing that alateM. persicaewere mainly responsible for spreading beet yellows virus. Once infection had been introduced into the root crops in the spring spread was mainly within fields, or between fields in the same neighbourhood.In areas where beet and mangold seed crops were grown intensively some infection was spread to the root crops by summer migrants from infected seed crops. Apart from this, the greater prevalence of yellows in seed crop areas was caused by the greater development ofM. persicaeinfestation of the root crops which occurs in these areas.The proportion of plants infected by spring migrants entering the root crops before the end of June was small and variable. It did not vary significantly between seed and non‐seed areas. This implies either that initial infection came equally from sources other than seed crops, or that, if the seed crops were the main sources of infection, winged aphids acquired infectivity by visiting them during migration, and later became very widely dispersed.In contrast to yellows, mosaic virus spread mainly in the neighbourhood of seed crops within the seed‐crop areas. No significant relation between aphid numbers and increase of infection was established, but there is a strong suggestion that alatae ofM. persicaeandA. fabaespread the virus, and that the contributions of both species are equal. This suggests that mosaic virus is not spread by movement of aphids within the root crops, but only by infective migrants coming from outside sources. As the virus is non‐persistent the sources must be near to the root crops, and as there is little internal spread many infective migrants are needed to cause a high level of infection. The seed crops fulfil these conditions as they are often severely infected with mosaic, and both vector species breed on them. The irregularity of the data relating aphid numbers to mosaic incidence is probably caused mainly by individual variation in the intensity of infection of seed crops, and in the proportion of migrants caught on the traps which act

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb02365.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

Field experiments made in eastern England between 1943 and 1951 showed thatMyzus persicaelived on the stecklings throughout some winters, and that most plants with yellows in transplanted seed crops were from infections that occurred in the steckling bed. A larger proportion of stecklings sown at the end of July or in early August became infected than of those sown about a month later. The incidence of yellows was reduced by nicotine sprays which cleared the stecklings of aphids after autumn migrations had ceased, thus preventing spread of the disease during the winter. A greater reduction was obtained with persistent and systemic organo‐phosphorous insecticides; in one experiment three applications of E 605 reduced incidence to one‐ninth that in unsprayed plots. However, in years when stecklings were exposed to large migrations of aphids, even plots sprayed three times had 78% of the plants with yellows. Although spraying often greatly reduces the incidence of yellows, it is unlikely to give adequate control in years and districts in which many viruliferous aphids move in the autumn. Spraying in September and October was usually more effective than in Aug

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb02366.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

Synergism between nicotine and pyrethrum applied by injection to adultOncopeltus fasciatusDal. has been reported by Turner (1951).When these insecticides were applied alone and as a mixture to adultTribolium castaneumHbst., using a dipping technique, the data indicated that independent joint action occurred. Similar action could be eliminated because the two insecticides had varying relative potency.Since the effect of the pyrethrins has been short‐lived in some insects, it was postulated that the absence of synergism might be caused by failure of the nicotine to reach a site of action while the pyrethrins were still acting.Application of nicotine, followed later by treatment with pyrethrins, gave evidence of synergism. A test in which the interval between treatments was varied from ¾ to 6 hr. showed that toxicity was greatest with the shortest interval between applications, and evidence of synergism had practically disappeared after 6 hr. The maximum amount of synergism observed was about twofo

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb02367.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

Nicotine and nicotine salts are taken up by the roots of plants from solutions, and when 0.01–0.001 % nicotine is used the plants become toxic toAphis fabaeand toPieris brassicaelarvae and can be shown to contain nicotine. The results withPhaedon cochleariaeadults and larvae are less satisfactory. No systemic action is observed when the nicotine is watered on to soil in which plants are growing and no nicotine can be detected in the plants. Apparently the nicotine is decomposed in the soil.When applied several times to the upper surface of a bean leaf nicotine kills aphids on the underside. There is some evidence that nicotine can be translocated further through the plant following leaf applications, but the toxic action at any distance is very weak in the plants used in the present experiments and can only be produced by frequent applications of rather concentrated nicotine solutions. Leaf absorption and subsequent translocation has not been observed with nicotine salts.The various organic bases, including some piperidine phosphonites and allied compounds tested, are of very little interest as contact or systemic insecticides against aphid

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb02368.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

The sharp limitation of synergistic action when equimolecular proportions of the pyrethrins and some of their synergists are tested against flying mosquitoes has been confirmed when such mixtures are employed in assays usingCalandra granariaL. crawling on oil‐films on filter‐paper.Limitation of the relative potencies of pyrethrum‐synergist mixtures appears to be a general property, and except for piperonyl butoxide the limiting relative potency is attained at equimolecular proportions of insecticide and synergist.These observations are discussed in connexion with a general theory of insecticidal a

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb02369.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

Some principles of testing for resistance in wild and laboratory stocks of insects are discussed, and experiments withCalandra granariaL. are described in which these insects are selected for pyrethrum resistance.A new method is described of expressing relative tolerances when the relevant regression lines are not parallel, based on the ‘generalized distance’ of Mahalanobis. The method may equally be used for the comparison of two insecticides giving rise to lines of different slope. A limited increase in resistance occurred on selection. Non‐random oscillatory sequences of slopes were observed when the resistant strain was assayed, and regression parameters computed. The nature of these oscillations is consi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb02370.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

The results of laboratory studies on nine species of warehouse Ptinid beetles at 25° C. and 70%r.h. are used to calculate by Leslie's methods, the statisticrmeasuring the intrinsic rate of increase of each species.Ptinus tectusBoield. has the highest value ofr—0–38, equivalent to a 39 % weekly increase or tenfold in under 2 months. Four species,Gibbium psylloides(Czemp.),Mezium affineBoield.,Stethomezium squamosumHinton andTrigonogenius globulusSol., are capable of tenfold increase in 3 months and the remaining four multiply more slowly, either because of a low oviposition rate (Eurostus), high developmental mortality (Niptus), or slow development (Ptinus fur(L.),P. sexpunctatusPanz.).Generally the intrinsic rate of increase falls with temperature due to lengthening of development and reduction of oviposition, but near the maximum of development it also falls because of high developmental mortality.Niptushas a higher rate of increase at 20° C. than at 25° C. which is close to its developmental maximum. Relative humidity has little effect except at the limits of humidity tolerance, but water must be occasionally available for the adult to drink, or oviposition and thus rate of increase is markedly depressed. Food mainly affects the rate of increase through its effect on developmental speed. Other factors are briefly considered.The statisticrapplies to a population which has a stable age distribution. For Ptinids the stable age population was found by calculation to contain between 5 and 11% of adults, whereas in the warehouse never less than 15% of the population found were adults. In a warehouse actual observed rates of increase reached a value equivalent tor= 0.24 per week over a period of 8 weeks. From observed temperature means and laboratory results a maximum ofr= 0.31 was predicted with a mean of 0.19 per week for a year. The value ofrobtained using the oviposition rate estimated in the warehouse was 0.1. Warehouse values ofrmay be below those predicted from laboratory results because oviposition is restricted due to lack of drinking water and often to overcrowding, mortality increased due to disease, parasites, predators, and accidental cannibalism, and developmental speed retarded due to cr

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb02371.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

The primitive (single oviposition period) method for determining the finite rate of natural increase (Λ) of an insect species which lays all its eggs quickly is described, together with a summary of a more accurate method introduced by P. H. Leslie and L, C. Birch of calculating the infinite (infinitesimal) rate of increase (r) of any species. The parameterris the natural logarithm of the parameter Λ. Two methods of simplifying this more accurate method are discussed and illustrated by six examples which are used to compare the results given by all four methods.The first modification of the Leslie‐Birch method provides a means of representing a long oviposition cycle by a single figure so that the final calculation resembles the primitive single period method. The oviposition period is divided into a number of convenient unit periods, and using a table of weighting factors provided, the number of eggs laid in each of these unit periods is converted into the number of eggs required to be laid in the first of these unit periods of oviposition to make an equivalent contribution to the rate of increase. The equivalent oviposition figures for all the unit periods are summed to provide one figure which represents the observed egg number and pattern.The second modification provides a means of representing the observed egg pattern by a constant rate of oviposition. This requires the same table of weighting factors but also needs a series of charts which are provided. This method usually gives a good answer at the first attempt, whereas the first modification usually requires two trial and error solutions to give an accurate estimate ofrand hence of Λ. Two of the examples show how the methods may be used for species for which information is scattered in the published literature. The minimum requirements for estimation ofrare information on the length of the developmental cycle, the rate of egg output of adults, mortality of all stages and the sex r

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb02372.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

A number of mono‐, di‐and trichloro‐β‐naphthols and the corresponding naphthyloxy‐n‐carboxylic acids were prepared. They were tested as systemic fungicides against chocolate spot of broad bean (Vicia faba) caused byBotrytis fabaeand as fungicidesin vitroby their effect on the germination of spores ofSclerotinia laxaand the growth of the mycelium ofBotrytis fabae.The systemic fungicide tests showed no difference in the activity of the compounds associated with different side chains, though there were slight but significant effects associated with different chlorine substitutions in the naphthalene nucleus. The 3:4‐dichloro‐2‐naphthol derivatives were more effective than the other compounds tested.Fungicide tests with the 1:3‐dichloro‐2‐naphthol derivatives suggested that there was some increase in toxicity to the spores ofSclerotinia laxawith increasing length of side chain. The effectiveness of the various chlorine‐substituted compounds in suppressing growth ofBotrytis fabaewas in the following descending order, 1:3:4‐trichloro‐, 1:3‐dichloro‐, 1:4‐dichloro‐and 3:4‐dichloro‐compounds. The concentrations required in agar culture to induce reductions ofB. fabaegrowth comparable to those found in the leaf could reasonably be expected to occur in the bean plants treated with

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb02373.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY