ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1967.tb04426.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

SUMMARYExperiments for nine successive years showed thatAphis fabaeScop. populations on mid‐March‐sown field beans were either large with peak densities between late June and mid‐July or very small with peak densities in early August. It is concluded that the largest populations develop when many plants have been colonized by primary migrants fromEuonymus europaeusand temperature and radiation are above average during June and early July, as in the year 1957. Cold, dull weather slows multiplication and decreases the size of the peak population even when there is a large initial colonization, as in 1954. The peak population may also be less than predicted from the initial colonization when natural enemies are exceptionally abundant in early June, as in the year 1960. Yield losses of mid‐March‐sown crops in years of largeA. fabaepopulations ranged from 53 % in 1954 (peak population of 1260 aphids per plant) to 100% in 1957 (6920 aphids per plant).Small summer populations with peak densities of about 0·2–85 aphids per plant developed on mid‐March‐sown plots in years when fewer than about 6% of the plants were colonized by primary migrants. Yield losses ranged from 6·3–13·6%.Three years' experiments indicated that crops sown in late April or May are relatively lightly infested in years when large populations develop on mid‐March‐sown crops. Conversely, they may be relatively heavily infested when the populations on these crops are small, as in 1955 when temperatures and sunshine during July and early August were above average.Small and large early summer populations tend to alternate in successive years. The alternation is upset by hot, sunny weather during July and August, and perhaps September and October, which compresses the population cycle Thus the large and small populations expected from this alternation in 1956 and 1960 developed instead during exceptionally fine weather in late summer 1955 and 1959, converting 1956 and 1960 to years of small and large

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1967.tb04427.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

SUMMARYParthenogenetic virginoparous apterae ofAphis fabaeScop. on field beans(Vicia faba)reproduced faster initially in populations of eight colonizing apterae than in those with 2–4 or 16–32 per plant. The aphids were at first mutually benefited but were quickly affected by competition as numbers rose above the critical density represented by about eight apterae and their first progeny. This is because the aphids remained densely aggregated and seemingly created a local shortage despite abundant food and space elsewhere on the plant. Such self‐induced competition provides the basis for self‐regulation of numbers ofA. fabaein relation to (1) food and space provided by the growing plant and (2) mortality from natural enemies and from other causes including insecticides.As competition increased, the multiplication ofA. fabaepopulations slowed, newly formed adult apterae emigrated and increasing numbers of alatae were formed. The mean weights of apterae decreased from about 1·8 mg. to 0·3 mg. and of alatae from 0·9 to 0·2 mg. Such decrease probably favours production of many adults that might otherwise fail to mature.Experiments in a glasshouse and in field cages indicated the success with which anA. fabaepopulation adapts to and exploits a growing plant. Field bean plants sown in mid‐March and infested as in the field produced an average of 15,000–17,000A. fabaeemigrants per plant of which 78–84% were adults (mostly alatae). This is equivalent to about 1600 million alate emigrants from 1 acre (0·4 hectare) of an infest

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1967.tb04428.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

SUMMARYThe influence of different aphid foods on larval development and adult fecundity ofAdalia bipunctataL. andCoccinella 7‐punctata L.was investigated. Certain aphids such asMyzus persicaeSulz. andAcyrthosiphon pisumHarris were suitable for both species.Megoura viciaeBuckt., was toxic toA. bipunctatabut not toC. 7‐punctata. Aphis fabaeScop., although a common natural prey ofA. bipunctata, slowed larval development, partly because it was nutritionally unsuitable. Fecundity of adults fed onA. fabaewas also reduced to less than half. Larvae and adults ofC. 7‐punctatadeveloped and reproduced as well onA. fabaeas on other suitable aphids.C. 7‐punctatacaught aphids more quickly thanA. bipunctata.Larvae of both species given relatively unsuitable prey fed more slowly than normal and consumed less of each aphid. The toxic aphidM. viciaewas rejected byA. bipunctataafter a short period of

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1967.tb04429.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

SUMMARYProcesses affecting the toxicity of diazinon to a susceptible and a resistant strain of houseflies were examined.More evidence was obtained to show that slower penetration of diazinon through the integument of resistant flies is a cause of resistance.Small amounts of two decomposition products were found in both strains. The decomposition mechanisms, in these strains were differently distributed and, although detoxication of diazinon in the two strains is quantitatively similar and small, it may contribute to resistance.Traces of diazoxon were detected when diazinon was incubated with tissue extracts of either strain.Tissue extracts of resistant, but not of susceptible, flies decomposed significant amounts of diazinon in 1 hr. and the ability to decompose diazoxon seems to be an important cause of resistance.Tissues of both strains sorbed diazinon from aqueous solution similarly; the quantities sorbed were large and suggest that sorption may increase the amount of poison needed inside the insects to kill, by between five and forty times.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1967.tb04430.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

SUMMARYThe cytological changes inNeurospora crassaconidia following treatment with captan at the ED50fungicidal dose have been examined by electron microscopy. With dormant conidia the only observable effect of captan was to produce a characteristic convoluted form of the nuclear membrane. It is suggested that this effect may be due to the reaction of captan with the sulphydryl groups of the nuclear proteins leading to an inhibition of cell division. The cytoplasmic membrane was unaffected by captan, confirming that this fungicide does not destroy cell permeability barriers.After incubation in Fries medium, captan‐treated spores showed an almost complete loss of internal fine structure. Similar results were obtained with ‘protoplasts’ ofN. crassawhich showed disorganization of mitochondrial structure after captan trea

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1967.tb04431.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

SUMMARYExperiments with fungicide mixtures used protectively and curatively against apple scab showed no advantage from adding phenylmercury chloride (PMC) to certain protective fungicides. Sulphur fungicides greatly impaired the curative activity of PMC, especially in mixtures applied 24 hr. after infection, but captan showed little and dodine acetate no such effect. PMC, however, contributed appreciably to the curative effectiveness of mixtures with captan or dodine acetate. Commercially prepared mixtures of dispersible sulphur with phenylmercury dimethyldithiocarbamate and of zineb with mancozeb gave promising results, and an experimental mixture of dodine/glyodin acetates at low rates was effective protectively and especially curatively.Dodine acetate, dichlofluanid, lime‐sulphur, and isobutyl‐o‐coumarate showed little translocated activity against scab when applied after infection, and PMC, which earlier showed strong translocated activity when applied in summer before infection, was much less effective when applied in spring 24 hr. after infection.Uncontrolled powdery mildew early in the scab‐incubation period greatly reduced the establishment of scab infection on the test plants (clonal root‐stocks); methods of mildew control in such experiments are

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1967.tb04432.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

SUMMARYDuring falls of rain before 5% of the haulm was destroyed by blight, most rain water was deposited on soil at the bottom of the ridge, and least at the top in crops of King Edward, Majestic, and Up‐to‐Date potatoes. Afterwards less water was trapped half way up the side of the ridge than above or below. Water was also channelled down the stems and, while these were upright, was deposited in the channel often formed around the stem bases by wind movement. Fewer than 500 sporangia per ml. were seen in water collected when blight was present in the crop.Growing tubers of Ulster Ensign and King Edward, inoculated withP. infestans, infected healthy tubers less than 1–3 cm. away, when the soil water content was greater than 20%, and sporulation on the inoculated tubers was maximal. Similarly inoculated Up‐to‐Date and Majestic tubers sporulated less abundantly and failed to infect healthy tubers.Sporulation also occurred on inoculated seed tubers, although infection of the haulm from these tubers could not be confirmed. Water movement from the seed tuber region to the furrows may occur under suitable c

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1967.tb04433.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

SUMMARYPhytophthora infestansinfects King Edward potato tubers more readily through inoculated eyes than through lenticels, but more lenticels than eyes became infected when whole tubers were sprayed with inoculum. The resistance of lenticels but not of eyes increased as tubers aged. The spores did not infect through intact periderm. The likelihood of tubers on plants grown in pots becoming infected by sporangial suspension poured on to the soil increased the nearer the tubers were to the soil surface, the stem, or the side of the pot. Naturally infected tubers, and those sprayed with sporangial suspension, had most eyes infected at the rose end, and most lenticels infected on the middle region of the tuber. Of naturally infected tubers, on which the site of infection could be identified, most were infected through eyes at the rose end.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1967.tb04434.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

SUMMARYIn two large‐scale observation trials on commercial farms inorganic nitrogen fertilizer was applied at 70 lb. N/acre (N1), 1401b. N/acre (N2) and at a normal commercial rate of 210 lb. N/acre (N3). Mean wilt incidence was 60 and 25% less with Ni and N2 respectively than with N3 during 5 years at one site and 3 years at the other. During these periods wilt declined progressively and this was tentatively attributed to the reduced intensity of host colonization, and to progressive declines in soil infectivity resulting from effects on the quantity, quality and longevity of annually produced inoculum.Marked annual fluctuations of wilt incidence and yields occurred at one site and these were associated with weather in the spring and early summer: wilt incidence was inversely related to soil temperature, and yield was directly related to rainfall. Yields were not diminished by the low‐N treatments, but clear correlations between yields and wilt incidence were probably obscured by the differential effects of weather conditions at the three levels of N application.The results emphasized the importance of reducing traditionally high N applications and, on farms where fluctuating wilt is severe, of applying the minimum levels of N commensurate with the maintenance of satisfactory yie

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1967.tb04435.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY