摘要:

SummarySitobion avenaewas introduced into areas within a field of winter wheat in Norfolk in mid‐May 1985, when the indigenous population was negligible. Aphid numbers in these areas increased for the first 3 wk and declined for the next 4. A secondS. avenueintroduction into the same areas and into previously uninfested areas was carried out 5 wk after the first introduction, when the crop was at ear emergence complete (G.S. 59). This increased aphid numbers in the previously uninfested areas, but numbers in the previously infested areas continued to decline to below the level in control areas during the subsequent 2 wk. Populations in all areas then increased rapidly to a maximum, followed by a rapid final decline. Monitoring of the aphid and natural enemy populations, and caging aphids onto the crop, revealed that the principal cause of the population decline around G.S. 59 was predation by syrphids. The relevance of these findings to the problem of forecastingS. avenaeoutbreaks is discussed, and a general explanation for cereal aphid outbreaks is put forwar

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1989.tb03355.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryIn three sets of data pooled over spring wheat varieties and lines a number of grain quality measurements were related to the levels of infestation bySitodiplosis mosellanalarvae. The Hagberg falling number value was negatively correlated with the proportion of damaged grains. The 1000‐grain weight, protein content and gluten content were not affected. Differences between cultivars in infestation and damage level were found to depend on the development phenology (timing of ear emergence) and on the percentage of damaged grains remaining in the yield after harvest. The falling number values were reduced most when the attainable values remained low in cultivars prone to sprouting damage, and in seasons with unfavourable weather conditions for quality maintenance.The proportion of damaged grains in relation to the number of larvae was well described by a logit‐transformed regression. Sampling for infestation level and preventive measures against quality loss are discus

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1989.tb03356.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryAn accumulated soil temperature model is described which calculates the first oviposition date for overwintered populations of the raspberry cane midge (Resseliella theobaldi). The model uses values for mean 10 cm soil temperature, derived from daily maximum and minimum air temperatures and 10 cm soil temperature at 0900 GMT. It was developed by minimising the variation between observed dates for the start of oviposition over an 8‐yr period and accumulated air or soil temperature, using a series of base temperatures. The best fit was obtained with soil temperatures accumulated above a base temperature of 4°C. Oviposition was predicted to start when the daily accumulated soil temperature reached 339°C days above a base temperature of 4°C.Field observations and model predictions suggested that emergence and oviposition dates were influenced by the direction of the slope of raspberry plantations. To compensate for this, an empirical correction has been incorporated into the model to advance or retard the predicted oviposition date by adjusting the estimated maximum soil temperature to allow for aspect. The geographical variation between dates for first oviposition was simulated by running the model for nine meteorological sites in the UK in 1985 and

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1989.tb03357.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummarySuction traps at Leeds University Farm, N. Yorkshire, monitored aerial populations of cereal aphids over three autumns. Different migration patterns were observed between the four main species,Sitobion avenae, Metopolophium dirhodum, Rhopalosiphum padiandR. insertum. The relevance of these patterns to the epidemiology of barley yellow dwarf virus (BYDV) is discussed.Transmission tests revealedS. avenaeto be the major vector of BYDV, rather thanR. padi, which is responsible for disease outbreaks in the south and west of Britain. An Infectivity Index (II) of 50 has been advocated forR. padi‐transmitted BYDV, above which economic damage is likely to occur. This value is shown not to be applicable to the Vale of York, and methods of adapting the data are proposed. Such adjusted II values depend on the behaviour and reproduction of the aphids during the transmission tests, and produce II values that correlate well with levels of field infection in the are

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1989.tb03358.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryWith the present research we tried to evaluate the contribution by maize (corn) to the spread of aphid vectors and in the maintenance of barley yellow dwarf virus (BYDV) in Friuli ‐ Venezia Giulia (North East Italy). We also wanted to examine differences between two corn genotypes in relation to aphid colonisation. Some aspects of plant colonisation and the frequency of BYDV infected colonies in the two cultivars are discusse

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1989.tb03359.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummarySporulation inA. brassicaeandA. brassicicolaon naturally‐infected leaf discs of oilseed rape and cabbage required humidities equal to or higher than 91.5% and 87% r.h. respectively. The optimum temperatures for sporulation were 18–24°C forA. brassicaeand 20–30°C forA. brassicicolaat which temperatures both fungi produced spores in 12–14 h. Above 24°C sporulation in A.brassicaewas inhibited. At sub‐optimal temperatures sporulation times for A.brassicicolawere significantly longer than for A.brassicaewith the differences increasing with decrease in temperature. Interrupting a 16‐h wet period at 20°C with a period of 2 h at 70% or 80% r.h. did not affect sporulation in either fungus but a dry interruption of 3–4 h inhibited sporulation in both. Exposure of both fungi to alternating wet (18 h at 100% r.h., 20°C) and dry periods (6 or 30 h at 5565% r.h., 20°C) did not affect the concentration of spores produced in each wet period. Sporulation times were not affected by either the host type of the age of the host tissue. White light (136 W/m2) inhibited sporulation in A.brassicaewith the degree of inhibition increasing with increasing light intensity. The effect of light on sporulation in A.brassic

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1989.tb03360.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryA new forecasting system for virus yellows incidence in sugar beet in the UK has been devised using multiple regression analyses. The forecast equations include data on (1) the previous year's virus incidence, (2) temperature in January and February and (3) the timing of the spring migration ofMytus persicae. Forecasts using the first two of these variables account for 63% of the variance in virus incidence in the main beet growing area of Eastern England and give growers information in time to decide on whether to apply aphicidal granules at drilling to control the vectors of the disease. Forecasts using all three variables account for 87% of the variance in virus incidence and can forewarn growers and the sugar industry of the likelihood of an epidemic. Forecasts for the northern and western regions of the beet growing area are derived from the forecast for the eastern region.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1989.tb03361.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryTwo serotypes of chloris striate mosaic virus (CSMV), paspalum striate mosaic virus (PSMV) and geminiviruses infectingBromus catharticusandDigitaria didactylawere investigated. Their field occurrence and experimental hosts are listed. Serial transmission data for CSMV by singleNesoclutha pallidashow a minimum latent period of 12–14 h, and regular transmission with occasional breaks for up to 50 days.Cicadulina bimaculatadid not transmit any isolates after plant feeding acquisition, but transmitted CSMV inefficiently after insect injection. The vector of PSMV was found to be a specific biotype ofN. pallidawhich bred only onPaspalumspp. The rate of transmission of CSMV with theChlorisbiotype ofN. pallidaand of PSMV with thePaspalumbiotype reachedc. 50% with single insects, but only when freshly‐infected source plants were used. Geminate particles were found in thin sections of leaf tissue infected with all four viruses, and partially purified preparations were made of three of these. In gel diffusion tests, the virus fromMicrolaena stipoidesproduced a spur reaction with CSMV, when reacted with CSMV antiserum. TheB. catharticusandD. didactylaisolates failed to react serologically with CSMV, maize streak or Vanuatu digitaria streak viru

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1989.tb03362.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryBeet yellows virus (BYV) and beet mild yellowing virus (BMYV) are introduced to sugar‐beet root crops in spring by winged aphids, and are spread within the crops from these foci of infection. The rate of spread is likely to be influenced by the speed with which the initially inoculated plants become sources of infection. Studies reported in this paper showed that when field‐grown sugar beet were inoculated at the 2–4 leaf stage with BYV, the virus was detected in the youngest leaves after 1 wk, in all leaves after 2 wk and was readily acquired and transmitted byMyzus persicaefrom these infected leaves. In contrast BMYV multiplied and spread more slowly in plants inoculated at the 2–4 leaf stage, and was not acquired and transmitted byM. persicaevery efficiently early in the season. When plants were inoculated at the 15–20 leaf stage there was less difference between the two viruses. The consequences of the observations in relation to aphid control are

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1989.tb03363.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryTobacco and pepper plants were inoculated with a mild strain of cucumber mosaic virus (CMV) with or without satellite RNA, then challenged by a virulent CMV strain devoid of satellite RNA and protection effects detected by assessment of symptoms and protein A sandwich ELISA for the challenge CMV strain. Protection was obtained both in the presence and the absence of satellite RNA in the preinoculating strain but was greater when it was present.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1989.tb03364.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY