Mangold clamps are over-wintering sources of the aphid-transmitted beet mosaic, beet yellows and beet mild yellowing viruses, and of several species of aphid, three of the most common in clamps being Myxuspersicae, Rhopalosiphoninus staphyleae tulipaellus and R. latysiphon. This study attempted to assess the relative importance of the different species in spreading viruses from clamps. Compared with M. persicae, R. s. tulipaellus and R. latysiphon are seldom trapped in flight, except near large infestations. Alatae of M. persicae and N. s. tulipaellus become common in clamps in April, but few fly below 15' C., a temperature seldom reached in eastern England in early spring. Flight muscle autolysis, which occurs later in R. s. tulipaellus and R. latysiphon than
The reaction of 25 UK pea cultivars to pea seedbornc mosaic virus (PSbMV) was studied in lhe glasshouse. All cultivars proved to be susceptible. When leaf or tendril samples from inoculated plant' wereanalysed, it was found that most combining culuvars had a lower virus content as measured byA4fIj' values in ELISA. than garden and vining cultivars, and that garden and vining cultivars had a simHllr virus content. Seed transmission of PSbMV in 20 cultivars ranged from OOft-t in cvs Maro, Princess an.d" Progreta to 74% in cv. Vedette. There was no obvious relationship between virus content and lhe, efficiency of seed transmission in different cultivars. Wide variation in percentage seed transmission between individuals of single cultivars was observed; for seven cvs (ST 2-49o/Q) tested, all showed some plants escaping seed transmission altogether. Seedlings infected through the seed showed symptonu similar to those in the infected parent plants. Virus particles were readily detectable by immunosorben electron microscopy in infected seedlings, and in elongated infected embryonic shoots produced 3 dayr, after seed germination, by ELISA. An ELISA lest of seed samples from cv. Waverex showed that virutw as as readily detected 3 days after germination as after growth to symptomatic seedlings (4 weeks), an4:p robably provides the most sensitive. accurate and time-saving assay for seed transmission of PSbM,V",
Experiments started in 1976Experiments started in , 1977Experiments started in and 1978 on Clay-with-Flints soil at Rothamsted tested the effects of combinations of eight two-level factors on spring-sown field beans. Factors tested, presence v. absence, were irrigation, nitrogen fertilizer, aldicarb, fonofos (dieldrin in 1976), benomyl to the seed bed, permethrin (fenitrothion in 1976), pirimicarb, benomyl foliar spray (not tested in 1976).The main pests and diseases present were nematodes of the genus Pratylenchus, the pea aphid Acyrthosiphon pisum, the pea and bean weevil Sitona lineatus, root blackening associated with the fungal genera Pythium and Fusarium, the foliar diseases chocolate spot, Botrytis spp., rust, Uromyces fabae and bean leaf roll virus.Incidence of these pests and diseases varied between years. Controlling those present increased yield by about 0-7 t grain/ha each year. The difficulty of apportioning this increase to particular pests and diseases is discussed. ' Irrigation increased total dry-matter production and grain yield in 1976 and 1978 but only total dry-matter production in 1977, when grain yield was lost because of lodging. Nitrogen fertilizer had little or no effect.The most favourable combinations of treatments gave yields of 3-4, 5-0 and 6-4 t grain/ha in the 3 years respectively. Small yields in 1976, despite irrigation, were attributed to premature senescence caused by exceptionally high temperatures. It is suggested that with good control of pests and diseases yields of at least 5 t/ha should be attainable on Clay-with-Flints soil without irrigation in years of average temperature and rainfall and yields in excess of 6 t/ha when the soil-moisture deficit is lessened by either above-average rainfall or irrigation.Treatments applied to the beans had little or no effect on two following crops of winter wheat. INTRODUCTIONseasonal variations in yield and to determine the size of yields when known pathological constraints The introduction of residual weedkillers and were removed. The pests under study were nemainsecticides able to control black bean aphids todes and insects, and the pathogens were root and (Aphis fabae Scop.) increased the prospects of foliar fungi and viruses. growing satisfactory crops of spring-sown field Of the migratory nematode genera present in beans (Viciafaba L.). Despite these introductions Rothamsted soils, Pratylenchus Filipjev and small average yield and large seasonal variations Tylenchorhynchus Cobb are known to damage roots are still major problems. Recently additional pests of field beans (Oostenbrink, 1954; Whitehead & and pathogens, whose incidence and ability to Fraser, 1972). Pratylenchus Micoletzsky and Helicause damage differ each season, have been shown cotylenchus Steiner are known to attack barley to attack beans. The experiments described here (Coursen, Rohde & Jenkins, 1958;Taylor, 1960). attempted to control a wide range of these to At Rothamsted the predominant genus attacking determine the extent to which this could lessen field be...
SUMMARYAlate Aphis fabae were often less efficient vectors than Myzus persicae of pea mosaic virus and sugar‐beet mosaic virus. Flight‐mature A. fabae rarely transmitted these viruses unless they had either flown (tethered) or fasted for several hours before feeding on infected plants; by contrast, flight‐mature M. persicae transmitted either virus before flying or fasting, though more frequently afterwards. There was little difference in the infectivity of the two species after they had flown and then fed for a short time on infected plants.Aphids flown for 1–5 hr. and then allowed a short feed on infected plants transmitted only slightly more often than aphids flown for 15 min., but they remained on the host plants longer. After flying for 15–60 min., many A. fabae settled permanently on broad bean plants, and a few on sugar‐beet plants, but most M. persicae flew off after feeding on these plants for a few hours.Many flight‐mature alatae of both species probed briefly before flying from a plant for the first time; more M. persicae than A. fabae transmitted after such pre‐flight probing on infected plants.The infectivity of flying or fasting alatae, and fasting apterae, decreased at similar rates. The rate of decrease was accelerated as the temperature rose, and few aphids transmitted after 30 min. at temperatures above 30 °C.PMV and SBMV, but not henbane mosaic virus, were transmitted more often by alatae than by apterae. The species of plant (broad bean or sugar beet) on which aphids developed did not affect their ability to transmit PMV or SBMV.
The temperature thresholds for wing‐beating and successful flight in alienicolae of Aphis fabae were found by flying tethered aphids in a falling temperature and by dropping free aphids in still air at different temperatures. The median temperature thresholds for wingbeating, horizontal and upward flight were 6.5°, 13° and 15° C respectively. ZUSAMMENFASSUNG UNTERE TEMPERATURSCHWELLEN FÜR DEN FLUG VON APHIS FABAE SCOP. Die Temperaturschwellen für Flügelschlag und erfolgreichen Flug wurden bei alienirolen Aphis fabae Scop, an gefesselten Aphiden bei fallenden Temperaturen ermittelt sowie durch Fallenlassen freier Blattläuse in ruhige Luft bei verschiedenen Temperaturen. Die mittlere Temperaturschwelle für Flügelschlag betrug 6,5° C (Flügelschläge eine Minute andauernd) und wurde vom Feuchtigkeitsgehalt der Luft sowie von der Abkühlungsrate (sowie möglicherweise von der Flugdauer) beeinflußt. Unter 9–10° C hielt der Flügelschlag mur für eine kurze Zeit an und die Schlagamplitude war bei diesen Temperaturen im allgemeinen gering. Die mittlere Temperaturschwelle für horizontalen Flug lag bei 13° C (unter 10° vollständige Verhinderung) und für Aufwärtsflug bei 15° C (unter 12° völlige Hemmung); die höhere Schwelle für den Aufwärtsflug steht wahrscheinlich mit höherem Stoffwechselbedarf in Verbindung. Nach einem Aufenthalt von 24 Stunden bei niederen Temperaturen (5–15° C) vor dem Flug flogen bei 12–13° C weniger Blattläuse, als wenn sie bei 20° C gehalten worden waren. Diese Ergebnisse gelten nur für die ersten wenigen Sekunden des Fluges.
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