摘要:

SUMMARYImmobilisation of aphids of three species,Schizaphis graminum, Myzus persicaeandDactynotus ambrosiae, was accomplished using low temperature (6 ± 1°C; or nitrogen (N2), argon (Ar), or carbon dioxide (CO2) gases at 25°C for 1,3,6, or 24 h. Mortality was recorded and also times until treated aphids first walked or probed. Cold immobilisation caused least mortality and allowed rapid recovery of walking and probing abilities. CO2treatment, even when accompanied by cyclic administration of bottled air, caused excessive mortality when used beyond 6 h, and long recovery times. After 24 h immobilisation with CO2aphids seldom walked or probed. N2or Ar gases, when administered with alternating cycles of bottled air, produced a nontoxic, hypoxic immobilisation from which aphids recovered fairly rapidly to walk and probe, apparently normal

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01451.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYPolyphagous predators (e.g. Araneae, Carabidae and Staphylinidae), collected from spring barley fields during 1981‐85, were examined by either gut dissection or a R.padi‐specific antiserum in enzyme linked immunosorbent assay (ELISA) in order to detect predation ofRhopalosiphum padiduring the aphids' establishment and exponential growth phases.Overall 18% ofc.3000 carabids dissected were shown to feed onR. padiduring the aphids' pre‐peak period. No overall relationship was found between percentage carabids withR. padiin the diet and peakR. padidensities. Relatively high proportions ofBembidionspp. (particularlyB. lampros) andPterostichus cupreusfed onR. padiduring the aphids' establishment phase, and proportions of those predator taxa containingR. padiincreased with increasingR. padidensities in both high and low aphid density years.P. melanariusandHarpalus rufipesmainly fed onR. padiduring the aphids' exponential growth phase.Overall 11% ofc.1350 predators examined in ELISA gave positive reactions to theR. padiantiserum. Relatively high proportions of linyphiid and lycosid spiders were positive throughout the aphid pre‐peak period. Several Acari, Opiliones,Trechusspp. (Carabidae),Philonthusspp. (Staphylinidae), Cantharidae and Chilopoda were positive mainly during the aphids' exponential growth phase. Sample sizes were small, however.Very few of theBembidionspp. tested in ELISA were positive compared with those examined by gut dissection. The maximum period ofR. padiprotein (antigen) detection inB. lamproswas related to temperature, i.e. 8.5 h at 30°C, 20.5 h at 20°C and 34.5 h at 10°C, respectively. It is suggested that the rate ofR. padiprotein digestion inB. lamprosis faster at higher temperatures than the rate of elimination of prey solids from the guts.Several key predators (in this caseB. lampros, P. cupreusand linyphiid spiders) which are abundant in spring cereal fields at a time whenR. padiemigrants arrive in the crop and which feed onR. padiduring the aphids' establishment phase, are identified. The results are compared with those from similar investigations elsewhere with predators ofSitobion avenaeandMetopolophiu

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01452.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYSitona lineatusdisplays two distinct flight periods; a post‐teneral flight in the late summer and a post‐diapausal flight in the spring. The late summer flight begins as soon as adults start to emerge from pupal cells during late July and continues until mid‐October. Maximum aerial density is observed in late August. Less than 10% of newly emerged adults leave the crop by flight, the rest remain in the soil or move to overwintering sites by walking. Spring flight begins in late March if temperatures are above the 12.5°C flight threshold and reaches a peak in mid‐April.Most migratory flight is downwind. Little trivial flight occurs and once individuals have located a crop, redistribution is by walking. Laboratory studies indicate that adults fly most often during the day, particularly at noon.The size of infestations appeared to be independent of the area of legumes grown in a locality with large differences occurring even between neighbouring fields.Examination of the yields of field experiments at Rothamsted demonstrate an unexpected trend for higher yields in later sown spring bean crops. This may be because late sowing avoids infestation by spring

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01453.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYRaspberry flowers were inoculated in the glasshouse and field with dry conidia ofBotrytis cinereaand the fruits derived from them subjected to post‐harvest rot tests atc.20°C and high humidity. Apparently healthy fully‐ripe picked fruits derived from inoculated flowers developed grey mould faster than those from non‐inoculated flowers in all tests.In the glasshouse experiments, fruits from inoculated tightly closed flower buds rotted more slowly than those from inoculated open flowers or those at later developmental stages. Fruits from inoculated whole flowers rotted more rapidly than those from emasculated flowers; the addition of pollen to emasculated flowers had little effect on post‐harvest grey mould.In the dry summer of 1984 no fruits in the field from inoculated whole flowers rotted before ripening, but in the wet season of 1985 pre‐harvest grey mould was common and the surviving healthy fruits rotted inc.1 day after picking.Only minor differences were detected in host susceptibility to post‐harvest grey mould in both glasshouse and field tests, the ranking of genotypes varied depending on whether or not flowers had been inoculated. The susceptibility of pistils of 40Rubusgenotypes to infection was examined 7 and 28 days after inoculation of stigmas with dry conidia. Conidia germinated on the stigmas and produced hyphae which grew through transmitting tissues of the styles to infect carpels symptomlessly in 17 red raspberries, one blackberry, twoRubusspp. and one hybrid. No germination occurred on stigmas of cv. Carnival and New York S

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01454.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYIn tests using pre‐soaked teliospores ofUrocystis agropyri, germination was stimulated by tissues from all parts of the host plant (wheat) irrespective of cultivar or resistance to flag smut. Seedling tissues of some non‐hosts (maize, rice, sorghum, cotton, mungbean and groundnut) also stimulated germination. Similar stimulatory effects were achieved by brief exposure to volatiles from wheat seedling tissues, and from the known sources of ethylene, ripening bananas, lemon fruit and ethephon (2‐chloroethyl phosphonic acid) solution. The possibility that ethylene may have a direct triggering effect on teliospore germination is disc

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01455.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYFoliar blight and dieback of durian seedlings and trees in Peninsular Malaysia was found to be caused byRhizoctonia solani(teleomorph ‐Thanatephoms cucumeris) The fungus grew well and produced abundant sclerotia at temperatures higher than 24°C with an optimum at 28°C. It grew poorly at 35°C and did not grow at 10°C. The strains studied were found to belong to the anastomosis group AG‐1. They were pathogenic on durian, papaya, cucumber, long bean,Mikaniaweed, padi, musk melon, mung bean,Zoysiagrass, Bermuda grass, and St Augustine grass. They were mildly pathogenic on groundnut, and non‐pathogenic on maize, guava andBrassica‘pak choy’. The disease was effectively controlled by foliar sprays of pencycuron and benomyl; triadimefon and an antagonistic bacterium suspension treatment were less effective and quintozene‐etridiazole mixture gave poor

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01456.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYExperiments carried out using a point inoculation method to infect potato tubers withPhoma exiguavar.foveatademonstrated considerable variation in pathogenicity among field isolates. This variation was unlikely to be due to differential reductions in isolate pathogenicities during axenic culture. However, fresh field isolates generally produced larger lesions than stored isolates. An investigation of the distribution of pathogenicity variation in the fungus revealed that differences among isolates from different lesions taken from the same potato stock were greater than those between stocks, but pathogenicity variation within each lesion isolate was small relative to that between isolates. The importance of using isolates with a high level of pathogenicity, hence recent field isolates, in studies of this pathogen is stressed.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01457.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYAppressoria were observed to develop in sequence up to three lobes, each of which may establish a penetration of the underlying host cell and, ultimately, give rise to a haustorium and elongating secondary hyphae (ESH). Upon fully susceptible, well‐watered seedling plants increased appressorium development in terms of lobe number led to reduced penetration success, as judged by ESH formation. A concomitant reduction in the initiation of further penetration attempts at lobes newly formed after earlier unsuccessful penetration attempts was also observed. The effects of increased plant age and water stress upon this interaction were examine

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01458.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYIn 1977 a sudden and dramatic epidemic of maize dwarf mosaic virus (MDMV) struck commercial fields of sweet corn in Minnesota causing multi‐million dollar losses. The epidemic was unusual in that MDMV historically had been confined to the southern United States and Ohio River Valley with only occasional occurrences reported from states bordering Canada. An extensive 5‐yr study of MDMV in Minnesota revealed a low incidence of MDMV from 1978 ‐ 81, and commercial fields badly infected in 1977 were not again infected. No evidence of wild host plants was found, neither was seed transmission in maize considered to be important, and MDMV strain ratios changed from year to year as did the distribution of infected fields. Concomitant studies on aphid retention revealed that MDMV could be retained by aphid vectors for more than 19 h, and that the 1977 epidemic was associated with a weather pattern that could be linked to potential aphid transport from the southern Great Plains of North America. All circumstantial evidence led to a long‐distance aphid transport hypothesis. This may be worth considering whenever unexpected epidemics of aphid‐transmitted non‐persistent viruses occur in regions where the particular virus is not endemic, and may also explain the widespread distribution of certain aphid‐transmitted non‐per

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01459.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYIn total, 17 589 aphids were assayed for rate of loss of inoculativity and maximum retention times of maize dwarf mosaic (MDMV). The Standard‐treatment, involved acquisition access to MDMV‐infected tissue followed by confinement of active aphids in Petri dishes. In addition various aphid immobilisation treatments were used to prevent probing on solid surfaces after acquisition access to simulate conditions experienced by wind‐borne aphids when aloft. Immobilisation treatments, using nitrogen or argon gases at 25°C, or cold treatments at 6°C after acquisition access greatly increased the efficiency of MDMV transmission by greenbugs,Schizaphis graminum, in an experimental design where insects were individually assayed for transmission over a 7 h period.Further tests in which groups of greenbugs were assayed for MDMV transmission revealed that MDMV strains may be retained for over 21 h, regardless of post‐acquisition access treatment. Experiments with other aphid vectors of MDMV (Dactynotus ambrosiae, Macrosiphum euphorbiae, Rhopalosiphum maidisandMyzus persicae) also demonstrated MDMV retention times exceeding 18 h.These results show that the rate at which aphids lose MDMV inoculativity is lower when solid surface probing behaviour is denied, and that MDMV retention times are longer than those previously published. The findings are discussed in relation to the epidemiology of nonpersistent viruses and their dispersal over great

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1987.tb01460.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY