Barley Yellow Dwarf Luteovirus (BYDV) Infectivity of Alate Aphid Vectors in Northeast Spain

Rhopalosiphum padi and Sitobion avenae alates were collected from colonised winter cereals and maize in N.E. Spain and fed on young wheat plants for 7–10 days in the glasshouse. Then, aphids were killed and the plants on which aphids reproduced were kept in the glasshouse for 30–40 days. ELISA of infested plants was made using polyclonal and monoclonal antisera against PAV-, RPV- and MAV-like isolates. In autumn and spring, MAV serotypes were transmitted by S. avenae and R. padi , mainly in mixed infections with PAV serotypes. This possibly explains the high frequency of MAV-like isolates and their previously recorded year-to-year stability in maize, grain and forage winter cereals and cereal volunteers. PAV-like isolates were rarely transmitted by S. avenae and its spread thus depends almost exclusively on R. padi. These results confirm the importance of forage cereals and cereal volunteers as virus sources for winter cereal infection in the autumn, and the latter as a source of BYDV for maize in spring.     

The Role of Maize in the Epidemiology of Barley Yellow Dwarf Virus in Northeast Spain

Barley yellow dwarf virus has been detected in maize by indirect enzyme-linked immunosorbent assay (ELISA) and by immunospecific electron microscopy (ISEM). Samples of maize collected in September 1988, 1989 and 1990 showed that this crop is an important reservoir of BYDV; MAV-like isolates were the most common although PAV-like and RPV-like isolates were also present. Earlier research in Spain had shown that PAV-like isolates were predominant. Thus the evidence from this work that MAV was the main isolate, and very widely spread, is important for future research on BYDV epidemiology in Spain.     

Some characteristics of monoclonal antibodies to a British M A V-like isolate of barley yellow dwarf virus

Rat monoclonal antibodies (MAbs) specific for a British F (MAV-like) isolate of barley yellow dwarf virus (BYDV) were produced and studied. In indirect ELISA using an antiserum to BYDV-F to trap virus from infected sap, the MAbs were shown to be specific for MAV-like isolates of BYDV from Britain, USA and Sweden but, in this test, they did not detect PAV-, RPV-, SGV- or RMV- like isolates of BYDV. In similar tests using homologous antisera to trap the viruses, the MAbs did not detect BYDV-PAV or -RPV or two other luteoviruses (potato leafroll and beet western yellows). One of the MAbs (MAFF 2) was partially purified from ascitic fluid, and used successfully in ELISA as a coating antibody and when conjugated to the enzyme alkaline phosphatase. Also, MAFF 2 successfully trapped BYDV-F particles when used to coat electron microscope grids. In indirect ELISA using three MAbs (MAFF 2, MAC 91 and MAC 92) it was possible to type the three major strain groups of BYDV, viz. MAV, PAV and RPV-like strains from Britain, USA and Europe.     

Production of cloned cDNA from a Swedish barley yellow dwarf virus isolate

A cDNA library was produced from the RNA of a Swedish MAV-like isolate of barley yellow dwarf virus (BYDV). The procedure involved random priming and the ds cDNA was cloned into the EcoRl site of the plasmid pUC19. Among the clones obtained some hybridised specifically with MAV-like isolates whereas others also hybridised with PAV-like isolates. Only very weak hybridisation was observed with an RPV-like isolate. An Australian cDNA clone, reported to be PAV-specific (pBY82, Waterhouse, Gerlach & Miller, 1986), hybridised with Swedish MAV-like but not with PAV-like isolates. Probes prepared from the clones detected virus in plant extracts by dot-blot hybridisation with sensitivity greater than that of ELISA. Virus was also readily detected in extracts of viruliferous aphids.     

Aphid Vectors of Barley Yellow Dwarf Virus in West-Central Morocco

The ability of seven aphid species, collected in west-central Morocco, to transmit barley yellow dwarf virus (BYDV) was determined. Aphids were either collected from grasses showing symptoms of BYDV infection or were allowed acquisition access to plants infected with a PAV-like isolate of BYDV before transfer to oat test plants. BYDV transmission by six of the seven aphid species was confirmed by ELISA test; only Melanaphis donacis failed to transmit. The six newly defined BYDV vector species brings the total known to occur in Morocco to ten.     

Non‐cultivated grass hosts of yellow dwarf viruses in Ethiopia and their epidemiological consequences on cultivated cereals

The yellow dwarf (YD) disease complex epidemics in cultivated cereals grown in a specific period of the year mainly depend on the presence of potential reservoir alternative hosts harbouring both the viruses and the vectors over the off‐season and serve as a source of inoculum in subsequent cropping season, further spread being supported by efficient aphid vectors. As such, an extensive and intensive exploration to generate base line information on the identity and prevalence of YD viruses [barley yellow dwarf virus (BYDV)‐PAV, BYDV‐MAV and BYDV‐SGV; cereal yellow dwarf virus (CYDV)‐RPV; and maize yellow dwarf virus (MYDV)‐RMV] on wild annual and perennial grasses and forage cereals alternative hosts was conducted consecutively during 2013–2015 main‐ and short‐rainy seasons in cereals growing belts of Ethiopia. Random sampling was employed to collect the samples that were tested by the tissue blot immunoassay (TBIA) to identify the YDVs associated with the hosts using a battery of virus‐specific polyclonal antibodies. Of 13,604 samples analysed, YDVs were detected in 392 (2.9%) samples, which consisted of various wild grasses, forage cereals and three cultivated crops. YDVs were identified from at least 26 grass species and forage cereals, some of them are new records, and some are previously documented hosts. To our knowledge, this is the first report of YDV infection of Andropogon abyssinicus (FresenR.Br. ex Fresen.) (BYDV‐PAV), Avena abyssinica Hochst (BYDV‐PAV), Bromus pectinatus Thunb. (BYDV‐PAV and BYDV‐MAV), Eragrostis tef (Zuccagni) Trotter (BYDV‐PAV), Eragrostis sp. (BYDV‐PAV), Hyparrhenia anthistrioides Stapf. (BYDV‐PAV), Panicum coloratum L. (BYDV‐PAV), Polypogon monspeliensis (L.) Desf. (BYDV‐PAV), Setaria pumila (Poir.) Roem & Schult (BYDV‐PAV, BYDV‐SGV and MYDV‐RMV), Setaria australiensis (Scribn. & Merrill) Vickery (BYDV‐PAV, BYDV‐MAV and CYDV‐RPV) and Snowdenia polystachya (Fresen.) Pilg (BYDV‐PAV, BYDV‐MAV, BYDV‐SGV, CYDV‐RPV and MYDV‐RMV).     

Identification, Distribution and Vector Population Dynamics of Barley Yellow Dwarf Virus in Three Cereal-Producing Areas of Spain

ELISA-based surveys during 1985–87 in three major cereal-growing areas of Spain confirmed the presence of barley yellow dwarf virus (BYDV). Samples of small grain cereals and grasses with and without BYDV-like symptoms were collected in the central, southwestern, and northeastern Spain. Infections were found in all cereal species sampled and in some grasses. About 37 % of the samples collected in 1985 were infacted with isolates of the PAV serotype. Isolates of the RPV serotype were less common, and were detected only in samples from the central region at El Encin, Madrid. Only a single sample, collected from El Encin in 1987, was unequivocally diagnosed as containing an isolate of the MAV serotype. Aphid vector population dynamics was monitored during fall and winter of 1984–87 in the central region. Rhopalosiphum padi L. appeared to be the most abundant species during fall and winter months, infesting grasses and volunteer wheat. Other species present were Sitobion avenae (F.), Metopolophium dirhodum (Walker) and Rhopalosiphum maidis (Fitch). Both R. padi and S. avenae seem to be anholocyclic in the central region of Spain, and are able to remain and reproduce on wheat volunteers and grasses until the beginning of spring. S, avenae populations increase quickly on wheat volunteers in April, while populations of R. padi remain low. Therefore, spread of S. avenae-transmitted BYDV types to neighbouring cereal fields seem more likely to occur than spread of other types. Other possible virus reservoirs, such as maize, also need investigation for a better understanding of BYDV epidemiology in the central and other cercal-growing areas of Spain.     

The effect of temperature and inoculation access period on the transmission of barley yellow dwarf virus byRhopalosiphum padi (L.) and Sitobion avenae (F.)

Winged individuals of Rhopalosiphum padi and Sitobion avenae transmitted the PAV-like and MAV-like isolates of barley yellow dwarf virus respectively. Success of transmission after inoculation access periods of 2, 6, 12, 24, 48 and 72 h were examined and survival, reproduction and movement of the aphid vectors were recorded at these times. The experiment was done at four different temperatures: 6^oC, 12^oC, 18^oC and 23^oC. For both isolates the inoculation efficacy did not increase after a 24 h inoculation access period and there was no difference in inoculation efficiency at the three highest temperatures, that at 6^oC being significantly lower than at 12^oC to 23^oC. The results suggest that autumn temperature is a critical factor for BYDV epidemiology in Britain with a small increase in autumn temperature leading to greatly increased infection rates.     

Occurrence of barley yellow dwarf virus (BYDV) isolates in different farmland habitats in western France and south-west England

The incidence and distribution of the three principal isolates of barley yellow dwarf virus (PAV, RPV and MAV) are described in winter cereal crops, cereal (stubble) regrowth and grasses from 11 sites in western France and south-west England during 1987 and 1988. Isolates were identified by indirect ‘sandwich’ ELISA using the monoclonal antibodies MAC91, MAC92 and MAFF2. More virus infection occurred in all localities and in most of the plant communities sampled, with the exception of perennial grass leys, in 1987 than in 1988. All three isolates were widespread. MAV was associated more with sites further north and PAV more with those further south. The geographical distribution of RPV was less variable. Underlying these trends, the relative abundance of isolates differed considerably between habitats. RPV always predominated in perennial grass leys and MAV in most cereal crops, although in the latter MAV was less prevalent in 1987 than in 1988. The greatest regional difference was found in stubble regrowth where PAV predominated in France but MAV predominated in England. Grasses from field margins (only sampled in England) were mainly infected by MAV and RPV. The implications of these findings for the epidemiology of BYDV are discussed, especially the roles of different host plant communities or habitats in the annual infection cycle of small-grain cereals.     

The effects of sowing date and choice of insecticide on cereal aphids and barley yellow dwarf virus epidemiology in northern England

During the mid-1980s, Sitobion avenae became recognised as an important vector of barley yellow dwarf virus (BYDV) in the Vale of York. A field trial at the University of Leeds Farm, North Yorkshire, was carried out during the autumn/winter of 1984-85 to evaluate different control procedures against S. avenae-transmitted BYDV and to investigate its epidemiology. Winter barley was sown on three dates in September, and plots were sprayed with either deltamethrin, demeton-S-methyl or pirimicarb on one of three dates between mid-October and mid-November, making a factorial design. Rhopalosiphum padi, the main vector of BYDV in southern England, were rarely found during the experiment, but the numbers of S. avenae were much higher, reaching a peak of 21% of plants infested in the unsprayed plots of the first sowing date. Single applications of each insecticide reduced populations of S. avenae to zero. Some treatments, particularly in the early sown plots and those treated with pirimicarb, however, did allow some recolonisation, and thus led to increased virus incidence and decreased yields. Sprays applied before the end of the migration of S. avenae were more efficient at controlling BYDV if the insecticide was persistent, otherwise a spray after this period, in November, was more effective. Virus incidence, although reduced by sprays, was generally low in plots sown on 18 and 27 September. In contrast, about 11% of plants were infected in unsprayed plots sown on 6 September and a small yield benefit was obtained with insecticidal treatments. Enzyme-linked immunosorbent assay (ELISA) of plants taken from the plots indicated that MAV- and PAV-like strains were present, and were most likely to have been transmitted by S. avenae.     

Winter wheat (Triticum aestivum) response to Barley yellow dwarf virus at various nitrogen application rates in the presence and absence of its aphid vector,Rhopalosiphum padi

Barley yellow dwarf (BYD) is one of the most common diseases of cereal crops, caused by the phloem‐limited, cereal aphid‐borne Barley yellow dwarf virus (BYDV) (Luteoviridae). Delayed planting and controlling aphid vector numbers with insecticides have been the primary approaches to manage BYD. There is limited research on nitrogen (N) application effects on plant growth, N status, and water use in the BYDV pathosystem in the absence of aphid control. Such information will be essential in developing a post‐infection management plan for BYDV‐infected cereals. Through a greenhouse study, we assessed whether manipulation of N supply to BYDV‐infected winter wheat, Triticum aestivum L. (Poaceae), in the presence or absence of the aphid vector Rhopalosiphum padi L. (Hemiptera: Aphididae), could improve N and/or water uptake, and subsequently promote plant growth. Similar responses of shoot biomass and of water and N use efficiencies to various N application rates were observed in both BYDV‐infected and non‐infected plants, suggesting that winter wheat plants with only BYDV infection may be capable of outgrowing infection by the virus. Plants, which simultaneously hosted aphids and BYDV, suffered more severe symptoms and possessed higher virus loads than those infected with BYDV only. Moreover, in plants hosting both BYDV and aphids, aphid pressure was positively associated with N concentration within plant tissue, suggesting that N application and N concentration within foliar tissue may alter BYDV replication indirectly through their influence on aphid reproduction. Even though shoot biomass, tissue N concentration, and water use efficiency increased in response to increased N application, decision‐making on N fertilization to plants hosting both BYDV and aphids should take into consideration the potential of aphid outbreak and/or the possibility of reduced plant resilience to environmental stresses due to decreased root growth.     

Cloning and Phylogenetic Analysis of Coat Protein of Barley yellow dwarf virus Isolates from Different Regions of Pakistan

Barley yellow dwarf virus (BYDVs) is an emerging threat for wheat and may seriously threaten its production, especially as climate change may result in increased infestation by aphids, the insect vectors of the virus. To assess the possibility of using pathogen‐derived resistance against the virus, the genetic diversity of BYDVs originating from different wheat‐growing areas of Pakistan where its incidence has been higher was investigated. Wheat samples with suspected symptoms of BYDVs were screened for the presence of Barley yellow dwarf and Cereal yellow dwarf viruses (B/CYDVs) subgroup 1 (Barley yellow dwarf virus‐PAV, BYDV‐MAV, BYDV‐SGV) and subgroup II (BYDV‐RPV, CYDV‐RPV, BYDV‐GPV) by PCR using basic multiplex oligonucleotides designed on coat protein (CP) of the virus. Of 37 samples tested, 13 were positive for BYDV subgroup I and only one sample was positive for BYDV subgroup II. Samples positive for subgroup I were further tested by PCR, and results showed that 10 samples were positive for BYDV‐PAV and three for BYDV‐MAV. DNA sequences of CP region of nine isolates (BYDV‐PAV) were determined and compared with available sequences in databases. Sequence analysis showed that three isolates (from Fatehjang, Nowshera and Attock districts) had maximum identity (92.8–94.6%) to BYDV‐PAS, and six isolates (from Peshawar, Islamabad Swabi and Faisalabad districts) had maximum identity (99.3–99.7%) to BYDV‐PAV. Thus BYDV‐PAV species may be dominant in northern wheat‐growing areas of Pakistan. The conserved nature of the BYDVs suggests that pathogen‐derived resistance strategies targeting the coat protein of the virus are likely to provide protection under field conditions.     

Serological and biological characterisation of isolates of barley yellow dwarf virus in Sweden in 1983

In 1983, cereal plants showing symptoms of barley yellow dwarf virus (BYDV), collected from 15 localities in Sweden, were tested for BYDV using enzyme-linked immunosorbent assay (ELISA). Antisera against two Swedish isolates of BYDV were used, a mild isolate (27/77) transmitted specifically by Sitobion avenae and a severe one (39/78) transmitted mainly by Rhopalosiphum padi. No virus was detected in 57 of 607 plants of oats and barley tested. Of the 550 plants in which virus was detected, 366 were infected with viruses similar to isolate 27/77, 116 with viruses similar to 39/78 and the remaining 68 reacted strongly with both antisera. When tested, the latter isolates were shown to be mixtures. Thirty-nine selected samples were also tested with antisera against the USA isolates RPV, RMV, MAV and PAV, and for transmission by S. avenae and R. padi. Twenty-six of these samples were transmitted specifically by S. avenae, one was transmitted only by R. padi and the remaining 12 samples were shown to be infected with a mixture of an S. avenae-specific isolate and one transmitted mainly by R. padi. Antisera against PAV and MAV each detected all isolates tested and the results were very similar to those with the antisera to the 39/78 and 27/77 isolates, respectively. None of the field isolates reacted with antisera against RMV or RPV. It was concluded that 1983 was an epidemic year for BYDV in Sweden and that isolates specifically transmitted by S. avenae predominated. Symptoms of infection by these isolates on oat plants ranged from mild to severe.     

The occurrence of barley yellow dwarf viruses in CIMMYT bread wheat nurseries and associated cereal crops during 1988–1990

Enzyme-linked immunosorbent assay (ELISA)-based surveys of the occurrence of five barley yellow dwarf virus (BYDV) serotypes (MAV, PAV and SGV in “Group 1”; RPV and RMV in “Group 2”) in CIMMYT bread wheat nurseries and other small grain crops in various locations world-wide were undertaken in 1988, 1989 and 1990. The objective was to investigate the relative occurrence of BYDV serotypes in areas relevant to CIMMYT cereal breeding programs. Overall, MAV and PAV serotypes predominated in the samples collected, though their relative frequencies depended on the location. SGV serotypes were uncommon in most locations. Group 2 serotypes occurred widely, but RMV serotypes were more common than RPV serotypes.     

Density-dependent mortality in Pinus sylvestris caused by the snow blight pathogen Phacidium infestans

Summary Relationships between disease incidence and the density of host plant populations were investigated in the Pinus sylvestris-Phacidium infestans host-fungal pathogen association, in which the season of death of plants killed up to 3 years previously could be accurately determined. Significant (P<0.05), positive density-dependent relationships between the proportion of plants dying in the winters of 1987–1988, 1988–1989 or 1989–1990 and the original stand density were detected in 12 of 26 comparisons. Of the remaining comparisons, all but three had positive regression coefficients for the same association. Plants killed up to 2 years previously contributed to inoculum production. The use of standing dead as a predictor in the analyses showed that the proportion of plants dying in the winters of 1988–1989 or 1989–1990 was generally better correlated with standing dead in the previous summer than with the density of the original population. Significant (P<0.05), positive density-dependent associations were also found between the proportion of living plants in 1990 infected with P. infestans and the number of standing dead plants in all nine comparisons. In contrast, only four of the nine associations between these proportions of infected plants and population density were significant. The strength of the density-dependent relationships varied substantially within and between sites. Much of this variation appears to be due to differences in the stage of development of the epidemics occurring at different sites.     

Surveys of stem base diseases and fusarium ear diseases in winter wheat in England, Wales and Scotland, 1989–1990

An investigation into the incidence of stem base diseases and the pathogens associated with them was undertaken on winter wheat samples collected at growth stages 31 and 73–75 in 1989 and 1990. Symptoms at growth stage 31 were classified into 10 different types based on visual characteristics. Although Pseudocercosporella herpotrichoides was associated mainly with eyespot lesions and Rhizoctonia spp. with sharp eyespot lesions, a significant number of isolates of each pathogen were taken from lesions classified as fusarium. Different types of fusarium lesion on stem bases at both growth stages were not associated with any one particular Fusarium or Microdochium species. 98% of P. herpotrichoides isolates obtained from eyespot lesions at growth stage 31 in 1989, and 87% of those obtained in 1990 were identified as the sub-species P. herpotrichoides var. acuformis, Microdochium nivale was more common than any of the Fusarium species at both growth stages, and was particularly prevalent in samples from Scotland at the earlier growth stage in 1989. Isolations from the top internodes at growth stage 73–75 indicated that systemic infection by Fusarium species, although present in some stems, was of little importance. Fusarium ear blight affected 0.4% of ears in 1989 and 0.5% in 1990. Glume spot lesions on the ears in 1990 were predominantly associated with Fusarium poae.     

Effects of Temperature on BYDV Concentration in Oat Plants and Virus Purification Efficiency, and Detection of a Putative Associated Satellite Virus

RPV and MAV-like serotypes of barley yellow dwarf virus (BYDV), designated R-568 and F, were found during sucrose density gradient centrifugation to suspend at 10 °C and 4 °C but to totally sediment at 15 °C and 12 °C, respectively. These properties were used to purify these serotypes, and antisera were then prepared.
Partially purified IgG from antiserum was used in immunosorbent electron microscopy (ISEM) and in enzyme-labelled immunosorbent (ELISA) tests to detect BYDV RPV-like serotypes. Using anti-BYDV R-568 polyclonal antiserum and the BYDV R-568 serotype in ISEM tests, isometric virus particles of two sizes were trapped: the 28 nm particles of BYDV R-568, and others 17 nm in diameter which may be those of a satellite virus.
The effects of temperatures on virus concentrations in oat plants infected with BYDV serotypes F and R-568 were investigated. BYDV F and R-568 concentrations in the roots and shoots were sensitive to changes in temperature between 10 °C and 25 °C. The concentrations of both viruses in the roots and shoots of infected plants could be manipulated by varying the temperature at which plants were grown. The ELISA absorbance values related to detection of F MAV-like serotypes were higher in roots and shoots of oats grown at 10 °C than for oats grown at 25 °C. Conversely, cool temperatures reduced the absorbance values for R-568 RPV-like serotype in the roots, but less significantly in the shoots.     

Vector specificity of barley yellow dwarf virus serotypes and variants in southwestern Idaho

Plants with symptoms of barley yellow dwarf virus (BYDV) obtained in infection feeding assays of aphids collected in the field in Idaho between 1986 and 1988 were tested for virus transmissibility by possible aphid vectors. Isolates obtained during 1987–1988 were also tested with a range of polyclonal antisera which distinguished PAV, MAV, SGV, RPV and RMV serotypes. In 1989 some Idaho (ID) BYDV isolates, maintained as standards for comparison, were serotyped and tested for aphid transmissibility, using 11 species of aphids. There was not always the expected correspondence between serotype and vector specificity for ID isolates. For isolates obtained from field-collected Rhopalosiphum padi, vector transmissibility and serotype corresponded with previous reports; however, 44% of isolates which were serotyped as RMV were also transmissible by species other than Rhopalosiphum maidis. Similarly, the transmissibility of the ID laboratory standards did not always conform to the reported vector specificity of serotypes. The laboratory ID-MAV culture was transmitted by Metopolophium dirhodum and Myzus persicae as well as by Sitobion avenae. The laboratory ID-SGV culture was transmitted by R. padi and 5. avenae as well as by Schizaphis graminum. The ID-RPV culture was transmitted by S. graminum and Rhopalosiphum insertum as well as R. padi. Both of two laboratory ID-RMV cultures were transmissible by R. insertum and R. padi transmitted one of them. The results indicate that, for isolates collected in Idaho, vector specificity cannot be assumed from their serotypes.     

Barley yellow dwarf virus: effects on carbohydrate metabolism in oat (Avena sativa) during cold hardening

Barley yellow dwarf virus (BYDV) causes significant losses in yield and in overwintering ability of winter cereals. Mechanisms by which the physiology of plants is affected by the virus are not clear. To see how carbohydrates in the crown of winter cereals were affected by BYDV, fructan isomers of degree of polymerization (DP) 3–5, fructan DP>6 and the simple sugars, glucose, fructose and sucrose, were measured before and during cold hardening in three oat ( Avena sativa L.) cultivars, 'Wintok', 'Coast Black' and 'Fulghum'. On a fresh weight basis fructan DP>6 decreased by 50% in infected 'Wintok' and 'Coast Black' and by 25% in 'Fulghum'. Two DP3, one DP4 and one DP5 isomer were significantly higher than non-infected controls. The percentages of simple sugars in infected crowns were significantly higher than controls in all three cultivars in every week except the first week of hardening. Crude enzyme extracts from BYDV infected plants incubated with sucrose suggested higher invertase and lower sucrose-sucrosyl transferase activity. When incubated with 1-kestose and neokestin, no significant difference was found in fructose fructosyl transferase or in hydrolase activity. The activity of unidentified enzymes catalysing the synthesis of larger (DP>5) fructan was altered by BYDV. The decrease of carbohydrates in the crown induced indirectly by BYDV may alter the plant's capacity to regenerate tillers in the spring. The ability of plants to prevent or tolerate carbohydrate fluctuations induced by BYDV infection may be an important genetically regulated characteristic for developing virus-resistant cultivars.     

Emergence and dynamics of cyclopoid copepods in an unpredictable environment

SUMMARY. 1. We studied species composition, abundance and population dynamics of cyclopoid copepods emerging from dormancy from the sediments of a temporary pond in South Carolina in 1985, 1988 and 1989. During a drought in 1988–89, the maximum hydroperiod was 19 days; in 1985 and late 1989-early 1990, the hydroperiods were 57 and 118 days. We also report on species present in 1984 and 1987, two years that had longer hydroperiods, and on abundance of cyclopoids in 1984. 2. Within a day after standing water appeared, fourth-instar copepodids of Diacydops haueri and D. crassicaudis brachycercus became active. These two species appeared every time the pond filled in winter, spring, or autumn. Other species, including Acanthocyclops vernalis, were usually not collected until weeks or months after the pond filled. Because the times and durations of fillings were extremely variable, species composition differed among years, with the most species (eleven) appearing in 1984, the year with the longest hydroperiod. 3. The abundances of emerging Diacydops were much lower in 1988 and 1989 (range of means from seven fillings in spring and autumn: 675–7382 animals m^?2) than 1985 (range of means from three fillings in winter: 26,037–107,418 animals m^?2). Low abundances of emerging animals could have been caused by poor survival of dormant animals, poor production during preceding seasons, or incomplete emergence of the dormant populations. 4. Substrate samples from the dry pond were collected in spring, summer, and autumn 1988 and winter 1989 to measure emergence of the cyclopoids in laboratory incubations. Population densities of emerging animals were much lower in 1988 and 1989 (range of means from seven experiments: 0–120 animals m^?2 over the first 3 days) than in similar experiments in 1984 (Taylor & Mahoney, 1990, means from two experiments: 3630 and 6890 animals m^?2). 5. Despite the low abundance of animals emerging from dormancy in late 1989, the cyclopoid populations in 1990 reached similar densities of copepodids (10^4?-10⁵ animals m^?2) to those reached in 1984 and 1985. These results suggest that short generation time and high reproductive capacity permit rapid recovery from population reductions.