Feeding behavior and transmission of barley yellow dwarf virus by Sitobion avenae on oats

Feeding behavior of Sitobion avenae F. (Homoptera: Aphididae) on oats (Avena sativa cv. Clintland 64) was electronically monitored, and waveforms corresponding to salivation, ingestion, and sieve element penetration described.During 90 min plant access, aphids ingested from phloem for 0–43 min (mean: 8.1 min) and non-phloem for 0–60 min (mean: 19 min). Only 65% of the aphids tested made phloem contact within 90 min, contacting phloem after 18–85 min (mean: 32 min). No significant difference was observed in the feeding behavior of aphids carrying barley yellow dwarf virus (BYDV) from that of non-viruliferous aphids.Penetration of a sieve element was a prerequisite for BYDV transmission but did not insure transmission. Penetration of one sieve element resulted in a 65% chance of transmission independent of the duration of phloem contact. The chance of transmission increased with increasing number of sieve element penetrations.Inoculation of oat seedlings with single, viruliferous aphids for 90 min is estimated to cause 54% of the plants to be infected. Also, it is estimated that no transmission can occur with plant access periods shorter than 17 min.

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Zusammenfassung Das Probeverhalten von Sitobion avenae F. (Homoptera: Aphididae) auf Hafer (Sorte Clintland 64) wurden elektronisch verfolgt. Drei Wellenformen (S=Speichelfluss, X-das Eindringen in ein Siebelement, I=Nahrungsaufname) wurden registriert. In histologischen Untersuchungen wurden diese Wellenformen mit der Position der Stechborsten korreliert. Wenn X-Wellen oder eine X-I-Folge registriert wurden, war die Stechborste immer im Phloëm; bei S-Wellen oder bei einer S-I-Folge, war die Stechborste nie im Phloëm.Die Blattläuse wurden auf gesunden, fünf Tage alten Pflanzen während 90 Min beobachtet. 65% der Blattläuse erreichten nach 18–85 Min (Durchschnitt 32 Min) das Phloëm. Innerhalb 90 Min nahmen die Blattläuse während 0–43 Min (Durchschnitt 8.1 Min) Saft aus dem Phloem und während 0–60 Min (Durchschnitt 19 Min) Saft aus dem Mesophyll auf. Keine signifikanten Unterschiede im Probeverhalten wurden bei Blattläusen mit und ohne Barley Yellow Dwarf Virus (BYDV) festgestellt.Blattläuse, die innerhalb 24 Stunden BYDV übermitteln können, wurden für Übertragungsversuche verwendet. Das Probeverhalten dieser Blattläuser wurde manipuliert, und die Leistungsfähigkeit der Übertragung mit einer immunologischen Technik (ELISA) untersucht. Um BYDV zu übertragen mussten die Blattläuse mit einem Siebelement in Kontakt kommen. Nach der Stechborstenpenetration in ein Siebelement wurden 65% der Pflanzen mit BYDV infiziert. Der Prozentsatz infizierter Pflanzen und der Virusiter in den infizierten Pflanzen waren mit der Dauer der Siebelement-penetration (Anzahl von X-Wellen) nicht proportional. Wenn die Blattläuse mit zwei oder drei Siebelementen in Kontakt kamen, wurde der Prozentsatz infizierter Pflanzen signifikant erhöht, während der Virustiter nich verändert wurde. Infektionsprozente niedriger als 100% nach Siebelement-penetration sind möglicherweise das Resultat von Unterschieden in den Siebelementen.Es wird geschätzt dass 50% Infektion eintritt, wenn Pflanzen während ungefähr 83 Min von einer einzelnen infizierten Blattlaus besogen werden. Keine Übertragung von BYDV kann eintreten, wenn die Probezeit weniger als 17 Minuten beträgt.

     

The barley yellow dwarf virus in Ukraine

Barley yellow dwarf virus (BYDV) has been identified in the Central region of the Ukraine. BYDV infection in winter wheat crops was shown to be highly harmful. There were no winter wheat cultivars being resistent to BYDV and tolerant cultivars occured rarely. In particular seasons BYDV may give rise to widescale epithoties.     

Properties and isolates of barley yellow dwarf virus

Barley yellow dwarf virus is persistently transmitted by a number of aphid species of which three, Rhopalosiphum padi, Sitobion avenae and Metopolophium dirhodum, are common in most years. Other aphids may be locally important. Isolates of the virus differ in their virulence and geographical distribution and are not transmitted equally well by all aphid vectors. Isolates with similar properties are grouped into strains according to their transmission by vectors and their severity. Changes in strain and aphid occurrence from year to year alter the incidence of virus and its effect on yield. These changes emphasize the need for detailed knowledge of cereal aphid biology and epidemiology of BYDV before effective control can be used.     

Feeding responses of two grain aphids to barley yellow dwarf virus-infected oats

The probing behavior of greenbugs, Schizaphis graminum (Rondani), and oat-bird cherry aphids, Rhopalosiphum padi (L.), was electronically monitored on healthy oats, Avena sativa (L.), and on oats infected with the RPV-NY isolate of barley yellow dwarf virus (BYDV). S. graminum fed better on infected oats than on healthy oats. This was manifested by a shorter time before initiation of committed phloem ingestion, and by increased duration of ingestion from phloem of infected compared to healthy plants. In addition, on infected oats S. graminum made fewer interruptions in their probing once their stylets were inserted into tissues, including phloem. R. padi fed similarly on infected and healthy oats, except that these aphids made fewer short probes to the phloem (lasting <15 min) on infected compared to healthy oats. BYDV infection of oats increased the rate of population growth of S. graminum relative to that on healthy oats but had no effect on the population growth of R. padi. The proportion of aphids of R. padi which developed into alatae on BYDV-infected oats was significantly greater than on healthy oats, but S. graminum showed no such response.

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Résumé Le comportement de sondage de S. graminum (Rond.) et de R. padi (L.) a été suivi électroniquement sur avoine (Avena sativa L.) saine ou contaminée par l'extrait RPV-NY du virus jaune du nanisme de l'orge (BYDV). S. graminum s'est mieux alimenté sur avoine contaminée que saine; ceci se traduisait par un temps de latence inférieur avant l'ingestion de phloème et par une prolongation de la période d'ingestion. De plus, sur avoine contaminée, S. graminum a moins souvent interrompu le sondage, une fois que les stylets avaient étè insérés dans les tissus, y compris le phloème. Les résultats avec R. padi présentaient les mêmes tendances, mais les améliorations des performances alimentaires de cette espèce sur avoine contaminée ont été moins nettes que pour S. graminum. La contamination de l'avoine par BYDV a accru le taux de croissance de la population de S. graminum par rapport à ce qui a été observé sur avoine saine; l'effet était moins prononcé pour R. padi. La proportion de pucerons devenant aliés était plus élevée sur avoine contaminée que saine, rien de tel n'a été observé avec S. graminum.

     

Evaluation of oat cultivars and lines under infection with barley yellow dwarf virus

Thirteen domestic and foreign oat cultivars and eight breeding lines bred from the University of Illinois were evaluated for resistance to barley yellow dwarf (BYD) using artificial inoculation with Rhopalosiphum padi viruliferous for an isolate of Barley yellow dwarf virus-PAV endemic to Moscow region origin. Cultivar Blaze and six Illinois lines showed the best grain yields under disease pressure that resembled a BYD epidemic.     

Interaction between barley yellow dwarf virus and rust in wheat, barley and oats, and the effects on grain yield and quality

In three separate experiments, the upper leaf surface of the fifth formed leaf of wheat cv. Highbury, the fourth and fifth leaves of barley cv. Julia and the third and fourth leaves of oat cv. Mostyn were inoculated in a spore settling tower with wheat brown rust (Puccinia recondita f. sp. tritici), barley brown rust (P. hordei) or oat crown rust (P. coronata f. sp. avenae), respectively. Fewer pustules developed on distal portions of leaves of plants infected with barley yellow dwarf virus (BYDV) than on similar portions of leaves from virus-free plants. There were no significant differences in the number of pustules on proximal leaf portions. In barley and oats, the number of pustules on distal leaf portions was negatively correlated with the amount of yellowing of the leaf areas scored. In wheat, symptoms of BYDV were mild and leaves were little affected by yellowing. The latent period of rust on wheat and oats was not affected by BYDV. In barley, BYDV reduced the latent period of rust on leaf 5, but not on leaf 4, and reduced it on proximal, but not distal, leaf portions. In other experiments, BYDV reduced the yield of wheat and oats by 44% and 66%, respectively, while BYDV-infected barley was almost sterile. The appropriate rust reduced the yield of wheat, barley and oats by 33%, 13% and 86%, respectively. When infected with both BYDV and rust, yield of wheat and oats was reduced by 63% and 91%, respectively. Neither BYDV nor rust affected the percentage crude protein content of wheat grain, nor did rust affect that of barley. In oats, BYDV and rust each significantly increased crude protein of grain, but rust infection of BYDV-infected plants tended to reduce it.     

The effects of barley yellow dwarf virus, aphids and honeydew on Cladosporium infection of winter wheat and barley

Prior infection of both wheat and barley plants by BYDV predisposed their ears to infection by Cladosporium spp. and Verticillium spp. Aphids and honeydew increased the incidence of Cladosporium on wheat ears but not on barley. This difference between crops was attributed to the larger number ot aphids on the wheat. In the glasshouse, aphids and honeydew, but not honeydew alone, increased Cladosporium populations.     

Sequence and organization of barley yellow dwarf virus genomic RNA.

The nucleotide sequence of the genomic RNA of barley yellow dwarf virus, PAV serotype was determined, except for the 5'-terminal base, and its genome organization deduced. The 5,677 nucleotide genome contains five large open reading frames (ORFs). The genes for the coat protein (1) and the putative viral RNA-dependent RNA polymerase were identified. The latter shows a striking degree of similarity to that of carnation mottle virus (CarMV). By comparison with corona- and retrovirus RNAs, it is proposed that a translational frameshift is involved in expression of the polymerase. An ORF encoding an Mr 49,797 protein (50K ORF) may be translated by in-frame readthrough of the coat protein stop codon. The coat protein, an overlapping 17K ORF, and a 3'6.7K ORF are likely to be expressed via subgenomic mRNAs.     

Inheritance and effectiveness of genes in barley that condition tolerance to barley yellow dwarf virus

Tolerance to barley yellow dwarf virus (BYDV) in five Ethiopian barley genotypes was conditioned by major genes which apparently occurred at, or near, the same chromosome locus in each genotype. The genes or alleles differed in effectiveness, one providing a high, three an intermediate and one a low level of tolerance. In plants having a slow rate of growth, the effectiveness of the tolerance genes tended to be masked, but the effectiveness of the gene or allele which provided the highest level of tolerance was masked to a lesser extent than that of genes or alleles providing low or intermediate levels of tolerance.     

Effects of straw disposal and tillage on spread of barley yellow dwarf virus in winter barley

The effects of straw baling or incorporation, combined with ploughing, non-inversion tillage, or direct drilling on the incidence of barley yellow dwarf virus (BYDV), were investigated in plots of winter barley. Virus infection was more prevalent after ploughing (> 40% of the plot area damaged) than after non-inversion tillage (9 – 24%) or direct drilling (< 3%). For each cultivation method, more infection was associated with straw baling than with straw incorporation. There was a strong negative correlation between plot yields and the incidence of BYDV(r= -0.87). Monthly pitfall sampling of non-specific aphid predators showed that the population activity of several taxa (e.g. Linyphiidae, and the larger species of adult and larval Carabidae and Staphylinidae) declined for a short period in autumn-winter following cultivation. The overall treatment-ranking for numbers of predators in autumn (direct drilled > non-inversion > ploughed) was the opposite of subsequent virus infection. The possible roles of aphid predators and other biological mechanisms in determining the observed effects on BYDV, are briefly discussed.     

The role of ants in the epidemiology of barley yellow dwarf virus

The effect of ant attendance on the spread of barley yellow dwarf virus by Schizaphis (Toxoptera) graminum (Rondani) was studied under field conditions. Aphids visited by ants multiplied more rapidly than unattended colonies. Secondary spread of virus is caused by apterae which leave overcrowded plants and become established on nearby hosts. Ant-mediated spread of virus is typically confined to the edges of the field. Excavations made by ants around subterranean parts of small grains provide shelter and a suitable feeding site for tht aphid vector.

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Zusammenfassung Die Anregung zur vorliegenden Arbeit wurde dadurch gegeben, daß während einer Schlechtwetterperiode auf unterirdischen Teilen von Hafer- und Gerstenpflanzen von Ameisen besuchte Blattlauskolonien beobachtet wurden. Es handelte sich dabei um die Ameise Lasius neoniger (Emery) und die Blattlaus Schizaphis graminum (Rondani), die als Getreideschädling und als Überträger der Gelbverzwergungsvirose der Gerste in Nordamerika außerordentlich schädlich ist.Die Ergebnisse der Studie bestätigen erneut ältere Beobachtungen, nach denen sich die Populationsdichte der von Ameisen besuchten Blattläuse erheblich erhöht. Verschiedentlich konnte nachgewiesen werden, daß Ameisen Blattlausfeinde, insbesondere Marienkäfer, vertreiben, sobald diese in ihr Territorium eindringen.Die durch Ameisen geförderte Ausbreitung des Virus muß im engen Zusammenhang mit der populationsfördenden Wirkung des Blattlausbesuches gesehen werden. Ungeflügelte Blattläuse verlassen übervölkerte Pflanzen und wandern in die Umgebung der Wirtspflanze ab. Dabei können Entfernungen zurückgelegt werden, die ohne weiteres ausreichen, benachbarte Pflanzen aufzufinden und gegebenenfals mit Virus zu infizieren. Dadurch, daß sich L. neoniger hauptsächlich an den Feldrändern aufhält, bleibt allerdings die Virusausbreitung auf diese Region beschränkt und dringt nicht weiter in den Bestand vor. Selbst unter günstigen Bedingungen, das heißt in der Gegenwart von Ameisen, Blattläusen und Virus während des anfälligen Jugendstadiums des Getreides, bleibt die Ausbreitung des Virus und der dadurch angerichtete Schaden eng lokalisiert.Eine gewisse Bedeutung in der Epidemiologie der Gelbverzwergungsvirose dürfte auch dem Vorkommen von Blattläusen auf unterirdischen Pflanzenteilen zuzuschreiben sein, weil die Läuse hier gegen Witterungs- und Feindeinwirkung geschützt sind.Die von verschiedenen Seiten beobachtete enge Bindung zwischen Ameisen und Blattläusen konnte in dem vorliegenden Fall nicht beobachtet werden. Ein besonderer Instinkt der Ameisen oder Blattläuse scheint mir zur Aufrechterhaltung der Wechselbeziehung nicht notwendig.

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Approved for publication by the Director of the South Dakota Agricultural Experiment Station as Journal Series No. 583.     

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.     

Variation in reaction to barley yellow dwarf virus in ryegrass and its inheritance

Genotypes of Italian and perennial ryegrass differed greatly in their reaction to infection with barley yellow dwarf virus (BYDV). One genotype of perennial ryegrass appeared unaffected, whilst the yield and height of other genotypes were reduced. Progeny of the Italian ryegrass genotypes showed a similar degree of variation. Tolerance, assessed by the effect of the virus on yield, was inherited in a wholly additive manner. Symptoms were rare and their severity was under both additive and non-additive genetic control and strongly correlated with increasing severity of reaction. The utilization of the variation in BYDV reaction in breeding programmes may prove difficult because plants with the highest performance tended to suffer most from BYDV infection, and half-sib progeny ranked in a different order of tolerance in the glasshouse from that of their respective parent genotypes in the field. It is suggested that the observed variation in BYDV response results from a readjustment in the balance of genotypically controlled and environmentally conditioned variation in plant growth.     

The effect of different virus isolates on the expression of tolerance to barley yellow dwarf virus in barley

A barley variety of Ethiopian origin, with a single Mendelian gene con-fering tolerance to barley yellow dwarf virus (BYDV), was equally tolerant to a number of isolates of the virus, whereas a susceptible European barley was more susceptible to isolates transmitted by Rhopalosiphum padi L. than to those transmitted by Macrosiphum (Sitobion) avenae (Fab). However, hybrids between these two varieties homozygous for the Ethiopian tolerance gene were more tolerant to ‘mild’ than to ‘severe’ isolates, irrespective of the vector specificity. The European variety was damaged more severely by all isolates when infected early than when infected late in its development, but the hybrids were damaged more severely by M. awraae-transmitted isolates when infected late. It is suggested that in susceptible plants the concentration, rather than the virulence, of the virus determines disease severity, whereas the reverse is true in plants possessing a gene which reduces virus multiplication. Virus concentration appears to determine the severity of R. padi-transmitted isolates, while virulence determines the severity of M. avenae-transmitted isolates. The latter would also seem to be adapted towards late infection.     

Species composition of aphid vectors (Hemiptera: Aphididae) of barley yellow dwarf virus and cereal yellow dwarf virus in Alabama and western Florida

Yellow dwarf is a major disease problem of wheat, Triticum aestivum L., in Alabama and is estimated to cause yield loss of 21-42 bu/acre. The disease is caused by a complex of viruses comprising several virus species, including Barley yellow dwarf virus-PAV and Cereal yellow dwarf virus-RPV. Several other strains have not yet been classified into a specific species. The viruses are transmitted exclusively by aphids (Hemiptera:Aphididae). Between the 2005 and 2008 winter wheat seasons, aphids were surveyed in the beginning of each planting season in several wheat plots in Alabama and western Florida Collected aphids were identified and bioassayed for their yellow dwarf virus infectivity. This survey program was designed to identify the aphid species that serve as fall vectors of yellow dwarf virus into winter wheat plantings. From 2005 to 2008, bird cherry-oat aphid, Rhopalosiphum padi (L.); rice root aphid, Rhopalosiphum rufiabdominale (Sasaki); and greenbug, Schizaphis graminum (Rondani), were found consistently between October and December. The species of aphids and their timing of appearance in wheat plots were consistent with flight data collected in North Alabama between 1996 and 1999. Both R. padi and R. rufiabdominale were found to carry and transmit Barley yellow dwarf virus-PAV and Cereal yellow dwarf virus-RPV. The number of collected aphids and proportion of viruliferous aphids were low. Although this study has shown that both aphids are involved with introduction of yellow dwarf virus to winter wheat in Alabama and western Florida, no conclusions can be made as to which species may be the most important vector of yellow dwarf virus in the region.     

The relationship between growth rate and the expression of tolerance to barley yellow dwarf virus in barley

Barley varieties were most tolerant to infection with barley yellow dwarf virus (BYDV) when they grew rapidly, whether the rate of growth was determined by manipulation of the environment or by the innate genetic constitution of the host. A specific, incompletely dominant gene conditioning a high level of tolerance to the virus in certain rapidly growing genotypes in which it occurred naturally, failed to do so when transferred to slower growing genotypes. However, reintroduction into genotypes capable of rapid growth led to full restoration of the gene's effectiveness. Virus-free aphids recovered BYDV less readily from quick- than from slow-growing genotypes, all homozygous for the tolerance gene.     

The role of subterranean aphids in the epidemiology of barley yellow dwarf virus

Survival and dispersal of three root aphid species under greenhouse conditions was greatly enhanced in the presence of Lasius neoniger Emery. the ant was observed carrying three root aphid species but not two above-ground species. All attempts to transmit barley yellow dwarf (BYDV) with Forda olivacea Rohwer, Geoica utricularia (Passerini), Anoecia setariae Gillette & Palmer, or Aphis maidiradicis Forbes failed. However, A. maidiradicis was able to transmit cucumber mosaic virus. Rhopalosiphum padi (L.) could acquire BYDV from barley roots, but it rarely infected plants when feeding on roots.

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Zusammenfassung Die vorliegende Arbeit versucht die Bedeutung unterirdisch lebender Blattläuse für die Gelbverzwergungsvirose der Gerste zu klären. Sie schliesst sich damit früheren Untersuchungen über die Beziehung zwischen Schizaphis graminis (Rond.), einem Vektor des Virus, und der Ameise Lasius neoniger Emery an.Es konnte beobachtet werden, dass L. neoniger drei Wurzellausarten wegtrug, die in einer Versuchsarena freigelassen wurden, während zwei oberirdisch-lebende Blattlausarten nicht transportiert wurden. Die Gegenwart von Ameisen im Versuchsareal förderte auch die Vermehrung von Wurzelläusen auf Getreide und deren Ausbreitung auf benachbarte Pflanzen. Diese ausbreitungsfördende Wirkung des Blattlausbesuchs könnte von epidemiologischer Bedeutung sein, falls sich Wurzelläuse als Vektoren erweisen sollten. Alle Versuche, das Virus mit Forda olivacea Rohwer, Geoica utricularia (Passerini), Anoecia setariae Gillette & Palmer oder Aphis maidiradicis Forbes zu übertragen, schlugen jedoch fehl. Das nichtpersistente Gurkenmosaik konnte allerdings durch A. maidiradicis übertragen werden.Neben den typischen Wurzelläusen wurden unterirdisch lebende Rhopalosiphum padi L. im Freiland angetroffen. Übertragungsversuche ergaben, dass das Gelbverzwergungsvirus von der Blattlaus aus den Wurzeln aufgenommen werden konnte, dagegen gelang es nur selten, Getreidepflanzen durch auf Wurzeln saugende Blattläuse zu infizieren. Da aber im Freiland die Mehrzahl der unterirdisch lebenden R. padi auf den leicht zu infizierenden Stengelteilen angetroffen wurden, dürfte dieser relativen Widerstandsfähigkeit der Wurzeln gegenüber der Virusinfektion keine grössere Bedeutung zukommen.

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Approved for publication by the Director of the South Dakota Agricultural Experiment Station as Journal Series No. 672.     

Transmission of barley yellow dwarf virus by field collected aphids (Homoptera: Aphididae) and their relative importance in barley yellow dwarf epidemiology in southwestern Idaho

Populations of cereal aphids were sampled from 1985–1988 and assayed for transmission of barley yellow dwarf virus (BYDV), Rhopalosiphum padi, Rho-palosiphum maidis, Sitobion avenae, Metopolophium dirhodum, Schizaphis graminum and Macrosiphum euphorbiae collected from host plants transmitted BYDV in bioassays. Of the 1028 Diuraphis noxia collected from plants, one may have transmitted BYDV. The isolate involved resembled SGV in serological and biological characteristics, but since it was not recoverable by any of more than 800 D. noxia subsequently tested, we suspect it may have been a contaminant. Among those aphids collected during the autumn from a suction trap adapted for live collection, R. padi transmitted BYDV most frequently. Other trapped species which transmitted BYDV included: R. maidis, Rhopalosiphum insertum, Macrosiphum euphorbiae, Metopolophium dirhodum and Ceruraphis eriophori. An adapted Infectivity Index indicated that R. padi is by far the most important vector of BYDV during the autumn sowing season in southwestern Idaho. Male R. padi consistently transmitted BYDV more frequently than did females collected during the same period.