Potato Virus Y Transmission Research Articles

Densovirus infection facilitates plant-virus transmission by an aphid.

The interactions among plant viruses, insect vectors, and host plants have been well studied; however, the roles of insect viruses in this system have largely been neglected. We investigated the effects of MpnDV infection on aphid and PVY transmission using bioassays, RNA interference (RNAi), and GC-MS methods and green peach aphid (Myzus persicae (Sulzer)), potato virus Y (PVY), and densovirus (Myzus persicae nicotianae densovirus, MpnDV) as model systems. MpnDV increased the activities of its host, promoting population dispersal and leading to significant proliferation in tobacco plants by significantly enhancing the titer of the sesquiterpene (E)-β-farnesene (EβF) via up-regulation of expression levels of the MpFPPS1 gene. The proliferation and dispersal of MpnDV-positive individuals were faster than that of MpnDV-negative individuals in PVY-infected tobacco plants, which promoted the transmission of PVY. These results combined showed that an insect virus may facilitate the transmission of a plant virus by enhancing the locomotor activity and population proliferation of insect vectors. These findings provide novel opportunities for controlling insect vectors and plant viruses, which can be used in the development of novel management strategies.

Insight into aphid mediated Potato Virus Y transmission: A molecular to bioinformatics prospective.

Potato, the world's most popular crop is reported to provide a food source for nearly a billion people. It is prone to a number of biotic stressors that affect yield and quality, out of which Potato Virus Y (PVY) occupies the top position. PVY can be transmitted mechanically and by sap-feeding aphid vectors. The application of insecticide causes an increase in the resistant vector population along with detrimental effects on the environment; genetic resistance and vector-virus control are the two core components for controlling the deadly PVY. Using transcriptomic tools together with differential gene expression and gene discovery, several loci and genes associated with PVY resistance have been widely identified. To combat this virus we must increase our understanding on the molecular response of the PVY-potato plant-aphid interaction and knowledge of genome organization, as well as the function of PVY encoded proteins, genetic diversity, the molecular aspects of PVY transmission by aphids, and transcriptome profiling of PVY infected potato cultivars. Techniques such as molecular and bioinformatics tools can identify and monitor virus transmission. Several studies have been conducted to understand the molecular basis of PVY resistance/susceptibility interactions and their impact on PVY epidemiology by studying the interrelationship between the virus, its vector, and the host plant. This review presents current knowledge of PVY transmission, epidemiology, genome organization, molecular to bioinformatics responses, and its effective management.

Potential Alternative Hosts and Transmissibility of Potato virus Y

To study the potential alternative hosts to Potato virus Y (PVY), thirteen different plant species, Solanum tuberosum cv. Spounta L., S. tuberosum cv. Cara L., Datura stramonium L., D. metel L., Nicotiana tabacum cv. White Burley L., Chenopodium amaranticolor (H.J.Coste & A.Reyn.) H.J.Coste & A.Reyn., Solanum lycopersicum L., S. melongena L., Capsicum annuum L., Phaseolus vulgaris L., Vicia faba L., Brassica oleracea L. and Lactuca sativa L., belonging to five botanical families were tested. Nine of the above tested plant species reacted to PVY isolate with different symptoms, while four of plant species D. stramonium, V. faba, B. oleracea and L. sativa did not react to PVY isolate. Mechanical transmission of PVY was confirmed from infected potato to healthy D. metel plants and back from PVY-inoculated D. metel to healthy potato plants with 100% success. Insect transmission was also confirmed from infected potato plants to healthy ones through aphid Myzus persicae with 80%. Virus particles of PVY were examined using transmission electron microscopy (TEM). Typical PVY particle size of 11 × 700 nm with flexuous filamentous shape was observed.

The cuticle protein MPCP2 is involved in Potato virus Y transmission in the green peach aphid Myzus persicae

Potato virus Y (PVY) is a destructive and widespread virus in a number of important crops, including potato. Aphid vectors spread this viral infection between plants in a non-persistent manner, and the green peach aphid (Myzus persicae) is the most efficient known vector. In this research, we investigated five cuticle proteins (CuPs) which are expected to be involved in virus transmission at the stylet of aphids. In an RNA interference (RNAi) gene-silencing assay with the green peach aphids (M. persicae), we evaluated the impact of these CuPs on the transmission of PVY with potato and tobacco plants. Using an oral RNAi bioassay where the aphids pierce-suck in an artificial diet that was supplemented with gene-specific dsRNA, the expression of only two CuPs, mpcp2 (DQ108935) and mpcp1 (AF435075.1), could be decreased by 63 and 75%, respectively. Expression of the other three CuPs could not be affected. Subsequently, we investigated what the effect is of the RNAi-mediated gene silencing on the transmission of PVY from potato to tobacco plants. These results showed with a high certainty of 99.5%, for the first time in vivo, a significant involvement of MPCP2 with a reduction of 47% (compared to the dsGFP control) in the transmission of PVY. For MPCP1, the effect was smaller with a reduction of 19% and lower certainty of 86%.

The Contribution of Endomycorrhiza to the Performance of Potato Virus Y-Infected Solanaceous Plants: Disease Alleviation or Exacerbation?

Solanaceae, comprising meaningful crops (as potato, tomato, pepper, eggplant, and tobacco), can benefit from a symbiosis with arbuscular mycorrhizal fungi (AMF), which improve plant fitness and support plant defense against pathogens. Currently, those crops are likely the most impacted by Potato virus Y (PVY). Unfortunately, the effects of AM symbiosis on the severity of disease induced by PVY in solanaceous crops remain uncertain, partly because the interplay between AMF and PVY is poorly characterized. To shed some light on this issue, available studies on interactions in tripartite association between the host plant, its fungal colonizer, and viral pathogen were analyzed and discussed. Although the best-documented PVY transmission pathway is aphid-dependent, PVY infections are also observed in the absence of insect vector. We hypothesize the existence of an additional pathway for virus transmission involving AMF, in which the common mycorrhizal network (CMN) may act as a potential bridge. Therefore, we reviewed (1) the significance of AM colonization for the course of disease, (2) the potential of AMF networks to act as vectors for PVY, and (3) the consequences for crop breeding and production of AM biofertilizers.

The Titre of the Virus in the Inoculum Affects the Titre of the Viral RNA in the Host Plant and the Occurrence of the Disease Symptoms

Potato virus Y (PVY) is the most economically important potato virus, therefore extensive research is focusing on elucidation of its interaction with the host. To obtain repeatable results, strict standardization of research methods is crucial. Mechanical inoculation by rubbing sap from a PVY infected plant onto the leaf surface together with a fine abrasive powder is the most convenient way of experimental transmission of PVY to host plants. However, factors determining reproducibility of this process need to be determined. In the present study, it was shown that higher titre of the virus in the inoculum resulted in faster increase of PVYNTN RNA titre in the inoculated leaves, as well as in faster translocation of PVYNTN from inoculated leaves into upper non-inoculated leaves. The final titre of PVYNTN RNA in upper non-inoculated leaves was independent of the virus titre in the inoculum. In addition, the occurrence of the disease symptoms was followed and the dependence to the titre of the virus in the inoculum was observed.

Evidence of Potato virus Y Spread through Post-Emergence Management Practices in Commercial Potato Fields

Potato virus Y (PVY) transmission was studied in six commercial potato fields in 2015 and 2016 in New Brunswick, Canada. Plants emerged from PVY-positive tubers, or PVY-free plants that were artificially inoculated with PVY shortly after emergence, were used as PVY inoculum plants in the study. In all trials, equal numbers of PVY inoculum plants from each of three strains common in the region, PVYO, PVYN:O and PVYNTN, were used. PVY inoculated into tractor-traffic rows showed 2 to 7 times as much PVY spread to previously virus-free plants by the end of the season (up to 48.5% in one tractor row, compared to a maximum of 16.3% in a distant control row unaffected by tractor traffic). Evidence supporting a hypothesis that tractor traffic enhances PVY transmission through aphid disturbance was observed by PVY spread in both directions along the rows, not biased in the direction of tractor travel, and that the ratio of spread of the three strains was nearly indentical in control and tractor rows. However, the lack of spread to immediately adjacent rows, and statistically significant spatial pattern matching the circumference of tractor wheels specific to each field support the hypothesis that direct mechanical transmission of wounded plant sap could also be a factor in the enhanced PVY transmission.

Effects of Aphidius gifuensis on the feeding behavior and potato virus Y transmission ability of Myzus persicae.

The stylet penetration behavior of aphids when feeding on plants is associated with virus acquisition and inoculation. Aphidius gifuensis (Ashmead) is a primary endoparasitoid of Myzus persicae (Sulzer) which is the most efficient vector of plant viruses. Information about the effects of parasitoid on aphid and virus transmission can provide an essential foundation for designing effective biological control strategies. This study aimed to investigate the effects of A. gifuensis on the feeding behavior and potato virus Y (PVY) transmission ability of M. persicae. The results showed that after M. persicae was parasitized by A. gifuensis, the duration of the first probe significantly decreased. Additionally, A. gifuensis exerted remarkable effects on aphid feeding in phloem ingestion. The contribution of the E1 waveform to the phloem phase was significantly higher in all parasitized aphids than in the control group. Although the time of infestation increased for parasitized aphids, the total duration of phloem sap ingestion decreased. Interestingly, the percentage of time M. persicae spent in the xylem and phloem phases only changed significantly on day 5. The percent transmission of PVY by the aphids parasitized on day 5 was lower than that in the control, but no significant differences were detected. The significance of this work is the demonstration that A. gifuensis can impede the feeding behavior of M. persicae, which sheds light on the biological basis of A. gifuensis as a natural enemy, but unfortunately does not provide an immediate solution for disrupting the transmission of PVY.

Dynamics of PVY strains in field grown potato: Impact of strain competition and ability to overcome host resistance mechanisms

Potato virus Y (PVY) is the most important viral pathogen affecting potato crops worldwide. PVY can be transmitted non-persistently by aphids that do not colonize the host plant, resulting in a rapid acquisition and transmission of the virus between plants. PVY exists as a complex of strains that can be distinguished according to their pathogenicity, serology and genomic analysis. While virus incidence remains low in Scottish seed potato crops, PVY has become the increasingly prevalent virus. The monitoring of PVYN and PVYO serotypes has revealed a recent shift towards PVYN which now accounts for more than 90% of all PVY cases. A survey of the molecular diversity of PVYN isolates indicated that 80%–90% belong to the recombinant European (EU)-NTN group, with North-American (NA)-NTN and non-recombinant EU-N variants accounting for the remainder. The shift from non-recombinant to recombinant PVY isolates is a common trend observed worldwide. Surveys of a range of PVY isolates representing the main strain and phylogenetic groups suggest that PVY has the ability to overcome hypersensitive response-mediated resistance with significant differences between isolates of the same strain group. Contrastingly, genes mediating extreme resistance (Ryadg, Rysto) provide efficient resistance to PVY transmission to progeny tubers. Transmission experiments in field conditions of PVY isolates representing the three main molecular groups (PVYO, PVYEU−NTN, PVYNA−NTN) indicate that PVYEU−NTN has the highest transmission rate. Our results suggest that PVYEU−NTN isolate has a competitive advantage over PVYO and PVYNA−NTN isolates which is likely to be an important factor in shaping the evolution of viruses and the population dynamics of PVY.

Stopped in its tracks: how λ-cyhalothrin can break the aphid transmission of a potato potyvirus.

Pyrethroids are one of the most widespread and commonly used classes of insecticide and are used in multiple roles, including protecting potato crops from virus vector aphids. Resistance in some genotypes of a few species is now widespread, but most species remain susceptible. The rate of virus transmission by two genotypes of the peach potato aphid, Myzus persicae, fed on potato virus Y (PVY)-infected leaves of potato treated with the pyrethroid λ-cyhalothrin was evaluated. The susceptible genotype, type J, was significantly inhibited from transmitting virus to uninfected seedlings. A genotype containing the M918L super knockdown resistance mutation conferring resistance to pyrethroids, type O, showed no inhibition of transmission. However, when survival of the aphids after exposure was compared, the pyrethroid had not killed the type J aphids. λ-Cyhalothrin in a commercial formulation disrupts PVY transmission by disorienting aphid vectors for a sufficient time for the virus to lose its transmissibility. However, M. persicae genotypes carrying the M918L mutation are not prevented from transmitting.

Mechanical Transmission of Potato Virus Y (PVY) Through Seed Cutting and Plant Wounding

The transmission of PVY strains, PVYO, PVYN:O, and PVYNTN via tuber cutting and plant wounding was investigated in PVY susceptible cultivars Shepody and Russet Norkotah. For the tuber cutting experiment, after one infected tuber was cut with a knife, four uninfected tubers were cut sequentially with the same knife without disinfecting it between the cuts. In the plant wounding experiments, wounds were induced in the healthy and infected plants of Shepody by bouncing, brushing, hammering, squeezing, and Carborundum rubbing treatments. These treatments allowed exchange of sap between the healthy and infected plants. Results demonstrated that seed cutting did not transmit PVY, whereas plant wounding treatments caused varying levels of PVY transmission, depending on the wounding treatment. Plant bouncing was the least effective whereas hammering was the most effective.

The use of test tube plantlets for the assessment of Potato virus Y transmission by Myzus persicae and Aphis glycines

Test tube plantlets were used to assess the transmission efficiency of Potato virus Y (PVY) from and to potato plants by the potato colonizing species green peach aphid (Myzus persicae) and the non-potato colonizing species soybean aphid (Aphis glycines). Similar levels of transmission of PVY by M. persicae were observed in the test tube plantlets and potted plants, demonstrating the reliability of this test for PVY transmission efficiency assay for aphids. The assay was then used to assess the transmission of PVYO and PVYN:O by M. persicae and A. glycines with two virus acquisition regimes, one with 5-min continuous probing and the other with 1-h acquisition access. The M. persicae mediated-transmission rate was 24.1% and 51.7% for PVYO and PVYN:O, respectively, under the 5-min acquisition regime; under the same acquisition regime, A. glycines led to 0.0% and 1.7% infection rates for PVYO and PVYN:O, respectively. Under the 1-h acquisition regime, no infection was observed except for PVYN:O by M. persicae, which exhibited an infection rate of 3.4%.

Efficacy of mineral oil combined with insecticides for the control of aphid virus vectors to reduce potato virus Y infections in seed potatoes (Solanum tuberosum)

Aphids are major vectors of plant viruses. Potato virus Y (PVY) is the most important aphid-transmitted virus affecting potato crops in Denmark. Because of a changed seed potato growing strategy, the seed potato area in Denmark is changing from regions with a low average temperature to regions with a higher average temperature. This means that the aphids may infest the potato crops earlier and the population development of the aphids may be faster, and consequently PVY may more easily become epidemic in seed potato crops. With a view to reducing the spread of PVY a 3-year experiment was carried out with a combination of mineral oil and insecticides. In 2005 and 2007 when a very high number of aphids were present, nearly all plants were infected with PVY. In 2006 with a lower number of aphids a smaller proportion of the plants were infected, and a tendency to a lower PVY incidence in mineral-oil treated plots was found, but more than the 8% threshold value. Even in plots where systemic neonicotinoids were applied and very few aphids were recorded, no significant reduction in infestation level of PVY was found. The present experiment shows that mineral oil and insecticides applied to potato crops each week for a 6-week period as protection against aphid transmission of PVY did not significantly reduce the level of PVY infestations in potatoes.

Within plant distribution of Potato Virus Y in hairy nightshade ( Solanum sarrachoides): An inoculum source affecting PVY aphid transmission

Potato virus Y (PVY) is vectored by several potato-colonizing and non-colonizing aphid species in a non-persistent manner and has a wide host range. It occurs naturally in several plant families. Myzus persicae and Macrosiphum euphorbiae are the most efficient potato-colonizing aphid vectors of PVY. Rhopalosiphum padi, a cereal aphid that migrates in large numbers through potato fields during the middle of the growing season, does not colonize potato plants but can transmit PVY. Hairy nightshade, Solanum sarrachoides, a prevalent annual solanaceous weed in the Pacific Northwest (PNW) of the United States, is an alternative host for PVY and a preferred host for M. persicae and M. euphorbiae. Hence, hairy nightshade plants might play an important role as an inoculum source in the epidemiology of PVY. We looked at titre accumulation and distribution of PVY O, PVY N:O and PVY NTN in S. sarrachoides and potato after aphid inoculation with M. persicae and studied the transmission of PVY O and PVY NTN, by M. persicae, M. euphorbiae and R. padi from hairy nightshade to potato plants. Virus titre at different positions on the plant was similar in S. sarrachoides and potato plants with strains PVY O and PVY N:O. Titres of PVY NTN were similar in S. sarrachoides and potato but differences in titre were observed at different positions within the plant depending on the plant phenology. Percentage transmission of PVY NTN by M. persicae and M. euphorbiae was twice as high (46 and 34%, respectively) from hairy nightshade to potato than from potato to potato (20 and 14%). Percentage transmission of PVY O by M. persicae and M. euphorbiae was not affected by the inoculum source. No effect of the inoculum source was observed in the transmission of either PVY strain by R. padi. These results show that hairy nightshade may be an equal or better virus reservoir than potato and thus, important in the epidemiology of PVY.

A Comparison of Disinfectants to Prevent Spread of Potyviruses in Greenhouse Tomato Production

Potyviruses, transmitted by a diverse array of common aphid species, infect a broad range of vegetable crops, and can be problematic in greenhouse tomato production. Once introduced, these viruses are believed to be transmitted plant-to-plant during pruning operations, and can infect large sections of a greenhouse, resulting in significant losses in fruit quality and yield. Several methods are used for virus management in greenhouse production, including rouging of diseased plants and treatment of tools and facilities with virucides to eradicate the virus responsible. To clarify potyvirus transmission efficiency from an infected source during pruning operations, experiments were conducted using direct and serial mechanical inoculation of Potato virus Y (PVY) using a scalpel dipped in a suspension of PVY-infected plant sap. Tests demonstrated that both serial and direct inoculation resulted in significant PVY transmission, but that transmission rates declined after the first few plants in serial transmission. Additional tests evaluated the efficiency of two virucides, a quaternary ammonium solution and sodium hypochlorite, for virus inactivation during pruning operations using a range of concentrations and time points. Results demonstrated that 0.5% sodium hypochlorite treatment for two seconds was sufficient for virus control, and superior to treatment with quaternary ammonium solutions. Accepted for publication 20 December 2010. Published 21 February 2011.

Sequence comparison of the HC-Pro and CP proteins of twoPotato virus Ystrains differing in aphid transmission and systemic movement

Nucleotide and amino acid sequences of the helper component protease (HC-Pro) and the coat protein (CP) of two Hungarian Potato virus Y (PVY) isolates, differing in aphid transmissibility were determined. Isolate PVY-5 belongs to the common “O” strain (PVY O ), whereas isolates PVY-98 and PVY-111 belong to the “N” (PVY N ) and the PVY-NTN and PVY-H to the “NTN” (PVY NTN ) strains, respectively. The PVY-5 isolate varied significantly from the others in aphid transmission and in the ability to systemically infect potato plants. To elucidate whether these differences were due to mutations affecting known functional motifs, the corresponding cistrons of the two proteins were sequenced and aligned. Our analysis showed that none of the well-known motifs, responsible for aphid transmission in the two proteins had been affected. However, the defective isolate had two natural mutations in the HC-Pro in the vicinity of the PTK motif, and a number of mutations in the CP, distributed both in the N-terminus and the central region. As these two proteins are the only known viral participants in the aphid transmission mechanism, it is likely that some of the observed mutations might be involved in this process. Thus, our results indicate that other, previously unidentified sequences or factors may influence virus-vector interactions and transmission of PVY.

Transient expression of homologous hairpin RNA interferes with PVY transmission by aphids

Hairpin RNAs have been used to confer resistance to viruses in plants through RNA silencing. However, it has not been demonstrated that RNA silencing was effective against inoculation by aphids of non-persistently transmitted viruses, the major route of plant virus spread in nature. As a proof-of-principle strategy, we made use of Agrobacterium tumefaciens to transiently express a hairpin RNA homologous to Potato virus Y (PVY) in plant tissues. A complete and specific interference with aphid transmission of PVY was achieved by inducers of RNA silencing, as demonstrated by specific siRNAs accumulation in agroinfiltrated tissues. To our knowledge, this is the first report of successful interference with non-persistent transmission of a plant virus using RNA interference.

Behavioral Response and Virus Vector Ability of Myzus persicae (Homoptera: Aphididae) Probing on Pepper Plants Treated with Aphicides

Behavioral response of the green peach aphid, Myzus persicae (Sulzer), to 3 different insecticides (cypermethrin, pirimicarb, and imidacloprid) was assessed on pepper plants, Capsicum annuum L., using electrical monitoring of aphid probing behavior. This technique enabled us to assess stylet penetration pathways as well as cell membrane punctures (potential drops). The effect of these insecticide treatments on potato virus Y (PVY) transmission by M. persicae also was tested. Pirimicarb and imidacloprid did not significantly affect probing behavior or PVY transmission efficiency when aphids were allowed a 10-min acquisition access period on infected insecticide-treated plants. Conversely, cypermethrin affected aphid behavior as well as PVY transmission efficiency. Aphids probing on cypermethrin-treated plants produced fewer (1.7 versus 3.3) and shorter (41 versus 152 s) penetrations than those probing on untreated plants. They also produced a lower number of potential drops (1.3 versus 4.2). Moreover, cypermethrin caused a paralysis of aphids within 2.5 min of exposure to the treated plants. Aphids were not able to subsequently inoculate healthy plants. However, when the acquisition access period was shorter than 2.5 min, aphids were able to efficiently transmit PVY despite the cypermethrin treatment of the virus source plant. The possible existence of an additional deterrent effect caused by cypermethrin on M. persicae and its implications in PVY epidemiology is discussed.

New Correlations Between Aphid Stylet Paths and Nonpersistent Virus Transmission

The electrical penetration graph technique was used to study probing behavior of the aphid Myzus persicae (Sulzer) during the transmission of potato virus Y (PVY) to pepper plants. Single aphids allowed a 5-min access to infected plants achieved 51.3% transmission efficiency. Aphids acquiring the virus probed the plant more frequently, but these probes were shorter than the ones produced by the aphids that were unable to acquire PVY. Moreover, aphids that transmitted PVY produced more intracellular punctures (as measured by potential drops), but their mean duration did not differ significantly from that of the aphids unable to transmit the virus. The mean duration of none of the potential drop subphases could be associated with PVY transmission. Two of the 18 behavioral variables analyzed proved critical for virus acquisition according to a stepwise logistic regression model. The 1st variable was the total number (observed during the entire 5-min register) of typical pulses recorded during subphase II3 of the potential drops (positive correlation). Subphase II3 is the last true intracellular distinct phase of a potential drop. The 2nd variable was the time elapsed from the last potential drop to the end of the probe (negative correlation). The implication of these results on the transmission mechanisms of nonpersistently transmitted viruses is discussed.

Seasonal Abundance of Aphid Vectors of Potato Virus Y in the Red River Valley of Minnesota and North Dakota

An epidemic of aphid-transmitted potato virus Y (PVY) in seed potato grown in the Red River Valley of Minnesota and North Dakota was the reason we began a study to determine which aphid species were found in traps placed near potato fields. Knowledge of which aphid species are present and which of these are known vectors of PVY is needed to develop management strategies that minimize virus spread. The spread of PVY to healthy indicator plants and captures of alate aphids in tile traps were monitored weekly for 3 yr consecutively (1992-1994) throughout the Red River Valley. Thirty-four aphid species were identified from green and yellow tile traps in 1992, 25 in 1993, and 26 in 1994. Yellow tile traps caught significantly more aphids overall than green tile traps and were significantly preferred by Aphis helianthi Monell, Capitophorus elaeagni (del Guercio), and Rhopalosiphummaidis (Fitch). Intervals of greatest aphid capture in green traps were generally between mid-July and mid-August at all sites in all 3 yr. Aphid captures at all sites were 3-25 times greater in 1992 and 1994 than in 1993. PVY infection of indicator plants exposed at the trapping sites also was greater in 1992 (25 plants) and 1994 (18 plants) than in 1993 (2 plants). Eighty-nine percent of PVY spread to indicator plants occurred between 8 July and 19 August. Eight species comprised 89.9% of the aphids collected in green traps during intervals of PVY transmission to indicator plants: Acyrthosiphon pisum (Harris), pea aphid; A. helianthi; C. elaeagni; Lipaphis erysimi (Kaltenbach), turnip aphid; R. maidis, com leaf aphid; R. padi (L.), bird cherry-oat aphid; Schizaphis graminum (Rondani), greenbug; and Sitobion avenae (F.), English grain aphid. Seven of these species were previously known PVY vectors. We found that A. helianthi transmitted PVY with low efficiency under greenhouse conditions. The 8 most common aphid species were associated with crops and weeds common in the Red River Valley. Our data suggest that although the relative importance of individual PVY vectors varies from year to year and location by location, total aphid captures may be the best indicator of the risk of PVY spread.