Transmission Of Non-persistent Viruses Research Articles

The impact of thiamethoxam on the feeding and behavior of 2 soybean herbivore feeding guilds.

Over the past few decades, inadvertent consequences have stemmed from the intensified use of neonicotinoids in agroecosystems. Neonicotinoid applications can result in both positive (e.g., reduced persistent virus transmission) and negative (e.g., increased host susceptibility) repercussions exhibiting ambiguity for their use in crop production. In soybean, aspects of neonicotinoid usage such as the impact on nonpersistent virus transmission and efficacy against nontarget herbivores have not been addressed. This study evaluated the interaction between the neonicotinoid thiamethoxam and soybean variety and the impact on different pest feeding guilds. Feeding and behavioral bioassays were conducted in the laboratory to assess the effect of thiamethoxam on the mortality and weight gain of the defoliator, Chrysodeixis includens (Walker). Bioassays evaluated impacts dependent and independent of soybean tissue, in addition to both localized and systemic efficacy within the soybean plant. Additionally, using the electrical penetration graph technique (EPG), the probing behavior of 2 piercing-sucking pests, Aphis gossypii Glover and Myzus persicae (Sulzer), was observed. Results from defoliator bioassays revealed thiamethoxam had insecticidal activity against C. includens. Distinctions in thiamethoxam-related mortality between bioassays dependent and independent of soybean tissue (~98% versus ~30% mortality) indicate a contribution of the plant towards defoliator-related toxicity. Observations of defoliator feeding behavior showed a preference for untreated soybean tissue relative to thiamethoxam-treated tissue, suggesting a deterrent effect of thiamethoxam. EPG monitoring of probing behavior exhibited a minimal effect of thiamethoxam on piercing-sucking herbivores. Findings from this study suggest neonicotinoids like thiamethoxam may provide some benefit via insecticidal activity against nontarget defoliators.

Effect of soybean variety and systemic induction on herbivore feeding guilds

Plants are attacked by a variety of herbivores and respond with localized or systemic defenses. Plant defense against one feeding guild (e.g. chewing, piercing/sucking) may also affect alternate feeding guilds. To optimize host plant resistance, interactions between feeding guilds must be understood. Aphids are plant virus vectors whose vector efficiency can be altered by plant defenses. To determine if systemic induction influences aphid feeding behaviors related to virus transmission, three soybean varieties, Davis, Lyon, and Progeny 4906RR, were induced by subjecting plants to soybean looper (SBL) herbivory, or exogenous applications of either jasmonic acid (JA) or salicylic acid (SA). Green peach aphid (GPA) apterae feeding behavior was recorded on induced and control plants using the Electrical Penetration Graph (EPG) technique. SBL growth bioassays were used to assess systemic induction. Previous SBL herbivory reduced SBL larval weights when fed Progeny 4906RR. JA reduced larval weights on Progeny 4906RR and Davis. SA increased SBL larval weights on Lyon. SBL herbivory decreased behaviors associated with nonpersistent virus transmission in Davis and Progeny 4906RR. JA altered behaviors associated with virus transmission in Davis and increased behaviors associated with virus acquisition in Progeny 4906RR. SA delayed probing in Davis, but increased behaviors associated with virus transmission in Progeny 4906RR and Lyon. Inducing host plant resistance with JA may reduce herbivore performance and increase nonpersistent virus transmission. Previous chewing herbivory may decrease nonpersistent virus transmission by aphids but is variety dependent.

Different Plant Viruses Induce Changes in Feeding Behavior of Specialist and Generalist Aphids on Common Bean That Are Likely to Enhance Virus Transmission.

Bean common mosaic virus (BCMV), bean common mosaic necrosis virus (BCMNV), and cucumber mosaic virus (CMV) cause serious epidemics in common bean (Phaseolus vulgaris), a vital food security crop in many low-to-medium income countries, particularly in Sub-Saharan Africa. Aphids transmit these viruses “non-persistently,” i.e., virions attach loosely to the insects' stylets. Viruses may manipulate aphid-host interactions to enhance transmission. We used direct observation and electrical penetration graph measurements to see if the three viruses induced similar or distinct changes in feeding behaviors of two aphid species, Aphis fabae and Myzus persicae. Both aphids vector BCMV, BCMNV, and CMV but A. fabae is a legume specialist (the dominant species in bean fields) while M. persicae is a generalist that feeds on and transmits viruses to diverse plant hosts. Aphids of both species commenced probing epidermal cells (behavior optimal for virus acquisition and inoculation) sooner on virus-infected plants than on mock-inoculated plants. Infection with CMV was especially disruptive of phloem feeding by the bean specialist aphid A. fabae. A. fabae also experienced mechanical stylet difficulty when feeding on virus-infected plants, and this was also exacerbated for M. persicae. Overall, feeding on virus-infected host plants by specialist and generalist aphids was affected in different ways but all three viruses induced similar effects on each aphid type. Specifically, non-specialist (M. persicae) aphids encountered increased stylet difficulties on plants infected with BCMV, BCMNV, or CMV, whereas specialist aphids (A. fabae) showed decreased phloem ingestion on infected plants. Probing and stylet pathway activity (which facilitate virus transmission) were not decreased by any of the viruses for either of the aphid species, except in the case of A. fabae on CMV-infected bean, where these activities were increased. Overall, these virus-induced changes in host-aphid interactions are likely to enhance non-persistent virus transmission, and data from this work will be useful in epidemiological modeling of non-persistent vectoring of viruses by aphids.

Endosymbionts Differentially Alter Exploratory Probing Behavior of a Nonpersistent Plant Virus Vector.

Insect endosymbionts (hereafter, symbionts) can modify plant virus epidemiology by changing the physiology or behavior of vectors, but their role in nonpersistent virus pathosystems remains uninvestigated. Unlike propagative and circulative viruses, nonpersistent plant virus transmission occurs via transient contamination of mouthparts, making direct interaction between symbiont and virus unlikely. Nonpersistent virus transmission occurs during exploratory intracellular punctures with styletiform mouthparts when vectors assess potential host-plant quality prior to phloem feeding. Therefore, we used an electrical penetration graph (EPG) to evaluate plant probing of the cowpea aphid, Aphis craccivora Koch, an important vector of cucurbit viruses, in the presence and absence of two facultative, intracellular symbionts. We tested four isolines of A. craccivora: two isolines were from a clone from black locust (Robinia pseudoacacia L.), one infected with Arsenophonus sp. and one cured, and two derived from a clone from alfalfa (Medicago sativa L.), one infected with Hamiltonella defensa and one cured. We quantified exploratory intracellular punctures, indicated by a waveform potential drop recorded by the EPG, initiation speed and frequency within the initial 15min on healthy and watermelon mosaic virus-infected pumpkins. Symbiont associations differentially modified exploratory intracellular puncture frequency by aphids, with H. defensa-infected aphids exhibiting depressed probing, and Arsenophonus-infected aphids an increased frequency of probing. Further, there was greater overall aphid probing on virus-infected plants, suggesting that viruses manipulate their vectors to enhance acquisition-transmission rates, independent of symbiont infection. These results suggest facultative symbionts differentially affect plant-host exploration behaviors and potentially nonpersistent virus transmission by vectors.

Stylet penetration behaviors of Myzus persicae (Hemiptera: Aphididae) on four Ipomoea spp. infected or noninfected with sweet potato potyviruses.

Myzus persicae (Sulzer) is an efficient vector of potyviruses in sweet potato, Ipomoea batatas (L.). These potyviruses also infect members of the morning glory family Ipomoea cordatotriloba Dennstedt and Ipomoea hederacea Jacqin commonly found within or around sweet potato fields. Infection of sweet potato with potyviruses increases the intrinsic rate of increase of M. persicae. Thus, from the epidemiological stand point, virus infection can modify vector population dynamics, and therefore increase virus spread. To better understand this, stylet penetration behaviors of M. persicae on virus infected and noninfected sweet potato cvs. 'Beauregard' and 'Evangeline', as well as morning glory plants I. cordatotriloba and I. hederacea were monitored. Stylet penetration behaviors associated with nonpersistent virus transmission such as time to first intracellular puncture (potential drop), number of potential drops, duration of potential drop, duration of potential drop subphase II-3, and number of potential drops with subphase II-3 pulses were significantly increased on virus-infected compared with noninfected Beauregard, but greatly reduced on virus-infected compared with noninfected I. hederacea plants. Stylet penetration behaviors associated with host acceptance such as reduced nonprobing duration and nonprobing events were greater on virus-infected compared with noninfected Beauregard plants. In contrast, on Evangeline, I. cordatotriloba and I. hederacea stylet penetration behaviors by M. persicae indicate it had less preference for virus-infected compared with noninfected plants.

NON-PERSISTENT TBV TRANSMISSION IN CORRELATION TO APHID POPULATION DYNAMICS IN TULIP FLOWER BULBS

Virus transmission by aphids causes millions of Euro’s damage in the flower bulb sector annually. Mineral oils and pyrethroids are applied weekly during the growth season to decrease the virus transmission by aphids in flower bulbs. Currently, little is known about the dynamics of aphid populations during the growth season of tulips and the accompanying risk of the non-persistent virus transmission of for example Tulip breaking virus (TBV). Therefore, population dynamics of aphids in tulip fields was monitored during three growing seasons. Simultaneously, the period of TBV transmission by aphids was investigated experimentally by exposing small tulip plots during specified intervals to naturally occurring aphids. Finally, timing of virus spread was correlated with aphid population dynamics and weather conditions. In 2007, TBV transmission started in April while the first aphids were found in May. Apparently, the first aphids of the season already contributed in great extend to the virus transmission and virus transmission was observed very locally in the tulip plots. A second, distinct TBV isolate was identified which resulted in the design of an improved TBV detection assay. The main objective of this research project is to enhance the knowledge about the risk of non-persistent virus transmission in relation to aphid population dynamics. This knowledge should enable us to formulate crop protection guidelines that are better fine-tuned with the risk of virus transmission and thereby decreasing the environmental damage caused by chemical crop protection.

Spatial and temporal distribution of winged aphids (Hemiptera: Aphididae) frequenting blueberry fields in southwestern British Columbia and implications for the spread of Blueberry scorch virus

AbstractAlate aphids were sampled in five fields of commercial blueberry, Vaccinium corymbosum L. (Ericaceae), during 2001 and 2002 using yellow tile, green tile, and Tremclad® yellow water traps. Eighty-seven species were identified among a total of 7722 alatae. Several of the species are known virus vectors, including Aphis fabae Scopoli, Brachycaudus helichrysi (Kaltenbach), Hyalopterus pruni (Geoffroy), Hyperomyzus lactucae (L.), Myzus persicae (Sulzer), Rhopalosiphoninus staphyleae (Koch), and Rhopalosiphum padi (L.). The number of species caught varied with year, and the number of species and the total number of alatae varied with field, trap colour, and season. More species were caught in 2001 than in 2002, in yellow than in green traps, and in the summer than in the spring or the autumn, and more alatae were caught in Tremclad® yellow traps than in yellow or green tile traps, and in the autumn than in the spring or the summer. However, numerous interactions limit generalizations. Analyses of the data for individual species revealed similar patterns and interactions. The effects of year, field, trap colour, and season varied with species. Given nonpersistent virus transmission and the large numbers of alatae caught of species that are known virus vectors, there is considerable potential for spread of Blueberry scorch virus by migrant aphids. Field- or area-specific and season-specific control strategies could be developed once the virus vector status of the different species is known. In addition, given the number of significant interactions observed in the data, there is a need to investigate alternative, generalized approaches to reducing virus transmission rates, such as applying whitewash or kaolin particle film to blueberry leaves.

Settlement rate of Aphis gossypii (Hemiptera, Aphididae) and transmission efficiency of Cucumber mosic virus in melons protected with kaolin-particle films

The objective of our study was to evaluate the effect of Surround (95% kaolin) on the settlement of Aphis gossypii Glover on melon plants and on the transmission of a non-persistent virus, Cucumber mosaic virus (CMV). The first step was to conduct a transmission experiment using apterae aphids under laboratory conditions. Results of these tests showed that Surround is unable to avoid the transmission of non-persistent viruses, although a significant reduction in the transmission rate of CMV in the Surround–treated plants was observed in some cases. Also, the efficacy of Surround was tested using alatae aphids that were released in large cages under greenhouse conditions. The results obtained indicated that there was a significant difference in one assay at 24 h, and in two assays at 48 h, when the mean number of aphids settled on test plants treated and untreated with Surround was compared. However, Surround was able to reduce the transmission rate of CMV by only 10% and there were no statistically significant differences between treated and untreated control plants under our experimental conditions.

Blockage of stylet tips as the mechanism of resistance to virus transmission by Aphis gossypii in melon lines bearing the Vat gene

Summary Aphis gossypii is the main virus vector in muskmelon crops. The melon gene Vat confers resistance to non‐persistent virus transmission by this aphid. The mechanism of this resistance is not well understood, but no relationship has been detected between resistance and the probing behaviour of aphids on resistant plants. Results presented here suggest that temporary blockage of aphid stylet tips preventing virus particle release may explain the resistance conferred by Vat gene. We performed experiments in which viruliferous aphids were allowed to probe different sequences of resistant (Vat‐bearing) and/or susceptible melon plants. The results demonstrated that A. gossypii inoculates Cucumber mosaic virus (CMV) efficiently in susceptible plants having previously probed resistant plants, showing that the resistance mechanism is reversible. Furthermore, the infection rate obtained for susceptible plants was the same (25%) regardless of whether the transmitting aphid had come directly from the CMV source or had subsequently probed on resistant plants. This result suggests that virus is not lost from stylet to plant during probing of resistant plants, supporting the temporary blockage hypothesis. We also found that the ability of Myzus persicae to transmit CMV is noticeably reduced after probing on resistant plants, providing evidence that this aphid species also responds to the presence of the Vat gene. Finally, we also found that in probes immediately after virus acquisition M. persicae inoculates resistant plants with CMV more efficiently than susceptible plants, perhaps because the Vat gene product induces increased salivation by this aphid.

Nonpersistent Virus Transmission Efficiency Determined by Aphid Probing Behavior During Intracellular Punctures

The probing behavior of starved and nonstarved Myzus persicae (Sulzer) on pepper plants was compared using the electrical penetration graph technique. Special attention was paid to the 1st intracellular puncture produced by the aphids, recorded as a potential drop waveform pattern. Previously fasted aphids produced potential drops with a longer phase II3 (3.6 versus 2.5 s), and typical II3 pulses were clearly visible in 89% of the records (versus only 61% for the nonstarved aphids). This ability of starved aphids to produce potential drops with a long phase II3 and its associated II3 pulses may account for the increase in potato virus Y (PVY) transmission efficiency when compared with nonstarved aphids (57 versus 4%). A new explanation to the "preacquisition starvation effect" is proposed based on our results. In a separate experiment, the early probing behavior of different aphid species [ M. persicae, Aphis gossypii Glover, Rhopalosiphum padi (L.), and Sitobion avenae (F.)] on pepper plants was compared. Again, the great variability observed in the morphology and duration of phase II3 of the potential drops could be correlated with differences in transmission efficiences. Individuals from species that transmitted PVY efficiently ( M. persicae and A. gossypii ) usually produced pds with long II3 phases and clear II3 pulses, whereas inefficient vectors ( R. padi and S. avenae ) showed short II3 phases and in many cases absence of II3 pulses. The implications of these findings for host-plant recognition and virus-vector specificity is discussed.

Early intracellular punctures by two aphid species on near-isogenic melon lines with and without the virus aphid transmission (Vat) resistance gene

The Vat resistance gene (in Cucumis melo L.) inhibits the transmission of non-persistent viruses by Aphis gossypii Glover, but does not affect transmission by Myzus persicae (Sulz.). To see whether this difference was behaviourally determined, we investigated the stylet penetration behaviour of these two aphid species by recording EPGs (Electrical Penetration Graphs) of 8 and 20 min on two sets of susceptible and resistant isogenic melon lines. During the 20 min EPG study, inoculation with CMV (Cucumber Mosaic Virus) was also investigated. For both sets of isogenic lines, the two aphid species were able to detect the presence of Vat. The mean duration of individual intracellular punctures on the resistant genotypes was significantly reduced for both M. persicae and A. gossypii (-10% and -8% respectively for duration of pattern ‘pd’ in the 20 min experiment); this reaction appeared faster for M. persicae, a species for which melon was not a suitable host-plant. Therefore, in contrast to Vat's anti-transmission effect, this behavioural effect was not aphid species-specific. Also, the frequency of intracellular punctures on the resistant genotypes was significantly reduced in A. gossypii (but not in M. persicae): on average, this frequency dropped from ≈0.65 pd.min-1 on the susceptible genotypes to ≈0.5 pd.min-1 on the resistant ones. It was concluded that (intracellular?) chemical cues were detected very early by aphids probing on the resistant genotypes carrying the Vat gene. However, a comprehensive analysis of the behavioural traits of both aphids on the two genotypes could not alone account for the complete inhibition of transmission which was found only to occur for A. gossypii on resistant genotypes. None of the differences detected (between aphid species or between plant genotypes) could account for the Vat phenotype, although they may explain quantitative differences in transmission efficiencies between aphid species. It was thus concluded that Vat effect was primarily chemically mediated. Finally, some intracellular punctures bearing typical subphases have been identified in both aphid species and were designated as ‘long potential drops’ (pd-L). For A. gossypii, these were observed early after plant contact and their mean duration was twice that of standard intracellular punctures (≈8.5 s vs ≈4.2 s). Although not necessary for CMV inoculation, the duration of such phases was positively correlated with a high transmission efficiency by A. gossypii on the susceptible genotype. The nature of this pattern and a putative mechanism of action of the Vat gene are discussed.

DIFFERENCE IN THE TRANSMISSION OF PVY° TO POTATO AND TOBACCO BY THE POTATO APHID, MACROSIPHUM EUPHORBIAE (THOMAS): EFFECTS OF PROBING DURATION AND FREQUENCY

AbstractThe probing behavior of the potato aphid, Macrosiphum euphorbiae (Thomas), is significantly different on potato than on tobacco plants. The higher frequency of short-duration probes, ideal for the transmission of nonpersistent viruses, is the apparent cause for the higher rate of potato virus Y° (PVY°) transmission on tobacco than on potato. However, experimental augmentation of short inoculation probes by M. euphorbiae on potato and tobacco failed to increase PVY° transmission on either. These results demonstrate the absence of a causal relationship between variations in probing behavior of M. euphorbiae and variations in the transmissibility of PVY° by this vector on tobacco and potato.

Control of non-persistently transmitted aphid-borne viruses

Transmission of non-persistent viruses, characterizedinter alia by acquisition and inoculation of virus during brief probes, absence of a latent period after acquisition, and loss of virus after short feeding periods, has not been reduced satisfactorily by vector control using insecticides. Breeding for resistance is one of the most efficient ways for control, but progress in breeding programs is slow, and resistance depending on one gene only is often overcome by new strains of the virus. Avoidance of infection, and the use of oil sprays, reflective surfaces, yellow sticky traps, white nets and border crops, are reviewed, as possible alternative control approaches. Of these, oil sprays are presently used in practice. The possible mechanisms of the mode of action of oils are discussed. It is expected that these methods, singly or in combination, may become of further importance, especially in highvalue crops such as virus-tested propagation material of flower bulbs and corms.

Temperature Effects on Aphid Transmission of Nonpersistent Viruses with Notes on Morphological Variation Within Clones of Aphids with Differing Vector Efficiencies1234

Additional studies have been made on transmission efliciency of 3 strains of potato virus Y (DPVY, MPVY, and RPVY) and 1 strain of cucumber mosaic virus (CMV) using the green peach aphid, Myzus persicae (Sulzer), and a green form of the potato aphid, Macrosiphum euphorbiac (Thomas). Acquisition temperatures of 10, 21-23, and 32°C were compared factorially with inoculation temperatures of 10, 21-23, and 32°C for most of the virus-vector combinations. Aphids always acquired virus at 10°C but sometimes failed to inoculate at this temperature. In contrast to earlier results, all virusvector combinations showed positive correlations between transmission efficiency and increasing temperature. Effects were more pronounced with increase in inoculation than with acquisition temperature. The potato aphid transmitted all 3 strains of potato virus Y with equal efficiency. Varying the transmission temperature and/or length of acquisition (access) feeding period resulted in similar changes in vector efficiency among alI 3 strains. However, the green peach aphid transmitted each strain of potato virus Y with a different efficiency. DPVY was not temperature labile as was RPVY, even though it also was transmitted inefficiently by green peach aphids. Apparently more than 1 mechanism is involved in the inefficient transmission by the green peach aphid of these 2 strains of potato virus Y. Morphological differences among clones of green peach, potato, and cotton aphids, Aphis gossypii Glover, were found in several instances. However, these differences were not associated consistently with virus-transmitting ability.

Effects of Temperature and Length of Acquisition Feeding Time on Transmission of Nonpersistent Viruses by Aphids1

Comparative transmission studies were made with 2 strains of potato virus Y (MPVY and RPVY) and of cucumber mosaic virus (CMV) using 7 clones of the green peach aphid, Myzus persicae (Sulzer), II clones of the cotton (melon) aphid, Aphis gossypii Glover, 4 clones of the green form of the potato aphid, Macrosiphum euphorbiae (Thomas), and 4 clones of the pink form of the potato aphid. Differences in transmission efficiency among clones of a given aphid species were almost as great as those found between aphid species. The effect on transmission efficiency of rearing the aphids on different host plant species was apparent only with the green peach aphid and PVY strains where aphids reared on kenaf, Hibiscus cannibinus L., were poorer vectors than those reared on pepper, Capsicum annum L., var. California wonder. Single clones of green peach, cotton, and pink and green forms of the potato aphid were selected from the above and used in transmission trials with the 3 viruses under temperature regimes of 50, 70, and 90°F. Using single acquisition feeding probes (9-60 seconds, depending on temperature) it was found that 4 vector-virus combinations transmitted optimally at 50°F, 6 transmitted optimally at 70°F, and 1 at 90°F. One combination failed to transmit. When the trials were repeated using the 3 temperatures and also 3 lengths of acquisition feeding (1 probe, 5 minutes, and 15 minutes) the effect on transmission of varying length of acquisition feeding was found to be independent of the temperature effect. The results with 1-probe acquisition feedings are interpreted as indicating that aphid behavior (probing?) was principally affected by changing temperature. It is believed that the general depression in transmission efficiency caused by increasing the length of acquisition feeding time at 70° and 90°F probably reflects the relative toxicities of the aphids' mouthparts (saliva?) to the viruses.