Aphid Dispersal Research Articles

Why aphid virus retention needs more attention: Modelling aphid behaviour and virus manipulation in non-persistent plant virus transmission.

Plant viruses threaten food security and are often transmitted by insect vectors. Non-persistently transmitted (NPT) plant viruses are transmitted almost exclusively by aphids. Because virions attach to the aphid's stylet (mouthparts) and are acquired and inoculated via brief epidermal probes, the aphid-virus interaction is highly transient, with a very short aphid virus retention time. Many NPT viruses manipulate their host plant's phenotype to change aphid behaviour to optimise virus transmission. Epidemiological models of this have overlooked a key feature of aphid NPT virus retention: probing or feeding on a plant causes aphids to lose the virus. Furthermore, experimental studies suggest aphids could possibly inoculate multiple healthy plants within one infective period if they do not feed. Consequences of this for virus manipulation of host plant phenotype have not been explored. Our new compartmental epidemiological model includes both behaviour-based aphid dispersal and infectivity loss rates, and the ability of infective aphids to probe multiple plants before virus loss. We use our model to explore how NPT virus-induced host phenotypes affect epidemic outcomes, comparing these results to representative previous models. We find that previous models behave fundamentally differently and underestimate the benefit of an 'attract-and-deter' phenotype, where the virus induces increased aphid attraction to infected plants but deters them from prolonged feeding. Our results also highlight the importance of characterising NPT virus retention upon the aphid during probing. Allowing for multiple infective probes increases disease incidence and the effectiveness of virus manipulation, with implications for epidemic prediction and control.

Why aphid virus retention needs more attention: modelling aphid behaviour and virus manipulation in non-persistent plant virus transmission.

Abstract Plant viruses threaten food security and are often transmitted by insect vectors. Non-persistently transmitted (NPT) plant viruses are transmitted almost exclusively by aphids. Because virions attach to the aphid's stylet (mouthparts) and are acquired and inoculated via brief epidermal probes, the aphid-virus interaction is highly transient, with a very short aphid virus retention time. Many NPT viruses manipulate their host plant's phenotype to change aphid behaviour to optimise virus transmission. Epidemiological models of this have overlooked a key feature of aphid NPT virus retention: probing or feeding on a plant causes aphids to lose the virus. Additionally, experimental studies suggest aphids could possibly inoculate multiple healthy plants within one infective period. However, consequences of this for virus manipulation of host plant phenotype have not been explored. Our new compartmental epidemiological model includes both behaviour-based aphid dispersal and infectivity loss rates, and the ability of infective aphids to probe more than one plant before virus loss. We use our model to explore how NPT virus-induced host phenotypes affect epidemic outcomes, comparing these results to representative previous models. We find that previous models behave fundamentally differently and underestimate the benefit of an 'attract-and-deter' phenotype, where the virus induces increased aphid attraction to infected plants but deters them from prolonged feeding. Our results also highlight the importance of characterising NPT virus retention upon the aphid during probing. Allowing for multiple infective probes increases disease incidence and the effectiveness of virus manipulation, with implications for epidemic prediction and control.

Cucumber mosaic virus epidemiology in pepper: Aphid dispersal, transmission efficiency and vector pressure

AbstractCucumber mosaic virus (CMV) causes significant damage and yield losses in peppers. The objective of this study is to determine the efficiency of prevalent aphid species occurring in pepper fields to transmit this virus within pepper plants and to identify their vector pressure in order to target the critical species implicated in CMV epidemics spread. Alatae and apterae were monitored in an experimental pepper field in northern Tunisia for 3 years. Sixty‐eight species were captured in winged form in yellow water traps. The most abundant species were Myzus persicae, Aphis gossypii, Aphis fabae, Aphis spiraecola, Acyrthosiphon pisum, Metopolophium dirhodum, Rhopalosiphum maidis, Aphis craccivora, Aphis nerii, Hyalopterus pruni, Sitobion avenae and Rhopalosiphum padi constituting 90% of aphid populations in the field. Their temporal dynamic showed a high period of flight activity from April to June and a second peak in September was registered. Two of these species, M. persicae and A. gossypii were also found in their wingless form on pepper leaves with a prevalence of 99.5% and 0.5%, respectively. The 12 most abundant aphid species were tested for their transmission efficiency of CMV (CMV‐pepp2 isolate) with A. gossypii as a reference vector. All aphids tested, including colonizing and non‐colonizing species on pepper, were verified to be vectors of this isolate. However, significant differences in the transmission efficiency were found between the aphid species (p < .001, SE = 7.29). M. persicae (60%) scored the highest transmission efficiency rate. Additionally, A. fabae solanella (50%) had higher transmission efficiency than the reference vector, A. gossypii (40%). H. pruni (16.67%) was documented as a new CMV vector to pepper. The single‐aphid transmission probabilities ranged from 0.7% to 16.7%. The calculated mean Vector Pressure Index (VPI) for these 12 species showed a stronger relationship with the specific aphid population variance (R = 0.89, p < .01) than the variation of the specific single‐aphid transmission probabilities (R = 0.62, p < .05). Indeed, for alate non‐colonizer vectors, A. spiraecola has recorded the highest mean VPI (27.5), despite its moderate transmission efficiency (23.33%). Nevertheless, for colonizer vectors in both winged and wingless forms, M. persicae had the highest mean VPI (49.26) of all vector species and was mostly present in its apterous form. The 12 vector species contributed to a total mean VPI of 133.48 during the surveyed periods. This research determined key features of CMV epidemiology in pepper crops that might be helpful for CMV disease management at an early stage.

Precipitation change accentuates or reverses temperature effects on aphid dispersal.

Global temperatures are generally increasing, and this is leading to a well documented advancement and extension of seasonal activity of many pest insects. Effects of changing precipitation have received less attention, but might be complex because rain and snow are increasing in some places but decreasing in others. This raises the possibility that altered precipitation could accentuate, or even reverse, the effects of rising temperatures on pest outbreaks. We used >592K aphid suction-trap captures over 15 years, in the heavily farmed central USA, to examine how the activity of Aphis glycines (soybean aphid), Rhopalosiphum maidis (corn aphid), and Rhopalosiphum padi (bird cherry-oat aphid) changed with variation in both temperature and precipitation. Increasing precipitation caused late-season flight activity of A. glycines and early-season activity of R. padi to shift earlier, while increasing temperature did the same for early-season activity of A. glycines and R. maidis. In these cases, precipitation and temperature exhibited directionally similar, but independent, effects. However, precipitation sometimes mediated temperature effects in complex ways. At relatively low temperatures, greater precipitation generally caused late-season flights of R. maidis to occur earlier. However, this pattern was reversed at higher temperatures with precipitation delaying late-season activity. In contrast, greater precipitation delayed peak flights of R. padi at lower temperatures, but caused them to occur earlier at higher temperatures. So, in these two cases the interactive effects of precipitation on temperature were mirror images of one another. When projecting future aphid flight phenology, models that excluded precipitation covariates consistently underpredicted the degree of phenological advance for A. glycines and R. padi, and underpredicted the degree of phenological delay for R. maidis under expected future climates. Overall, we found broad evidence that changing patterns of aphid flight phenology could only be understood by considering both temperature and precipitation changes. In our study region, temperature and precipitation are expected to increase in tandem, but these correlations will be reversed elsewhere. This reinforces the need to include both main and interactive effects of precipitation and temperature when seeking to accurately predict how pest pressure will change with a changing climate.

A trail pheromone mediates the mutualism between ants and aphids

Mutualisms, such as the ones between ants and aphids, evolve and persist when benefits outweigh the costs from the interactions between the partners. We show here that the trail pheromone of the red imported fire ant, Solenopsis invicta, can enhance these benefits by suppressing aphid dispersal and stimulating their reproduction. The ant's mutualistic partner, the cotton aphid Aphis gossypii, was found to readily perceive and respond to two specific trail pheromone components. Two pheromone components, Z,E-α-farnesene and E,E-α-farnesene, both suppressed walking dispersal of apterous aphids, whereas only the major pheromone component, Z,E-α-farnesene, also increased aphid reproduction rate. The ants, as well as the aphids, benefit from this inter-species function of the trail pheromone. For the ants it increases and prolongs the availability of honeydew as a key food source, whereas the aphid colony benefits from faster population growth and continuous ant-provided protection. These findings reveal a hitherto unknown mechanism by which ants and aphids both increase the benefits that they provide to each other, thereby likely enhancing the stability of their mutualistic relationship.

Modeling the dispersal of wind-borne pests: Sensitivity of infestation forecasts to uncertainty in parameterization of long-distance airborne dispersal

Modeling dispersal of wind-borne pests can be a valuable tool in a broader context of areawide integrated pest management. In such models both biotic and abiotic factors play important roles. Many aspects of the life cycle and dispersal of the focal species are typically well studied and represented with robust measures. However, some important assessments may be either lacking or based on difficult to obtain measurements. For example, investigations of population processes occurring at broad spatial scales pose logistical difficulties, and consequently the corresponding estimates may be biased. This is true in the case of long-distance airborne dispersal, in which aloft characteristics of dispersal are particularly difficult to estimate. In this study we assessed the sensitivity of regional infestation forecasts of sorghum by sugarcane aphids [Melanaphis sacchari (Zehntner)] to uncertainty in parameterization of measures meant to represent important aspects of long-distance airborne dispersal in the southern-to-central Great Plains of North America. We focused on dispersal duration, take-off height, and maximum dispersal height as three critical parameters that control wind-borne long-distance dispersal of aphids. The 63 investigated combinations of values of these parameters had largely equivalent region-wide impact on timing of first forecasted infestation (equivalence margin of 7 days) and the impact on the probability of forecasted infestation was equivalent (equivalence margin of 0.1). The spatial variability in estimates depended on local specificity of the modeled landscape, and it was larger in areas where infestations were less frequent, primarily in eastern Kansas, Oklahoma, and northern Texas.

The miR-9b microRNA mediates dimorphism and development of wing in aphids

Wing dimorphism is a phenomenon of phenotypic plasticity in aphid dispersal. However, the signal transduction for perceiving environmental cues (e.g., crowding) and the regulation mechanism remain elusive. Here, we found that aci-miR-9b was the only down-regulated microRNA (miRNA) in both crowding-induced wing dimorphism and during wing development in the brown citrus aphid Aphis citricidus We determined a targeted regulatory relationship between aci-miR-9b and an ABC transporter (AcABCG4). Inhibition of aci-miR-9b increased the proportion of winged offspring under normal conditions. Overexpression of aci-miR-9b resulted in decline of the proportion of winged offspring under crowding conditions. In addition, overexpression of aci-miR-9b also resulted in malformed wings during wing development. This role of aci-miR-9b mediating wing dimorphism and development was also confirmed in the pea aphid Acyrthosiphon pisum The downstream action of aci-miR-9b-AcABCG4 was based on the interaction with the insulin and insulin-like signaling pathway. A model for aphid wing dimorphism and development was demonstrated as the following: maternal aphids experience crowding, which results in the decrease of aci-miR-9b. This is followed by the increase of ABCG4, which then activates the insulin and insulin-like signaling pathway, thereby causing a high proportion of winged offspring. Later, the same cascade, "miR-9b-ABCG4-insulin signaling," is again involved in wing development. Taken together, our results reveal that a signal transduction cascade mediates both wing dimorphism and development in aphids via miRNA. These findings would be useful in developing potential strategies for blocking the aphid dispersal and reducing viral transmission.

Previous exposures to cues from conspecifics and ladybird beetles prime antipredator responses in pea aphids Acyrthosiphon pisum (Hemiptera: Aphididae)

When prey encounter predators, they exhibit antipredator responses to reduce their risk of predation. Delayed responses can be fatal. Because prey can assess the risk of predation using predation-related cues, previous exposures to these cues could affect subsequent antipredator responses. We tested this possibility using the pea aphid Acyrthosiphon pisum Harris (Hemiptera: Aphididae) and its predator the Asian ladybird beetle, Harmonia axyridis Pallas (Coleoptera: Coccinellidae). Aphids disperse from their host plants after sensing predators. We investigated whether previous exposures to cues from conspecifics and ladybird beetles affected the dispersal rates of aphids encountering predators. The cues contained visual, chemical, and vibrational information from aphids and ladybird beetles. Aphids that had previously been exposed to these cues increased dispersal rates and, consequently, suffered less predation than unexposed aphids. To clarify how aphids increased their dispersal rate, we examined their feeding times. Aphids that had been exposed to cues reduced feeding times compared with unexposed conspecifics. Therefore, we further tested whether the predator-induced dispersal of non-feeding aphids was greater than that of feeding conspecifics and found correlated differences. Previous exposures to cues from conspecifics and predators may allow prey to tune their antipredator responses to predation risk prior to further predator encounters.

Short-Term Increases in Aphid Dispersal From Defensive Dropping Do Not Necessarily Affect Long-Term Biological Control by Parasitoids.

Foxglove aphid (Aulacorthum solani (Kaltenbach) (Hemiptera: Aphididae)) is one of the principal aphid pests of greenhouse ornamental crops in North America. Biological control of foxglove aphid mostly relies on the use of Aphidius ervi Haliday (Hymenoptera: Braconidae). However, studies indicate that A. ervi may not be adapted to search for A. solani, and that in response to parasitoid attack aphids can drop and/or disperse, which may aggravate an infestation. Our goal was to further describe the searching behavior of A. ervi in the presence of foxglove aphids, the corresponding defensive behavior of foxglove aphid and the short- and medium-term effects on both pest dispersal and control by A. ervi. Behavioral observations were done on top and bottom leaves infested with foxglove aphid and a high release rate of A. ervi. Parasitoids tended to land on top leaves; however, more aphids were parasitized on bottom leaves, leading to equal numbers of parasitoid attacks in both locations. Most aphids dropped off the plant in the presence of a parasitoid. In large cage experiments, aphids were allowed to distribute naturally and A. ervi was released. The parasitoid still caused a high rate of aphid dropping. However, only a few aphids were able to successfully reach new plants, and most of these mummified over time. Our studies confirm that parasitoid-induced dispersal of foxglove aphid in greenhouse crops does occur, but also suggests this should not necessarily be a barrier to adoption of biological control, as A. ervi controls the aphids over time.

Dispersion of Myzus persicae and transmission of Potato virus Y under elevated CO2 atmosphere

AbstractMost phytoviruses use insect vectors to spread and infect the surrounding crop plants. Because atmospheric gas concentrations alter the physiology and metabolism of plants, we hypothesize that the concentration of carbon dioxide (CO2) affects the spread of viruses, due to modifications in the feeding behavior of the vector. Tobacco plants, Nicotiana tabacum L. (Solanaceae), and green peach aphids, Myzus persicae (Sulzer) (Hemiptera: Aphididae), were cultivated under ambient (450 p.p.m., termed aCO2) and elevated (800 p.p.m., eCO2) concentrations of CO2. For each atmospheric condition, we first evaluated the ability of the Potato virus Y to spread in a small experimental design, from a central infected tobacco plant to two surrounding circles of healthy plants in presence of aphid vectors for 7 days. The number of aphids recovered on each plant and the infection status of the plants (i.e., healthy vs. infected) were assessed at the end of the experiment. We also evaluated the ability of aphids to transmit the virus under the two experimental atmospheres, by immediately transferring a single insect from an infected plant to a healthy one. The presence of virus in healthy plants was then determined. We found that aphid dispersal, as well as the associated spread of viruses, did not differ between the two atmospheres. On the other hand, we found that aphids grown under eCO2 were more efficient in transmitting viruses to healthy plants compared to aphids reared under aCO2 conditions. The results of this experiment indicate that: (1) the ability of an aphid vector to spread a phytovirus is not affected by the level of CO2 at short time and spatial scales, but (2) the concentration of CO2 may affect plant defenses or the feeding behavior of herbivorous insects, resulting in more efficient viral transmission from the vector to the host plant.

Plant response to feeding aphids promotes aphid dispersal

AbstractPlant responses against biotic stress agents are affected by a number of environmental conditions, including the presence of other pests and pathogens. Moreover, the impact of infestation on subsequent plant colonization by conspecifics can vary, reflecting the high diversity in the co‐evolutionary processes shaping host‐plant interactions. Here, we address this issue by studying how aphid–plant interplay can influence the subsequent colonization of zucchini plants (Cucurbita pepo L., Cucurbitaceae) by conspecific Aphis gossypii Glover (Hemiptera: Aphididae, Aphidini). Previous infestation does not impact development time, longevity, and fertility of aphids. However, a previous infestation affects the distribution of the newly produced nymphs on the plant – they actively disperse on the plant, rather than starting their feeding activity where they were originally deposited, as observed in controls. Interestingly, this altered dispersal behaviour is reproduced by saliva application, suggesting the occurrence of an elicitor triggering a plant response affecting the strategy of host‐plant colonization by A. gossypii. The hypothesis that salicylic acid (SA) induction can trigger the observed behavioural response in a secondary infestation, was confirmed by exposure to methyl salicylate, a volatile product of the SA pathway. This evidence was further corroborated by analysis of gene expression profiles. Aphid infestation showed a transcriptional up‐regulation of genes underlying the biosynthesis of SA and of genes modulating the SA‐mediated defence response. Collectively, the experimental data consistently indicate regulation of aphid behaviour, mediated by plant metabolic changes following aphid infestation.

Estimation of the dispersal distances of an aphid-borne virus in a patchy landscape.

Characterising the spatio-temporal dynamics of pathogens in natura is key to ensuring their efficient prevention and control. However, it is notoriously difficult to estimate dispersal parameters at scales that are relevant to real epidemics. Epidemiological surveys can provide informative data, but parameter estimation can be hampered when the timing of the epidemiological events is uncertain, and in the presence of interactions between disease spread, surveillance, and control. Further complications arise from imperfect detection of disease and from the huge number of data on individual hosts arising from landscape-level surveys. Here, we present a Bayesian framework that overcomes these barriers by integrating over associated uncertainties in a model explicitly combining the processes of disease dispersal, surveillance and control. Using a novel computationally efficient approach to account for patch geometry, we demonstrate that disease dispersal distances can be estimated accurately in a patchy (i.e. fragmented) landscape when disease control is ongoing. Applying this model to data for an aphid-borne virus (Plum pox virus) surveyed for 15 years in 605 orchards, we obtain the first estimate of the distribution of flight distances of infectious aphids at the landscape scale. About 50% of aphid flights terminate beyond 90 m, which implies that most infectious aphids leaving a tree land outside the bounds of a 1-ha orchard. Moreover, long-distance flights are not rare–10% of flights exceed 1 km. By their impact on our quantitative understanding of winged aphid dispersal, these results can inform the design of management strategies for plant viruses, which are mainly aphid-borne.

Forest fragmentation may endanger a plant‐insect interaction: the case of the highly specialist native aphid Neuquenaphis staryi in Chile

Abstract The diversity and distribution of the genetic variation in forest phytophagous insect populations can be highly sensitive to forest fragmentation. This should be particularly evident for monophagous insects living on endangered host plants. The aphid Neuquenaphis staryi uses the tree Nothofagus alessandrii, commonly named Ruil, exclusively as a host. Nothofagus alessandrii is an endemic and endangered species whose distribution is highly fragmented in the unique Maulino temperate forests of the coastal range of Central Chile. Here, we provide proof of the specialist status of N. staryi and provide evidence on the genetic diversity and structure of their populations sampled on distinct remnant fragments of the Ruil forest. A sample representing 480 individuals collected from five fragments of Ruil forests revealed 147 distinct multilocus genotypes at six microsatellite loci. Clonal diversity and other genetic parameters were consistent with aphids reproducing by cyclic parthenogenesis and showed few signs of diversity loss. The genetic differentiation among populations was significant as evidenced by the presence of at least three genetic clusters, which are mostly explained by low migration due to geographic barriers that restrict aphid dispersion. Our results suggest that forest fragmentation imposes genetic discontinuities on a highly specialised phytophagous insect, which may have important implications for the conservation status of this ancient aphid‐plant interaction.

Aphid orientation and performance in glasshouses under different UV‐A/UV‐B radiation regimes

AbstractVisual cues leading to host selection and landing are of major importance for aphids and evidence suggests that flight activity is very dependent on ultraviolet (UV)‐A radiation in the environment. At the same time research on insect plant hosts suggest that the UV‐B component can deter some pests via changes in secondary metabolite chemistry. Here, we examine the potential of UV (UV‐A/UV‐B) radiation to control insect pests in the glasshouse environment. We first examined artificial exposure to UV‐B and the potential to trigger morphological and biochemical modifications in pepper (Capsicum annuum L., Solanaceae) with implications for the fitness of green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae). UV‐B caused accumulation of leaf secondary metabolites and soluble carbohydrates, and stimulated photosynthetic pigments. However, UV‐B did not impact on foliar protein content and aphid performance was unaffected. Next, we studied how altering the UV‐A/UV‐B ratio environment affected aphid orientation and spatial distribution over time, either directly or by exposing plants to supplemental UV before insect introduction. Aphids directly settled and dispersed on their host pepper plants more readily in the presence of supplemental UV‐A and UV‐B. In the control treatment with ambient glasshouse UV‐A and UV‐B, insects remained more aggregated. Furthermore, insects were less attracted to peppers pre‐exposed to supplemental UV‐A and UV‐B radiation. Our results suggest that suppression of UV‐A and UV‐B inside the protected environment reduces aphid colonization and dispersal. Furthermore, application of moderate exposure of young pepper plants to supplemental UV‐B radiation could aid in protection from the colonization by phytophagous insects.

Winged Pea Aphids Can Modify Phototaxis in Different Development Stages to Assist Their Host Distribution.

The pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae), shows wing polyphenism (winged and wingless morphs) in its life cycle. The winged morph is adapted for dispersal; its two developmental adult stages (for dispersal and reproduction) are based on its breeding periods. The two morphs show different phototactic behavior and the winged can change its preference to light according to the developmental stages. To determine the mechanism and ecological functions of phototaxis for A. pisum, we first investigated the phototaxis of the two aphid morphs at different stages and analyzed the phototactic response to lights of different wavelengths; the correlation between alate fecundity and their phototactic behaviors were then studied. Finally, we focused on the possible functions of phototaxis in aphid host location and distribution in combination with gravitaxis behaviors. Negative phototaxis was found for breeding winged adults but all the other stages of both winged and wingless morphs showed positive phototaxis. The reactions of the aphids to different wavelengths were also different. Nymph production in winged adults showed negative correlation to phototaxis. The dopamine pathway was possibly involved in these behavior modifications. We speculated that winged adults can use light for dispersal in the early dispersal stage and for position holding in the breeding stage. Based on our results, we assume that light signals are important for aphid dispersal and distribution, and are also essential for the pea aphids to cope with environmental changes.

Impact of aphid alarm pheromone release on virus transmission efficiency: When pest control strategy could induce higher virus dispersion

Aphids cause serious damages to crops not only by tacking sap but also by transmitting numerous viruses. To develop biological control, the aphid alarm pheromone, namely E-β-farnesene (EβF), has been demonstrated to be efficient to repel aphids and as attract beneficials, making it a potential tool to control aphid pests. Considering aphids also as virus vectors, changes of their behavior could also interfere with the virus acquisition and transmission process. Here, a combination of two aphid species and two potato virus models were selected to test the influence of EβF release on aphid and virus dispersion under laboratory conditions. EβF release was found to significantly decrease the population of Myzus persicae and Macrosiphum euphorbiae around the infochemical releaser but simultaneously also increasing the dispersal of Potato Virus Y (PVY). At the opposite, no significant difference for Potato Leaf Roll Virus (PLRV) transmission efficiency was observed with similar aphid alarm pheromone releases for none of the aphid species. These results provide some support to carefully consider infochemical releasers not only for push–pull strategy and pest control but also to include viral disease in a the plant protection to aphids as they are also efficient virus vectors. Impact of aphid kinds and transmission mechanisms will be discussed according to the large variation found between persistent and non persistent potato viruses and interactions with aphids and related infochemicals.

Infection of host plants by Cucumber mosaic virus increases the susceptibility of Myzus persicae aphids to the parasitoid Aphidius colemani.

Plant viruses can profoundly alter the phenotypes of their host plants, with potentially far-reaching implications for ecology. Yet few studies have explored the indirect, host-mediated, effects of plant viruses on non-vector insects. We examined how infection of Cucurbita pepo plants by Cucumber mosaic virus (CMV) impacted the susceptibility of aphids (Myzus persicae) to attack by the parasitoid wasp Aphidius colemani. In semi-natural foraging assays, we observed higher rates of aphid parasitism on infected plants compared to healthy plants. Subsequent experiments revealed that this difference is not explained by different attack rates on plants differing in infection status, but rather by the fact that parasitoid larvae successfully complete their development more often when aphid hosts feed on infected plants. This suggests that the reduced nutritional quality of infected plants as host for aphids—documented in previous studies—compromises their ability to mount effective defenses against parasitism. Furthermore, our current findings indicate that the aphid diet during parasitoid development (rather than prior to wasp oviposition) is a key factor influencing resistance. These findings complement our previous work showing that CMV-induced changes in host plant chemistry alter patterns of aphid recruitment and dispersal in ways conducive to virus transmission.

Plant resistance reduces the strength of consumptive and non-consumptive effects of predators on aphids.

1. The impact of predators on prey has traditionally been attributed to the act of consumption. Prey responses to the presence of the predator (non-consumptive effects), however, can be as important as predation itself. While plant defences are known to influence predator-prey interactions, their relative effects on consumptive vs. non-consumptive effects are not well understood. 2. We evaluated the consequences of plant resistance and predators (Hippodamia convergens) on the mass, number of nymphs, population growth, density and dispersal of aphids (Macrosiphum euphorbiae). We tested for the effects of plant resistance on non-consumptive and consumptive effects of predators on aphid performance and dispersal using a combination of path analysis and experimental manipulation of predation risk. 3. We manipulated plant resistance using genetically modified lines of tomato (Solanum lycopersicum) that vary incrementally in the expression of the jasmonate pathway, which mediates induced resistance to insects and manipulated aphid exposure to lethal and risk predators. Predation risk predators had mandibles impaired to prevent killing. 4. Plant resistance reduced predation rate (consumptive effect) on high resistance plants. As a consequence, predators had no impact on the number of nymphs, aphid density or population growth on high resistance plants, whereas on low resistance plants, predators reduced aphid density by 35% and population growth by 86%. Path analysis and direct manipulation of predation risk showed that predation risk rather than predation rate promoted aphid dispersal and varied with host plant resistance. Aphid dispersal in response to predation risk was greater on low compared to high resistance plants. The predation risk experiment also showed that the number of aphid nymphs increased in the presence of risk predators but did not translate into increased population growth. 5. In conclusion, the consumptive and non-consumptive components of predators affect different aspects of prey demography, acting together to shape prey population dynamics. While predation risk accounts for most of the total effect of the predator on aphid dispersal and number of nymphs, the suppressive effect of predators on aphid population occurred largely through consumption. These effects are strongly influenced by plant resistance levels, suggesting that they are context dependent.

Potential Overwintering Locations of Soybean Aphid (Hemiptera: Aphididae) Colonizing Soybean in Ohio and Wisconsin.

Soybean aphids, Aphis glycines Matsumura, depend on long-distance, wind-aided dispersal to complete their life cycle. Despite our general understanding of soybean aphid biology, little is explicitly known about dispersal of soybean aphids between winter and summer hosts in North America. This study compared genotypic diversity of soybean aphids sampled from several overwintering locations in the Midwest and soybean fields in Ohio and Wisconsin to test the hypothesis that these overwintering locations are sources of the soybean colonists. In addition, air parcel trajectory analyses were used to demonstrate the potential for long-distance dispersal events to occur to or from these overwintering locations. Results suggest that soybean aphids from overwintering locations along the Illinois-Iowa border and northern Indiana-Ohio are potential colonists of soybean in Ohio and Wisconsin, but that Ohio is also colonized by soybean aphids from other unknown overwintering locations. Soybean aphids in Ohio and Wisconsin exhibit a small degree of population structure that is not associated with the locations of soybean fields in which they occur, but that may be related to specific overwintering environments, multiple introductions to North America, or spatial variation in aphid phenology. There may be a limited range of suitable habitat for soybean aphid overwintering, in which case management of soybean aphids may be more effective at their overwintering sites. Further research efforts should focus on discovering more overwintering locations of soybean aphid in North America, and the relative impact of short- and long-distance dispersal events on soybean aphid population dynamics.

Direct effect of ozone pollution on aphids: revisiting the evidence at individual and population scales

AbstractMost of our knowledge about the consequences of tropospheric ozone pollution on aphid–plant interaction assumes the absence of a direct effect of ozone on aphids. However, the biological effects of ozone encompass changes in reactive oxygen species signalling, oxidative stress accumulation, and the immune response of both plants and animals. The main objective of this work was to evaluate the direct effect of ozone on Metopolophium dirhodum (Walker) aphids (Hemiptera: Aphididae), linking mechanisms that operate at individual scale (oxidative stress parameters and aphid‐bacteria symbiosis persistence) with their consequences at population scale (mortality, dispersion, and population growth). Two experiments were conducted in open‐top chambers with three contrasting ozone exposure regimes (6 h at 0.5 ± 0.3, 50 ± 5, or 150 ± 10 p.p.b.) and artificial diets to evaluate the direct effect of ozone on aphids. Exposure of aphids to ozone increased insect mortality compared to the control treatment. However, the populations established from the surviving insects of each treatment increased similarly. Consistently, aphid symbiosis with Buchnera aphidicola Munson et al. (Proteobacteria) and Hamiltonella defensa Moran et al. (Enterobacteriaceae) persisted in all treatments. Ozone also affected aphid behaviour. The proportion of insects dispersing from diet cages was lower in the ozone treatments than in the control treatment. In addition, lipid peroxidation was higher at 150 p.p.b. than at 50 p.p.b. treatment, although not different from that in the control. The reduction in aphid dispersion coupled with increased mortality suggests that direct exposure to ozone could lower aphid efficiency as virus vectors. These results could be partially associated with mechanisms operating at individual scale (accumulation of oxidative damage). Overall, these experiments encourage reconsidering the impact of the direct effects of ozone on aphids when assessing the consequences of this component of global change on plant–aphid interactions.