Showing papers on "Aphid published in 2019"

Obligate bacterial endosymbionts limit thermal tolerance of insect host species.

Abstract: The thermal tolerance of an organism limits its ecological and geographic ranges and is potentially affected by dependence on temperature-sensitive symbiotic partners. Aphid species vary widely in heat sensitivity, but almost all aphids are dependent on the nutrient-provisioning intracellular bacterium Buchnera, which has evolved with aphids for 100 million years and which has a reduced genome potentially limiting heat tolerance. We addressed whether heat sensitivity of Buchnera underlies variation in thermal tolerance among 5 aphid species. We measured how heat exposure of juvenile aphids affects later survival, maturation time, and fecundity. At one extreme, heat exposure of Aphis gossypii enhanced fecundity and had no effect on the Buchnera titer. In contrast, heat suppressed Buchnera populations in Aphis fabae, which suffered elevated mortality, delayed development and reduced fecundity. Likewise, in Acyrthosiphon kondoi and Acyrthosiphon pisum, heat caused rapid declines in Buchnera numbers, as well as reduced survivorship, development rate, and fecundity. Fecundity following heat exposure is severely decreased by a Buchnera mutation that suppresses the transcriptional response of a gene encoding a small heat shock protein. Similarly, absence of this Buchnera heat shock gene may explain the heat sensitivity of Ap. fabae Fluorescent in situ hybridization revealed heat-induced deformation and shrinkage of bacteriocytes in heat-sensitive species but not in heat-tolerant species. Sensitive and tolerant species also differed in numbers and transcriptional responses of heat shock genes. These results show that shifts in Buchnera heat sensitivity contribute to host variation in heat tolerance.

Transmission of a New Polerovirus Infecting Pepper by the Whitefly Bemisia tabaci.

Abstract: Many animal and plant viruses depend on arthropods for their transmission. Virus-vector interactions are highly specific, and only one vector or one of a group of vectors from the same family is able to transmit a given virus. Poleroviruses (Luteoviridae) are phloem-restricted RNA plant viruses that are exclusively transmitted by aphids. Multiple aphid-transmitted polerovirus species commonly infect pepper, causing vein yellowing, leaf rolling, and fruit discoloration. Despite low aphid populations, a recent outbreak with such severe symptoms in many bell pepper farms in Israel led to reinvestigation of the disease and its insect vector. Here we report that this outbreak was caused by a new whitefly (Bemisia tabaci)-transmitted polerovirus, which we named Pepper whitefly-borne vein yellows virus (PeWBVYV). PeWBVYV is highly (>95%) homologous to Pepper vein yellows virus (PeVYV) from Israel and Greece on its 5' end half, while it is homologous to African eggplant yellows virus (AeYV) on its 3' half. Koch's postulates were proven by constructing a PeWBVYV infectious clone causing the pepper disease, which was in turn transmitted to test pepper plants by B. tabaci but not by aphids. PeWBVYV represents the first report of a whitefly-transmitted polerovirus.IMPORTANCE The high specificity of virus-vector interactions limits the possibility of a given virus changing vectors. Our report describes a new virus from a family of viruses strictly transmitted by aphids which is now transmitted by whiteflies (Bemisia tabaci) and not by aphids. This report presents the first description of polerovirus transmission by whiteflies. Whiteflies are highly resistant to insecticides and disperse over long distances, carrying virus inoculum. Thus, the report of such unusual polerovirus transmission by a supervector has extensive implications for the epidemiology of the virus disease, with ramifications concerning the international trade of agricultural commodities.

Aphid infestation leads to plant part-specific changes in phloem sap chemistry, which may indicate niche construction

Abstract: Phloem sap quality can differ between and within plants, and affect the performance of aphids. In turn, aphid infestation may change the chemical composition and nutritional value of phloem sap. However, the effects of different aphid species on the overall phloem sap composition of distinct parts within plant individuals in relation to aphid performance remain unclear. To test the specificity of plant responses to aphids, we used two chemotypes of Tanacetum vulgare plants and placed the monophagous aphids Macrosiphoniella tanacetaria and Uroleucon tanaceti on different plant parts (stems close to the inflorescence, young and old leaves). Aphid population growth was determined and sugars, organic acids, amino acids and metabolic fingerprints of phloem exudates were analysed. Macrosiphoniella tanacetaria performed best on stems, whereas U. tanaceti performed best on old leaves, indicating differences in niche conformance. Aphid infestation led to distinct changes in the phloem exudate composition of distinct metabolite classes, differing particularly between plant parts but less between chemotypes. In summary, plant responses to aphids are highly specific for the chemotype, plant part, metabolite class and aphid species. These changes may indicate that aphids construct their own niche, optimizing the food quality on the plant parts they prefer.

Topical dsRNA delivery induces gene silencing and mortality in the pea aphid

Abstract: BACKGROUND With the growing number of available aphid genomes and transcriptomes, an efficient and easy-to-adapt tool for gene function study is urgently required. RNA interference (RNAi), as a post-transcriptional gene silencing mechanism, is important as a research tool for determining gene functions and has potential as a novel insect control strategy. However, these applications have been hampered by the lack of effective dsRNA delivery approaches in aphids. RESULTS Here, we developed a convenient and efficient dsRNA delivery method, topical RNAi, in aphids. An investigation of its dose and time-dependent RNAi efficiencies revealed that with as little as 60 ng dsRNA per adult pea aphid (Acyrthosiphon pisum), the indicator gene, Aphunchback, could be significantly silenced within 2 h of exposure. The method was further validated by successfully silencing other different genes, and it was also efficient toward two other aphid species, Aphis citricidus and Myzus persicae. Furthermore, a noticeable mortality was also observed in pea aphids using topical RNAi-mediated gene silencing, within 4 days post-dsRNA application for four out of seven tested genes. CONCLUSION Compared with the currently used dsRNA delivery methods in aphids, microinjection and ingestion, topical RNAi is time- and cost-effective, which could greatly influence RNAi-based gene functional studies and potential candidate gene selection for developing RNAi-based aphid control strategies in the future. © 2019 Society of Chemical Industry.

Manipulation of Aphid Behavior by a Persistent Plant Virus.

Abstract: Plants are frequently infected with cytoplasmic RNA viruses that persist for many generations through nearly 100% vertical transmission without producing any symptoms. Movement between plant cells and horizontal transmission have not been observed with these viruses; instead, they are distributed to all host cells through host cell division. Jalapeno peppers (Capsicum annuum) are all infected with Pepper cryptic virus 1 (PCV-1; family Partitiviridae). We compared the effect of odor cues from PCV-1-infected (J+) and virus-free (J-) jalapeno peppers on the aphid Myzus persicae, a common vector of acute plant viruses. Pairwise preference experiments showed a stark contrast to insect-plant interactions in acute virus infections-that is, the virus-infected plants deterred aphids. The acute plant virus Cucumber mosaic virus (CMV) manipulates its host's volatile emissions to attract aphid vectors and facilitate its transmission. We inoculated J+ and J- plants with CMV. Volatiles of J+ and J- CMV-infected plants were more attractive to aphids than those of J+ and J- mock-inoculated plants. However, in pairwise preference experiments with J+ CMV- and J- CMV-infected plants, aphids preferred the J- CMV volatile blend. Aphid reproduction on J+ and J- plants was measured as an indicator of the effect of PCV-1 on host quality for aphids. Aphid reproduction on J+ plants was more than 2-fold lower than that on J- plants.IMPORTANCE This study demonstrates that a persistent plant virus can manipulate aphid behavior. This manipulation is in stark contrast to previously described effects of acute viruses on their hosts that facilitate their transmission. This study demonstrates a positive relationship between Pepper cryptic virus 1 and jalapeno pepper (Capsicum annuum) plants wherein the virus protects the plants from the vector of acute viruses and reduces aphid herbivory. This work reveals an important implication of persistent plant viruses for pest and pathogen management in agriculture.

Trichoderma atroviride P1 Colonization of Tomato Plants Enhances Both Direct and Indirect Defense Barriers Against Insects.

Abstract: Numerous microbial root symbionts are known to induce different levels of enhanced plant protection against a variety of pathogens. However, more recent studies have demonstrated that beneficial microbes are able to induce plant systemic resistance that confers some degree of protection against insects. Here, we report how treatments with the fungal biocontrol agent Trichoderma atroviride strain P1 in tomato plants induce responses that affect pest insects with different feeding habits: the noctuid moth Spodoptera littoralis (Boisduval) and the aphid Macrosiphum euphorbiae (Thomas). We observed that the tomato plant-Trichoderma P1 interaction had a negative impact on the development of moth larvae and on aphid longevity. These effects were attributed to a plant response induced by Trichoderma that was associated with transcriptional changes of a wide array of defense-related genes. While the impact on aphids could be related to the up-regulation of genes involved in the oxidative burst reaction, which occur early in the defense reaction, the negative performance of moth larvae was associated with the enhanced expression of genes encoding for protective enzymes (i.e., Proteinase inhibitor I (PI), Threonine deaminase, Leucine aminopeptidase A1, Arginase 2, and Polyphenol oxidase) that are activated downstream in the defense cascade. In addition, Trichoderma P1 produced alterations in plant metabolic pathways leading to the production and release of volatile organic compounds (VOCs) that are involved in the attraction of the aphid parasitoid Aphidius ervi, thus reinforcing the indirect plant defense barriers. Our findings, along with the evidence available in the literature, indicate that the outcome of the tripartite interaction among plant, Trichoderma, and pests is highly specific and only a comprehensive approach, integrating both insect phenotypic changes and plant transcriptomic alterations, can allow a reliable prediction of its potential for plant protection.

Insecticidal activity of the essential oil from Schizogyne sericea (Asteraceae) on four insect pests and two non-target species

Abstract: Salado (Schizogyne sericea) is an aromatic shrub occurring very frequently in the coastal areas of Tenerife, Canary Islands. Herein, we investigated whether the essential oil produced by salado under salt stress could be effective as a botanical insecticide against a panel of target insects such as larvae and adults of the filariasis vector Culex quinquefasciatus, the peach-potato aphid Myzus persicae, the housefly Musca domestica and the tobacco cutworm Spodoptera littoralis. The essential oil, which was characterized by p-cymene, isobornyl acetate and thymol esters, as detected by gas chromatographic analysis, was highly effective against larvae of C. quinquefasciatus (LC50 of 49.1 mL.L−1) and adults of M. persicae (LC50 of 2.1 mL.L−1). On the other hand, little toxicity was found on adult females of C. quinquefasciatus and M. domestica, as well as on larvae of S. littoralis. Finally, the S. sericea essential oil was not toxic to selected non-target organisms, 3rd instar larvae and adults of the ladybug Harmonia axyridis or adults of the earthworm Eisenia fetida. Overall, the present research supports a possible use of salado oil in eco-friendly insecticidal formulations useful to manage culicine larval populations as well as M. persicae aphids.

Development of Economic Thresholds for Sugarcane Aphid (Hemiptera: Aphididae) in Susceptible Grain Sorghum Hybrids.

Abstract: Sugarcane aphid, Melanaphis sacchari Zehtner (Hemiptera: Aphididae), outbreaks on grain sorghum were first detected in the United States in 2013. The spread of sugarcane aphid across the sorghum-producing regions of North America necessitated increased insecticide use to mitigate economic loss. A field experiment to develop economic thresholds for sugarcane aphid was conducted 15 times across seven locations across the southern United States during 3 yr (2014-2016). Grain sorghum hybrids were evaluated by measuring yield in response to a range of aphid infestations. Yield-aphid population density relationships were described by linear function, which facilitated calculating economic injury levels and economic thresholds. The slopes of the yield-aphid density regressions were significant, negative, and relatively stable across locations, years, and agronomic conditions. The relationships aggregated into two groups, populations that exhibited relatively slow and fast population growth, and common economic injury levels were determined using control costs and market values of grain. Average economic injury levels of 37 and 102 aphids per leaf were most applicable to the two groupings of sorghum/aphid relationships and aphid population growth. Using field-based sugarcane aphid population doubling time estimated from weekly observations of aphid densities, economic thresholds were calculated, ranging from 19 to 132 aphids per leaf across the 15 locations-years. Without site-specific knowledge of a slow-growing aphid population and given cost and market price variability of the system, a 40 aphid per leaf threshold is most prudent to use across the range of hybrid, environmental, and market conditions experienced in this study.

RNA interference-mediated knockdown of voltage-gated sodium channel (MpNav) gene causes mortality in peach-potato aphid, Myzus persicae.

Abstract: Voltage-gated sodium channels (VGSC) are transmembrane proteins that generate an action potential in excitable cells and play an essential role in neuronal signaling. Since VGSCs play a crucial role in nerve transmission they have become primary targets for a broad range of commercial insecticides. RNA interference (RNAi) is a valuable reverse genetics tool used in functional genomics, but recently, it has also shown promise as a novel agent that could be used to control agricultural insect pests. In this study, we targeted the VGSC (MpNav) gene in the peach-potato aphid Myzus persicae, by oral feeding of artificial diets mixed with dsRNAs. Knock-down of MpNav gene expression caused up to 65% mortality in 3rd instar nymphs. Moreover, significantly lower fecundity and longevity was observed in adult aphids that had been fed with dsMpNav solution at the nymphal stage. Analysis of gene expression by qRT-PCR indicated that the aphid mortality rates and the lowered fecundity and longevity were attributable to the down-regulation of MpNav by RNAi. Taken together, our results show that MpNav is a viable candidate target gene for the development of an RNAi-based bio-aphicide.

Effects of RNAi-based silencing of chitin synthase gene on moulting and fecundity in pea aphids (Acyrthosiphon pisum)

Abstract: The pea aphid, Acyrthosiphon pisum, is an important agricultural pest and an ideal model organism for various studies. Chitin synthase (CHS) catalyses chitin synthesis, a critical structural component of insect exoskeletons. Here, we identified a CHS gene from A. pisum, ApisCHS. The ApisCHS expression profiles showed that ApisCHS was expressed in various developmental stages and in all tested tissues of A. pisum, including the epidermis, embryo, gut and haemolymph. Notably, ApisCHS exhibited peak expression in the middle of each nymphal period and was extremely highly expressed in the epidermis and embryo. RNA interference (RNAi) showed that ~600 ng of dsRNA is an effective dose for gene silencing by injection for dsRNA delivery; moreover, 1200 ng·μL−1 dsRNA induced CHS gene silencing by a plant-mediated feeding approach. A 44.7% mortality rate and a 51.3% moulting rate were observed 72 h after injection of dsApisCHS into fourth-instar nymphs, compared with the levels in the control (injected with dsGFP). Moreover, a longer period was required for nymph development and a 44.2% deformity rate among newborn nymphs was obtained upon ingestion of dsApisCHS. These results suggest that ApisCHS plays a critical role in nymphal growth and embryonic development in pea aphids, and is a potential target for RNAi-based aphid pest control.

Transcriptional and Chemical Changes in Soybean Leaves in Response to Long-Term Aphid Colonization.

Abstract: Soybean aphids (Aphis glycines Matsumura) are specialized insects that feed on soybean (Glycine max) phloem sap. Transcriptome analyses have shown that resistant soybean plants mount a fast response that limits aphid feeding and population growth. Conversely, defense responses in susceptible plants are slower and it is hypothesized that aphids block effective defenses in the compatible interaction. Unlike other pests, aphids can colonize plants for long periods of time; yet the effect on the plant transcriptome after long-term aphid feeding has not been analyzed for any plant-aphid interaction. We analyzed the susceptible and resistant (Rag1) transcriptome response to aphid feeding in soybean plants colonized by aphids (biotype 1) for 21 days. We found a reduced resistant response and a low level of aphid growth on Rag1 plants, while susceptible plants showed a strong response consistent with pattern-triggered immunity. GO-term analyses identified chitin regulation as one of the most overrepresented classes of genes, suggesting that chitin could be one of the hemipteran-associated molecular pattern that triggers this defense response. Transcriptome analyses also indicated the phenylpropanoid pathway, specifically isoflavonoid biosynthesis, was induced in susceptible plants in response to long-term aphid feeding. Metabolite analyses corroborated this finding. Aphid-treated susceptible plants accumulated daidzein, formononetin, and genistein, although glyceollins were present at low levels in these plants. Choice experiments indicated that daidzein may have a deterrent effect on aphid feeding. Mass spectrometry imaging showed these isoflavones accumulate likely in the mesophyll cells or epidermis and are absent from the vasculature, suggesting that isoflavones are part of a non-phloem defense response that can reduce aphid feeding. While it is likely that aphid can initially block defense responses in compatible interactions, it appears that susceptible soybean plants can eventually mount an effective defense in response to long-term soybean aphid colonization.

Defence gene expression and phloem quality contribute to mesophyll and phloem resistance to aphids in wild barley.

Abstract: Aphids, including the bird cherry-oat aphid (Rhopalosiphum padi), are significant agricultural pests. The wild relative of barley, Hordeum spontaneum 5 (Hsp5), has been described to be partially resistant to R. padi, with this resistance proposed to involve higher thionin and lipoxygenase gene expression. However, the specificity of this resistance to aphids and its underlying mechanistic processes are unknown. In this study, we assessed the specificity of Hsp5 resistance to aphids and analysed differences in aphid probing and feeding behaviour on Hsp5 and a susceptible barley cultivar (Concerto). We found that partial resistance in Hsp5 to R. padi extends to two other aphid pests of grasses. Using the electrical penetration graph technique, we show that partial resistance is mediated by phloem- and mesophyll-based resistance factors that limit aphid phloem ingestion. To gain insight into plant traits responsible for partial resistance, we compared non-glandular trichome density, defence gene expression, and phloem composition of Hsp5 with those of the susceptible barley cultivar Concerto. We show that Hsp5 partial resistance involves elevated basal expression of thionin and phytohormone signalling genes, and a reduction in phloem quality. This study highlights plant traits that may contribute to broad-spectrum partial resistance to aphids in barley.

Ethylene signaling mediates potyvirus spread by aphid vectors.

Abstract: Plant pathogens can influence host characteristics such as volatile emissions, nutrient composition or plant color, modulating vector and non-vector insect dynamics in the ecosystem. While previous research has focused on insect attraction and dispersal to infected plants, little is known about mechanisms mediating these interactions. Here, we investigate the role of ethylene in green peach aphid (Myzus persicae) attraction to potyvirus-infected plants. In our experiments, we utilized two different potyviruses, Potato virus Y (PVY) and Turnip mosaic virus, in lab and field experiments. Consistent with previous studies, we show that greater numbers of aphids settle on potyvirus-infected plants in the lab and greater numbers of aphids are found in PVY-infected potato (Solanum tuberosum) fields compared to controls. In laboratory experiments, inhibition of ethylene signaling in plants either chemically or genetically prevented aphids from preferentially settling on potyvirus-infected plants. Virus spread was reduced in lab arenas by over 80% when ethylene signaling was inhibited chemically. Despite this, ethylene inhibition had no significant impact on virus spread in field mesocosms. Our results indicate that induction of ethylene signaling by potyviruses mediates aphid attraction to infected plants and virus spread; however, additional factors may contribute to plant-vector dynamics in complex communities. Specific components of ethylene signaling may be important targets for future management of vector-borne viruses and research on mechanisms mediating plant-vector-virus interactions.

Untargeted Metabolomics Approach Reveals Differences in Host Plant Chemistry Before and After Infestation With Different Pea Aphid Host Races

Abstract: The pea aphid (Acyrthosiphon pisum), a phloem-sucking insect, has undergone a rapid radiation together with the domestication and anthropogenic range expansion of several of its legume host plants. This insect species is a complex of at least 15 genetically different host races that can all develop on the universal host plant Vicia faba. However, each host race is specialized on a particular plant species, such as Medicago sativa, Trifolium pratense, or Pisum sativum, which makes it an attractive model insect to study ecological speciation. Previous work revealed that pea aphid host plants produce a specific phytohormone profile depending on the host plant - host race combination. Native aphid races induce lower defense hormone levels in their host plant than non-native pea aphid races. Whether these changes in hormone levels also lead to changes in other metabolites is still unknown. We used a mass spectrometry-based untargeted metabolomic approach to identify plant chemical compounds that vary among different host plant-host race combinations and might therefore, be involved in pea aphid host race specialization. We found significant differences among the metabolic fingerprints of the four legume species studied prior to aphid infestation, which correlated with aphid performance. After infestation, the metabolic profiles of M. sativa and T. pratense plants infested with their respective native aphid host race were consistently different from profiles after infestation with non-native host races and from uninfested control plants. The metabolic profiles of P. sativum plants infested with their native aphid host race were also different from plants infested with non-native host races, but not different from uninfested control plants. The compounds responsible for these differences were putatively identified as flavonoids, saponins, non-proteinogenic amino acids and peptides among others. As members of these compound classes are known for their activity against insects and aphids in particular, they may be responsible for the differential performance of host races on native vs. non-native host plants. We conclude that the untargeted metabolomic approach is suitable to identify candidate compounds involved in the specificity of pea aphid - host plant interactions.

Invasive Cereal Aphids of North America: Ecology and Pest Management

Abstract: Aphid invasions of North American cereal crops generally have started with colonization of a new region or crop, followed by range expansion and outbreaks that vary in frequency and scale owing to geographically variable influences. To improve understanding of this process and management, we compare the invasion ecology of and management response to three cereal aphids: sugarcane aphid, Russian wheat aphid, and greenbug. The region exploited is determined primarily by climate and host plant availability. Once an area is permanently or annually colonized, outbreak intensity is also affected by natural enemies and managed inputs, such as aphid-resistant cultivars and insecticides. Over time, increases in natural enemy abundance and diversity, improved compatibility among management tactics, and limited threshold-based insecticide use have likely increased resilience of aphid regulation. Application of pest management foundational practices followed by a focus on compatible strategies are relevant worldwide. Area-wide pest management is most appropriate to large-scale cereal production systems, as exemplified in the Great Plains of North America.

Categories of Resistance to Sugarcane Aphid (Hemiptera: Aphididae) Among Sorghum Genotypes.

Abstract: The sugarcane aphid Melanaphis sacchari (Zehnter) (Hemiptera: Aphididae) has emerged as a potential threat to sorghum (Sorghum bicolor (L.) Moench) production in the United States. Since the late summer of 2013, finding and advancing M. sacchari-resistant germplasm has been a priority for all stakeholders involved. We evaluated 23 sorghum genotypes for resistance to the sugarcane aphid by testing for tolerance, and antixenosis. In addition, nine sorghum germplasm were evaluated for the expression of antibiosis. Free-choice and no-choice tests were conducted to explore the functional categories of resistance. Levels of resistance to M. sacchari were compared with the known resistant 'TX 2783' and the susceptible 'KS 585'. Sorghum entries AG1201, AG1301, W844-E, and DKS 37-07 were identified as expressing tolerance, antibiosis, and antixenosis, while H13073 expressed antibiosis and GW1489 expressed both tolerance and antibiosis. These resistant sorghums identified during this study will have a significant impact on reducing economic damage from the sugarcane aphid infestations.

Pectin Methylesterases Modulate Plant Homogalacturonan Status in Defenses against the Aphid Myzus persicae

Abstract: Because they suck phloem sap and act as vectors for phytopathogenic viruses, aphids pose a threat to crop yields worldwide. Pectic homogalacturonan (HG) has been described as a defensive element for plants during infections with phytopathogens. However, its role during aphid infestation remains unexplored. Using immunofluorescence assays and biochemical approaches, the HG methylesterification status and associated modifying enzymes during the early stage of Arabidopsis (Arabidopsis thaliana) infestation with the green peach aphid (Myzus persicae) were analyzed. Additionally, the influence of pectin methylesterase (PME) activity on aphid settling and feeding behavior was evaluated by free choice assays and the Electrical Penetration Graph technique, respectively. Our results revealed that HG status and HG-modifying enzymes are significantly altered during the early stage of the plant-aphid interaction. Aphid infestation induced a significant increase in total PME activity and methanol emissions, concomitant with a decrease in the degree of HG methylesterification. Conversely, inhibition of PME activity led to a significant decrease in the settling and feeding preference of aphids. Furthermore, we demonstrate that the PME inhibitor AtPMEI13 has a defensive role during aphid infestation, since pmei13 mutants are significantly more susceptible to M. persicae in terms of settling preference, phloem access, and phloem sap drainage.

Global Responses of Resistant and Susceptible Sorghum (Sorghum bicolor) to Sugarcane Aphid (Melanaphis sacchari).

Abstract: The sugarcane aphid (Melanaphis sacchari) has emerged as a significant pest for sorghum. The use of sugarcane aphid-resistant sorghum germplasm with integrated pest management strategies appears to be an excellent solution to this problem. In this study, a resistant line (RTx2783) and a susceptible line (A/BCK60) were used to characterize the differences in plant responses to the sugarcane aphid through a series of experiments, which examined global sorghum gene expression, aphid feeding behavior and inheritance of aphid resistance. The global transcriptomic responses to sugarcane aphids in resistant and susceptible plants were identified using RNA-seq and compared to the expression profiles of uninfested plants at 5, 10, and 15 days post-infestation. The expression of genes from several functional categories were altered in aphid-infested susceptible plants, which included genes related to cell wall modification, photosynthesis and phytohormone biosynthesis. In the resistant line, only 31 genes were differentially expressed in the infested plants relative to uninfested plants over the same timecourse. However, network analysis of these transcriptomes identified a co-expression module where the expression of multiple sugar and starch associated genes were repressed in infested resistant plants at 5 and 10 days. Several nucleotide-binding-site, leucine-rich repeat (NBS-LRR) and disease resistance genes similar to aphid resistance genes identified in other plants are identified in the current study which may be involved in sugarcane aphid resistance. The electrical penetration graph (EPG) results indicated that sugarcane aphid spent approximately twice as long in non-probing phase, and approximately a quarter of time in phloem ingestion phase on the resistant and F1 plants compared to susceptible plant. Additionally, network analysis identified a phloem protein 2 gene expressed in both susceptible and resistant plants early (day 5) of infestation, which may contribute to defense against aphid feeding within sieve elements. The resistant line RTx2783 displayed both antixenosis and antibiosis modes of resistance based on EPG and choice bioassays between susceptible, resistant and F1 plants. Aphid resistance from RTx2783 segregated as a single dominant locus in the F2 generation, which will enable breeders to rapidly develop sugarcane aphid-resistant hybrids using RTx2783 as the male parent.

Pathogenic modification of plants enhances long-distance dispersal of nonpersistently transmitted viruses to new hosts.

Abstract: Aphids spread the majority of plant viruses through nonpersistent transmission (NPT), whereby virus particles attach transiently to these insects' probing mouthparts. Virus acquisition from infected plants and inoculation to healthy host plants is favored when aphids briefly probe plant epidermal cells. It is well established that NPT virus infection can alter plant-vector interactions, and, moreover, such pathogen modifications are found in a range of plant and animal systems. In particular, viruses can make plants more attractive to aphids but inhibit aphid settling on infected plants. It is hypothesized that this viral "reprogramming" of plants promotes virus acquisition and encourages dispersal of virus-bearing aphids to fresh hosts. In contrast, it is hypothesized that virus-induced biochemical changes encouraging prolonged feeding on infected hosts inhibit NPT. To understand how these virus-induced modifications affect epidemics, we developed a modeling framework accounting for important but often neglected factors, including feeding behaviors (probing or prolonged feeding) and distinct spatial scales of transmission (as conditioned by wingless or winged aphids). Analysis of our models confirmed that when viruses inhibit aphid settling on infected plants this initially promotes virus transmission. However, initially enhanced transmission is self-limiting because it decreases vector density. Another important finding is that virus-induced changes encouraging settling will stimulate birth of winged aphids, which promotes epidemics of NPT viruses over greater distances. Thus our results illustrate how plant virus modifications influence epidemics by altering vector distribution, density, and even vector form. Our insights are important for understanding how pathogens in general propagate through natural plant communities and crops.

Silencing an essential gene involved in infestation and digestion in grain aphid through plant-mediated RNA interference generates aphid-resistant wheat plants.

Abstract: Aphids are major agricultural pests which cause significant yield losses of crop plants each year by inflicting damage, both through the direct effects of feeding and by vectoring debilitating plant viruses. In the absence of genetic plant resistance, insecticide treatments remain the main means for aphid control. However, excessive dependence on insecticides is undesirable because of the development of insecticide resistance, the potential negative effects on non-target organisms and environmental pollution (Yu et al., 2014). This article is protected by copyright. All rights reserved.

Aphid effector Me10 interacts with tomato TFT7, a 14-3-3 isoform involved in aphid resistance

Abstract: We demonstrated previously that expression of Macrosiphum euphorbiae salivary protein Me10 enhanced aphid reproduction on its host tomato (Solanum lycopersicum). However, the mechanism of action of Me10 remained elusive. To confirm the secretion of Me10 by the aphid into plant tissues, we produced Me10 polyclonal antibodies. To identify the plant targets of Me10, we developed a tomato immune induced complementary DNA yeast two-hybrid library and screened it with Me10 as bait. Immunoprecipitation and bimolecular fluorescence complementation (BiFC) assays were performed to validate one of the interactions in planta, and virus-induced gene silencing was used for functional characterization in tomato. We demonstrated that Me10 is secreted into the plant tissues and interacts with tomato 14-3-3 isoform 7 (TFT7) in yeast. Immunoprecipitation assays confirmed that Me10 and its homologue in Aphis gossypii, Ag10k, interact with TFT7 in planta. Further, BiFC revealed that Me10 interaction with TFT7 occurs in the plant cell cytoplasm. While silencing of TFT7 in tomato leaves did not affect tomato susceptibility to M. euphorbiae, it enhanced longevity and fecundity of A. gossypii, the non-host aphid. Our results suggest the model whereby TFT7 plays a role in aphid resistance in tomato and effectors of the Me10/Ag10k family interfere with TFT7 function during aphid infestation.

The preference-performance relationship as a means of classifying parasitoids according to their specialization degree.

Abstract: Host range in parasitoids could be described by the preference-performance hypothesis (PPH) where preference is defined as host acceptance and performance is defined as the sum of all species on which parasitoid offspring can complete their life cycle. The PPH predicts that highly suitable hosts will be preferred by ovipositing females. However, generalist parasitoids may not conform to this hypothesis if they attack a large range of hosts of varying suitability. Under laboratory conditions, we tested the PPH relationship of three aphid parasitoids currently considered as generalist species (Aphelinus abdominalis, Aphidius ervi, Diaeretiella rapae). As expected, the three parasitoids species showed low selectivity, i.e., females stung all aphid species encountered (at least in some extent). However, depending on the parasitoid species, only 42%-58% of aphid species enabled producing parasitoid offspring. We did not find a correlation between the extent of preference and the performance of three generalist aphid parasitoids. For A. ervi, host phylogeny is also important as females showed higher attack and developmental rates on hosts closely related to the most suitable one. In addition, traits such as (a) the presence of protective secondary endosymbionts, for example, Hamiltonella defensa detected in Aphis fabae and Metopolophium dirhodum and (b) the sequestration of plant toxins as defense mechanism against parasitism, for example, in Aphis nerii and Brevicoryne brassicae, were likely at play to some extent in narrowing parasitoid host range. The lack of PPH relationship involved a low selectivity leading to a high adaptability, as well as selection pressure; the combination of which enabled the production of offspring in a new host species or a new environment. Testing for PPH relationships in parasitoids may provide useful cues to classify parasitoids in terms of specialization degree.

Bottom-up effects of endophytic Beauveria bassiana on multitrophic interactions between the cotton aphid, Aphis gossypii , and its natural enemies in melon

Abstract: Entomopathogenic fungi are now known to have an endophytic capacity that induces a wide range of changes in the composition of plant nutrients and/or defensive compounds. These changes could influence interactions between the plant and higher trophic levels. In this study, we evaluated the predation/parasitism efficacy of larvae of the lacewing, Chrysoperla carnea, and the braconid parasitoid, Aphidius colemani, when offered aphids that had been challenged by the entomopathogenic fungus Beauveria bassiana. Aphids were either inoculated directly with a fungal suspension (lacewing bioassay only) or had been feeding on melon plants endophytically colonized by B. bassiana. Our results indicate that B. bassiana application did not significantly influence the number of aphid prey consumed by lacewings, or the time took them to consume each aphid. In a choice bioassay, C. carnea larvae preferred to feed on aphids reared on B. bassiana-colonized plants compared with control plants. In another choice assay, the number of aphids parasitized by A. colemani and their sex ratio were not influenced by whether the aphids had been feeding on B. bassiana-colonized plants or not. Our findings support the hypothesis that endophytic entomopathogenic fungi can be used in combination with other natural enemies, such as predators and parasitoids, in Integrated Pest Management programmes.

Host relatedness influences the composition of aphid microbiomes

Abstract: Animals are host to a community of microbes, collectively referred to as their microbiome, that can play a key role in their hosts' biology. The bacterial endosymbionts of insects have a particularly strong influence on their hosts, but despite their importance we still know little about the factors that influence the composition of insect microbial communities. Here, we ask: what is the relative importance of host relatedness and host ecology in structuring symbiont communities of diverse aphid species? We used next-generation sequencing to compare the microbiomes of 46 aphid species with known host plant affiliations. We find that relatedness between aphid species is the key factor explaining the microbiome composition, with more closely related aphid species housing more similar bacterial communities. Endosymbionts dominate the microbial communities, and we find a novel bacterium in the genus Sphingopyxis that is associated with numerous aphid species feeding exclusively on trees. The influence of ecology was less pronounced than that of host relatedness. Our results suggest that co-adaptation between insect species and their facultative symbionts is a more important determinant of symbiont species presence in aphids than shared ecology of hosts.

CIRCADIAN CLOCK-ASSOCIATED1 Controls Resistance to Aphids by Altering Indole Glucosinolate Production

Abstract: CIRCADIAN CLOCK-ASSOCIATED1 (CCA1), a well-known central circadian clock regulator, coordinates plant responses to environmental challenges. Its daily rhythmic expression in Arabidopsis (Arabidopsis thaliana) confers host resistance to the caterpillar Trichoplusia ni. However, it is unclear whether CCA1 plays a role in defense against phloem sap-feeding aphids. In this study, we showed that green peach aphid (Myzus persicae) displayed an intrinsic circadian feeding rhythm. Under constant light, wild-type Columbia-0 (Col-0) Arabidopsis plants coentrained with aphids in the same light/dark cycles exhibited greater antixenotic activity than plants preentrained in the opposite cycle from the aphids. Consistently, circadian mutants cca1-1, cca1-11, lhy-21, ztl-1, ztl-4, and lux-2 suffered more severe damage than Col-0 plants when infested by aphids, suggesting that the Arabidopsis circadian clock plays a defensive role. However, the arrhythmic CCA1 overexpression line (CCA1-OX) displayed strong antixenotic and antibiotic activities despite its loss of circadian regulation. Aphids feeding on CCA1-OX plants exhibited lower reproduction and smaller body size and weight than those on Col-0. Apparently, CCA1 regulates both clock-dependent and -independent defense responses. Systematic investigation based on bioinformatics analyses indicated that resistance to aphids in CCA1-OX plants was due primarily to heightened basal indole glucosinolate levels. Interestingly, aphid feeding induced alternatively spliced intron-retaining CCA1a/b transcripts, which are normally expressed at low levels, whereas expression of the major fully spliced CCA1 transcript remained largely unchanged. We hypothesize that posttranscriptional modulation of CCA1 expression upon aphid infestation maximizes the potential of circadian-mediated defense and stress tolerance while ensuring normal plant development.