Showing papers on "Aphid published in 2021"

Aphid diversity in two food legume crops: fava bean and pea in Naciria region, and first record of Melanaphis sacchari (Zehntner, 1897) in Algeria

Abstract: Beans and peas are very important legumes because of their importance in human food and their high protein contents, as well as their role in the supply of atmospheric nitrogen to the soil. However, these crops are subject to various pest outbreaks, reducing their yield. The purpose of this study is to carry out an exhaustive inventory of aphids present on bean (Faba bean and Seville variety) and pea crops (Merveille De Kelvedone and Utrillo variety) in the region of Naciria (Boumerdes), in order to evaluate the diversity and abundance of aphids present in these crops. Sampling of aphid populations has been done using two trapping techniques: Barber pitfall trap and yellow traps. The results obtained express a richness of 48 aphid species, with one Melanaphis sacchari species identified for the first time in Algeria. 28 species are inventoried in the pea crop of Utrillo variety, 27 species on the Merveille de Kelvedone variety, 21 species in the bean crop of Seville variety (Vicia faba major) and 20 species on the faba bean (Vicia faba minor).

Nanocarrier-delivered dsRNA suppresses wing development of green peach aphids.

Abstract: RNA interference (RNAi) has developed rapidly as a potential 'green' pest management strategy. At present, most studies have focused on the screening of aphid lethal genes, whereas only a few studies have been conducted on wing development, which is crucial for aphid migration and plant-virus dissemination. Here, the Myzus persicae genes vestigial (vg) and Ultrabithorax (Ubx) related to wing development, were cloned. These two genes were expressed in various tissues of 3rd-instar winged aphids. The mRNA level of vg was high in 3rd -instar nymphs, whereas the expression level of Ubx was high in adults. The nanocarrier-mediated delivery system delivered double-stranded RNAs for aphid RNAi using topical and root applications. The expression levels of vg and Ubx were down-regulated by 44.0% and 36.5% respectively, using the topical application. The simultaneous RNAi of the two target genes caused 63.3% and 32.2% wing aberration rates using topical and root applications, respectively. The current study provided a promising method for controlling aphid migration to alleviate the spread of insect transmitted plant diseases. This article is protected by copyright. All rights reserved.

Long-term studies on the evolution of resistance of Myzus persicae (Hemiptera: Aphididae) to insecticides in Greece

Abstract: The aphid Myzus persicae s.l. (Hemiptera: Aphididae) is an important pest of many crops worldwide with a complex life cycle, intensely controlled by chemical pesticides, and has developed resistance to almost all used insecticides. In Greece, the aphid exhibits high genetic variation and adaptability and it is a classic example of evolution in the making. We have been studying M. persicae for over 20 years, on different host plants and varying geographical areas, analyzing its bio-ecology and the ability to develop resistance to insecticides. In this review, we present new and historical data on the effectiveness of insecticides from seven chemical groups used to control the aphid in Greece and the incidence of seven resistance mechanisms, including the new fast-spreading R81T point mutation of the postsynaptic nicotinic acetylcholine receptor. Thousands of samples were tested by biological, biochemical and molecular assays. The aphid populations were found to have developed and maintain resistance at medium to high levels to organophosphates, carbamates, pyrethroids and neonicotinoids for decades. In the latter group, a marked increase is recorded during an ~10-year period. The data analyzed and the extensive bibliography, advocate the difficulty to control the aphid making the design and application of IPM/IRM programs a challenge. We discuss principles and recommendations for the management of resistance, including the use of compounds such as flonicamid, spirotetramat, flupyradifurone and sulfoxaflor. We emphasize that resistance is a dynamic phenomenon, changing in time and space, requiring, therefore, continuous monitoring.

Seed inoculations with entomopathogenic fungi affect aphid populations coinciding with modulation of plant secondary metabolite profiles across plant families

Abstract: Entomopathogenic fungi (EPF) can display a plant-associated lifestyle as endophytes. Seed application of EPF can affect insect herbivory above ground, but the mechanisms behind this are not documented. Here we applied three EPF isolates, Beauveria bassiana, Metarhizium brunneum and M. robertsii, as seed inoculation of wheat and bean, and evaluated the effects on population growth of aphids, Rhopalosiphum padi and Aphis fabae, respectively. In wheat and bean leaves, we quantified benzoxazinoids and flavonoids, respectively, in response to EPF inoculation and aphid infestation to elucidate the role of specific plant secondary metabolites (PSMs) in plant-fungus-herbivore interactions. Inoculations of wheat and bean with M. robertsii and B. bassiana reduced aphid populations compared with control treatments, whereas M. brunneum unexpectedly increased the populations of both aphids. Concentrations of the majority of PSMs were differentially altered in EPF-treated plants infested with aphids. Changes in aphid numbers were associated with PSMs regulation rather than EPF endophytic colonisation capacity. This study links the effects of EPF seed inoculations against aphids with unique PSM accumulation patterns in planta. The understanding of PSM regulation in tri-trophic interactions is important for the future development of EPF for pest management.

Diversity of bacteria associated with Hormaphidinae aphids (Hemiptera: Aphididae).

Abstract: Bacteria are ubiquitous inhabitants of animals. Hormaphidinae is a particular aphid group exhibiting very diverse life history traits. However, the microbiota in this group is poorly known. In the present study, using high-throughput sequencing of bacterial 16S ribosomal RNA gene amplicons, we surveyed the bacterial flora in hormaphidine aphids and explored whether the aphid tribe, host plant and geographical distribution are associated with the distribution of secondary symbionts. The most dominant bacteria detected in hormaphidine species are heritable symbionts. As expected, the primary endosymbiont Buchnera aphidicola is the most abundant symbiont across all species and has cospeciated with its host aphids. Six secondary symbionts were detected in Hormaphidinae. Arsenophonus is widespread in Hormaphidinae species, suggesting the possibility of ancient acquisition of this symbiont. Ordination analyses and statistical tests show that the symbiont composition does not seem to relate to any of the aphid tribes, host plants or geographical distributions, which indicate that horizontal transfers might occur for these symbionts in Hormaphidinae. Correlation analysis exhibits negative interference between Buchnera and coexisting secondary symbionts, while the interactions between different secondary symbionts are complicated. These findings display a comprehensive picture of the microbiota in Hormaphidinae and may be helpful in understanding the symbiont diversity within a group of aphids.

Reduced insecticide susceptibility of the wheat aphid Sitobion miscanthi after infection by the secondary bacterial symbiont Hamiltonella defensa

Abstract: Background Bacterial symbionts in insects, especially aphids, have a major influence on host adaptation. We previously showed that infection with the secondary symbiont Hamiltonella defensa increases the fitness of the wheat aphid Sitobion miscanthi, yielding increases in fitness parameters such as adult weight and offspring number. However, whether H. defensa affects the sensitivity of host aphids to insecticides remains unknown. Results We tested the effects of H. defensa on host aphid susceptibility to the insecticides chlorpyrifos methyl, imidacloprid, cyantraniliprole and acetamiprid. Our results showed that compared with Hamiltonella-free aphid clones, Hamiltonella-infected aphid clones exhibited lower sensitivity to most of the tested insecticides at low concentrations. Quantitative polymerase chain reaction showed that the density of H. defensa in the infected clones was slightly decreased at 24 h but then sharply increased until the late stage after treatment with the different insecticides. H. defensa in the host aphids was detected by fluorescence in situ hybridization and was localized to the aphid hindgut. Levels of the detoxification enzymes acetylcholinesterase, glutathione transferase and carboxylesterase were significantly higher in Hamiltonella-infected clones than in Hamiltonella-free clones. Conclusions The findings indicated that infection with H. defensa reduced aphid susceptibility to the investigated insecticides at low concentrations, potentially by increasing detoxification enzyme activity in the host. Therefore, symbiont-mediated insecticide resistance should be taken into account when performing resistance-monitoring studies. Studies of symbiont-mediated insecticide resistance may enhance our understanding of the emergence of insecticide resistance in agricultural systems. © 2020 Society of Chemical Industry.

Leaf structural traits rather than drought resistance determine aphid performance on spring wheat

Abstract: Drought represents one of the most severe constraints to agricultural production; therefore, resistance to drought has the highest priority in the development of new cultivars. How insect pests respond to drought-resistant cultivars is poorly understood. In this study, by using the rose-grain aphid, Metopolophium dirhodum (Walker), in controlled laboratory conditions, we investigated the level of antibiosis of six commercially available cultivars of spring wheat (Triticum aestivum L.), which differed in their resistance to drought (drought-resistant cultivars: Septima, Jarissa and Seance; drought-sensitive cultivars: Quintus, Kabot and SW Kadrilj). Leaf morphological and structural traits were also measured for each cultivar to determine which leaf traits may be responsible for the observed differences. We used an age-stage, two-sex life table approach for comprehensive quantification of the aphid response to a particular cultivar and for projecting population growth. Although we found significant differences in all the life table and population growth parameters between the cultivars (SW Kadrilj was the most resistant to the aphids and Septima and Quintus were the most susceptible to the aphids), resistance to drought alone did not explain the observed variation. The cultivars also varied in most of the morphological and structural leaf traits measured. An increase in cuticle thickness at the cell junction above the major vein hampered the development of the aphid nymphs, which resulted in slower rates of population increase. Trichome density seemed to reduce the survival of the aphid nymphs. These two traits support not only drought resistance in general but also resistance to aphids and are potentially useful for selection in the future breeding of cereals.

Aphidophagous hoverflies reduce foxglove aphid infestations and improve seed set and fruit yield in sweet pepper.

Abstract: Background Larvae of many hoverfly species prey upon aphids, whereas the adults, by relying on nectar and pollen, contribute to the pollination of many plant species. Despite their great potential for pest control and pollination, important gaps still exist regarding the efficacy of hoverflies in regulating infestations of major aphid pests in augmentative biological control programs. Here, we tested the potential of the commercially available hoverflies Eupeodes corollae and Sphaerophoria rueppellii to regulate populations of the foxglove aphid Aulacorthum solani in sweet pepper. Results In a semi-field experiment, aphid numbers were 93.2% and 78.4% lower in the E. corollae and S. rueppellii treatments, respectively, compared to the control. Fruit yield was increased by 390% and 361% and seed set by 395% and 399% for E. corollae and S. rueppellii. In a separate laboratory trial, we found that under conditions of limited prey, hoverfly larvae did not complete development, but that larvae of S. rueppellii survived significantly longer than larvae of E. corollae. Conclusion We have shown for the first time that E. corollae and S. rueppellii can reduce infestations of foxglove aphid in sweet pepper. The limited amount of prey, related to the small size of the A. solani colonies, means that hoverfly larvae were often not able to complete development. In practice, repeated releases of hoverflies possibly in combination with other natural enemies might be used to achieve effective suppression of A. solani infestations. This article is protected by copyright. All rights reserved.

Involvement of chemosensory proteins in host plant searching in the bird cherry-oat aphid

Abstract: Chemosensory systems are considered to play an important role in host plant selection in herbivorous insects. However, few studies have focused on chemosensory proteins (CSPs) for aphid host-location mechanisms. The roles of CSPs in searching for different Poaceae species (wheat, barley, triticale, maize and sorghum) were tested in Rhopalosiphum padi, an important cereal pest. The olfactometer assays showed that R. padi responds to plant odors. Seven R. padi CSP genes were identified. Influence of aphid morph, tissue and starvation state on expression patterns of CSPs was evaluated. Expression levels of CSP1, CSP4, CSP5 and CSP6 in winged aphids were significantly higher than those in wingless ones. Transcription levels of four genes (CSP1, CSP4, CSP5 and CSP6) were relatively higher in the head with antennae, and the four genes tended to be upregulated following starvation. Silencing of three CSPs (CSP4, CSP5 and CSP6) altered aphid host-location behavior in response to the five different host plants tested. Three volatile compounds of host plants (octanal, [E]-2-hexenol and linalool) have significant attraction to winged R. padi according to the four-arm olfactometer tests. Molecular docking predicted hydrogen bonding sites which played key roles in the binding of CSP4, CSP5 and CSP6 with volatile compounds. Knockdown of CSP4 or CSP5 significantly decreased the staying time of R. padi in the arms with octanal. However, knockdown of CSP6 could not affect the response of R. padi to octanal. These results bring evidence for the involvement of three CSPs in R. padi host-location behavior.

Combining host plant resistance and foliar insecticide application to manage Melanaphis sacchari (Hemiptera: Aphididae) in grain sorghum

Abstract: Sugarcane aphid, Melanaphis sacchari (Zehtner), recently emerged as a severe economic pest of sorghum in the USA. This insect was first discovered in the USA feeding on grain sorghum in Texas in 20...

Engineering a Culturable Serratia symbiotica Strain for Aphid Paratransgenesis

Abstract: Aphids are global agricultural pests and important models for bacterial symbiosis. To date, none of the native symbionts of aphids have been genetically manipulated, which limits our understanding of how they interact with their hosts. Serratia symbiotica CWBI-2.3T is a culturable, gut-associated bacterium isolated from the black bean aphid. Closely related Serratia symbiotica strains are facultative aphid endosymbionts that are vertically transmitted from mother to offspring during embryogenesis. We demonstrate that CWBI-2.3T can be genetically engineered using a variety of techniques, plasmids, and gene expression parts. Then, we use fluorescent protein expression to track the dynamics with which CWBI-2.3T colonizes the guts of multiple aphid species, and we measure how this bacterium affects aphid fitness. Finally, we show that we can induce heterologous gene expression from engineered CWBI-2.3T in living aphids. These results inform the development of CWBI-2.3T for aphid paratransgenesis, which could be used to study aphid biology and enable future agricultural technologies.IMPORTANCE Insects have remarkably diverse and integral roles in global ecosystems. Many harbor symbiotic bacteria, but very few of these bacteria have been genetically engineered. Aphids are major agricultural pests and an important model system for the study of symbiosis. This work describes methods for engineering a culturable aphid symbiont, Serratia symbiotica CWBI-2.3T These approaches and genetic tools could be used in the future to implement new paradigms for the biological study and control of aphids.

Seed priming with calcium chloride enhances wheat resistance against wheat aphid Schizaphis graminum Rondani

Abstract: Background Calcium is an essential macronutrient for plant growth. Although it has been shown that exogenous Ca application can increase plant resistance to abiotic stress, little is known about its potential to enhance plant tolerance to biotic stress. Here, we investigated whether pretreatment of wheat (Triticum aestivum L.) seeds with calcium chloride (CaCl2 ) improves plant resistance against wheat aphid (Schizaphis graminum Rondani). The developmental time, population size, feeding behavior of aphids on plants grown from CaCl2 - and water-pretreated seeds, and plant defense responses to aphid attack were investigated. Results Seed pretreatment with CaCl2 extended aphid development time and reduced aphid population size and feeding efficiency. In addition, the pretreatment significantly increased the concentration of Ca2+ in wheat leaves, and upregulated expression levels of TaCaM genes and callose synthase genes (TaGSL2, TaGSL8, TaGSL10, TaGSL12, TaGSL19, TaGSL22 and TaGSL23). Callose concentration in the leaves of plants grown from CaCl2 -pretreated seeds increased significantly upon aphid attack. Further, callose deposition was observed mainly in the phloem. Conclusion These results suggest that seed pretreatment with CaCl2 primes the plant response against wheat aphid attack, leading to modulation of callose deposition in the phloem in response to aphid attack. © 2021 Society of Chemical Industry.

Plant resistance in different cell layers affects aphid probing and feeding behaviour during non-host and poor-host interactions.

Abstract: Aphids are phloem-feeding insects that cause economic losses to crops globally. Whilst aphid interactions with susceptible plants and partially resistant genotypes have been well characterized, the interactions between aphids and non-host species are not well understood. Unravelling these non-host interactions can identify the mechanisms which contribute to plant resistance. Using contrasting aphid-host plant systems, including the broad host range pest Myzus persicae (host: Arabidopsis; poor-host: barley) and the cereal pest Rhopalosiphum padi (host: barley; non-host: Arabidopsis), we conducted a range of physiological experiments and compared aphid settling and probing behaviour on a host plant vs either a non-host or poor-host. In choice experiments, we observed that around 10% of aphids selected a non-host or poor-host plant species after 24 h. Using the Electrical Penetration Graph technique, we showed that feeding and probing behaviours differ during non-host and poor-host interactions when compared with a host interaction. In the Arabidopsis non-host interaction with the cereal pest R. padi aphids were unable to reach and feed on the phloem, with resistance likely residing in the mesophyll cell layer. In the barley poor-host interaction with M. persicae, resistance is likely phloem-based as phloem ingestion was reduced compared with the host interaction. Overall, our data suggest that plant resistance to aphids in non-host and poor-host interactions with these aphid species likely resides in different plant cell layers. Future work will take into account specific cell layers where resistances are based to dissect the underlying mechanisms and gain a better understanding of how we may improve crop resistance to aphids.

The Effectiveness of Physical and Chemical Defense Responses of Wild Emmer Wheat Against Aphids Depends on Leaf Position and Genotype

Abstract: The bird cherry-oat aphid (Rhopalosiphum padi) is one of the most destructive insect pests in wheat production. To reduce aphid damage, wheat plants have evolved various chemical and physical defense mechanisms. Although these mechanisms have been frequently reported, much less is known about their effectiveness. The tetraploid wild emmer wheat (WEW; Triticum turgidum ssp. dicoccoides), one of the progenitors of domesticated wheat, possesses untapped resources from its numerous desirable traits, including insect resistance. The goal of this research was to determine the effectiveness of trichomes (physical defense) and benzoxazinoids (BXDs; chemical defense) in aphid resistance by exploiting the natural diversity of WEW. We integrated a large dataset composed of trichome density and BXD abundance across wheat genotypes, different leaf positions, conditions (constitutive and aphid-induced), and tissues (whole leaf and phloem sap). First, we evaluated aphid reproduction on 203 wheat accessions and found large variation in this trait. Then, we chose eight WEW genotypes and one domesticated durum wheat cultivar for detailed quantification of the defense mechanisms across three leaves. We discovered that these defense mechanisms are influenced by both leaf position and genotype, where aphid reproduction was the highest on leaf-1 (the oldest), and trichome density was the lowest. We compared the changes in trichome density and BXD levels upon aphid infestation and found only minor changes relative to untreated plants. This suggests that the defense mechanisms in the whole leaf are primarily anticipatory and unlikely to contribute to aphid-induced defense. Next, we quantified BXD levels in the phloem sap and detected a significant induction of two compounds upon aphid infestation. Moreover, evaluating aphid feeding patterns showed that aphids prefer to feed on the oldest leaf. These findings revealed the dynamic response at the whole leaf and phloem levels that altered aphid feeding and reproduction. Overall, they suggested that trichomes and the BXD 2,4-dihydroxy-7- methoxy-1,4-benzoxazin-3-one (DIMBOA) levels are the main factors determining aphid resistance, while trichomes are more effective than BXDs. Accessions from the WEW germplasm, rich with trichomes and BXDs, can be used as new genetic sources to improve the resistance of elite wheat cultivars.

GNBP1 as a potential RNAi target to enhance the virulence of Beauveria bassiana for aphid control

Abstract: Gram-negative binding proteins (GNBPs) are important in the innate immune system of insects in recognition of fungi pathogen, such as Beauveria bassiana. However, this information in aphids is not clear, which might be exploited to develop a novel aphid control strategy based on integrating RNAi and B. bassiana. Here, we firstly identified two GNBPs, ApGNBP1 and ApGNBP2, using the model aphid Acyrthosiphon pisum, and observed that two ApGNBPs were highly expressed in hemolymph and fat body as well as upon the injection of β-1,3-glucan and heat-killed B. bassiana. Intriguingly, RNAi-based silencing of ApGNBP1 but not ApGNBP2 decreased the activity of immune-related phenoloxidase. This led to the increased virulence of B. bassiana in A. pisum upon silencing of ApGNBP1, and the synergetic effects were also observed in other two aphids: Myzus persicae and Aphis citricidus. Importantly, no negative effects were detected in aphid predator Propylaea japonica under the co-application of the RNAi in targeting ApGNBP1 and B. bassiana. Taking together, we conclude that GNBP1 could be an optimal target in aphid control by combining RNAi, entomopathogenic fungi and ladybeetle predator.

Cytochrome P450s CYP380C6 and CYP380C9 in green peach aphid facilitate its adaptation to indole glucosinolate‐mediated plant defense

Abstract: Background Overexpressing CIRCADIAN CLOCK ASSOCIATED1 in Arabidopsis thaliana (CCA1-ox) increases indole glucosinolate production and resistance to green peach aphid (Myzus persicae). Little is known of how aphids respond to this group of plant defense compounds or of the underlying molecular mechanism. Results Aphids reared on CCA1-ox for over 40 generations (namely the CCA population) became less susceptible to CCA1-ox than aphids maintained on the wild-type Col-0 (namely the COL population). This elevated tolerance was transgenerational as it remained for at least eight generations after the CCA population was transferred to Col-0. Intriguingly, transcriptome analysis indicated that all differential cytochrome P450 monooxygenase genes (MpCYPs), primarily MpCYP4s, MpCYP380s and MpCYP6s, were more highly expressed in the CCA population. Application of a P450 inhibitor to the CCA population resulted in decreased aphid reproduction on CCA1-ox, which was not observed if aphids were reared on Col-0. When indole glucosinolate biosynthesis in CCA1-ox was blocked using virus-induced gene silencing, the effect of the P450 inhibitor on the CCA population was attenuated, affirming the essential role played by MpCYPs in counteracting the defense mechanism in CCA1-ox that is low or absent in Col-0. Furthermore, we used host-induced gene silencing to identify MpCYP380C6 and MpCYP380C9 that specifically facilitated the CCA population to cope with CCA1-mediated plant defense. Expression profiles revealed their possible contribution to the transgenerational tolerance observed in aphids. Conclusion MpCYP380C6 and MpCYP380C9 in aphids play a crucial role in mitigating indole glucosinolate-mediated plant defense, and this effect is transgenerational.

The boom and bust of the aphid's essential amino acid metabolism across nymphal development.

Abstract: Within long-term symbioses, animals integrate their physiology and development with their symbiont. In a model nutritional mutualism, aphids harbor the endosymbiont, Buchnera, within specialized bacteriocyte cells. Buchnera synthesizes essential amino acids (EAAs) and vitamins for their host, which are lacking from the aphid’s plant sap diet. It is unclear if the aphid host differentially expresses aphid EAA metabolism pathways and genes that collaborate with Buchnera for the production of EAA and vitamins throughout nymphal development when feeding on plants. It is also unclear if aphid bacteriocytes are differentially methylated throughout aphid development as DNA methylation may play a role in gene regulation. By analyzing aphid gene expression, we determined that the bacteriocyte is metabolically more active in metabolizing Buchnera’s EAAs and vitamins early in nymphal development compared to intermediate or later immature and adult lifestages. The largest changes in aphid bacteriocyte gene expression, especially for aphid genes that collaborate with Buchnera, occurred during the 3rd to 4th instar transition. During this transition, there is a huge shift in the bacteriocyte from a high energy “nutrient-consuming state” to a “recovery and growth state” where patterning and signaling genes and pathways are upregulated and differentially methylated, and de novo methylation is reduced as evidenced by homogenous DNA methylation profiles after the 2nd instar. Moreover, bacteriocyte number increased and Buchnera’s titer decreased throughout aphid nymphal development. These data suggest in combination that bacteriocytes of older nymphal and adult lifestages depend less on the nutritional symbiosis compared to early nymphal lifestages.

Glandular Trichome-Derived Mono- and Sesquiterpenes of Tomato Have Contrasting Roles in the Interaction with the Potato Aphid Macrosiphum euphorbiae

Abstract: Secondary metabolites produced in glandular trichomes of tomato are involved in interactions with herbivores. In cultivated tomato (Solanum lycopersicum) glandular trichomes accumulate a blend of abundant monoterpenes and smaller amounts of a few sesquiterpenes. These mono- and sesquiterpenes are synthesized by three terpene synthases, TPS20 as well as TPS9 and TPS12, respectively. To study effects of these terpenes on performance and choice behavior of potato aphid (Macrosiphum euphorbiae), we utilized two tomato trichome mutants, hairless and odorless-2, that are differently affected in mono- and sesquiterpene production. Non-choice assays demonstrated that longevity and fecundity of M. euphorbiae were increased when kept on the trichome mutants. A principal component analysis of these aphid performance parameters and terpene production in the trichome mutants indicated that longevity and fecundity of M. euphorbiae were negatively correlated with production of the TPS12-derived sesquiterpenes β-caryophyllene and α-humulene. While we had previously shown that addition of pure β-caryophyllene/α-humulene to an artificial feeding diet affected M. euphorbiae apterae survivorship and feeding behavior, no such effects were observed here upon addition of a mixture of pure TPS20-derived monoterpenes. In olfactometer assays M. euphorbiae alates displayed differential choice behaviors towards the hairless and odorless-2 mutants suggesting a role of TPS20-derived monoterpenes in aphid attraction, which was further confirmed using a mixture of pure monoterpenes. Our analyses revealed contrasting roles of glandular trichome-derived terpenes in S. lycopersicum. While TPS12-derived sesquiterpenes contribute to host plant resistance against M. euphorbiae, TPS20-derived monoterpenes appear to be exploited as cue for host plant orientation by aphids.

A root aphid Aploneura lentisci is affected by Epichloë endophyte strain and impacts perennial ryegrass growth in the field

Abstract: The aphid Aploneura lentisci is widespread in Australia and New Zealand, living all year round on roots of its secondary grass hosts. The fungal endophyte (Epichloe festucae var. lolii), strain AR37 in Lolium perenne is known to greatly reduce populations and was a likely reason for the superior growth and persistence of this association previously observed in the field. Aphid populations were quantified in a field trial near Ballarat, comparing yields of perennial ryegrass infected with eight different endophyte strains and an endophyte-free (Nil) control in a common ryegrass background (Grasslands Samson (G. Samson)). AR37 and another endophyte strain, AR5, had significantly fewer aphids than all other endophytes. These differences were significantly related to yield increases taken before and after sampling that persisted until the end of the trial. In a pot trial comparing commercially available ryegrass-endophyte combinations with equivalent Nil controls, aphid numbers were lower on G. Samson AR37 and Banquet II with AR5 (Endo®5) than on all other cultivar-endophyte combinations. Compared with Nil controls, the common toxic strain in G. Samson, and two strains in Trojan also reduced aphid numbers. The AR5 endophyte produces the alkaloid ergovaline but high concentrations of this in roots of potted plants could not account for differences in root aphid numbers. Root concentrations of epoxyjanthitrems, the only known alkaloids produced by AR37, were low and unlikely to be the cause of resistance to A. lentisci.

Proteome changes in pepper ( Capsicum annuum L.) leaves induced by the green peach aphid ( Myzus persicae Sulzer)

Abstract: Aphid attack induces defense responses in plants activating several signaling cascades that led to the production of toxic, repellent or antinutritive compounds and the consequent reorganization of the plant primary metabolism. Pepper (Capsicum annuum L.) leaf proteomic response against Myzus persicae (Sulzer) has been investigated and analyzed by LC-MS/MS coupled with bioinformatics tools. Infestation with an initially low density (20 aphids/plant) of aphids restricted to a single leaf taking advantage of clip cages resulted in 6 differentially expressed proteins relative to control leaves (3 proteins at 2 days post-infestation and 3 proteins at 4 days post-infestation). Conversely, when plants were infested with a high density of infestation (200 aphids/plant) 140 proteins resulted differentially expressed relative to control leaves (97 proteins at 2 days post-infestation, 112 proteins at 4 days post-infestation and 105 proteins at 7 days post-infestation). The majority of proteins altered by aphid attack were involved in photosynthesis and photorespiration, oxidative stress, translation, protein folding and degradation and amino acid metabolism. Other proteins identified were involved in lipid, carbohydrate and hormone metabolism, transcription, transport, energy production and cell organization. However proteins directly involved in defense were scarce and were mostly downregulated in response to aphids. The unexpectedly very low number of regulated proteins found in the experiment with a low aphid density suggests an active mitigation of plant defensive response by aphids or alternatively an aphid strategy to remain undetected by the plant. Under a high density of aphids, pepper leaf proteome however changed significantly revealing nearly all routes of plant primary metabolism being altered. Photosynthesis was so far the process with the highest number of proteins being regulated by the presence of aphids. In general, at short times of infestation (2 days) most of the altered proteins were upregulated. However, at longer times of infestation (7 days) the protein downregulation prevailed. Proteins involved in plant defense and in hormone signaling were scarce and mostly downregulated.

Drought has negative consequences on aphid fitness and plant vigor: Insights from a meta-analysis.

Abstract: Aphids are abundant in natural and managed vegetation, supporting a diverse community of organisms and causing damage to agricultural crops. Due to a changing climate, periods of drought are anticipated to increase, and the potential consequences of this for aphid-plant interactions are unclear.Using a meta-analysis and synthesis approach, we aimed to advance understanding of how increased drought incidence will affect this ecologically and economically important insect group and to characterize any potential underlying mechanisms. We used qualitative and quantitative synthesis techniques to determine whether drought stress has a negative, positive, or null effect on aphid fitness and examined these effects in relation to (a) aphid biology, (b) geographical region, and (c) host plant biology.Across all studies, aphid fitness is typically reduced under drought. Subgroup analysis detected no difference in relation to aphid biology, geographical region, or the aphid-plant combination, indicating the negative effect of drought on aphids is potentially universal. Furthermore, drought stress had a negative impact on plant vigor and increased plant concentrations of defensive chemicals, suggesting the observed response of aphids is associated with reduced plant vigor and increased chemical defense in drought-stressed plants.We propose a conceptual model to predict drought effects on aphid fitness in relation to plant vigor and defense to stimulate further research.

Serratia symbiotica Enhances Fatty Acid Metabolism of Pea Aphid to Promote Host Development

Abstract: Bacterial symbionts associated with insects are often involved in host development and ecological adaptation. Serratia symbiotica, a common facultative endosymbiont harbored in pea aphids, improves host fitness and heat tolerance, but studies concerning the nutritional metabolism and impact on the aphid host associated with carrying Serratia are limited. In the current study, we showed that Serratia-infected aphids had a shorter nymphal developmental time and higher body weight than Serratia-free aphids when fed on detached leaves. Genes connecting to fatty acid biosynthesis and elongation were up-regulated in Serratia-infected aphids. Specifically, elevated expression of fatty acid synthase 1 (FASN1) and diacylglycerol-o-acyltransferase 2 (DGAT2) could result in accumulation of myristic acid, palmitic acid, linoleic acid, and arachidic acid in fat bodies. Impairing fatty acid synthesis in Serratia-infected pea aphids either by a pharmacological inhibitor or through silencing FASN1 and DGAT2 expression prolonged the nymphal growth period and decreased the aphid body weight. Conversely, supplementation of myristic acid (C14:0) to these aphids restored their normal development and weight gain. Our results indicated that Serratia promoted development and growth of its aphid host through enhancing fatty acid biosynthesis. Our discovery has shed more light on nutritional effects underlying the symbiosis between aphids and facultative endosymbionts.

Can Insectary Plants Enhance the Presence of Natural Enemies of the Green Peach Aphid (Hemiptera: Aphididae) in Mediterranean Peach Orchards?

Abstract: Conservation biological control could be an alternative to insecticides for the management of the aphid Myzus persicae (Sulzer). To develop sustainable strategies for M. persicae control in peach orchards in the Mediterranean, a 2-yr field experiment was conducted to identify the key predators of the aphid; to determine whether the proximity of insectary plants boost natural enemies of M. persicae in comparison to the resident vegetation; and whether selected insectary plants enhance natural enemy populations in the margins of peach orchards. Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae) and Episyrphus balteatus De Geer (Diptera: Syrphidae) were the most abundant predators found among sentinel aphid colonies, accounting for 57% and 26%, respectively. Samplings during 2015 yielded twice as many hoverflies in M. persicae sentinel plants close to the insectary plants as those close to the resident vegetation. The abundance of other natural enemies in sentinel plants, depending on their proximity to the insectary plants, was not significantly different in either of the 2 yr. Hoverflies hovered more often over the insectary plants than over the resident vegetation and landed significantly more often on Lobularia maritima (L.) Desv., Moricandia arvensis (L.) DC., and Sinapis alba L. (Brassicales: Brassicaceae) than on Achillea millefollium L. (Asterales: Compositae). Parasitoids were significantly more abundant in L. maritima and A. millefollium. The vicinity of selected insectary plants to peach orchards could improve the presence of hoverflies, which might benefit the biological control of M. persicae.

Microbiota associated with Mollitrichosiphum aphids (Hemiptera: Aphididae: Greenideinae): diversity, host species specificity and phylosymbiosis

Abstract: Symbiotic association is universal in nature, and an array of symbionts play a crucial part in host life history. Aphids and their diverse symbionts have become a good model system to study insect-symbiont interactions. Previous symbiotic diversity surveys have mainly focused on a few aphid clades, and the relative importance of different factors regulating microbial community structure is not well understood. In this study, we collected 65 colonies representing eight species of the aphid genus Mollitrichosiphum from different regions and plants in southern China and Nepal and characterized their microbial compositions using Illumina sequencing of the V3 - V4 hypervariable region of the 16S rRNA gene. We evaluated how microbiota varied across aphid species, geography and host plants and the correlation between microbial community structure and host aphid phylogeny. Heritable symbionts dominated the microbiota associated with Mollitrichosiphum, and multiple infections of secondary symbionts were prevalent. Ordination analyses and statistical tests highlighted the contribution of aphid species in shaping the structures of bacterial, symbiont and secondary symbiont communities. Moreover, we observed a significant correlation between Mollitrichosiphum aphid phylogeny and microbial community composition, providing evidence for a pattern of phylosymbiosis between natural aphid populations and their microbial associates.

Mild Drought Facilitates the Increase in Wheat Aphid Abundance by Changing Host Metabolism

Abstract: Water shortages and water pollution are current issues in ecosystems around the world, and the stress induced by drought can further increase negative impacts on agriculture in these areas. In the present experiment, we examined the effect of mild drought on wheat plants grown in association with the wheat aphid Sitobion avenae Fabricius (Hemiptera: Aphididae) in 2019 and 2020. Using plot experiments, we tested the hypothesis that mild drought tends to enhance the performance of this wheat aphid by changing the nutritional quality of the wheat plants. We found that mild drought treatment significantly increased aphid abundance and population growth rates. Also, mild drought significantly increased total amino acid concentration of the wheat ear as well as concentrations of key amino acids, including Arg, Ile, Leu, Lys, Phe, Try, Gly, Ala, Tyr, and Cys in 2019, and Arg, Ile, Leu, Lys, Gly, and Cys in 2020. Mild drought led to a shift in the composition of amino acids in the plants, causing cascading effects at higher trophic levels. Such changes suggest that the carrying capacity of the environment with respect to aphids will increase if mild drought events continues to increase in frequency with climate change.

Developing a decision-making framework for insect pest management: a case study using Aphis glycines (Hemiptera: Aphididae).

Abstract: Background The profitability of farming varies based on factors such as a crop's market value, input costs and occurrence of resistant pests, all capable of altering the value of pest management tactics in an integrated pest management program. We provide a framework for calculating expected yield and expected net revenue of pest management scenarios, using the soybean aphid (Aphis glycines) as a case study. Foliar insecticide and host-plant resistance are effective management tactics for preventing yield loss from soybean aphid outbreaks; however, pyrethroid-resistant aphid populations pose a management challenge for farmers. We evaluated eight scenarios relevant to soybean aphid management in Iowa with varying probabilities of aphid outbreaks and insecticide-resistant aphids occurring. Results Our equation suggests that insecticide use is profitable when the probability of an aphid outbreak is ≥29%, and soybean production will become more costly with increasing probability of pyrethroid-resistant aphids. If farmers continue to use pyrethroids, they will not experience financial consequences from pyrethroid-resistant aphids until the chance of insecticide resistance is 48%. Aphid-resistant varieties provided consistent yield and offered the highest net revenue under all conditions. Conclusion This framework can be used for other crop-pest systems to evaluate the profitability of management tactics and investigate how resistance impacts revenue for farmers. Including the cost of resistance in crop budgets can help farmers and agronomic consultants comprehend these impacts and enhance decision-making to increase revenue and curb resistance development.

Cotton Chitinase Gene GhChi6 Improves the Arabidopsis Defense Response to Aphid Attack

Abstract: Despite the involvement of many members of the chitinase family in the plant immune system, the exact functions of most chitinases remain poorly understood, especially in plant defense responses to phytophagous insects. Here, the gene GhChi6, which encodes a chitinase protein in Gossypium hirsutum, was shown to be induced by cotton aphid feeding and mechanical wounding. Overexpression of GhChi6 in Arabidopsis plants improved their defense response to aphids. The activities of chitinase and PPO in GhChi6 transgenic Arabidopsis plants were higher than those in wild-type plants. Callose deposition in leaves from GhChi6 transgenic Arabidopsis plants was clearly increased compared with wild-type plants. The levels of AtEDS1, AtPAD4, and AtEDS5 in the SA signaling pathway were higher in GhChi6 transgenic Arabidopsis Line4 than those in wild-type plants, while the expression levels of AtLOX2 in the JA signaling pathway and AtEIN2 in the ethylene signaling pathway were lower in GhChi6 transgenic Arabidopsis Line4 than those in wild-type plants. These results collectively showed that the cotton chitinase gene GhChi6 modulated the plant defense response to aphid attack, which may help guide strategies for improving cotton aphid prevention.