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Abstract The adaptability of insects to hosts has long been a focal point in the study of insect-plant interactions. The pea aphid (Acythosiphon pisum), a significant pest of numerous leguminous crops, not only inflicts direct economic losses but also disseminates various plant viruses. To understand how pea aphids adapt to diverse alfalfa varieties. We analyzed the differentially expressed genes (DEGs) of pea aphids in distinct alfalfa varieties using transcriptome sequencing, and subsequently conducted functional validation of these genes. Comparative analysis between pea aphids feeding on susceptible and resistant strains revealed that DEGs in aphids feeding on resistant strains were primarily associated with transcriptional enrichment in the sugar, amino acid, protein, and lipid metabolism pathways. Fourteen DEGs related to adaptation of the pea aphid to alfalfa were chosen, including five carboxylesterases (CarE), four cytochrome P450s, three glutathione S-transferases, and two peroxidases (POD). RT-qPCR results indicated significant up-regulation of two carboxylesterase genes and two peroxidase genes after 24 h of feeding resistant alfalfa (Gannong 5, GN5) compared to the susceptible varieties (Hunter River, LRH), particularly highlighting the high expression levels of ApCarE4 and ApPOD3. Simultaneously, RNAi-induced knockdown of ApCarE4 and ApPOD3 led to a higher mortality of pea aphids in the alfalfa Hunter River. These results indicate that ApPOD3 and ApCarE4 are involved in the detoxification of metabolic functions in the adaptation of pea aphids to host switching. These findings contribute to the understanding of pea aphid adaptation to host plants and lay a foundation for further exploration of the physiological roles of carboxylesterase and peroxidase genes in pea aphids.

Alfalfa (Medicago sativa L.) is an economically important forage legume. As a result of the extensive and intensive cultivation of alfalfa planting and the gradual expansion of planting areas, pest occurrence has increased in frequency. Aphids are one of the main pests that threaten the growth and productivity of alfalfa. After an aphid outbreak, alfalfa yield and quality are commonly greatly reduced. At present, there are few studies on alfalfa plants infested with aphids, so it is imperative to study the regulatory mechanisms of aphid infestation tolerance in alfalfa. In this study, alfalfa plants from the variety "Wudi" were investigated, and pea aphids were selected for inoculation. The transcriptome and metabolome data were analyzed at three time points (0 d, 1 d, and 4 d), revealing 3458 differentially expressed genes and 358 differential metabolites. Trend analysis of DEGs and DAMs revealed that the former were significantly enriched in three distinct trends, whereas the latter were significantly enriched in only one. Moreover, 117 important hub genes associated with alfalfa response to aphid infestation were screened by WGCNA. By mapping DEGs and DAMs to KEGG pathways, it was found that the "phenylpropanoid biosynthesis", "flavonoid biosynthesis", and "isoflavonoid biosynthesis" pathways play an important role in alfalfa responses to aphid infestation. These results further elucidate the regulatory mechanism of alfalfa in response to aphid infestation and provide valuable information for breeding new aphid-resistant plant varieties. [ABSTRACT FROM AUTHOR]

Simple Summary: Pea aphids (Acyrthosiphon pisum) serve as a model insect for ecological research and have recently emerged as a significant pest of alfalfa. Amino acid uptake and balance in insects typically rely on amino acid transporters. In this investigation, RT-qPCR was employed to examine the distinct gene expression patterns of seven amino acid transporters subsequent to pea aphid feeding on resistant and susceptible alfalfa varieties. RNA interference targeting the pea aphid ACYPI000536 and ACYPI004320 genes was carried out via a plant-mediated approach, elucidating the preliminary functions of these genes. The study revealed that down-regulating the ACYPI000536 gene led to increased histidine and lysine levels in pea aphids, subsequently elevating mortality post-feeding on the susceptible alfalfa variety "Lie Renhe". Conversely, down-regulating the ACYPI004320 gene resulted in elevated phenylalanine levels in pea aphids, leading to reduced mortality following feeding on the highly resistant alfalfa variety "Gannong 5". In recent years, pea aphids have become major pests of alfalfa. Our previous study found that "Gannong 5" is a highly aphid-resistant alfalfa variety and that "Lie Renhe" is a susceptible one. The average field susceptibility index of "Gannong 5" was 31.31, and the average field susceptibility index of "Lie Renhe" was 80.34. The uptake and balance of amino acids in insects are usually dependent on amino acid transporters. RT-qPCR was used to detect the relative expression levels of seven amino acid transporter differential genes in the different instar pea aphids fed on resistant and susceptible alfalfa varieties after 24 h, and two key genes were selected. When pea aphids fed on "Gannong 5", the expression of ACYPI004320 was significantly higher than that in pea aphids fed on "Lie Renhe"; however, the expression of ACYPI000536 was significantly lower than that in pea aphids fed on "Lie Renhe". Afterward, the RNA interference with pea aphid ACYPI000536 and ACYPI004320 genes was performed using a plant-mediated method, and gene function was verified via liquid chromatography–mass spectrometry and pea aphid sensitivity to aphid-resistant and susceptible alfalfa varieties. The results showed that the down-regulation of the ACYPI000536 gene expression led to an increase in the histidine and lysine contents in pea aphids, which, in turn, led to an increase in mortality when pea aphids fed on the susceptible variety "Lie Renhe". The down-regulation of the ACYPI004320 gene expression led to an increase in phenylalanine content in pea aphids, which, in turn, led to a decrease in mortality when pea aphids fed on the resistant variety "Gannong 5". [ABSTRACT FROM AUTHOR]

Many species of insects show phenotypically plastic dispersal traits in response to suboptimal environmental conditions. These polyphenetic traits can have large impacts on the population dynamics of the dispersing insects. Therefore, it is important to understand what environmental factors affect the development of dispersal traits and how these factors affect population dynamics via immigration/emigration.Pea aphids (Acyrthosiphon pisum) exhibit a polyphenetic wing dimorphism in which individuals are either winged (alate) or not (apterous). The production of alate offspring is determined by environmental cues experienced by the mother. Environmental factors associated with these cues have been intensively studied, with crowding, host plant quality, natural enemies, fungal infection, and viral infection being shown to affect the production of pea aphid alates under controlled laboratory conditions. Nonetheless, environmental factors affecting alate production have rarely been studied in field populations of pea aphids.Using data from a three‐year study of alate production in 5–9 alfalfa (lucerne) fields, we examined the effects of (i) pea aphid abundance, (ii) host plant maturity, (iii) temperature, (iv) predator and herbivore abundance, (v) parasitism, and (vi) entomopathic fungal incidence. In twice‐weekly samples taken over the growing season, alate production ranged from 0% to 83% of the nymphal population.Pea aphid abundance, temperature, and alfalfa maturity together explained 67% of the variation in alate production. The other factors we investigated explained little variation. These results suggest there is a limited number of key environmental factors that consistently predict changes in alate production in field populations, while many factors identified in lab studies may be unimportant. Our results highlight the value of investigating factors affecting the expression of plastic traits in insect species at a broad spatiotemporal scale and under natural conditions. [ABSTRACT FROM AUTHOR]

This study was conducted to determine distribution pattern and related parameters of spotted alfalfa aphid, Therioaphis maculata (Buckten), pea aphid, Acyrthosiphon pisum (Harris) and two coccinellid species (Coccinella septempunctata L. and Hippodamia variegata Goeze) in six alfalfa fields during two growing seasons, 2016 and 2017. Weekly sampling was started when alfalfa plants reached 10 cm in height and continued until harvest. Each field was divided into 20m×20m plots. Two samples per plot per sampling time were randomly taken using a 1 × 1 m quadrat, to count adult coccinellids. Twenty alfalfa stems (longer than 10cm) per plot were randomly cut and shaken eight times on a white pan to record the aphids' density. The aphids that fell into the pan were counted and recorded. The ratio of variance to mean, as well as Taylor’s power law (TPL) and Iwao’s patchiness index (IPI), were used to determine the spatial distribution patterns of the insects. The variance exceeded the mean on all sampling dates, which may imply an aggregative distribution. Aggregation was also confirmed by using regression coefficient of both TPL (parameter b) and coefficient of IPI (β), which both were significantly above unity. Correlation between aphid counts and those of the coccinellids indicated that there was a positive but weak relationship between predator and prey densities in the fields, although a weak correlation may imply that factors other than prey accessibility contribute to the spatial distribution of the predators. Using different statistical methods provides useful information about the spatial distribution and dispersal pattern of aphids and natural enemies in alfalfa fields, and this information can be used in the biological control of pests. [ABSTRACT FROM AUTHOR]

Alfalfa (Medicago sativa L.) hosts several species of aphid, Acyrthosiphon pisum (Harris), Aphis craccivora Koch and Therioaphis trifolii (Monell). The preference of the aphids of alfalfa plants for dense assemblies or individual plants, as well as for healthy or infested plants, was investigated in the field as in the laboratory. Years of field research have revealed the specific preferences of all three species of aphid. A. pisum and T. trifolii are most commonly found in alfalfa crops, while A. craccivora is mostly found on alfalfa weeds. Also, a single species of aphid alone is usually present on a plant. In order to determine the reason for this clear preference and to establish whether at the very beginning, i.e. at the stage of choosing a host, aphid species distance themselves from each other, we tested the effect of the volatiles of healthy and infested plants on their attractiveness to aphids. A. craccivora is repelled by the volatiles of dense crops and plants previously infested with one of the other two species. A. pisum and T. trifolii choose a dense assembly of plants, repelled by the volatiles of plants previously infested with A. craccivora. A. pisum displays the weakest competitive traits, and A. craccivora the strongest. This research showed that competition between aphid species does not occur only when they find themselves on the same plant at the same time, fighting for resources, but also in the choice of plant, in order to avoid later competition. [ABSTRACT FROM AUTHOR]

Summary: Plant disease occurs simultaneously with insect attack. Arbuscular mycorrhizal fungi (AMF) modify plant biotic stress response. Arbuscular mycorrhizal fungi and pathogens may modify plant volatile organic compound (VOC) production and insect behavior. Nevertheless, such effects are rarely studied, particularly for mesocosms where component organisms interact with each other.Plant‐mediated effects of leaf pathogen (Phoma medicaginis) infection on aphid (Acyrthosiphon pisum) infestation, and role of AMF (Rhizophagus intraradices) in modifying these interactions were elucidated in a glasshouse experiment. We evaluated alfalfa disease occurrence, photosynthesis, phytohormones, trypsin inhibitor (TI) and total phenol response to pathogen and aphid attack, with or without AMF, and aphid behavior towards VOCs from AMF inoculated and non‐mycorrhizal alfalfa, with or without pathogen infection.AM fungus enhanced alfalfa resistance to pathogen and aphid infestation. Plant biomass, root : shoot ratio, net photosynthetic rate, transpiration rate, stomatal conductance, salicylic acid, and TI were significantly increased in AM‐inoculated alfalfa. Arbuscular mycorrhizal fungi and pathogen significantly changed alfalfa VOCs. Aphids preferred VOCs of AM‐inoculated and nonpathogen‐infected to nonmycorrhizal and pathogen‐infected alfalfa.We propose that AMF alter plant response to multiple biotic stresses in ways both beneficial and harmful to the plant host, providing a basis for strategies to manage pathogens and herbivore pests. [ABSTRACT FROM AUTHOR]

Host plant shifts are central to diversification in insect herbivores. Many mechanisms can cause host shifts in insects, but one relatively unexplored mechanism is whole‐genome duplication (WGD) in the host plant. WGD, or polyploidy, is common in plants and causes spontaneous changes in physiology, morphology, and palatability that could impact the ability of herbivores to feed and develop on newly formed polyploids (neopolyploids).Here the authors tested if WGD affected the preference and performance of the specialist aphid, Acyrthosiphon pisum (pea aphids). Pea aphids seasonally form specialised lineages or 'host forms' on many host plant species including alfalfa and red clover. Aphid host forms on alfalfa and red clover naturally exist on different cytotypes of their respective hosts, with red clover aphids feeding on diploid clover and alfalfa aphids feeding on tetraploid alfalfa. Therefore, the authors predicted that these host forms would have a higher preference for and performance on their respective natal host cytotype.Neither host form exhibited a preference for a particular cytotype, but there were modest changes in aphid performance based on host cytotype. Specifically, aphids specialised to red clover had higher fecundity on diploid red clover than on neotetraploid red clover. Together, these results showed that both host forms were able to recognise and accept different cytotypes of the two host species, but only one host form experienced trade‐offs in performance when feeding on neotetraploids. These results suggest that WGD may act as a mechanism of host expansion in pea aphids as plants speciate via WGD. [ABSTRACT FROM AUTHOR]

Facultative bacterial endosymbionts are prevalent in aphid pest species and key organisms for the rapid adaptation to changing environment conditions under agricultural management. Facultative endosymbiont interactions allow beneficial phenotypes of insect hosts, providing resistance against natural enemies, fungal infections as well as enhanced resistance to thermal conditions, among others. These interactions have been highlighted as important modulators in the evolution of aphid defenses, being a key aspect for the invasive potential of aphids as pests. In this study, we have examined the bacterial community diversity associated to the pea aphid Acyrthosiphon pisum on alfalfa (Medicago sativa L.) crops in Central Chile by determining the presence and abundance of the seven most common facultative endosymbionts reported for aphid species, including: Hamiltonella defensa, Regiella insecticola, Serratia symbiotica, Spiroplasma sp., Rickettsia sp., Rickettsiella viridis and Fukatsuia symbiotica (or pea aphid X-type symbiont' PAXS), using a PCR-based approach across species-specific primers, in 16 alfalfa fields during the Chilean spring in the Maule Region. We reported six of the seven endosymbiont species studied, observing a high frequency of infected aphids being the endosymbiont H. defensa, the most predominant among the aphid populations in the different alfalfa fields studied. As H. defensa has been extensively studied in its defensive role to parasitoids, we discuss implications for biological control of this aphid pests. We also discuss the absence of a relevant defensive endosymbiont such as F. symbiotica in the Chilean pea aphid populations and potential implications for the success of the pea aphid biological control program. [ABSTRACT FROM AUTHOR]

Simple Summary: Maximizing the combination of biological control by natural enemies and plant resistance is a key strategy for controlling aphids in various crop systems. In our study, some alfalfa cultivars were found to have resistance to the pea aphid, Acyrthosiphon pisum, a dominant pest in alfalfa fields in northwestern China. In addition, natural enemies were able to significantly suppress this aphid, regardless of the resistance level of the nine cultivars tested. Moreover, the biological control efficacies of predators, parasitoids, and mixed populations of natural enemies were 85%, 42%, and 88%, respectively. Conservation of natural enemies in the field is an ecologically sound and efficient approach to the management of the pea aphid in alfalfa crops. The pea aphid, Acyrthosiphon pisum Harris, is a major pest of alfalfa in northwestern China. However, the roles of different groups of natural enemies in combination with aphid-resistant cultivars in the suppression of the pea aphid have not been clarified under field conditions. In this study, we used experimental cages to better understand the top-down (natural enemies) and bottom-up (nine alfalfa cultivars) biological processes, as well as the individual roles of the two processes, in the control of the pea aphid. There was a significant difference in resistance among cultivar classes revealed when natural enemies were excluded. The functional contribution of top-down suppression was higher than the bottom-up process, with natural enemies significantly suppressing aphid populations, regardless of the resistance level of different alfalfa cultivars. The mean biological efficacies of predators, parasitoids, and mixed populations of natural enemies were 85%, 42%, and 88%, respectively. Overall, our study indicated that natural enemies play a critical role in suppressing aphid populations, especially in the summer, whereas cultivar resistance did not combine effectively with natural enemies to inhibit the growth of aphids. Conservation biological control (CBC) can be implemented in the alfalfa production regions in northwestern China to reduce the overreliance on insecticides for the control of pests and mitigate their harmful effects on humans, ecosystems, and biodiversity. [ABSTRACT FROM AUTHOR]

Pea aphid (Acyrthosiphon pisum) infestation leads to withering, reduced yield, and lower quality of the host plant. Arbuscular mycorrhizal (AM) fungi have been found to enhance their host plants' nutrient uptake, growth, and resistance to biotic stresses, including pathogen infection and insect pest infestation. Therefore, we evaluated the effects of AM fungus Rhizophagus intraradices on alfalfa defense responses to pea aphid infestation. Aphid infestation did not affect the colonization of AM fungus. The inoculation of AM fungus, on average, enhanced alfalfa catalase and the contents of salicylic acid and trypsin inhibitor by 101, 9.05, and 7.89% compared with non-mycorrhizal alfalfa, respectively. In addition, polyphenol oxidase activities significantly increased by six-fold after aphid infestation in mycorrhizal alfalfa. Moreover, the fungus significantly (p < 0.05) improved alfalfa shoot N content, net photosynthetic and transpiration rates, and shoot dry weight in aphid infected treatment. The aphid infestation changed the total volatile organic compounds (VOCs) in alfalfa, while AM fungus enhanced the contents of methyl salicylate (MeSA). The co-expression network analysis of differentially expressed genes (DEGs) and differentially expressed VOCs analysis showed that three DEGs, namely MS.gene23894, MS.gene003889, and MS.gene012415, positively correlated with MeSA both in aphid and AM fungus groups. In conclusion, AM fungus increased alfalfa's growth, defense enzyme activities, hormones, and VOCs content and up-regulated VOC-related genes to enhance the alfalfa's resistance following aphid infestation. [ABSTRACT FROM AUTHOR]

Life table data of the green pea aphid, Acyrthosiphon pisum (Harris) reared on four different resistant alfalfa varieties, i.e. 5S43, TG4 CW044026 (abbreviated as TG4), TG7 CW2883 (abbreviated as TG7), and Aurora were analyzed using the age-stage, two-sex life table. A higher proportion of alate adults were observed on 5S43, TG7, and Aurora; while a higher proportion of apterous adults occurred on TG4. The contributions of alate aphids to the finite rate of increase (λ), intrinsic rate of increase (r), and net reproductive rate (R 0) were higher than apterous aphids on 5S43, TG7, and Aurora, while apterous aphids contributed more to λ, r , and R 0 on TG4. The highest population parameters were observed on TG4 (r = 0.208 d−1, λ = 1.231 d−1, and R 0 = 18.8 offspring/individual), while the lowest values were on TG7 (r = 0.129 d−1, λ = 1.138 d−1, and R 0 = 9.9 offspring/individual). Because the age-stage, two-sex life table is capable of describing the stage differentiation, it enables the calculation of the stable stage distribution (SSD). A higher proportion of adult A. pisum was observed in SSD than in fourth instar nymphs. Population simulation showed the stage structure will approach SSD. Because the R 0 and the mean generation time (T) values do not reflect the population growth rate, their use as population fitness parameters should be avoided. These findings can be utilized in helping to select resistant alfalfa varieties to effectively manage the pea aphid. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Agricultural Sciences, Belgrade is the property of University of Belgrade, Faculty of Agriculture and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simple Summary: Aphis craccivora Koch (cowpea aphid, CPA), Acyrthosiphon pisum Harris (pea aphid, PA) and Therioaphis trifolii Buckton (spotted alfalfa aphid, SAA) are the three species of devastating pests on alfalfa in China. A study was conducted in the laboratory for identification and characterization of resistance to these three aphids among 16 of the main alfalfa cultivars planted in China. Resistance was indicated by antibiosis, antixenosis, and measuring feeding behavior using EPG (electrical penetration graph). The results indicated that different alfalfa cultivars have significantly different resistance levels to a particular species of aphid, and the same alfalfa variety also has different resistance to the three aphid species. Specifically, we evaluated the resistance of different alfalfa cultivars to CPA, which can help us for further study on the defense mechanism against CPA and for better management of this pest. Aphids on alfalfa (Medicago sativa) including Aphis craccivora Koch (cowpea aphid, CPA), Acyrthosiphon pisum Harris (pea aphid, PA) and Therioaphis trifolii Buckton (spotted alfalfa aphid, SAA) cause significant yield losses worldwide. In this experiment, the development of these three species of aphids on 16 alfalfa cultivars was compared. The results showed that the plant cultivar had a significant influence on the development of aphids as there are significant differences in the body weight of aphids reared on different alfalfa cultivars. In addition, antibiosis between the alfalfa cultivars Pegasis and Gannong NO.9 and the three species of aphids was evaluated by measuring aphid body weight and fecundity. Antixenosis was measured using choice tests, and feeding behavior was quantified using electrical penetration graphs (EPG). The Pegasis cultivar was observed to have both antibiosis and antixenosis effects with CPA, but was susceptible to PA and SAA compared with the Gannong NO.9 cultivar. CPA had less mean body weight, less fecundity, and shorter feeding time on the Pegasis cultivar, and preferred to settle on Gannong NO.9 cultivar. In contrast, Gannong NO.9 exhibits antibiosis and antixenosis to PA and SAA compared with Pegasis, as shown by lower body weight, lower fecundity and chose to settle less often, but EPG data showed that PA and SAA showed no different significance in feeding behavior between Pegasis and Gannong NO.9. [ABSTRACT FROM AUTHOR]

Natural enemies that can use multiple habitats are thought to better withstand disturbances in agricultural systems than natural enemies that are habitat specialists. This is because habitat generalists have populations in multiple habitats that can serve as sources of immigrants into an agricultural crop following a disturbance. In contrast, the dynamics of habitat specialists are tightly coupled with those of one agricultural crop. Nonetheless, some habitat specialists are successful in highly disturbed environments. To test how the magnitude of within‐field disturbance affects biological control agents, we conducted a large‐scale field manipulation in alfalfa fields and monitored the response of pea aphids, habitat‐generalist predators, a habitat‐specialist parasitoid (Aphidius ervi), and hyperparasitoids of A. ervi. The manipulation involved three treatments: harvesting normally (intermediate disturbance); spraying insecticide immediately after harvesting (high disturbance); and harvesting in strips (low disturbance). As a group, the habitat‐generalist predator species showed a range of responses to disturbances, from no response to decreases in abundance in the high‐disturbance treatment, indicating differences in their response to the density of pea aphids following disturbances. Surprisingly, percentage parasitism by the habitat‐specialist parasitoid was little affected by experimental disturbance manipulations. Furthermore, two of the four hyperparasitoids of A. ervi were negatively affected by the magnitude of disturbance, suggesting that disturbance could have an indirect positive effect on A. ervi. These results suggest that a habitat specialist can overcome the detrimental effects of disturbances without using alternative habitats. In addition, disturbance can sometimes benefit biological control agents by disproportionally negatively affecting their enemies from the fourth trophic level. [ABSTRACT FROM AUTHOR]

Host adaptation has the potential to cause rapid genetic variation in symbiotic microorganisms in insects. How mutations in symbiotic viruses favor viral fitness in hosts and even influence host adaptability to new environments remains elusive. Here, we explored the role of genetic divergence at one site of a symbiotic virus, Acyrthosiphon pisum virus (APV), in the host aphid's adaptation to unfavorable plants. Based on the transcriptomes of the pea aphid Vicia faba colony and Vicia villosa colony, 46 single nucleotide polymorphism (SNP) sites were found in the APV genomes from the two aphid colonies. One SNP at site 5,990, G5990A, located at the RNA-dependent RNA polymerase (RdRp) domain, demonstrated a predominance from G to A when the host aphids were shifted from V. faba to the low-fitness plants V. villosa or Medicago sativa. This SNP resulted in a substitution from serine (S) to asparagine (N) at site 196 in RdRp. Although S196N was predicted to be located at a random coil far away from conserved functional motifs, the polymerase activity of the N196 type of RdRp was increased by 44.5% compared to that of the S196 type. The promoted enzymatic activity of RdRp was associated with a higher replication level of APV, which was beneficial for aphids as APV suppressed plant's resistance reactions toward aphids. The findings showed a novel case in which mutations selected in a symbiotic virus may confer a favor on the host as the host adapts to new environmental conditions. [ABSTRACT FROM AUTHOR]

Simple Summary: Resistance of a Pisum fulvum and five Pisum sativum genotypes to Acyrthosiphon pisum pea and alfalfa-adapted biotypes was evaluated by measuring aphid body mass, confirming the variable resistance level of these genotypes. The feeding behavior of the aphids on the Pisum genotypes was then examined by electropenetrography (EPG). The EPG results suggested that the resistance of Pisum genotypes to non-adapted A. pisum resides in mesophyll and phloem tissues while the resistance variation of P. sativum to pea adapted aphids may be influenced by the quality of phloem sap. Resistant genotypes of crops have emerged as an alternative and sustainable solution to pesticide use against pest insects. The resistance depends on the genetic diversity of the host plant and the pest species and can cause an alteration of the insect behavior. The aim of this work was to characterize the resistance level of different Pisum genotypes (one P. fulvum and five P. sativum genotypes) to two biotypes of the aphid Acyrthosiphon pisum, respectively adapted to pea and alfalfa, by measuring the individual aphid weight and analyzing aphid feeding behavior by electropenetrography (EPG). Aphid body mass was influenced by Pisum genotypes reflecting variation in their resistance level. P. fulvum was the most resistant to the A. pisum pea biotype (ArPo28 clone) and showed intermediate resistance to the A. pisum alfalfa biotype (LSR1 clone). The resistance levels of the five P. sativum genotypes to the two aphid biotypes were variable and more pronounced for the alfalfa biotype. EPG data showed that ArPo28 on P. fulvum and LSR1 on all the Pisum genotypes spent shorter time phloem feeding compared to ArPo28 on P. sativum genotypes, indicating that the resistance of Pisum genotypes to non-adapted A. pisum resides in mesophyll and phloem cells. In the meantime, ArPo28 on P. sativum genotypes with a different level of resistance spent a similar length of time phloem feeding, indicating that the quality of phloem sap of the resistance genotypes may not be optimal for the aphid. The study indicated that the resistance of Pisum genotypes to the two A. pisum biotypes involves different genetic factors and mechanisms that affect the aphid differently. [ABSTRACT FROM AUTHOR]

Alfalfa (Medicago sativa L.) is attacked by pests that cause serious damage when not controlled. Among the insect pests are pea aphid, Acyrthosiphon pisum Harris; spotted alfalfa aphid, Therioaphis maculata Buckton; armyworm, Spodoptera exigua Hübner; alfalfa leafhopper, Empoasca fabae Harris; and threecornered alfalfa hopper, Spissistilus festinus Say. In the Comarca Lagunera, insecticides seldom are used to control alfalfa pests that are regulated by beneficial insects. However, species that provide this service are little known. The objective of this study was to identify Trichogrammatidae collected with a sweep net each week from 3 March to 30 December 2011 in an alfalfa plot at the Unidad de Producción 18 de Julio at Universidad Autonoma Chapingo at Bermejillo, Durango. Species identified were Aphelinoidea nr. roja Triapitsyn 2005; Oligosita sanguina Girault 1911; Paracentrobia punctata Howard 1897; Ufens nr. simplipenis Owen 2005; and Trichogramma pretiosum Riley 1879. A. nr. roja, O. sangunea, P. punctata, T. pretiosum, and U. nr. simplipenis on alfalfa are new records for Mexico. With the exception of T. pretiosum, the other species are pest insects with sucking habits. [ABSTRACT FROM AUTHOR]

The examination of the compatibility between agricultural practices and biocontrol activities is crucial for establishing an efficient, eco‐friendly, and sustainable pest management program. In this study, we examined the population dynamics of two specialist aphids, the English grain aphid (Sitobion avenae) on potted wheat and the pea aphid (Acyrthosiphon pisum) on potted alfalfa, as well as the biocontrol activity of a generalist predator, the harlequin ladybird beetle (Harmonia axyridis). We investigated their responses to the presence of the intercropping partner plant species (alfalfa and wheat, respectively) through plant volatiles or visual cues at three nitrogen fertilizer levels in a greenhouse. In the absence of the predator, the English grain aphid population growth rate increased significantly with increasing nitrogen levels, whereas the pea aphid population increased significantly more slowly in response to high nitrogen levels. The English grain aphid and pea aphid population dynamics were unaffected by the presence of the intercropping partner. However, the presence of the intercropping partner enhanced the control of both aphid populations by the harlequin ladybird beetle. Increasing nitrogen fertilizer levels decreased the predation rates, which were otherwise increased by the intercropping partner. The beneficial effects of the intercropping partner were eventually non‐existent at the highest nitrogen level tested. These results imply that the interaction between the presence of intercropping partner and the nitrogen fertilizer application affects the biocontrol activity of the natural enemies of insect pests. Thus, the compatibility between agricultural intensification and biocontrol strategies in integrated pest management programs need to be investigated. [ABSTRACT FROM AUTHOR]

The pea aphid, Acyrthosiphon pisum Harris, is able to colonize various habitats and form genetically distinct biotypes worldwide. In Chile, few genotypes are dominating in space and time and are qualified as "superclones". Here, we compared in the laboratory different biological features of the most common clones of A. pisum collected from pea (Ap1) and alfalfa (Ap2) fields, in order to gain some insight on their differential ability to colonize broad bean plants. We also studied their probing behavior, profiled their proteome and characterized their community of endosymbionts. We found that the Ap1 genotype performed better on Vicia faba and realized more salivation events in phloem than Ap2. In addition, Ap1 presented a higher prevalence of the endosymbiont Serratia symbiotica. Among the total of 40 proteins that were differentially expressed, 14 and 26 were upregulated in Ap1 and Ap2 genotypes, respectively. The symbionin from Buchnera aphidicola was found to be upregulated in Ap1. A field experiment showed that both genotypes were able to colonize wild legumes, with Ap1 reproducing better on Vicia nigricans than Ap2. However, Ap2 exhibited higher reproduction in the other three wild legumes, suggesting higher invasiveness capacity on wild plants. Variation in the ability to colonize, feeding behavior and the putative involvement of differentially regulated proteins between Ap1 and Ap2 are discussed in relation to their respective endosymbiotic composition, nutritional lifestyle and consequences on their "superclone" status. [ABSTRACT FROM AUTHOR]

Two members of the genus Capulavirus (Geminiviridae) are transmitted by aphids including Alfalfa leaf curl virus (ALCV) transmitted by Aphis craccivora. The capulavirus Euphorbia caput-medusae latent virus was shown here to be transmitted also by A. craccivora , using the population EuphorbiaSA. ALCV was transmissible by several A. craccivora populations including Robinia, but not the EuphorbiaSA population, reflecting a high transmission specificity. Typical of the circulative-persistent mode of transmission, ALCV persists through insect molts. ALCV accumulation and localization were analyzed in whole insects, midguts, hemolymphs, and heads of aphids from vector and non-vector populations of A. craccivora and from the non-vector species Acyrthosiphon pisum. Vector and non-vector populations could be distinguished by contrasted virus accumulations and midgut intracellular localization consistent with a gut barrier to the transmission of ALCV in A. pisum and a primary salivary gland barrier in A. craccivora. • ALCV is transmitted by Aphis craccivora in a persistent circulative mode. • At least two capulaviruses are transmitted by members of the A. craccivora group. • Not all A. craccivora populations are vectors of ALCV. • In Acyrthosiphon pisum the gut was identified as an ALCV transmission barrier. • In A. craccivora the salivary glands were identified as an ALCV transmission barrier. [ABSTRACT FROM AUTHOR]

Effector proteins play crucial roles in determining the outcome of various plant-parasite interactions. Aphids inject salivary effector proteins into plants to facilitate phloem feeding, but some proteins might trigger defense responses in certain plants. The pea aphid, Acyrthosiphon pisum , forms multiple biotypes, and each biotype is specialized to feed on a small number of closely related legume species. Interestingly, all the previously identified biotypes can feed on Vicia faba ; hence, it serves as a universal host plant of A. pisum. We hypothesized that the salivary effector proteins have a key role in determining the compatibility between specific host species and A. pisum biotypes and that each biotype produces saliva containing a specific mixture of effector proteins due to differential expression of encoding genes. As the first step to address these hypotheses, we conducted two sets of RNA-seq experiments. RNA-seq analysis of dissected salivary glands (SGs) from reference alfalfa- and pea-specialized A. pisum lines revealed common and line-specific repertoires of candidate salivary effector genes. Based on the results, we created an extended catalogue of A. pisum salivary effector candidates. Next, we used aphid head samples, which contain SGs, to examine biotype-specific expression patterns of candidate salivary genes. RNA-seq analysis of head samples of alfalfa- and pea-specialized biotypes, each represented by three genetically distinct aphid lines reared on either a universal or specific host plant, showed that a majority of the candidate salivary effector genes was expressed in both biotypes at a similar level. Nonetheless, we identified small sets of genes that were differentially regulated in a biotype-specific manner. Little host plant effect (universal vs. specific) was observed on the expression of candidate salivary genes. Analysis of previously obtained genome re-sequenced data of the two biotypes revealed the copy number variations that might explain the differential expression of some candidate salivary genes. In addition, at least four candidate effector genes that were present in the alfalfa biotype but might not be encoded in the pea biotype were identified. This work sets the stage for future functional characterization of candidate genes potentially involved in the determination of plant specificity of pea aphid biotypes. [ABSTRACT FROM AUTHOR]

BACKGROUND: Pea aphid (Acyrthosiphon pisum Harris) is one of the major pests in alfalfa crops, causing significant yield losses. (E)‐β‐farnesene (EβF), an alarm pheromone released by pea aphid, is generic to many species of aphids, and is used to minimize potential danger from predators and parasitoids by avoiding the source of the pheromone. RESULTS: In this study, EβF synthase gene was constructed into a plant expression vector, and overexpressed in alfalfa (Medicago sativa L.), with expression among transgenic lines confirmed by qRT‐PCR. Subcellular localization analysis showed that EβF synthase gene was expressed in the plasma membrane and nucleus of the leaf. GC/MS of extraction from transgenic alfalfa indicated emission of EβF ranging from 5.92 to 13.09 ng day−1 g−1 fresh tissue. Behavior assays in Y‐olfactometers demonstrated that transgenic alfalfa expressing AaEβF gene could repel pea aphids, with aphids taking a significantly longer time to select a transgenic line compared with the control line (P < 0.01). CONCLUSION: We have demonstrated a potentially valuable strategy of using EβF synthase genes for aphid control in alfalfa. © 2018 Society of Chemical Industry This study explored that the ectopic expression of AaEβF induced the emission of (E)‐β‐farnesene in alfalfa. The emission affected the aphid behavior and repelled pea aphids from the transgenic alfalfa plants. [ABSTRACT FROM AUTHOR]

One of the most serious pests of commercial Fabaceae crops especially alfalfa is the pea aphid Acyrthosiphon pisum Harris. The pea aphid damages crops directly caused chlorosis and necrosis, leading to significant alfalfa loss worldwide. Hence the need for aphid management and use of insecticides. It was studied the effect of a biological insecticide Agricolle and two biological nano-fertilizers (Nagro and Lytovit) to a control of pea aphid, Acyrthosiphon pisum (Hemiptera, Sternorrhyncha: Aphididae) and changes in plastid pigment and total nitrogen contents in alfalfa. On the basis of the sweeping with the entomological net average number of aphids and mortality were calculated on the 1, 5, 7 and 9 days after treatment. It was found that the treatment with biological products Agricolle, Nagro and Litovit used alone and in combinations reduced Acyrthosiphon pisum density in a different range. After application of Agricolle with Nagro combination, followed by Agricolle was found the lowest density and the highest aphid mortality. Biological products increased the total pigment content as the highest impact demonstrated used of Agricolle with Nagro-33.4 % increase, followed by treatment with Nagro-29.6 %. Chlorophyll a to chlorophyll b as well as green pigments to carotenoids ratio determined plants treated with Agricolle + Nagro and Nagro as plants with the best physiological state. Alfalfa fixed the most nitrogen (respectively more with 2.77 and 2.95 kg N/kg dry mass yield in compared to control) in the combined treatment of Aricolle with Nagro and Litovit. [ABSTRACT FROM AUTHOR]

One of the most serious pests of commercial Fabaceae crops especially alfalfa is the pea aphid Acyrthosiphon pisum Harris. The pea aphid damages crops directly caused chlorosis and necrosis, leading to significant alfalfa loss worldwide. Hence the need for aphid management and use of insecticides. It was studied the effect of a biological insecticide Agricolle and two biological nano-fertilizers (Nagro and Lytovit) to a control of pea aphid, A. pisum (Hemiptera, Sternorrhyncha: Aphididae) and changes in plastid pigment and total nitrogen contents in alfalfa. On the basis of the sweeping with the entomological net average number of aphids and mortality were calculated on the 1, 5, 7 and 9 days after treatment. It was found that the treatment with biological products Agricolle, Nagro and Litovit used alone and in combinations reduced A. pisum density in a different range. After application of Agricolle with Nagro combination, followed by Agricolle was found the lowest density and the highest aphid mortality. Biological products increased the total pigment content as the highest impact demonstrated used of Agricolle with Nagro-33.4% increase, followed by treatment with Nagro-29.6%. Chlorophyll a to chlorophyll b as well as green pigments to carotenoids ratio determined plants treated with Agricolle + Nagro and Nagro as plants with the best physiological state. Alfalfa fixed the most nitrogen (respectively more with 2.77 and 2.95 kg N/kg dry mass yield in compared to control) in the combined treatment of Aricolle with Nagro and Litovit. [ABSTRACT FROM AUTHOR]

Organic pesticides can be excellent alternatives to chemical pesticides. They occupy an important place in the plant protection sector. Evaluation of the efficacy was conducted using an alginate from seaweed (organic insecticide) and two organic fertilizers (highly concentrated complex organic fertilizer and natural CO2 fertilizer), used alone and in combinations to control major pests in alfalfa seed production such as alfalfa seed chalcid Bruchophagus roddi Guss., alfalfa plant bug, Adelphocoris lineolatus Goeze and pea aphid, Acyrthosiphon pisum Harr. We conducted field trials during three growing seasons. Treatments were carried out at the beginning of the flowering stage in second regrowth. The seaweed alginate had high efficacy and excellent control on the three insect species density one week after treatment (over 80%), while the complex organic fertilizer exhibited insecticidal action against pests and its effect exceeded 60% seventy days after treatment and provided a medium level of control. The mix of the two organic products provided the highest efficacy and long-lasting effects on the three insect species and additive effects were observed. The combination realized the highest seed yield and an increase of 29.7%. Treatment with organic products is suitable for organic farming. [ABSTRACT FROM AUTHOR]

Although phytophagous insects can vary genetically in host use and exhibit long-range movements, the combined implications of these phenomena for pest management have received limited attention., To address this, we surveyed the genetic diversity of pea aphid Acyrthosiphon pisum using twelve microsatellite loci and assessed host association patterns and annual movement from a putative source region (Columbia River Basin) to the Palouse region of northern Idaho and western Washington, where the aphid is a pest of pea Pisum sativum., A total of 320 identified unique genotypes clustered into four genetic groups, with two host plant associations: alfalfa Medicago sativa (three genetic groups), and pea Pisum sativum and vetch Vicia villosa (one genetic group). All four genetic groups occurred in the Columbia River Basin and in migrant aphids collected in pan traps during spring colonization in the Palouse during 2 years of this study. Patterns of group arrival on the Palouse were spatially structured early in the season, consistent with differing migration patterns. Despite genetic diversity of migrants, a single genetic group became predominant in pea crops each year., Clonal laboratory colonies of pea aphids established from field-collected specimens and representing two predominant genetic groups exhibited reciprocal performance trade-offs, with alfalfa being a poor host for a pea-associated aphid genotype and vice versa., Synthesis and applications. Annual spring migrants of pea aphids in the pea production region of the Palouse are genetically diverse, with different host plant affinities consistent with origination from source populations in the Columbia River Basin. As the season progresses, a single genetic group adapted to pea becomes predominant in the crop. Management of pea aphid in the Palouse will be improved by monitoring the temporal and spatial variation of specific genetic groups of the aphid arriving as immigrants during each crop season, providing this information to producers and adjusting estimates of risk of crop damage accordingly. The principle could apply to other pest species with host-adapted populations that colonize crops on an annual basis. [ABSTRACT FROM AUTHOR]

Two important lady beetle species commonly found in alfalfa fields in Iran are the variegated lady beetle Hippodamia variegata Goeze and the seven spotted lady beetle Coccinella septempunctata (Linnaeus, 1758) (Coleoptera: Coccinellidae). These two species attack many aphid species including the pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae). In this study, the seasonal population changes of A. pisum, H. variegata, C. septempunctata and the parasitoid, Dinocampus coccinellae (Schrank) (Hymenoptera: Braconidae) were studied in alfalfa fields in the 2012 and 2013 seasonal periods. The highest ladybird densities were noted on July 5, 2012 and on September 6, 2013 (17.2±2.8 and 13.4±1.6) individuals per 20 sweeps, respectively. Parasitism rates by D. coccinellae ranged from approximately 3 to 6% in two subsequent years, respectively. Parasitism was higher early in the growing season. Most parasitised ladybirds were females. There was no significant relationship between the temperature and relative humidity with pea aphid populations, although the aphid populations declined during the hot summer period. In contrast, the relationship between temperature and the H. variegata population was significant and positive in both years of the study. It has been shown that these lady beetle species have a major role in reducing the pea aphid populations in alfalfa fields. Due to the relatively low percentage of field parasitism by D. coccinellae, this parasite might not reduce the biocontrol efficiency of lady beetle species. [ABSTRACT FROM AUTHOR]

The biological control service supplied to croplands is a result of the predator community present within a focal crop, which is likely influenced by surrounding landscape composition and configuration. In this study, using cage experiments in two regions near Santiago, we determined if predator communities supplied a significant biological control service in alfalfa fields, examined how the abundance of exotic and native coccinellids, as well as other key predator groups, influenced biological control of aphids and measured how landscape composition and heterogeneity at three spatial scales influenced this service. We found that predators significantly suppressed aphid populations in both regions, but the relative importance of predators versus landscape variables on biological control differed between regions. In the region where predators were abundant, biological control was higher and related to the abundance of native coccinellids and syrphids, highlighting the importance of native species as providers of crucial ecological services. In the region where predators were not abundant, biological control was lower, and it was related to landscape composition, being positively associated with the abundance of woodlots and urban habitats, and negatively associated with fruit crops in the landscape. Therefore, landscape effects on biological control service may be weaker than local factors, and only become important when local predator abundance is low. [ABSTRACT FROM AUTHOR]

Long-term environmental changes will likely alter the strengths of interactions between species and consequently their population dynamics, leading to changes in the stability of ecological systems. While an increasing number of empirical studies have shown that environmental changes can alter the strengths of species interactions, these studies are typically short (,1-2 generations) and therefore give only partial information about longer term population dynamics. To focus on longer term dynamics, we investigated population cycles of pea aphids and their most common parasitoid, Aphidius ervi, in Wisconsin, USA. Data collected over three years in alfalfa fields showed an apparent host—parasitoid population cycle. Furthermore, higher pea aphid population growth rates and increased parasitism were correlated with higher naturally occurring temperatures. While these effects were observed with seasonal fluctuations in temperature, they beg the question of how longterm changes in mean annual temperature might change aphid-parasitoid population cycles, a question which we further pursued with laboratory experiments. To quantify temperaturedependent demographic parameters, we used short-term (,1 generation) experiments conducted at 20°C and 27°C. The higher temperature increased aphid and parasitoid development rates, adult aphid life span and fecundity, and parasitoid attack rates. We then conducted multi-generation population-level laboratory experiments to reveal the effects of temperature (208C vs. 278C) on population dynamics. We fit the resulting time series data using a nonlinear age-structured state-space model to estimate population-level processes that could not be estimated in short-term laboratory experiments. Using the model, we parsed out the demographic rates that had the largest impacts on aphid-parasitoid population cycles. This analysis showed that there were frequent contrasts in the effects of temperature operating through different demographic rates. For example, the temperature-dependent increase in aphid development rate decreased cycle amplitude, while the increase in parasitoid attack rate increased cycle amplitude. There were also striking interactions among demographic rates. For example, the temperature-dependent increase in aphid development rate could either increase or decrease the cycle period depending on the values of other demographic rates. Although these complexities make predictions difficult, overall they suggest that increasing long-term mean temperature will decrease the period, increase the amplitude, and tend to destabilize pea aphid—A. ervi dynamics. [ABSTRACT FROM AUTHOR]

Predicted increases in atmospheric carbon dioxide ( CO2) concentrations could modify crop resistance to insect herbivores by altering plant quality. The short generation times of aphids may allow them to exploit such changes and colonise previously resistant plant genotypes. Lucerne ( Medicago sativa) has undergone global selective breeding against aphids, including the pea aphid, Acyrthosiphon pisum. The purpose of this study was to characterise how ambient CO2 ( aCO2) and elevated ( eCO2) (400 and 600 µmol mol−1, respectively) affected plant physiological traits potentially linked to aphid resistance, focussing on foliar amino acid concentrations, across five M. sativa genotypes with varying resistance to A. pisum. These included susceptible (Hunter River), low (Trifecta), moderate (Aurora and Genesis) and high resistance (Sequel). Under eCO2, root nodulation doubled and essential amino acid concentrations increased by 86% in resistant Sequel, whereas essential amino acid concentrations decreased by 53% in Genesis. Moreover, concentrations of lysine, an amino acid whose deficiency has been linked previously to A. pisum resistance in M. sativa, increased by 127% in Sequel at eCO2. Compared with aCO2, aphid colonisation of Sequel plants rose from 22% to 78% and reproduction rates increased from 1.1 to 4.3 nymphs week−1 under eCO2 conditions. In contrast, Genesis became more resistant at eCO2 compared with plants at aCO2; aphid colonisation rates fell from 78% to 44% of plants and reproductive rates decreased from 4.9 to 1.7 nymphs week−1. In conclusion, predicted changes in atmospheric CO2 concentrations could either reduce (Sequel) or enhance (Genesis) resistance to aphids, which might be linked to quantitative and qualitative changes in foliar amino acids. [ABSTRACT FROM AUTHOR]

Climate change can affect species directly and indirectly by altering interactions between species within communities. These indirect effects can ramify through a community and affect many species, including some that may not have been directly affected by the perturbation. Identifying these chains of indirect effects is difficult, and most studies only follow indirect effects across two or three species. Here, we use a factorial field experiment to demonstrate that precipitation affects spotted aphids through a complex chain of indirect interactions that are mediated by other herbivores and a generalist predator. We experimentally simulated drought, which reduced water content in alfalfa plants. While water stress in alfalfa had no direct effect on spotted aphids, it lowered the population growth rate of pea aphids, another common alfalfa pest. Because ladybeetle predators were attracted to high pea aphid densities, predator densities were lower in drought treatments. Consequently, spotted aphid densities were released from top-down control (apparent competition) in drought treatments and reached densities three times higher than spotted aphids in ambient treatments with high pea aphid densities. Thus, drought affected spotted aphids in the interaction chain: drought --» alfalfa --> pea aphids --> predators --» spotted aphids. This result illustrates the lengthy path that indirect effects of climate change may take through a community, as well as the importance of community-level experiments in determining the net effect of climate change. [ABSTRACT FROM AUTHOR]

Highlights: [•] Acyrthosiphon pisum was used as sentinel prey in alfalfa to study predators segregation. [•] A seasonal, day–night and foliage–ground segregation of predators was observed. [•] Coccinellids were the main predators, with daytime activity mainly in spring and summer. [•] Syphids were the main nighttime predators in spring and summer. [•] More predatory activity was observed on the foliage than on the ground. [ABSTRACT FROM AUTHOR]

Lucerne or alfalfa Medicago sativa is the most important temperate forage legume worldwide. Only one or two varieties of lucerne were grown in the U.S.A. and Australia (the two leading exporters of lucerne) before the late 1950s and late 1970s, respectively. These dates coincided with the arrival of aphid species, which devastated lucerne stands and prompted the development of aphid resistant cultivars., Lucerne-feeding aphids, including bluegreen aphids Acyrthosiphon kondoi, pea aphids Acyrthosiphon pisum, spotted alfalfa aphids Therioaphis trifolii maculata and cowpea aphids Aphis craccivora, however, still present significant risks for the lucerne industry worldwide and account for 25% of global production losses. Moreover, increased production costs, negative environmental effects and emerging aphid resistance to insecticide applications have led to a narrowing of management options against lucerne aphids., Understanding lucerne aphid biology and trophic ecology will be needed to develop future management practices, including biological control. We review and synthesize research on the four lucerne aphid species, focussing on cultivar resistance and their interactions with other organisms, including predators, parasitoids, entomopathogens and bacterial symbionts. The effects of global climate change are considered, with a particular emphasis on the potential for compromised aphid resistance in lucerne cultivars under future climates., We conclude by identifying future research questions and perspectives for the sustainable management of lucerne aphids. These include the characterization of plant secondary metabolites associated with natural enemy recruitment, an understanding of the role of endosymbionts in cultivar resistance and a better comprehension of multi-trophic interactions of lucerne aphids, both with other herbivores and higher trophic groups. [ABSTRACT FROM AUTHOR]

We examined the effects of nonhost plant diversity and predators on the potato leafhopper, Empoasca fabae (Harris), the pea aphid, Acyrthosiphon pisum (Harris), and their primary host plant, alfalfa, Medicago sativa L. Potato leafhopper intensity (i.e., leafhoppers/alfalfa stem density) and plant damage (i.e., hopperburn) were significantly greater in alfalfa mono- than in polycultures of alfalfa mixed with nonhost plant species. There was no significant effect of nonhost plant diversity on pea aphid intensity or on predator abundance. Predator:prey ratios were higher in poly- than in monoculture. One predator, Nabis sp., was selected for further study. A microcosm experiment indicated that Nabis is an effective predator of both herbivores, and suggested that nonhost plant diversity may enhance the predation of leafhoppers by Nabis. These results suggest that nonhost plant diversity and Nabis limit leafhopper populations and protect alfalfa from herbivory. The potential for nonhost plants to increase herbivore movement and vulnerability to predation is discussed. [ABSTRACT FROM AUTHOR]

Field assessments were conducted to examine the interplay between host plant and predation in complex agricultural mosaic on pea aphid clover and alfalfa races. In one experiment, we examined the relative fitness on clover race (CR) and alfalfa race (AR) pea aphids on broad bean, red clover and alfalfa alone. But because clover is typically grown in a more complex agricultural mosaic with alfalfa and broad bean, a second experiment was conducted to assess the fitness consequences under predation in a more complex agricultural field setting that also included potential apparent competition with AR pea aphids. In a third experiment we tested for the effect of differential host race density on the fitness of the other host race mediated by a predator effect. CR pea aphids always had fitness losses when on broad bean (had lower fitness on broad bean relative to red clover) and fitness benefits when on red clover (higher fitness on red clover relative to broad bean), whether or not in apparent competition with alfalfa race aphids on bean and alfalfa. AR suffered fitness loss on both alfalfa and bean in apparent competition with CR on clover. Therefore we can conclude that the predation rate between host races was highly asymmetrical. The complexity of the agricultural mosaic thus can influence prey selection by predators on different host plants. These may have evolutionary consequences through context dependent fitness benefits on particular host plants. [ABSTRACT FROM AUTHOR]

Flavonoids play an important role in interactions of plants with the environment. Liquid chromatography (HPLC) was used to determine the flavonoid profiles (especially luteolin, tricin, and chrysoeriol glycosides), their total concentrations, and changes in the amounts of eight flavones found in the aerial parts of alfalfa (Medicago sativa L.) (Fabaceae) Radius cv., uninfested and infested by the pea aphid (Acyrthosiphon pisum Harris) (Homoptera: Aphididae). It was shown that both control and infested green aerial parts of alfalfa plants had similar flavonoid profiles. The dominant flavonoid of alfalfa was compound 7-O-[2-O-feruloyl-ß-D-glucuronopyranosyl(1→2)-O-ß-D-glucuronopyranosyl]-4'-O-ß-D-glucuronopyranosideluteolin. Compound 7-O-{2'-O-feruloyl-[ß-D-glucuronopyranosyl(1→3)]-O-ß-D- glucuronopyranosyl(1→2)-O-ß-D-glucuronopyranosidetricin was present in the smallest amounts. The total concentration of flavones was rather high and ranged from 11.13 to 12.34 mg/g d.m., but there were no significant differences between uninfested and infested alfalfa plants. There was a correlation between the concentration of flavonoid glycosides in the alfalfa plants and pea aphid abundance. Pea aphid daily fecundity per female was affected by luteolin, tricin, and chrysoeriol glycosides and the level of chrysoeriol glycosides affected ingestion of xylem sap by the aphid. This finding may indicate that the studied flavonoid glycoside forms are biologically active in alfalfa -- A. pisum interactions. [ABSTRACT FROM AUTHOR]

Abstract: The availability of plant resources to omnivorous arthropod predators may have a positive, negative or negligible effect on their population densities and predation rates, depending on the availability of prey. At high prey densities, flowering buckwheat has been shown to negatively impact populations of the brown lacewing, an omnivorous predator, due to the probable increase in parasitism rate of lacewing larvae by their primary parasitoid, Anacharis zealandica. However, little is known about the effect of buckwheat flowers on this insect community at low prey densities. We used field cages to assess the effects of nectar provision by flowering buckwheat on the population dynamics of the pea aphid, the brown lacewing and its parasitoid A. zealandica in an alfalfa field, under low aphid densities in the New Zealand summer. The insects were sampled every 2weeks with a suction device, then counted and released on each sampling date from 15 January to 15 March 2007. Buckwheat significantly increased lacewing populations and significantly decreased aphid numbers by 70% and 39%, respectively. The buckwheat had its greatest effect at the end of summer (February/March) for both these species. It had no effect on A. zealandica abundance. [ABSTRACT FROM AUTHOR]

Reproductive potentials were compared for a large invasive lady beetle, sevenspotted lady beetle, Coccinella septempunctata L. (Coleoptera: Coccinellidae), and a set of four smaller native North American species that have been displaced from alfalfa, Medicago sativa L., fields in Utah. The invader rapidly attained predominance in these fields during years when aphid populations were high. In a laboratory experiment, females were provided with excess numbers of their principal prey in these fields, pea aphids, Acyrthosiphon pisum (Harris). Among the five species, both the number and total volume of eggs (number x mean egg volume) produced per day increased with increasing female size and were greatest for C. septempunctata. Rates of reproduction also increased with increasing female size within species. Similarly sized females of C. septempunctata and transverse lady beetle, Coccinella transversoguttata richardsoni (Brown), laid similar total volumes of eggs per day, but females of the invasive species had more ovarioles and laid larger numbers of individually smaller eggs. In summary, when feeding on abundant prey in a habitat in which it predominates, the invasive C. septempunctata gains reproductive advantage over native, North American lady beetles, from its large body size and its investment in many small eggs. The results support the generalization that high fecundity linked with large body size may often be one important factor that promotes the dominance of introduced species over native competitors in resource-rich environments. [ABSTRACT FROM AUTHOR]

Aphidophagous lady beetles enhance their foraging success in natural settings by consuming other types of food in addition to aphids. Frass analysis was used to examine natural diets of female lady beetles in fields of alfalfa (Medicago sativa L.) in northern Utah. The first (spring) alfalfa crop was censused in 2004 and 2005 to determine the diet of female adults of the introduced Coccinella septempunctata L., and two native species, C. transversoguttata richardsoni Brown, and Hippodamia convergens Guerin. The proportion of females of the three lady beetle species that fed on pea aphids [Acyrthosiphon pisum (Harris)] and alfalfa weevil larvae [Hypera postica (Gyllenhal), an abundant alternative prey] increased from early to late season during the first crop. A corresponding seasonal decrease occurred in the proportion of females consuming other types of arthropods (e.g., thrips and collembolans) and nonarthropod food (pollen and fungal spores). Overall, frass analysis indicated that the diets of C. septempunctata and the two native species in alfalfa were similar in their inclusion of a broad variety of foods. The study shows that frass analysis can provide a good overview of the diets of lady beetles in natural settings. [ABSTRACT FROM AUTHOR]

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The relationships between predatory Heteroptera and their potential prey species were investigated during two crop seasons in an inter-mountain area close to the Pyrenees (Iberian Peninsula). Regression was used to analyze the potential numerical responses shown by heteropterans to aphids and other potential prey during alfalfa intercuts (the plant growth period between cuts) of high aphid occurrence. The most abundant heteropterans were Orius spp., Nabis spp. and mirids, and all were present in alfalfa stands throughout the season. Acyrthosiphon pisum was the prevalent species during the 2nd intercut, Therioaphis trifolii during the 4th and Aphis craccivora during the 5th. We performed simple regression analysis between the Orius sp., Nabis sp. and mirids and the prevalent aphid species, forward multiple regression analysis between heteropterans and all possible soft-bodied prey species; and both analyses for coccinellids, as relative aphid predator specialists. The heteropterans responded numerically to A. pisum but not to T. trifolii or A. craccivora. Heteropterans also showed numerical responses to other potential prey (leafhoppers, thrips, and other soft bodied prey) that remained at low densities throughout the season. All these preys may contribute to the presence of heteropterans in alfalfa stands throughout the season. The results suggest that heteropterans may contribute to reduce A. pisum, particularly at the beginning of the growing season, and on other potential pests when they invade or recolonize alfalfa, and may help to delay or prevent the build-up of these pest populations. [ABSTRACT FROM AUTHOR]

We studied the development and feeding behaviour of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), on the Radius and Sapko alfalfa ( Medicago sativa L.) (Fabaceae) cultivars. Three saponins and flavones were identified in the alfalfa cultivars after thin layer chromatography separation. Cultivar Radius differed from Sapko in that it had a higher level of saponins, including zanhic acid tridesmoside and 3-GlcA,28-AraRhaXyl medicagenic acid glycoside. The flavones identified, including 7- O-β-D-glucuronopyranosyl-4′- O-[2′- O-E-feruloyl- O-β-D-glucuronopyranosyl(1→2)- O-β-D-glucuronopyranoside] apigenin, 7- O-{2- O-E-feruloyl-[β-D-glucuronopyranosyl(1→3)]- O-β-D-glucuronopyranosyl(1→2)- O-β-D-glucuronopyranoside} apigenin, and 4′- O-[2′- O-E-feruloyl- O-β-D-glucuronopyranosyl(1→2)- O-β-D-glucuronopyranoside] apigenin, occurred in tissues of both alfalfa cultivars. However, cv. Radius had very low mean flavonoid concentrations in comparison to cv. Sapko. Pea aphids that fed on cv. Radius plants showed a reduction in reproduction and survival. The aphid pre-reproductive period on cv. Radius was prolonged and the reproductive and post-reproductive periods on cv. Radius were reduced, compared to those on cv. Sapko. Cultivar Radius also negatively influenced aphid probing behaviour. This was especially the case during the initial period of the pathway phase. The results suggested that alfalfa cv. Radius, which had a higher level of saponins and a lower level of flavonoids, was less accepted by the pea aphid. [ABSTRACT FROM AUTHOR]

Abstract: Pea aphid fed on a high-saponin line of alfalfa showed reduction of reproduction and survival, and disturbance in development of its population. This line negatively influenced aphid probing behaviour, particularly prolonging the non-probing period and probing of the peripheral tissues (epidermis and mesophyll) and shortening the period of phloem sap ingestion. The high-saponin line of alfalfa differed from the low-saponin one by the presence of zanhic acid tridesmoside and a higher level of 3-GlcA,28-AraRhaXyl medicagenic acid glycoside. The saponins incorporated into sucrose–agarose gels significantly reduced number of the aphid probes into the gels and extended their duration in comparison to the control gels (without tested compounds). Role of zanhic acid tridesmoside and 3-GlcA,28-AraRhaXyl medicagenic acid glycoside as potential factors for partial resistance of alfalfa towards the pea aphid is discussed. [Copyright &y& Elsevier]

The pea aphid, Acyrthosiphon pisum, encompasses distinct host races specialized on various Fabaceae species, but the extent of genetic divergence associated with ecological specialization varies greatly depending on plant and geographic origins of aphid populations. Here, we studied the genetic structure of French sympatric pea aphid populations collected on perennial (pea and faba bean) and annual (alfalfa and red clover) hosts using 14 microsatellite loci. Classical and Bayesian population genetics analyses consistently identified genetic clusters mostly related to plant origin: the pea/faba bean cluster was highly divergent from the red clover and the alfalfa ones, indicating they represent different stages along the continuum of genetic differentiation. Some genotypes were assigned to a cluster differing from the one expected from their plant origin while others exhibited intermediate genetic characteristics. These results suggest incomplete barriers to gene flow. However, this limited gene flow seems insufficient to prevent ecological specialization and genetic differentiation in sympatry. [ABSTRACT FROM AUTHOR]