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Plant breeding is used to develop crops with host resistance to aphids, however, virulent biotypes often develop that overcome host resistance genes. We tested whether the symbionts, Arsenophonus (A) and Wolbachia (W), affect virulence and fecundity in soybean aphid biotypes Bt1 and Bt3 cultured on whole plants and detached leaves of three resistant, Rag1, Rag2 and Rag1  +  2, and one susceptible, W82, soybean genotypes. Whole plants and individual aphid experiments of A. glycines with and without Arsenophonus and Wolbachia did not show differences in overall fecundity. Differences were observed in peak fecundity, first day of deposition, and day of maximum nymph deposition of individual aphids on detached leaves. Bt3 had higher fecundity than Bt1 on detached leaves of all plant genotypes regardless of bacterial profile. Symbionts did not affect peak fecundity of Bt1 but increased it in Bt3 (A+W+) and all Bt3 strains began to deposit nymphs earlier than the Bt1 (A+W−). Arsenophonus in Bt1 delayed the first day of nymph deposition in comparison to aposymbiotic Bt1 except when reared on Rag1  +  2. For the Bt1 and Bt3 strains, symbionts did not result in a significant difference in the day they deposited the maximum number of nymphs nor was there a difference in survival or variability in number of nymphs deposited. Variability of number of aphids deposited was higher in aphids feeding on resistant plant genotypes. The impact of Arsenophonus on soybean aphid patterns of fecundity was dependent on the aphid biotype and plant genotype. Wolbachia alone had no detectable impact but may have contributed to the increased fecundity of Bt3 (A+W+). An individual based model, using data from the detached leaves experiment and with intraspecific competition removed, found patterns similar to those observed in the greenhouse and growth chamber experiments including a significant interaction between soybean genotype and aphid strain. Combining individual data with the individual based model of population growth isolated the impact of fecundity and host resistance from intraspecific competition and host health. Changes to patterns of fecundity, influenced by the composition and concentration of symbionts, may contribute to competitive interactions among aphid genotypes and influence selection on virulent aphid populations. [ABSTRACT FROM AUTHOR]

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is one of the greatest threats to soybean production, and both trend analysis and periodic analysis of its population dynamics are important for integrated pest management (IPM). Based on systematically investigating soybean aphid populations in the field from 2018 to 2020, this study adopted the inverse logistic model for the first time, and combined it with the classical logistic model to describe the changes in seasonal population abundance from colonization to extinction in the field. Then, the increasing and decreasing phases of the population fluctuation were divided by calculating the inflection points of the models, which exhibited distinct seasonal trends of the soybean aphid populations in each year. In addition, multifactor logistic models were then established for the first time, in which the abundance of soybean aphids in the field changed with time and relevant environmental conditions. This model enabled the prediction of instantaneous aphid abundance at a given time based on relevant meteorological data. Taken as a whole, the successful approaches implemented in this study could be used to build a theoretical framework for practical IPM strategies for controlling soybean aphids.

Plant breeding is used to develop crops with host resistance to aphids, however, virulent biotypes often develop that overcome host resistance genes. We tested whether the symbionts, Arsenophonus (A) and Wolbachia (W), affect virulence and fecundity in soybean aphid biotypes Bt1 and Bt3 cultured on whole plants and detached leaves of three resistant, Rag1, Rag2 and Rag1  +  2, and one susceptible, W82, soybean genotypes. Whole plants and individual aphid experiments of A. glycines with and without Arsenophonus and Wolbachia did not show differences in overall fecundity. Differences were observed in peak fecundity, first day of deposition, and day of maximum nymph deposition of individual aphids on detached leaves. Bt3 had higher fecundity than Bt1 on detached leaves of all plant genotypes regardless of bacterial profile. Symbionts did not affect peak fecundity of Bt1 but increased it in Bt3 (A+W+) and all Bt3 strains began to deposit nymphs earlier than the Bt1 (A+W−). Arsenophonus in Bt1 delayed the first day of nymph deposition in comparison to aposymbiotic Bt1 except when reared on Rag1  +  2. For the Bt1 and Bt3 strains, symbionts did not result in a significant difference in the day they deposited the maximum number of nymphs nor was there a difference in survival or variability in number of nymphs deposited. Variability of number of aphids deposited was higher in aphids feeding on resistant plant genotypes. The impact of Arsenophonus on soybean aphid patterns of fecundity was dependent on the aphid biotype and plant genotype. Wolbachia alone had no detectable impact but may have contributed to the increased fecundity of Bt3 (A+W+). An individual based model, using data from the detached leaves experiment and with intraspecific competition removed, found patterns similar to those observed in the greenhouse and growth chamber experiments including a significant interaction between soybean genotype and aphid strain. Combining individual data with the individual based model of population growth isolated the impact of fecundity and host resistance from intraspecific competition and host health. Changes to patterns of fecundity, influenced by the composition and concentration of symbionts, may contribute to competitive interactions among aphid genotypes and influence selection on virulent aphid populations. [ABSTRACT FROM AUTHOR]

Simple Summary: Understanding how insect predators utilize different crops and natural habitats is crucial to improve the ecological service of pest control in agricultural landscapes. The aim of this study was to develop a better understanding of how adjacent habitats contribute predators during pest outbreaks. We used a soybean aphid outbreak to test how adjacent habitats impact predator movement and abundance in soybean. We found that hoverflies and ladybeetles were the most common predators moving into soybean and their movement was related to the presence of aphids. In general, we found annual crops had more predators than a perennial crop or habitat. Our study suggests that adjacent wheat and canola fields result in more predators moving into soybean to control aphids than adjacent alfalfa or woody vegetation. Crops and semi-natural habitats provide predator populations with varying floral and prey resources, but their individual role on predator movement has seldom been studied. Here, we tease apart the role of adjacent habitats, predator abundance in the adjacent habitat, and soybean aphid (Aphis glycines Matsumura) abundance in soybean (Glycine max (L.) Merr.) on predator movement into soybean. We studied 12 soybean fields adjacent to alfalfa (Medicago sativa L.), canola (Brassica napus L.), spring wheat (Triticum aestivum L.), or woody vegetation, during a soybean aphid outbreak. Bidirectional Malaise traps and sticky traps were used to quantify predator movement between and abundance within soybean and adjacent habitats, respectively. Field plant counts were conducted to quantify aphid abundance in soybean. Coccinellidae and Syrphidae were the two most abundant families collected. Coccinellids and Eupeodes americanus (Wiedemann) (Diptera: Syrphidae) had net movement in soybean and their movement increased with aphid abundance. Movement of E. americanus was highest from wheat, coccinellid abundance was higher in wheat than woody vegetation, Toxomerus marginatus (Say) (Diptera: Syrphidae) abundance was highest in canola, and all other predators were more abundant in canola than woody vegetation. In general, our study suggests that annual crops have and provide more predators to soybean during aphid outbreaks than perennial habitats. [ABSTRACT FROM AUTHOR]

Plant breeding is used to develop crops with host resistance to aphids, however, virulent biotypes often develop that overcome host resistance genes. We tested whether the symbionts, Arsenophonus (A) and Wolbachia (W), affect virulence and fecundity in soybean aphid biotypes Bt1 and Bt3 cultured on whole plants and detached leaves of three resistant, Rag1, Rag2 and Rag1 + 2, and one susceptible, W82, soybean genotypes. Whole plants and individual aphid experiments of A. glycines with and without Arsenophonus and Wolbachia did not show differences in overall fecundity. Differences were observed in peak fecundity, first day of deposition, and day of maximum nymph deposition of individual aphids on detached leaves. Bt3 had higher fecundity than Bt1 on detached leaves of all plant genotypes regardless of bacterial profile. Symbionts did not affect peak fecundity of Bt1 but increased it in Bt3 (A+W+) and all Bt3 strains began to deposit nymphs earlier than the Bt1 (A+W−). Arsenophonus in Bt1 delayed the first day of nymph deposition in comparison to aposymbiotic Bt1 except when reared on Rag1 + 2. For the Bt1 and Bt3 strains, symbionts did not result in a significant difference in the day they deposited the maximum number of nymphs nor was there a difference in survival or variability in number of nymphs deposited. Variability of number of aphids deposited was higher in aphids feeding on resistant plant genotypes. The impact of Arsenophonus on soybean aphid patterns of fecundity was dependent on the aphid biotype and plant genotype. Wolbachia alone had no detectable impact but may have contributed to the increased fecundity of Bt3 (A+W+). An individual based model, using data from the detached leaves experiment and with intraspecific competition removed, found patterns similar to those observed in the greenhouse and growth chamber experiments including a significant interaction between soybean genotype and aphid strain. Combining individual data with the individual based model of population growth isolated the impact of fecundity and host resistance from intraspecific competition and host health. Changes to patterns of fecundity, influenced by the composition and concentration of symbionts, may contribute to competitive interactions among aphid genotypes and influence selection on virulent aphid populations.

The soybean aphid is one of the main damaging pests of soybean. Host resistance can effectively reduce the loss caused by the damage of soybean aphid. There are abundant soybean germplasm in China, however, few aphid resistant soybeans were identified and genetic backgrounds of them were poorly characterized. In this study, 22 soybean accessions with high soybean aphid resistance (resistant rating of 1) were identified from 1469 accessions by evaluation in the net house. Detailed evaluation of aphid resistance revealed that all of these 22 soybeans possess good resistance when infested with three initial densities of aphids (2, 10, and 50 aphids per plant). Sixteen SSR markers flanking the published aphid resistance genes including Rag1, rag1b, rag1c, Rag2, Rag3, Rag3b, Rag3d, Rag3e, rag3, rag4 and Rag5 had been identified. Meanwhile, SNPs of these 22 highly resistant soybeans and 11 check accessions carrying known Rag genes were genotyped by a genome-wide genotyping array containing 158,327 SNPs. These SSR markers and SNPs flanking Rag genes were then used to characterize the aphid resistance in the identified resistant soybeans. Fourteen of these accessions were found to carry resistance gene Rag2, six accessions carry Rag2 and Rag3/Rag3b/Rag3d/rag3, and one accession carries Rag1/rag1c and Rag2. Another one accession probably has novel aphid resistance genes since it harbors unique haplotype in the interval containing all tested Rag genes. These highly aphid resistant accessions and the information of aphid resistant loci provide valuable sources for further isolation of aphid resistance genes and breeding aphid resistant soybean cultivars. [ABSTRACT FROM AUTHOR]

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an important soybean pest in North America. In this study, A. glycines was fed on detached leaves of Glycine max (L.) Merrill (Fabaceae) at 20, 23, 26, 29, and 32 °C under 3 rearing methods: leaf-disc method, filter paper method, and moisturized cotton method. Aphis glycines life parameters, including nymph stage duration, adult lifespan, adult fecundity, adult body size, and intrinsic rate of increase were measured. There were no significant differences in nymph stage duration among these rearing methods at 20 to 32 °C. Within this temperature range, the filter paper method and the moisturized cotton method resulted in similar or greater adult lifespans, adult fecundities, adult body sizes, and intrinsic rates of increase in comparison to the leaf-disc method. When nymphs of A. glycines were reared at 20 to 29 °C, the experimental labor required for the moisturized cotton method was less than that for the filter paper method and the leaf-disc method. Considering the development, reproduction, and experimental labor, the moisturized cotton method is recommended as a good detached leaf method for rearing individual A. glycines. These conclusions will be useful and informational for researchers who study A. glycines, especially when selecting methods to rear A. glycines individually in the laboratory. El pulgón de la soja, Aphis glycines Matsumura (Hemiptera: Aphididae), es una plaga importante de la soja en América del Norte. En este estudio, A. glycines fue alimentado con hojas desprendidas de Glycine max (L.) Merrill (Fabaceae) a 20, 23, 26, 29 y 32 °C bajo 3 métodos de crianza: método de disco de hoja, método de papel de filtro y método de algodón humedecido. Se midieron los parámetros de vida del A. glycines, incluyendo la duración de la estadio del ninfa, la duración de vida de los adultos, la fecundidad, el tamaño corporal adulto y la tasa intrínseca de aumento. No hubo diferencias significativas en la duración del estadio de ninfa entre estos métodos de crianza a 20 a 32 °C. Dentro de este rango de temperatura, el método del papel de filtro y el método del algodón humedecido dieron resultados similares o mayores sobre la duración de vida de los adultos, la fecundidad, el tamaño corporal de adultos y la tasa intrínseca de aumento en comparación con el método del disco de hoja. Cuando se criaron las ninfas a una temperatura de 20 a 29 °C, el trabajo experimental requerido para el método del algodón humedecido fue menor que los métodos del papel de filtro y del disco de hoja. Teniendo en cuenta el desarrollo, la reproducción y el trabajo experimental, se recomienda el método del algodón humedecido como un buen método de hojas sueltas para criar los individuales de A. glycines. Estas conclusiones serán útiles e informativas para los investigadores que estudian A. glycines, especialmente al seleccionar métodos para criar A. glycines individualmente en el laboratorio. [ABSTRACT FROM AUTHOR]

Crops and semi-natural habitats provide predator populations with varying floral and prey resources, but their individual role on predator movement has seldom been studied. Here, we tease apart the role of adjacent habitats, predator abundance in the adjacent habitat, and soybean aphid (Aphis glycines Matsumura) abundance in soybean (Glycine max (L.) Merr.) on predator movement into soybean. We studied 12 soybean fields adjacent to alfalfa (Medicago sativa L.), canola (Brassica napus L.), spring wheat (Triticum aestivum L.), or woody vegetation, during a soybean aphid outbreak. Bidirectional Malaise traps and sticky traps were used to quantify predator movement between and abundance within soybean and adjacent habitats, respectively. Field plant counts were conducted to quantify aphid abundance in soybean. Coccinellidae and Syrphidae were the two most abundant families collected. Coccinellids and Eupeodes americanus (Wiedemann) (Diptera: Syrphidae) had net movement in soybean and their movement increased with aphid abundance. Movement of E. americanus was highest from wheat, coccinellid abundance was higher in wheat than woody vegetation, Toxomerus marginatus (Say) (Diptera: Syrphidae) abundance was highest in canola, and all other predators were more abundant in canola than woody vegetation. In general, our study suggests that annual crops have and provide more predators to soybean during aphid outbreaks than perennial habitats.

The soybean aphid (Aphis glycines Matsumura) is an economically important invasive pest of soybean. In addition to damage caused by soybean aphid feeding on the phloem sap, this insect also transmits many plant viruses, including soybean mosaic virus (SMV). Previous work has shown that plant viruses can change plant host phenotypes to alter the behavior of their insect vectors to promote virus spread, known as the vector manipulation hypothesis. In this study, we used electropenetography (EPG) to examine the effects of two plant viruses on soybean aphid feeding behavior: SMV, which is transmitted by many aphid species including the soybean aphid, and bean pod mottle virus (BPMV), which is transmitted by chrysomelid and some coccinellid beetles but not aphids. These two viruses often co-occur in soybean production and can act synergistically. Surprisingly, our results showed little to no effect of SMV on soybean aphid feeding behaviors measured by EPG, but profound differences were observed in aphids feeding on BPMV-infected plants. Aphids took longer to find the vascular bundle of BPMV-infected plants, and once found, spent more time entering and conditioning the phloem than ingesting phloem sap. Interestingly, these observed alterations are similar to those of aphids feeding on insect-resistant soybean plants. The cause of these changes in feeding behavior is not known, and how they impact virus transmission and soybean aphid populations in the field will require further study. [ABSTRACT FROM AUTHOR]

The soybean aphid poses a severe threat to soybean quality and yield by sucking phloem sap and transmitting plant viruses. An early-maturing and highly resistant soybean landrace, Fangzheng Moshidou, with markedly reduced aphid colonization has been identified by screening of aphid-resistant soybean accessions. In a population derived from the cross of Fangzheng Moshidou with the susceptible cultivar Beifeng 9, resistance was conferred by a single dominant gene. Three linked markers, Satt114, Satt334, and Sct_033, on chromosome 13 were identified by bulked-segregant analysis. Additional simple-sequence repeat and single-nucleotide polymorphism (SNP) markers were developed for gene mapping. The resistance of Fangzheng Moshidou was fine-mapped to the interval between the SNP markers YCSNP20 and YCSNP80, corresponding to 152.8 kb in the Williams 82 assembly 2 genome. This region was near the reported loci Rag2 and Rag5 but did not overlap the interval containing them. A unique haplotype is described for Fangzheng Moshidou that distinguishes it from soybean accessions PI 587972, PI 594879, and PI 567301B in the interval containing Rag2 and Rag5. These results indicate that Fangzheng Moshidou harbors a novel gene at a tightly linked resistance locus, designated as RagFMD. Fourteen candidate genes were annotated in the fine-mapping region, including seven NBS-LRR genes, which are usually considered resistance genes in plant defense. Most of these candidate genes showed variations distinguishing the resistant and susceptible parents and some genes also showed differences in expression between the two parental lines and at several times after aphid infestation. Isolation of RagFMD would advance the study of molecular mechanisms of soybean aphid resistance and contribute to precise selection of resistant soybeans. [ABSTRACT FROM AUTHOR]

The cascading effects of microbe–plant symbioses on the second trophic level, such as phytophagous insects, have been most studied. However, few studies have examined the higher third trophic level, i.e., their natural enemies. We investigated the effects of the symbiotic associations between an arbuscular mycorrhizal (AM) fungus, Rhizophagus irregularis (Glomerales: Glomeraceae), a nitrogen-fixing bacterium, Bradyrhizobium japonicum (Rhizobiales: Bradyrhizobiaceae), and soybean, Glycine max (L.) Merr. (Fabaceae) on two natural enemies of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), the ladybird beetle Coleomegilla maculata (De Geer) (Coleoptera: Coccinellidae), and the parasitoid Aphelinus certus Yasnosh (Hymenoptera: Aphelinidae). We measured the growth and survival in the predator and parasitoid reared on aphids feeding on soybean inoculated seedlings. The rhizobium symbiosis alone was affected with a decreased rate of parasitoid emergence, presumably due to decreased host quality. However, number of mummies, sex-ratio, development time, and parasitoid size were all unaffected by inoculation. AM fungus alone or co-inoculated with the rhizobium was unaffected with any of the parameters of the parasitoid. For the predator, none of the measured parameters was affected with any inoculant. Here, it appears that whatever benefits the microbe–plant symbioses confer on the second trophic level are little transferred up to the third. [ABSTRACT FROM AUTHOR]

The soybean aphid poses a severe threat to soybean quality and yield by sucking phloem sap and transmitting plant viruses. An early-maturing and highly resistant soybean landrace, Fangzheng Moshidou, with markedly reduced aphid colonization has been identified by screening of aphid-resistant soybean accessions. In a population derived from the cross of Fangzheng Moshidou with the susceptible cultivar Beifeng 9, resistance was conferred by a single dominant gene. Three linked markers, Satt114, Satt334, and Sct_033, on chromosome 13 were identified by bulked-segregant analysis. Additional simple-sequence repeat and single-nucleotide polymorphism (SNP) markers were developed for gene mapping. The resistance of Fangzheng Moshidou was fine-mapped to the interval between the SNP markers YCSNP20 and YCSNP80, corresponding to 152.8 kb in the Williams 82 assembly 2 genome. This region was near the reported loci Rag2 and Rag5 but did not overlap the interval containing them. A unique haplotype is described for Fangzheng Moshidou that distinguishes it from soybean accessions PI 587972, PI 594879, and PI 567301B in the interval containing Rag2 and Rag5. These results indicate that Fangzheng Moshidou harbors a novel gene at a tightly linked resistance locus, designated as RagFMD. Fourteen candidate genes were annotated in the fine-mapping region, including seven NBS-LRR genes, which are usually considered resistance genes in plant defense. Most of these candidate genes showed variations distinguishing the resistant and susceptible parents and some genes also showed differences in expression between the two parental lines and at several times after aphid infestation. Isolation of RagFMD would advance the study of molecular mechanisms of soybean aphid resistance and contribute to precise selection of resistant soybeans.

Knockdown resistance (kdr) and super-kdr (skdr) point mutations have been identified in the voltage-gated sodium channel (vgsc) para genes in several aphid species with resistance to pyrethroids, but have not been confirmed in Aphis glycines Matsumura (Hemiptera: Aphididae), a serious soybean crop pest with resistance to pyrethroids. We used the A. glycines genome assembly GenBank accession number VYZN00000000 to mine potential vgsc para-ortholog genes, and amplicon-seq to screen for kdr and skdr mutations in nine populations from North Central USA with different pyrethroid susceptibility, sampled in 2018-2019. As was found in other aphids, two putative vgsc genes (vgsc1 and vgsc2) were identified in the same scaffold, oriented in opposite directions ~4 kb distant from each other. The vgsc1 gene coded heterodimer 1 (AglNav1) containing the VGSC domains I and II, while vgsc2 coded heterodimer 2 (AglNav2) with domains III and IV. Three splice variants were identified for each vgsc gene. The mutations M918L (skdr), M918I and L925M were identified in domain II in the IIS4-IIS5 linker region, and mutation L1014F (kdr) in the IIS6 segment. Although all mutations were found as heterozygotes, the population with the single M918L mutation and most populations with multiple mutations (M918I+L1014F or L925M+L1014F) exhibited a pyrethroid resistance phenotype, confirmed by λ-cyhalothrin exposure bioassays. The kdr and skdr point mutations in soybean aphid are the same point mutations associated with the target site insensitivity to pyrethroids in other arthropods and very likely contribute to resistance in soybean aphid. [ABSTRACT FROM AUTHOR]

BACKGROUND: Managing insect virulence can extend the durability of host‐plant resistant crops. Genetically modified resistant crops continue to be successful because of insect‐resistant management strategies that delay resistance such as multiple toxins and a susceptible refuge. These strategies may also be useful for host‐plant resistant crops, but more research is needed on their applicability. We investigated the interaction between a susceptible refuge and an insecticidal seed treatment to manage virulence in the soybean aphid. We tested four scenarios of an insecticidal seed treatment (plus an untreated control) in a microcosm containing 25% aphid‐susceptible (refuge) and 75% aphid‐resistant soybeans. Independent cohorts of plants were infested every week with avirulent and virulent aphids at equal frequencies. We used a molecular marker to estimate the change in virulence frequency across different plant maturities (from 7 to 42 days after planting). RESULTS: The presence of an insecticidal seed treatment on either the susceptible or resistant soybean decreased the overall population size of the soybean aphid. However, the insecticidal seed treatment impacted both virulent and avirulent aphids similarly, and only altered frequencies in favor of virulence when the sole susceptible plant (i.e., refuge) was treated. CONCLUSION: Under our experimental conditions, the frequency of avirulent aphids persisted with the use of a refuge. Although an insecticidal seed treatment decreased the overall aphid population size, it did not appear to benefit virulence management. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Abstract Many RNA viruses have genetically diverse populations in a single host. Important biological characteristics may be related to the levels of diversity, including adaptability, host specificity, and host range. Shifting the virus between hosts might result in a change in the levels of diversity associated with the new host. The level of genetic diversity for these viruses is related to host, vector and virus interactions, and understanding these interactions may facilitate the prediction and prevention of emerging viral diseases. It is known that luteoviruses have a very specific interaction with aphid vectors. Previous studies suggested that there may be a tradeoff effect between the viral adaptation and aphid transmission when Soybean dwarf virus (SbDV) was transmitted into new plant hosts by aphid vectors. In this study, virus titers in different aphid vectors and the levels of population diversity of SbDV in different plant hosts were examined during multiple sequential aphid transmission assays. The diversity of SbDV populations revealed biases for particular types of substitutions and for regions of the genome that may incur mutations among different hosts. Our results suggest that the selection on SbDV in soybean was probably leading to reduced efficiency of virus recognition in the aphid which would inhibit movement of SbDV through vector tissues known to regulate the specificity relationship between aphid and virus in many systems.

The cascading effects of microbe–plant symbioses on the second trophic level, such as phytophagous insects, have been most studied. However, few studies have examined the higher third trophic level, i.e., their natural enemies. We investigated the effects of the symbiotic associations between an arbuscular mycorrhizal (AM) fungus, Rhizophagus irregularis (Glomerales: Glomeraceae), a nitrogen-fixing bacterium, Bradyrhizobium japonicum (Rhizobiales: Bradyrhizobiaceae), and soybean, Glycine max (L.) Merr. (Fabaceae) on two natural enemies of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), the ladybird beetle Coleomegilla maculata (De Geer) (Coleoptera: Coccinellidae), and the parasitoid Aphelinus certus Yasnosh (Hymenoptera: Aphelinidae). We measured the growth and survival in the predator and parasitoid reared on aphids feeding on soybean inoculated seedlings. The rhizobium symbiosis alone was affected with a decreased rate of parasitoid emergence, presumably due to decreased host quality. However, number of mummies, sex-ratio, development time, and parasitoid size were all unaffected by inoculation. AM fungus alone or co-inoculated with the rhizobium was unaffected with any of the parameters of the parasitoid. For the predator, none of the measured parameters was affected with any inoculant. Here, it appears that whatever benefits the microbe–plant symbioses confer on the second trophic level are little transferred up to the third.

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. [ABSTRACT FROM AUTHOR]

Parasitoid lifespan is influenced by nutrient availability, thus the lifespan of parasitoids that rely on their hosts for nutritional resources (either via host feeding or by consuming honeydew) should vary with host density. We assessed the survival and reproduction of one such species, Aphelinus certus—a parasitoid of the soybean aphid, Aphis glycines—over a range of host densities using a laboratory assay. We found a positive, asymptotic relationship between host density and the lifespan and fecundity of A. certus that was supported by a traditional survivorship analysis as well as a logistic model. Parasitoids from this assay were also used to develop a wing wear index relating setae damage to parasitoid age. This index was used to estimate the life expectancy of field-collected parasitoids, which was shorter than the life expectancy of laboratory-reared female parasitoids. Finally, host-density-dependent parasitoid lifespan was incorporated into a coupled-equations matrix population model that revealed that decreasing the degree of host density dependence leads to higher equilibrium host densities and changes in the quality of equilibrium (e.g. stable limit cycles). These results detail the relatively unstudied phenomenon of host-density-dependent parasitoid lifespan and suggest that differences between laboratory- and field-determined parasitoid life expectancy have important implications for population dynamics and the biological control of insects. [ABSTRACT FROM AUTHOR]

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), continues to be the most economically important arthropod pest of soybean in the Midwest. Currently, management tactics for A. glycines rely on scouting and application of broad-spectrum insecticides. However, broad-spectrum insecticides are toxic to most natural enemies of this aphid. Selective insecticides may provide an alternative strategy for suppressing A. glycines populations while conserving populations of its natural enemies. Therefore, the aim of this study was to evaluate the potential lethal and sublethal effects of sulfoxaflor (a relatively new selective insecticide), to 2 of this pest's natural enemies, Chrysoperla rufilabris (Burmeister) (Neuroptera: Chrysopidae) and Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae). Laboratory bioassays were performed on first instars of both predators with residual toxicity evaluated over time until adult emergence. Parameters evaluated were mortality and developmental time for larvae and pupae, and adult body size. Fecundity also was determined for C. rufilabris. We found that sulfoxaflor was not toxic to first instar C. rufilabris. However, developmental time to adult was significantly delayed after exposure to this insecticide, but fecundity and body size were not negatively affected. For H. convergens, sulfoxaflor at 25% of the field rate was toxic to first instars. No significant differences were found with regard to developmental time and body size. It is important to note that sulfoxaflor, though relatively less toxic than some insecticides, is not entirely without consequence if natural enemies are exposed. The present study emphasizes the importance of examining earlier life stages and potential sublethal effects when evaluating the toxicity of insecticides in the presence of natural enemies. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms of pyrethroid resistance is essential to the effective management of pesticide resistance in Aphis glycines Matsumura (Hemiptera: Aphididae). We mined putative detoxifying enzyme genes in the draft genome sequence of A. glycines for cytochrome oxidase P450 (CYP), glutathione-S-transferase (GST) and esterases (E4 and carboxylesterases-CES). Aphids from clonal populations resistant to pyrethroids from three sites in Minnesota, USA, were screened against a diagnostic LC 99 concentration of either λ-cyhalothrin or bifenthrin and detoxifying enzyme genes expression in survivors was analyzed by qPCR. Their expression profiles were compared relative to a susceptible clonal population. We found 61 CYP (40 full-length), seven GST (all full-length), seven E4 (five full-length) and three CES (two full-length) genes, including 24 possible pseudogenes. The detoxifying enzymes had different expression profiles across resistant aphid populations, possibly reflecting differences in the genetic background and pyrethroid selection pressures as the number of constitutively overexpressed detoxifying enzyme genes was correlated with the level of resistance. Our findings will strengthen the understanding of the pyrethroid resistance mechanisms in A. glycines. Unlabelled Image • Aphis glycines had 61 CYP, 7 GST, 7 E4 and 3 CES genes. • Detoxifying enzymes had different expression profiles across aphid populations. • Number of constitutively overexpressed genes correlated with the level of resistance. • 11 constitutively overexpressed in all resistant populations exposed to pyrethroids. • 5 constitutively and inducibly overexpressed in at least one resistant population. [ABSTRACT FROM AUTHOR]

The use of aphid-resistant soybean varieties containing Rag genes can provide an effective pest management strategy against soybean aphid (Aphis glycines Matsumura). However, the compatibility between soybean containing Rag genes and the management of other potential soybean pests (i.e., nontarget herbivores) is poorly understood. Therefore, our goal was to (1) assess the efficacy of pyramided (Rag1+Rag2) aphid-resistant soybean for reduction of soybean aphid populations, and (2) determine if aphid-resistant soybean affects populations of nontarget herbivores under field conditions. To accomplish these goals, field experiments were conducted in southeast Minnesota from 2015 to 2017 for a total of five site-years using whole-plant counts to assess soybean aphid densities and sweep-net sampling to estimate nontarget herbivore densities in plots of near-isoline soybean with Rag1+Rag2 (i.e., resistant) or no Rag genes (i.e., susceptible). Plant genotype (i.e., resistant or susceptible) affected seasonal abundance of soybean aphid, with fewer soybean aphids on aphid-resistant than susceptible soybean. Furthermore, plant genotype affected seasonal abundance of bean leaf beetle (Cerotoma trifurcata Forster), green cloverworm (Hypena scabra Fabricius), and potato leafhopper (Empoasca fabae Harris). Aphid-resistant soybean was associated with increased seasonal abundance of bean leaf beetle and reduced seasonal abundance of potato leafhopper and green cloverworm. The abundance of these herbivores was also associated with seasonal abundance of soybean aphid as a covariate. Results presented here confirm the efficacy of aphid-resistant soybean with Rag1+Rag2 against soybean aphid and show that aphid-resistant soybean can influence the seasonal abundance of nontarget herbivores in soybean. However, the magnitude of impacts of aphid-resistant soybean on nontarget herbivores was relatively small and likely of little-to-no agronomic significance, which suggests compatibility of aphid-resistant soybean with management of other potential pests. [ABSTRACT FROM AUTHOR]

BACKGROUND: Beta‐aminobutyric acid (BABA) confer plant resistance to a broad spectrum of biotic and abiotic stresses. The soybean aphid (SBA), is native to eastern Asia and is a predominant insect pest of soybean. Both isoflavone and lignin pathway are important branches of the general phenylpropanoid pathway, which would be likely associated with resistance against soybean aphid. However, little is known about the role of the phenylpropanoid pathway in defense response to SBA as induced by BABA application. RESULTS: The application of BABA effectively enhanced soybean resistance against Aphis glycines, the soybean aphid. Consistent with significantly increased content of isoflavones, especially genistein, the related biosynthetic genes were upregulated by use of BABA. Lignin, another important defense component against arthropods, accumulated at a high level and four lignin biosynthesis related genes were also activated. Additionally, BABA application augmented the expression of callose synthase genes and increased callose deposition in SBA‐infested seedlings. In non‐caged and caged tests, SBA numbers were significantly reduced in BABA‐treated seedlings. CONCLUSION: These results demonstrate that application of BABA has an obvious positive effect on soybean resistance to aphids, and this defense response partly depends on the potentiation of isoflavone biosynthesis and callose deposition. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Since the discovery of the invasive soybean aphid, Aphis glycines Matsumura, in the USA in 2000, populations have expanded throughout the Midwestern USA and Canada. Its negative economic impact on soybean [Glycine max (L.) Merr.] yield provides the impetus to continue investigating the effectiveness of host plant resistance which has been affected by soybean aphid biotypes that overcome soybean plants containing Rag (resistance to A. glycines) genes. In this study, 14 aphid clones collected on soybean and buckthorn (Rhamnus cathartica L.) plants along with four known aphid biotypes (from our stock collection) were evaluated in no-choice assays by quantifying the number of aphids on soybean genotypes with Rag genes and the susceptible cultivar Williams 82. No-choice assays were conducted using detached leaves and whole plants. Inconsistent responses of the biotypes from the stock collection by using detached leaves confirm the efficacy of whole plant assays to accurately differentiate biotypes. None of the biotypes or field clones from Illinois, Indiana and South Dakota overcame the resistance of soybean genotypes LD14-8004 (Rag1) and PI437696. A soybean aphid clone from Wooster, Ohio readily colonized LD14-8002 (Rag2), but did not overcome any of the other resistance genes indicating that it is different from biotypes 3 and 4, which also overcome LD14-8002 (Rag2) and, respectively, LD14-8004 (Rag1) and LD14-8006 (Rag3). [ABSTRACT FROM AUTHOR]

Cultivation of aphid-resistant soybean varieties can reduce yield losses caused by soybean aphids. However, discovery of aphid biotypes that are virulent on resistant soybean greatly threatens sustained utilization of host plant resistance to control soybean aphids. The objective of this study was to identify and genetically characterize aphid resistant soybean accessions in a diverse collection of 308 plant introductions in maturity groups (MG) I and II. In large-scale screening experiments conducted in the greenhouse, we identified 12 soybean accessions (10 aphid-resistant and 2 moderately resistant), including nine previously not reported for resistance against soybean aphids. Three accessions (PI 578374, PI 612759C, and PI 603546A) and the Rag3 resistant check (PI 567543C) were susceptible when infested with a high initial aphid level but resistant when infested with a low initial aphid level, a phenomenon termed as density-dependent aphid resistance. Six accessions (PI 054854, PI 378663, PI 578374, PI 612759C, PI 540739, and PI 603546A) conferred antibiosis, five (PI 438031, PI 603337A, PI 612711B, PI 437950, and PI 096162) conferred both antibiosis and antixenosis, while one (PI 417513B) had neither when tested in no-choice and pairwise choice experiments. Molecular genotyping of the 12 accessions using single-nucleotide polymorphism (SNP) markers linked to known aphid resistance (Rag) genes revealed that PI 578374 and PI 540739 did not have any tested marker variants and could potentially carry unreported Rag genes. Genome-wide association analyses for MG I accessions identified genomic regions associated with aphid resistance on chromosomes 10 and 12 for each level of initial aphid colonization. [ABSTRACT FROM AUTHOR]

Thiamethoxam, an insecticide used in soybean seed treatments, effectively suppresses soybean aphids (Aphis glycines) Matsumura (Hemiptera: Aphididae) for a short time after planting. However, exactly when and how quickly soybean aphid populations could increase is unknown. Likewise, we lack data on virulent soybean aphid biotypes (that can overcome soybean resistance) when fed on seed-treated soybean. Determining the survival of soybean aphids over time on insecticidal seed-treated soybean is critical for improving soybean aphid management and may provide insights to manage aphid virulence to aphid resistant-soybean. In greenhouse and field experiments, aphid-susceptible soybean plants (with and without an insecticidal seed treatment) were infested at 7, 14, 21, 28, 35, and 42 days after planting (DAP). We compared aphid survival among biotypes 1 (avirulent) and 4 (virulent) and insecticide treatment 72 h after infestation. We also measured thiamethoxam concentrations in plant tissue using liquid chromatography-tandem mass spectrometry. As expected, soybean aphid survival was significantly lower on seed-treated soybean up to 35 DAP for both biotypes, which correlates with the decrease of thiamethoxam in the plant over time. Moreover, we found no significant difference between avirulent and virulent biotype survivorship on insecticidal seed-treated soybean plants, although we did find significantly greater survival for the virulent biotype compared with the avirulent biotype on untreated soybean in the field. In conclusion, our study further characterized the relative short duration of seed treatment effectiveness on soybean aphid and showed that survivorship of virulent aphids on seed-treated soybean is similar to avirulent aphids. [ABSTRACT FROM AUTHOR]

Coevolutionary interactions between pathogens and their insect vectors can dramatically impact the fitness of herbivorous insects and patterns of plant disease transmission. Soybean mosaic virus (SMV) is a common disease in soybean production worldwide. Infected seed is the primary source of inoculum in fields and the virus is secondarily spread among plants by the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in a nonpersistent manner. In this study, we compared the biological fitness of A. glycines colonizing both SMV-infected and uninfected soybean plants. Aphids feeding on SMV-infected soybean seedlings were significantly smaller and lighter than those feeding on uninfected plants across life stages. SMV infection caused delayed development of aphid nymphs on soybean seedlings, but this was more than compensated by a reduction in the pre-reproductive period of apterous adults. The fecundity of A. glycines was reduced when feeding on SMV-infected seedlings, resulting in a lower reproductive rate, a longer generation time, and a slower population doubling time. A smaller proportion of aphid offspring developed into alatae when feeding on SMV-infected soybean seedling, and these took longer to mature than their counterparts on uninfected plants. We infer that SMV infection has significantly negative effects on the biological performance of A. glycines, which may be consistent with the long-term coevolution of SMV, soybean, and A. glycines in the transmission cycle of SMV. [ABSTRACT FROM AUTHOR]

The development of soybeans tolerant to the soybean aphid [ Aphis glycines Matsumura (Hemiptera: Aphididae)] remains unexplored. The objectives of this research were to determine the susceptibility of two high-yielding soybean [ Glycine max (L.) Merrill (Fabales: Fabaceae)] genotypes involved in a breeding platform to develop aphid-tolerant recombinant inbred lines (RILs); characterize the peroxidase activity and relative expression of peroxidase transcripts in the parents of RILs; and identify an assay to phenotype aphid-tolerant RILs. Enzyme kinetic assays documented the total peroxidase activity for tolerant (KS4202), susceptible (SD76R), and two high-yielding (U09-105007 and U11-611112) soybeans during two vegetative stages (V1 and V3) at three sampling days (D4, D6, and D8 after aphid introduction). Enzyme kinetic assays showed that V3 infested tolerant and U11-611112 plants had significantly higher peroxidase activity than their respective control plants at D4, and infested tolerant plants were also higher than control plants at D6. There were no apparent trends when comparing the expression of peroxidase-specific transcripts in the absence of aphids (basal levels) in both V1 and V3. Relative expression analyses of two peroxidase transcripts (PRX52 and PRX2) performed to compare differences among the soybean genotypes indicated that, despite basal levels being similar for the treatments analyzed, tolerant soybeans had a tendency for a higher expression of PRX52 in the presence of aphids. Based on the different patterns observed and the feasibility of analyses performed in this study, enzyme kinetics using V3 infested plants may be a marker for screening RILs in a breeding program targeting the development of aphid-tolerant soybeans. [ABSTRACT FROM AUTHOR]

Transgenic glyphosate-resistant (GR) soybean ( Glycine max L. Merr.) is cultivated throughout the United States. Soybean growth is influenced by the presence of weeds, although managing non-crop vegetation can potentially impact soil arthropods, which are being increasingly recognized for their impacts on soil health, plant growth, and above-ground trophic interactions. We investigated how weed management (weedy controls, hand-weeded, glyphosate herbicide) and soil insecticide (chlorpyrifos) application affected densities of soil arthropods, soil nutrient availability, soybean growth and yield, and densities of an above-ground herbivore on sandy and clayey soils for two consecutive growing seasons. The soil insecticide treatment was intended to lower densities of subterranean arthropods to gain insight into how their presence influenced other factors, although their densities were primarily reduced the first year of the study. Surprisingly, weed management and soil insecticide use had virtually no interactive effects on any response. Weed presence had a positive effect on soil K at the sandy site and on nodule density per unit root. Negative effects of weed management on plant growth and aphids were related to the presence of weeds rather than herbicide use. Reduced soybean aphid density (at the clayey site) and soil P availability (at the sandy site) were associated with insecticide treated plots. Conversely, several measures of plant productivity, including number of nodules per unit root, and root and shoot biomass increased in +insecticide plots compared to other treatments, although effect strength depended on year and location. Collembola were the dominant soil microarthropod, and their densities in 2012 were negatively associated with nodule numbers in 2013. One explanatory hypothesis is that increased plant growth in plots treated with insecticide was caused by altered soil arthropod-microorganism interactions, possibly affecting arbuscular mycorrhizae function. This work highlights the importance of management decisions that affect soil arthropods in annual legume production systems. [ABSTRACT FROM AUTHOR]

Aphis glycines Matsumura (Hemiptera: Aphididae) is a serious pest of soybean in North America. Plant resistance is a valuable tool for the management of this pest, and a better understanding of the interactions between aphid and soybeans expressing varying levels and different categories of resistance can assist in the development of aphid resistant or tolerant genotypes. The electrical penetration graph (EPG) technique was used to evaluate the feeding behavior of A. glycines (biotype 1) on 4 soybean genotypes: (1) 'Dowling' (contains Rag1 gene and exhibits antibiosis); (2) PI 200538 (contains Rag2 gene and exhibits antixenosis); (3) KS4202 (exhibits tolerance); and (4) 'SD76RR' (susceptible to aphid). Aphids spent shorter periods in the sieve element phase on 'Dowling' and exhibited a greater number of pathway phases, non-probing events, and a longer time in nonprobing events in PI 200538 and 'Dowling.' For 'SD76RR' and KS4202, aphids demonstrated more sustained phloem ingestion, spent shorter time in non-probing events, and exhibited fewer pathway phases and potential drops. These results indicate that resistance factors are present in the phloem of 'Dowling.' For PI 200538, it is suggested that antixenotic factors are involved in resistance to A. glycines. Because KS4202 is tolerant to biotype 1 of A. glycines, the suitability of this genotype was expected already. This study provides important data that contribute to the understanding of how soybean aphids (biotype 1) feed on soybean genotypes with various aphid resistant genes and categories. In addition to assisting in the distinction between resistance categories, these results are useful in soybean breeding programs focusing on developing genotypes with greater resistance to insects. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: The soybean cyst nematode, Heterodera glycines, and soybean aphid, Aphis glycines, are invasive, widespread and economically important pests of soybean, Glycine max, in North America. Management of these pests relies primarily on use of pesticides and soybean germplasm with genetic resistance. A 3‐year field study and complementary greenhouse experiment were conducted to determine the benefits of host plant resistance (HPR) and pesticidal seed treatments for managing pest populations and preserving soybean yield. RESULTS: Host plant resistance significantly decreased the abundance of A. glycines and, in most study sites, suppressed H. glycines. Neonicotinoid seed treatment reduced A. glycines abundance on the cultivar that was susceptible to both aphids and nematodes, but abamectin nematicide seed treatment had no effect on H. glycines populations in the field or greenhouse. CONCLUSION: These results suggest that the seed treatments included in our experiments may suppress pests, but not consistently for all soybean cultivars or study sites. Ultimately, HPR more consistently reduced pest numbers compared with the use of pesticidal seed treatments. The planting of HPR cultivars should be a primary tool for integrated pest management of both soybean pests. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The risks associated with soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in the North Central soybean systems has fostered the adoption of prophylactic chemical control practices, such as planting seeds treated with neonicotinoid insecticides, especially thiamethoxam. Consequently, there is a concern that increased selection pressure imposed on the arthropod-pest complex by this insecticide may lead to resistance. Therefore, in vivo bioassays were conducted to determine the susceptibility of soybean aphid to thiamethoxam among North Central U.S. populations. Concentration-mortality data were collected using contact glass-vial and detached-leaf systemic bioassays. The results of these experiments indicate that both bioassays were reliable to detect shifts in susceptibility between different soybean aphid clones. The LC50s of field populations of soybean aphid were significantly different when mortality was recorded in contact and systemic exposure assays. Nevertheless, the magnitude of the resistance ratios was consistent in both methods. In addition, a significant increase in the LC50 and EC50 values was observed among field populations tested in detached-leaf systemic bioassays. These results represent the first extensive efforts to identify the variability in susceptibility of soybean aphid to thiamethoxam in the North Central United States Therefore, our results provide a baseline for future assessment and contribute to a better understanding of the applicability of in vivo bioassays for susceptibility monitoring and resistance detection of soybean aphid to thiamethoxam. [ABSTRACT FROM AUTHOR]

This research represents a forward step in the control of Aphis glycines. Essential oils from Acorus tatarinowii, Mentha haplocalyx, and Stemona japonica were studied for repellency and anti-molting activities. For the laboratory choice-experiment, of two soybean plants with 4 to 6 leaves each, one was treated with either a single or a mixture of essential oils, while the other was treated with a control solution. The plants were then placed in a cage and twenty aphids were released between the two plants. For no-choice tests, only one plant, treated with essential oil, was placed in the center of a cage and 20 aphids were released around the plant. Viable aphid numbers on plants were recorded at 6, 12, 24, and 36 hours after initiating each test. After 36 hours of observation, numbers of exuviae around the plant were recorded in the no-choice test. In the greenhouse experiment, two potted faba bean plants were used. Five mL of essential oil was sprayed on one plant, and 5 mL of control solution on the other plant. One hundred adult aphids were released into each cage between the two plants. Repellency was observed at 12 and 24 hours of exposure. A mixture of A. tatarinowii plus S. japonica oils demonstrated maximum repellency in both lab (71.25 ± 3.50%) and greenhouse (85.61 ± 1.56). Anti-molting activities were observed when the essential oil of S. japonica was used. Results suggest that a mixture of A. tatarinowii and S. japonica essential oils are effective at controlling A. glycine. [ABSTRACT FROM AUTHOR]

Soybean aphid (Aphis glycines Matsumura) is a pest of soybean in the northern Midwest whose migratory patterns have been difficult to quantify. Improved knowledge of soybean aphid overwintering sites could facilitate the development of control efforts with exponential impacts on aphid densities on a regional scale. In this preliminary study, we explored the utility of variation in stable isotopes of carbon and nitrogen to distinguish soybean aphid overwintering origins. We compared variation in bulk 13C and 15N content in buckthorn (Rhamnus cathartica L.) and soybean aphids inWisconsin, among known overwintering locations in the northern Midwest. Specifically, we looked for associations between buckthorn and environmental variables that could aid in identifying overwintering habitats. We detected significant evidence of correlation between the bulk 13C and 15N signals of soybean aphids and buckthorn, despite high variability in stable isotope composition within and among buckthorn plants. Further, the 15N signal in buckthorn varied predictably with soil composition. However, lack of sufficient differentiation of geographic areas along axes of isotopic and environmental variation appears to preclude the use of carbon and nitrogen isotopic signals as effective predictors of likely aphid overwintering sites. These preliminary data suggest the need for future work that can further account for variability in 13C and 15N within/among buckthorn plants, and that explores the utility of other stable isotopes in assessing likely aphid overwintering sites. [ABSTRACT FROM AUTHOR]

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is native to Asia where it is an occasional pest of soybean, Glycine max (L.). Aphis glycines was found during 2000 in North America and since then has spread throughout much of the area where soybean is grown. In Asia, A. glycines seldom reaches damaging levels; however in North America, it has become the most important insect pest of soybean, decreasing yields and incurring large control costs. Field surveys and exclosure experiments in China showed that natural enemies can limit soybean aphid abundance. A project to find, evaluate, and introduce Asian natural enemies into North America was initiated in 2001, with an emphasis on parasitoids. To ensure that introductions of exotic parasitoids would have minimum impact on non-target species, we tested host specificity of all candidates for introduction. Here we report results of experiments on host specificity of 13 populations in seven species from three species complexes in the genus Aphelinus (Hymenoptera: Aphelinidae). In no-choice laboratory experiments, four species had broad host ranges and one species had an intermediate host range. However, two species, Aphelinus glycinis and Aphelinus rhamni , had narrow host ranges, being restricted to some species in the genus Aphis . We also report the results of experiments on the mechanisms of host specificity in the parasitoid species with intermediate to narrow host ranges. Most of this host specificity can be explained by differences in the behavior of females when they encountered different aphid species. Females of these species rarely approached, stung, oviposited or host fed on aphids outside the genus Aphis . Even within the genus Aphis , Aphelinus glycinis and Aphelinus rhamni parasitized primarily Aphis glycines and closely related species. From these results, we conclude that Aphelinus glycinis and Aphelinus rhamni are excellent candidates for introduction into the North America to control Aphis glycines . [ABSTRACT FROM AUTHOR]

Since the discovery of Aphis glycines Matsumura (Hemiptera: Aphididae) in the United States, the primary management tactic has been foliar insecticides. Alternative management options such as host plant resistance to A. glycines have been developed and their effectiveness proved. However, the use of host plant resistance was complicated by the discovery of multiple, virulent biotypes of A. glycines in the United States that are capable of overcoming single Rag genes, Rag1 and Rag2, as well as a two-gene pyramid of Rag1+Rag2. However, current models predict that the virulent allele frequency of A. glycines decreases in response to the use of pyramided Rag genes, suggesting that pyramids represent a more sustainable use of these traits. Previous research has demonstrated that virulent biotypes can be effectively managed using a three-gene pyramid of Rag1+Rag2+Rag3. Additional Rag-genes have been discovered (Rag4 and Rag5), but whether the incorporation of these genes into novel three-gene pyramids will improve efficacy is not known. We tested single-gene (Rag1 and Rag2) and pyramid cultivars (Rag1+Rag2, Rag1+Rag2+Rag3, Rag1+Rag2+Rag4) to multiple biotypes in laboratory assays. Our results confirm that the Rag1+Rag2+Rag3 pyramid effectively manages all known A. glycines biotypes when compared with cultivars that are overcome by the associated biotype. Our results indicate that Rag1+Rag2+Rag4 would be an effective management option for biotype-1, biotype-2, and biotype-3 A. glycines, but had a negligible impact on biotype-4. [ABSTRACT FROM AUTHOR]

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an important pest that can cause significant economic damage to soybean. Synthetic insecticides are currently employed as the main management strategy to control A. glycines ; however, over-use of these products has stimulated research in the development of alternative management methods, including botanical derivatives. In this study, we evaluated the bioactivity of Annona mucosa and A. muricata seed extracts and a formulation based on acetogenins (Anosom® 1 EC, 10,000 ppm) compared to the pyrethroid insecticide lambda-cyhalothrin (Warrior II®) on A. glycines. Initially, the insecticidal effect was assessed in vial bioassays and the concentration-response curves were estimated (LC 50 /LC 90 for A. muricata 305.721 ppm/1290.3 ppm and A. mucosa 134.229 ppm/487.890 ppm, respectively). In the systemic effect bioassay, the same extracts were used (at 100, 500, 1,000, 5000 and 10,000 ppm), showing a reduction in the number of insects on the trifoliates. Both extracts at LC 50 and LC 90 were used in a behavior test, indicating that they are repellent and Warrior II® was attractive for the insects. The LC 90 rates were also used in lethal time (LT) and in greenhouse bioassays. The LT 50 for A. mucosa and A. muricata extracts was around 20 h. All treatments showed insect mortality rates above 65%, reaching 100% for Warrior II®, followed by the LC 90 of A. mucosa (92.1%). The results demonstrate the potential of Annona spp. derivatives for the management of A. glycines in soybean, and these Annonaceae-derived seed extracts could likely serve as an additional IPM tool to improve A. glycines control strategies in organic farming systems. [Display omitted] • The potential of annonaceous derivatives on Aphis glycines was investigated. • Ethanolic seed extracts were the most active against A. glycines. • A. mucosa and A. muricata showed efficacy superior to an acetogenin-bases bioinsecticide. • The biopesticides were highly harmful to A. glycines. [ABSTRACT FROM AUTHOR]

Agricultural intensification has resulted in the homogenization of agricultural landscapes, leading to the loss of crop and habitat diversity, and a higher rate of chemical inputs in the landscape, negatively impacting natural enemy communities and their ability to provide pest control services. Landscape heterogeneity is thought to benefit predator populations (increasing landscape complementation) and lower pest colonization (decreasing resource concentration); however, few studies have determined the relative importance of these two processes in pest suppression. Here, we tease apart direct and indirect impacts of landscape heterogeneity on experimental populations of soybean aphid excluded from and open to predation, in 23 soybean fields in Manitoba, in 2017 and 2018. Field plant counts and sweep net samples were conducted to determine aphid and predator abundances, respectively, and Malaise traps were used to quantify predator movement into soybean. Landscape effects differed between a soybean aphid outbreak year (2017) versus a non-outbreak year (2018). We found that crop diversity at a 1.5 km radius had negative impacts on aphid colonization during the outbreak year, resulting in greater aphid suppression but no impacts on predator movement. Edge density at a 1.5 km radius increased aphid suppression during the low aphid year. Predator movement and abundance were driven by aphid colonization in soybean, and syrphid and coccinellid abundance were 33-fold and 15-fold more abundant in the high compared to the low aphid year. Thus, our study revealed complementary effects of landscape heterogeneity on aphid suppression: a reduction of resource concentration associated with increased crop diversity and resulting in bottom-up effects during an outbreak, and an increase in landscape complementation associated with increased edge density and top-down control in a low aphid year. Increasing crop diversity seems a promising strategy to mitigate aphid outbreaks without compromising food production. • Crop diversity has bottom-up effects in reducing aphid colonization. • Reduced aphid colonization benefits aphid suppression. • Edge density benefits aphid suppression in a low aphid year. • Predator movement and abundance respond to soybean aphid density. • Coccinellidae and Syrphidae increased 15- and 33-fold in response to aphid outbreaks. [ABSTRACT FROM AUTHOR]